Hydrogen in the UK

Isambard Kingdom Brunel

Friends, on Monday I visited a Brunel University Hydrogen Event. This meant getting up(!) and travelling far beyond the borders of Teddington on TWO buses – so when I arrived in Uxbridge at  11:00 a.m. it had already been an exciting day for a retiree like me.

It was the kind of event I might have attended when I worked at NPL, but when I worked for NPL I would have gone along to promote something, or to give a talk. So it was liberating to be there with no agenda: I went with the simple goal of educating myself. And I did learn a thing or two. So I thought I would jot down a few of the things I learned.

Thing#1: Electrolysers

I learned that ITM Power is one of the world’s leading manufacturers of electrolysers, with a capacity to manufacturer around 1 GW of electrolysers per year – in the UK! Remember that only hydrogen manufactured using electrolysis powered by renewable electricity has the capability to create green hydrogen with practically zero CO2 emissions.

Thing#2: Fuel Cell Vehicles

I learned that many people are still very keen on fuel-cell powered vehicles. Talking with a fellow delegate I pointed out the relative inefficiency of using fuel cell vehicles (FCVs) compared to battery electric vehicles (BEVs) – you can read my previous article on this here. However the delegate was dismissive of efficiency as a metric, whereas I consider it to be overwhelmingly important.

Remember that if we begin with 100 kWh of renewable electricity, after creating hydrogen we will have only 80% of the energy available, and only half of that makes it to the wheels of the vehicle – so only 40% of the initial energy is useful. However if we use that renewable electricity to charge a battery and discharge it, around 85% of the energy is useful.

What this means is that to run a fleet of vehicles using hydrogen fuel cells requires more than twice the renewable electricity resource. In the future we may have an excess of renewable electricity, but this will not be the case for many years.

The delegate explained that efficiency was only relevant if a BEVs had the capacity of a FCV, by which I think they were referring to power and range. So the delegate thought that fuel-cell drive trains would ‘win’ in this area. And it may be that for large vehicles or trains, there may be a niche for fuel cells, but I remain sceptical.

Things#3: Hydrogen Combustion Engines 

To my surprise some people are still pursuing hydrogen combustion for motive applications.

Some people are working on retrofit apparatus for existing diesel engines and some are working on radical new concepts which would operate at very high temperatures and have a thermodynamic efficiency approaching 70% compared with about 25% for a conventional  Internal Combustion Engine (ICE) car i.e. ICE cars throw away 75% of the energy of combustion as heat.

A 3-D printed model of a hydrogen internal combustion engine.

I would have dismissed this completely, but Japanese manufacturers are still clinging to the idea (News Story 18 May 2023) and one of the world’s leading manufacturer’s of construction equipment – JCB – is planning on using such engines in their vehicles.

Reflections

Click on Image for a larger version. The discussion panel consisting of (from Left to Right): Ben Madden, Rita Wadey, Ben Todd and the keynote speaker, Graham Cooley.

The keynote presentation was given by Dr. Graham Cooley, CEO of ITM-Power, and I found it quite inspiring. I won’t try to précis the talk but instead just note one point.

He noted that technological cultures are built on both molecules and electrons. Historically we have started with hydrocarbon molecules (coal, oil and gas), and burned these molecules to make electricity. But in the current energy transformation, this pattern is being reversed. For a green technological culture, we start with renewable electricity and use that to make molecules – specifically hydrogen – which then seeds the synthesis of larger molecules. I guess this seems obvious to a man who runs an electrolyser firm!

The discussion panel was fascinating, consisting of an investor, an entrepreneur and a policy specialist. Collectively their comments painted a picture of an ever-changing forest of complex incentives, indecision in government, and continuing lack of support. In short, nothing new.

When I asked the panel’s views about heating, one panel member pointed out the astonishing extent and complexity of the gas distribution network, and commented that “...if they can’t find something to put in their pipes, they’re toast!“. I think this explains the desperate efforts of the gas companies to promote hydrogen for home heating – something which would be a disaster for the UK.

Conclusion

Friends, I went along to this event to learn, and I learned that there is a lot of experience in a range of hydrogen technologies in the UK and that Brunel University is full of smart, business-focussed engineers.

But overall I was surprised at the continued focus of research on hydrogen for transport. I wish all the companies involved well, but I didn’t understand their enthusiasm.

I didn’t see any work on hydrogen for aviation, and as I see it, hydrogen for terrestrial transport will only be a niche market – heavy equipment and large lorries. And this niche market is a market that will inevitably contract as battery technology improves, providing vehicles with ever improving specifications in terms of range, load and cost.

But what do I know? Time will tell.

 

 

A Short Talk about my Low-Carbon Home

Friends, today I abandoned my usual Saturday morning ritual of doing a quiz and a crossword with my wife at our local café.

Instead I travelled far beyond the borders of Teddington to give a  “A Short Talk about my Low-Carbon Home” at the Kingston Efficient Homes Show. There were many celebrities there include Ed Davey, the leader of the Liberal Democrats, and the Green Man, whom Wikipedia informs me is not in fact a pagan mythological figure.

The Green Man visited the Kingston Efficient Homes Show.

I was a little discombobulated at the start of the talk because nobody turned up to introduce me, and the clock in the lecture room was slow. And so while I was just waiting to start, I should already have started. And at the end I was being told to wind up, when in fact I still had many minutes left. Hey Ho.

I promised the audience I would put the Powerpoint slides from the show here, and below is a belated re-recording of the 20 minute talk for those who missed it. Somehow, it is 30 minutes long :-(.

Reflection 

I found the event very moving: it was full of people trying to make the world a better place.

• There were slightly bewildered members of the public prepared to spend money on heat pumps and insulation and solar PV and batteries.
• There were installers – the shock troops on the front line of combating climate change.
• There were architects – including the designers of the fantastic Bale House in Hastings.
• There were members of the local Council and politicians.

But one thing annoyed me: the endless request for estimates of ‘payback time’ or ‘return on investment’.

As Bill Nye, the mild-mannered American science communicator so eloquently put it, “The planet is on fire“. And people still want to find out whether it’s worth their while to put out the fire? He was actually rather more pithy than that.

If you found that video amusing, here’s another more upbeat version.

The Economics of Home Solar PV

Friends, you may find this hard to believe, but someone posted something incorrect on Twitter the other day. They suggested that home installations of solar PV will soon become uneconomic.

I commented that I didn’t agree. But to my surprise, several people commented further suggesting that Home Solar was not only uneconomic, it was tantamount to theft!

At first I was bewildered: How could these people be so wrong? But then it turned out these people were economists, and so were quite un-phased by being wrong.

But after an extended exchange, I began to understand their perspective, and that is what this article is about. I still think they are wrong, but the perspective shift was interesting.

Home Solar PV: Simple Economics

The economics of home solar PV are fairly straightforward. A system of 10 panels (~£5,000) and a 5 kWh battery (~£5,000) will conservatively generate around 3,500 kWh/year of electricity which is roughly the annual usage of electricity by a household. The system will generate (on average) about 15 kWh/day in summer and perhaps just 2 kWh/day in winter depending on local shading.

Typically around 2,000 kWh will be used within the home saving (at current prices) 2,000 × 34p/kWh ~ £680/year which would otherwise have been purchased. Additionally, the extra 1,500 kWh will be exported earning a much less impressive 5p/kWh or £75 /year. So a roughly £10,000 investment has a return on investment of ~£750/year, a nominal 7.5%/year return. It’s possible to do a bit better or a bit worse depending on panel orientation and battery size.

By any conventional economic assessment, this is a reasonable investment.

Home Solar PV: Simple Carbonomics

Considering the carbon dioxide emissions avoided, the home solar PV system above might involve roughly 2,100 kg (2.1 tonnes) of embodied carbon dioxide emissions. That’s based on:

• Panels: ~400 kgCO2 per peak power (in kW) of a panel – leading to around 1.6 tonnes of emissions (Links 1, 2).
• Battery: ~100 kgCO2 per kWh of storage – leading to around 0.5 tonnes of emissions for a 5 kWh battery (Link)

Each kWh of electricity generated might avoid nominally 0.23 kgCO2 emissions. And so the system would avoid 3,500 x 0.23kg ~800 kgCO2/year. Additionally, by using the battery to avoid consumption at peak hours, the system could also help reduce grid costs and the use of ‘peaker’ plants.

This is a pretty reasonable carbon investment.

Home Solar PV: How could this not make sense?

So from an economic and carbonomic point of view, Home Solar PV systems with or without batteries definitely make sense. So what was this Twitterista going on about?

Well it turns out that they were not talking about the UK but were instead referring to (if I recall correctly) Belgium or Holland. In these countries the majority of people do not pay fixed price tariffs on their electricity. Instead they pay tariffs which change every 30 minutes depending on market conditions. In the UK this practice is not at all common.

And the situation they were referring to was the situation where there was so much solar power being made available by large solar farms, that while the sun was shining, solar power would cover the majority of electricity required. At this point, the economic market value of any extra solar generation would be zero.

This is a situation that will become increasingly possible as we expand renewable generation and the market will need to evolve to cope with this reality. But in the UK it would not make much difference. Most of the electricity generated on a rooftop is used within the home, and this avoids paying the market rate, so the savings would be unchanged. However, the price paid for exporting electricity might possibly fall to zero, but since that was only worth £75/year, it doesn’t really significantly the economics.

If consumers were exposed to market electricity prices that varied every 30 minutes through the day, then the cost of buying electricity when the Sun shone might fall to zero, and so consumers would be able to have free electricity whether or not they had a solar PV system on their home. In this situation, having a home battery would make a lot of sense because one could fill it for free!

But that is not the situation in the UK. I think it is good to have relatively fixed tariffs so that people can budget for likely electricity costs. In this way, professional traders take calculated risks for which they earn a reward. I think that is better than exposing us to the risks of a market which when under stress can become extremely volatile, and potentially bankrupt people who keep their electricity on when the system is under stress. For example, in the 2021 power crisis in Texas, in between blackouts, the price for some customers rose to $9/kWh – up from a few cents per kWh resulting in some customers facing bills of $1,000/day.

So the situation in which half-hourly market prices sometimes falls to zero is unlikely to affect the UK market directly. And even it did, people with home solar would still be getting free electricity at times when the market cost was not zero.

At the heart of this persons argument was an economic rationale that any investment in an economic activity which is sub optimal – represents a waste. This is based on a hyper-capitalistic view of society in which optimal capital deployment will result in optimal outcome. This is patently, just not in correspondence with reality.

Home Solar PV: Theft?

Theft! Surely I was dealing with an idiot here? But here is their argument.

The tariffs we pay for electricity are divided into two parts:

• a so-called ‘standing charge’ typically about £0.40/day and
• a ‘unit’ charge of typically £0.34/kWh.

Originally the idea was that this reflected the cost structure of the electricity supply industry.

• The ‘standing charge’ would pay for the costs of the electricity network that gave us the possibility of buying electricity, whether we used 1 kWh/day or 100 kWh.
• The ‘unit charge’ would pay for the extra costs – notably the fuel – used to generate every extra unit of electricity.

So with this structure, using solar PV to go ‘off grid’, I would still pay the standing charge, and so contribute my fair share to the maintenance of the electricity network.

However, standing charges are no longer just a way to pay for the fixed costs of the electricity network. They now include costs of paying for the mass failure of electricity companies in 2021/22, and elements of subsidy for ‘greener’ generation. And some elements of the unit charge actually reflect fixed costs.

So if I avoid paying for units of electricity, I am avoiding paying for some of the fixed costs of the network, and thus forcing those costs to be paid by people who can’t install solar PV. In short, by using solar PV I am stealing from the community and increasing the cost of electricity for everyone else. At this point I would understand if you wanted to just stop reading – why read words by a social reprobate like me?

Except of course that this is just nonsense. There is nothing that I – or anyone else – can do about the assignment of fixed costs to standing/unit charges. The whole mess is the combined result of weak regulation, energy industry lobbying, and government meddling. All no doubt undertaken with the aim of ‘making things better’. But if the side-effect of these historical changes is to cast someone trying to reduce carbon dioxide emissions as a thief, then I think that view is non-sense.

From a wider perspective, we see that the costs of regulatory failure have been assigned to electricity bills rather than gas bills. This political choice drives people to continue to use gas for heating when using heat pumps would save the country money AND reduce carbon dioxide emissions. So by a similar argument, gas users are ‘stealing’ from electricity users.

In short, our energy supply market contains distortions. All the companies that went bust made large profits which were privatised, but their losses are now being spread over all our bills. In other words, the profits were privatised and the losses socialised: standard operating procedure in a mis-regulated monoply. This is a failure of market design and regulation and it’s not my fault!

Home Solar PV: But I’ve got no roof?

Of course if you don’t have a roof, you may feel excluded from this discourse. But by using Ripple, you can buy a fraction of a solar park, and a pro-rata share of the profits will be deducted from your energy bill.

Having previously built one wind turbine (Graig Fatha), and commenced construction of the 8-turbine Kirk Hill Wind Farm, Ripple are now (Spring 2023) looking for people to contribute money to build a solar park in Devon.

The deal is this:

• You can buy a share of the solar park from £25 to a value equivalent to 120% of annual electricity consumption priced at roughly £1/kWh.
• So if annual electricity usage is 2,900 kWh, then if you pay roughly £3,000, you will own a fraction of a solar park that will generate as many kWh as you use in a year.
• Their financial projection is summarised below:

It’s clear the projected savings are modest (~ £180/year) which for a £3,000 investment amounts to about 6%/year.

But it is interesting to compare these cost with the costs of the home solar PV system described above. The Ripple investment is cheaper per kWh generated and gives you less to worry about. For example, you don’t have to worry about pigeons. Of course, none of this is financial advice: honestly: don’t listen to me. I only care about the carbon dioxide.

Keep your eye on the carbon

If you are fortunate enough to have a few thousand pounds to invest, then putting your money into renewable energy projects either on your roof or remotely via Ripple is – in my estimation – a pretty reasonable thing to do. Whatever the location, this reduces the demand for electricity generated by gas-fired power stations and so reduces our country’s carbon dioxide emissions.

Arguments about this being unfair are – I think – spurious. We live in a society in which almost all economic activity generates a ‘trickle-up’ effect that enriches the already wealthy and in general gives rise to net carbon dioxide emissions. In this context, spending resources on renewable energy projects is amongst the least worst things we can do – and helps to build a renewable energy infrastructure from which we will all benefit.

 

Hydrogen for Home Heating is a Scam.

Friends, you may have heard that using hydrogen for home heating is somehow a ‘green solution’ to the question of how we should heat our homes in the future. This is not the case, but fossil fuel companies are still promoting the idea (1 , 2):

• Firstly they suggest that hydrogen heating for a home just replaces a familiar boiler with an outwardly similar device at lower upfront cost than a heat pump.
• Secondly, they additionally spread fear, uncertainty, and doubt (FUD) about heat pumps.

Hy Street!

Companies are preparing hydrogen-burning boilers for domestic applications

Remember each year they delay the transition to heating our homes with renewable energy is another year of profits for their shareholders, and ongoing pollution of our atmosphere. And a world in which we use hydrogen for home heating is a world in which demand for methane (so-called ‘natural’ gas) will increase – not decrease as it must if we are ever to reach net zero.

This article is an explanation of why hydrogen is not any kind of a solution for home heating. It’s complex, but I’ll do my best to be as clear as possible.

But I urge you to keep in mind the key characteristics that any solution to the problem of home-heating must have in order to qualify as a solution:

• It must have drastically reduced carbon dioxide emissions – with an ideal limit of zero emissions.
• And it must have a way to begin that reduction right now: we really have no time left.

If a proffered solution does not meet these goals, it is not a solution at all: it’s a scam.

Shades of Hydrogen

When one combines hydrogen (H2) with the oxygen (O2) in the air to release heat, no carbon dioxide is produced. The exhaust gas is pure water, H2O. So at the point of combustion, all hydrogen is nominally free of harmful emissions.

But to understand its environmental impact one must take account of the amount of carbon dioxide emitted in the preparation of the hydrogen gas, and its transport to the point of combustion. The pre-history of the hydrogen gas is commonly summarised by a colour pre-fix. However, is not actually coloured and it behaves identically no matter how it is prepared.

• Green Hydrogen: Hydrogen which is prepared from water using renewable electricity is referred to as Green Hydrogen. Ideally, it has no associated carbon dioxide or methane emissions.
• Grey Hydrogen: Hydrogen which is prepared by combining water with methane at high temperatures (so-called Steam Reforming) is referred to as Grey Hydrogen. This process produces carbon dioxide which is emitted into the atmosphere.
• Blue Hydrogen: Hydrogen which is prepared by Steam Reforming but in which the emissions are captured is referred to as Blue Hydrogen. This process still produces carbon dioxide emissions because the capture process is never 100% efficient, and it is generally powered by burning methane.

A recent analysis (link) has estimated the  carbon dioxide emissions associated with the production of Grey and Blue Hydrogen. Its estimates of the carbon dioxide equivalent emissions associated with an amount of hydrogen gas which releases 1 kWh of heat are shown in the chart below:

Click on image for a larger version. Chart showing the carbon dioxide equivalent emissions from burning pure methane, green, blue and grey hydrogen. For blue and grey hydrogen, the emissions are shown with and without the effect of methane leaks. A methane leakage rate of 3.5% is assumed.

As discussed below, in this abbreviation the ‘eq’ stands for equivalent. This can be compared with the carbon dioxide emissions associated with simply burning the methane gas directly.

There are two contributory factors to this result. The first factor is the inefficiency of carbon capture and the fact that extra energy is required to process either grey or blue hydrogen.

The second factor is an assessment of rate of methane leaks – so-called ‘fugitive’ methane emissions. The author’s central estimate is that in the global supply chain, around 3.5% leaks directly into the atmosphere. Evaluated over 20 years, this fugitive methane has a heating effect of around 84 times as much as the same amount of carbon dioxide. The warming effect of the fugitive emissions is expressed in terms of the equivalent amount of carbon dioxide emissions which would produce the same warming.

So according to this study, if we convert methane to hydrogen assuming reasonable (3.5%) estimates of methane leakage, there are no reductions in emissions at all. In fact, there is an increase in emissions! If we unrealistically/optimistically assume no methane leakage, then grey hydrogen still has increased emissions, and blue hydrogen offers a maximum reduction in emissions of just 20%.  There is no path to zero emissions using either grey or blue hydrogen.

So the outcome of this research is that using methane  to prepare Blue or Grey Hydrogen may slightly reduce emissions, but even in the best circumstances, not by much. Only Green hydrogen offers the possibility of a fuel which would reduce emissions to zero.

Pure Green Hydrogen

It is not possible to send green hydrogen – or any other colour of hydrogen to our homes at the minute. Firstly, the gas distribution network is currently being used for methane! Secondly, there is not enough hydrogen to supply to the UK. And thirdly, compared to methane, hydrogen has a very low energy density i.e. energy per cubic metre. So to deliver the same heating power into our homes as methane currently does, we would need to operate the gas delivery system at roughly 3 times its current pressure.

Operating a hydrogen gas distribution system at high pressure is a bad idea for all kinds of reasons, but I don’t want to dwell on those reasons right now. All I want to point out is that even with the most ‘advantageous’ assumptions, we are decades away from switching to a pure hydrogen gas distribution system. In those decades, fossil fuel companies propose that we basically just keep burning methane – and delivering them their profits.

But referring back to the start of this article, if we can’t start now, then what is being proposed is not a solution. It’s a scam designed to keep us using methane gas for decades more.

A foot in the door: Hydrogen-Methane Mixtures

So the fossil-fuel industry’s plan to place themselves at the heart of future home-heating is the proposal to mix hydrogen with methane and distribute this through the existing gas infrastructure. Existing boilers can tolerate up to about 20% of hydrogen mixed into the methane, and their power output will only fall by about 7%.

The effect on carbon dioxide emissions per kWh of heating delivered is shown in the two figures below. The first graph is based on an assumption of 3.5% leakage of methane and the second assumes an unrealistic 0% leakage rate.

Click on image for a larger version. Graph showing the CO2-equivalent emissions as the fraction of hydrogen mixed into methane gas is varied from 0% to 20%. A methane leakage rate of 3.5% is assumed.

Click on image for a larger version. Graph showing the CO2-equivalent emissions as the fraction of hydrogen mixed into methane gas is varied from 0% to 20%. A methane leakage rate of 0% is assumed.

Assuming a 3.5% leakage rate, adding either Grey or Blue hydrogen to methane increases the so-called carbon intensity of the fuel mixture i.e. adding hydrogen increases the amount of carbon dioxide equivalent emissions per kWh of heating delivered.

Assuming a 0% leakage rate, adding Grey hydrogen to methane increases the carbon intensity of the fuel mixture but blue hydrogen could slightly reduce the carbon intensity, but only by around 1%.

So when it comes to mixtures of hydrogen in methane, adding blue or grey hydrogen generally results in an increase in the amount of carbon dioxide emissions rather than a reduction. So using blue or grey hydrogen does not represent a solution to the problem of carbon dioxide emissions. And of course, neither blue nor grey hydrogen are renewable – they still depend on endless mining of natural gas – and that is why they are being promoted: they allow fossil fuel companies to continue to carry on as before.

But what about green hydrogen?

Green Hydrogen

Looking at the graphs above one might think that green hydrogen looks like a possible solution to the home-heating problem: it does result in reduced carbon intensity of a green hydrogen/methane mixture. And in a hypothetical future world with a hydrogen grid, it might deliver heating with nominally zero associated emissions.

However, home-heating with green hydrogen is still a bad idea. To understand why one needs consider the renewable energy used to create the green hydrogen.

To create 1 kg of green hydrogen from water using electrolysis requires a minimum of 39.4 kWh of renewable electricity. When that hydrogen is later burned in air, all of that energy will be returned as heat.

But electrolysis is typically only 75% efficient, so more typically it requires 39.4/0.75 ~ 52 kWh of renewable electricity  to create 1 kg of  green hydrogen which will provide 39.4 kWh of heating. And since boilers are typically not 100% efficient, the amount of heat delivered into the home would be reduced further – to (say) 85% of 39.4 kWh – i.e. 33.5 kWh.

Is there something better that we could do with that renewable electricity?

With regard to home heating, Yes. If that 52 kWh of renewable electricity was used to power heat pumps, it would deliver approximately 156 kWh of heat to homes, more than 5 times as much heat as could be delivered by 1 kg of hydrogen.

Click on image for a larger version. Chart showing the amount of home-heating available from 1 kWh of renewable electricity.

This means that to create the same amount of renewable heat, heating homes with hydrogen would require five times as much renewable resource: five times as many wind and solar farms!

Now a hydrogen boiler is cheaper than a heat pump. In ‘ball park’ figures, let’s say that a hydrogen boiler might cost £3,000 to install and a heat pump might cost £10,000. These costs would be paid by the homeowner or landlord. This makes a hydrogen boiler look cheap at first sight.

But the cost to build five times the amount of renewable resource is very large

If we consider the cheapest renewable resource, onshore wind, a 10 MW turbine- big enough to generate on average around 3.5 MW of renewable electricity – this will likely cost around £10M. Nominally this single turbine would supply roughly 3,500 homes with 1 kW of electricity continuously, so one might guesstimate the cost as around £2,800 per household for 1 kW of continuous power.

So if we consider the total system costs, we have:

• For a hydrogen boiler, the ‘local’ cost is £3,000 + 5 × £2,800 to build the required renewable electricity resource to create the hydrogen. So the total cost is ~£17,000.
• For a heat pump, the ‘local’ cost is £10,000 + 1 × £2,800 to build the required renewable electricity resource. So the total cost is ~£12,800.

Now this is very much a ‘back of the envelope’ calculation – and there are many things I have not included, such as cost of building either a hydrogen capable gas grid, or improvements to the electricity grid. And I don’t put any store in the particular numbers in this calculation. But the calculation demonstrates that a green hydrogen ‘solution’ has very large costs that are not immediately apparent. And in the end, all those costs will be paid for by the consumers of the gas: us.

And friends, the UK is nowhere near having sufficient renewable capacity to generate these vast amounts of renewable green hydrogen. So the plan that the fossil fuel companies will try to sell is that they will start with blue hydrogen – and promise to slowly add green hydrogen to the mix. But of course, this will barely reduce emissions at all. But at its heart, the entire hydrogen for home-heating proposal is a scam to allow them to keep producing their toxic products.

In contrast, every home converted to using a heat pump immediately saves tonnes of CO2 emissions per year. So lowering the upfront cost of installing a heat pump through low-cost loans and grants is actually a national saving: it avoids the phenomenal costs of building the vast renewable resources required to produce green hydrogen.

So is Green Hydrogen pointless?

No! Green hydrogen is really important. If we want to live renewable lives then green hydrogen will be essential for some processes. But home-heating is just not one of those processes.

Michael Leibrich has produced a ‘Clean Hydrogen Ladder’ showing processes for which use of green hydrogen will be unavoidable, and processes for which green hydrogen will be uncompetitive.

Click on image for a larger version. The ‘Clean Hydrogen Ladder’. The use of green hydrogen is unavoidable in order to make fertiliser or feed stock for the chemical industry. But it is uncompetitive for applications such as domestic heating.

And we definitely need loads of green hydrogen to serve as feedstock for the chemical industry and for the manufacture of products like steel and fertiliser.

Summary

The solution to our home-heating problem is heat pumps: air source, ground source, air-to-air or air-to-water.

The idea of using hydrogen for home-heating is wasteful. It is a ruse of fossil fuel companies to allow them to keep producing their toxic products. Please don’t fall for this scam.

Perfect Solar Days

Friends, March may have been depressingly dull, but the start of April has been upliftingly sunny. And Tuesday April 4th was a perfect solar day.

Perfect solar days are days in which the sun shines unremittingly from dawn until dusk, with not a cloud in the sky: such days are rare: Typically there are around 10 per year and I try record the solar PV generation from each one. I do this using data from the Tesla App which records solar generation every 5 minutes via a current transformer (CT) clamp on the cable from the inverters.

The graph below shows 12 perfect (or near perfect) solar days from 2021 and 2022. The days are not evenly spaced because I can’t control the weather!

Click on image for a larger versions. Graph showing the daily hour-by-hour generation for a series of near-perfect solar days in 2021 and 2022.

Attentive readers will recall that in November 2022 I had eight extra solar panels installed on the east-facing roofs of Podesta Towers (link). I had expected that these would contribute nothing to solar generation in winter, but that generation would be significant in spring, summer and autumn.

The graphs below show the generation profile for each day for which there is reasonably well-corresponding day from before the new panels were installed. As expected the new generation is very weak in December and January, but by April has grown significantly.

As expected the extra generation from the panels on the North and East is in the morning. Happily, the maximum power looks like it will peak in summer at less than 5 kW – the maximum rating of the cable between the inverters and the consumer unit.

Click on image for a larger versions. Graph showing the daily hour-by-hour generation for a series of near-perfect solar days in 2021 and 2022.

Overall

The aim of the installing the new panels was to create extra generation in the spring and summer which would hopefully be enough to keep the house off-grid for 6 months. This goal has been hampered by the dullness of March, but things seem to be returning to normal now. However the weather is still cold enough to require the heat pump to stay running for another month or so, increasing domestic consumption.

The graphs below all have a vertical axis of kWh/day and the data are smoothed to highlight trends: They compare:

• Domestic consumption and solar generation. One can see that solar generation is rising to be roughly equal to domestic consumption and should soon exceed it.
• Domestic consumption and Grid Consumption. In winter, the two are practically equal, but in spring, grid use is falling as we rely more on solar energy.
• Net Grid Consumption/Export and solar generation. As solar generation rises  we have become net exporters of electricity.

Click on image for a larger versions. Graphs variation of Daily Consumption, Daily Grid Consumption, Net Grid Consumption and Solar PV generation, all expressed in units of kW/day.

 

Another Heat Pump Spreadsheet: Beyond the Rule of Thumb

Friends, around a year ago I wrote an article and made a YouTube video about using a ‘Rule of Thumb’ for estimating the size of heat pump required to replace a gas boiler in a dwelling.

The ‘Rule of Thumb’ is splendidly simple: one just divides the previous year’s gas consumption by 2,900 to give the heat pump size in kilowatts. So if a dwelling used 10,000 kWh of gas the previous year, then one would estimate that it needed a 3.4 kW heat pump. The YouTube video explaining why the rule works has been watched an astonishing 37,000 times, and many people have left comments telling me they found the rule helpful and accurate.

The basic reason the rule works is because (a) most gas consumption is spent heating homes (rather than heating hot water or food) and (b) the climate of the southern half of the UK does not vary that much. The rule of thumb uses gas consumption as an indicator of the amount heat which enters a dwelling and uses climate data – in the form of heating degree days – to estimate how cold it gets in a particular locale. You can find a detailed description here, here, here and here!

But one or two people have told me that it gave them answers they thought were quite wrong. It turned out that these people often only put their gas boilers on for an hour or two per day, and so most of the time their dwellings were unheated. Alternatively, some people – particularly with families – used a lot of hot water every day – and so this formed an unusually large fraction of their gas consumption.

So I thought it would be nice to develop something just a little more sophisticated than the ‘Rule of Thumb’ that would take account of some of these factors. I did this last summer and sent it to an academic expert for feedback. The feedback was devastating: they basically told me that everything was wrong. And despite trying to modify the spreadsheet to meet their criticism, they seemed unmollified. So, shaken, I abandoned the idea for a while.

But recently I have been thinking about the idea again and decided that in fact I thought the spreadsheet was useful after all, and that it could also help with one other problem: sizing of radiators.

The reason I think this endeavour is important is that people who are thinking about installing heat pumps have faced a campaign by the fossil fuel industry and their knowing (and unknowing) shills, a campaign designed to instil fear, uncertainty and doubt (FUD). Every year of delay in installing heat pumps keeps the profits of fossil fuel companies healthy, and impoverishes the world in which our children will have to live.

This is not to say that there are not legitimate questions and uncertainties about installing a heat pump. So this spreadsheet is a transparent tool that can help people make rational choices and – I hope – help them to overcome the FUD.

• You can download the spreadsheet here:Link
• Spreadsheet updated to version 6.01 on 3/3/23

I have tried to make the spreadsheet Good For Nothing™ 🙂 . But mistakes will have slipped through: if you find one, please accept my apology in advance and let me know in the comments.

Spreadsheets Galore

The ‘spreadsheet’ is actually six spreadsheets linked together in an Excel™ Workbook. Each Spreadsheet has its own ‘tab’. Six spreadsheets may sound daunting, but really this could all be on one spreadsheet. Using several sheets actually makes things simpler.

Click on image for a larger version. The introductory ‘tab’ of the Excel™ Workbook showing the other 6 tabs. Users are recommended to save the downloaded copy and experiment with a ‘working copy’.

• The first spreadsheet helps people estimate the average temperature in their dwelling, and also the maximum temperature they like.
• The second spreadsheet helps people estimate the amount of hot water they use.
• The third spreadsheet uses the ideas behind the Rule of Thumb, but modified to take account of the estimates on the first two spreadsheets. It suggests a likely required size of heat pump and a few other building parameters that specialists might find interesting.
• The fourth spreadsheet allows people to see how the area of radiators and the type of radiators affects how hot the water flowing through the radiators needs to be in order to keep their home at the maximum temperature they desire.
• The fifth spreadsheet allows people to make more detailed calculations based on the number, size and type of radiators in their own dwelling.
• Finally, the sixth spreadsheet summarises the results from the previous spreadsheets and estimates the likely savings in cost and carbon dioxide emissions.

Let me show you each spreadsheet works in a little more detail.

Sheet 1: Household Temperature

Click on image for a larger version. Spreadsheet designed to allow a user to indicate the temperature changes in their home throughout a typical winter day.

Click on image for a larger version. As above, but showing a different temperature profile.

On this tab of the workbook, one can specify how the temperature varies inside a dwelling on a typical winter day. There are four times periods and each one can be set to one of three user-chosen temperatures.

The spreadsheet then calculates:

• The average temperature in the dwelling which is useful for calculating the average heat loss and hence energy consumption.
• The maximum temperature required which determines the required power of a heat pump able to heat the dwelling.

Sheet 2: Domestic Hot Water

Click on image for a larger version. Do you know how much hot water your dwelling uses each day.

I have been told that – in the absence of any other information – a good guess for the amount of gas used to heat hot water in a household is 3 kWh per person per day. This tab uses this figure to estimate how much of the annual gas usage is for domestic hot water.

If a user somehow has a better estimate, they can use their own estimate instead.

Sheet 3: Main Calculation

Click on image for a larger version. This ‘tab’ carries out the main heat pump size calculation.

This tab carries out the same calculation as the Rule of Thumb but now with a little more information about a particular user’s dwelling. It incorporates the data from the first two tabs on average and maximum temperatures and domestic hot water usage. It asks the user for the annual gas consumption and their approximate location (within around 100 miles). The location is used to estimate how cold the weather is likely to have been based on analysis of the heating degree-day records from 21 locations in the UK and Ireland.

Click on image for a larger version. This tab carries out the main heat pump size calculation.

The spreadsheet then estimates several parameters that characterise the level of thermal insulation of the dwelling and – most importantly from the perspective of this article – the heat pump size required for the dwelling.

Sheet 4: Radiators

Click on image for a larger version. This tab allows users to see how the area of radiators, and the type of radiators affect the performance of the heating system.

This tab allows users to see how – in general – the area of radiators, and the type of radiators affects the performance of the heating system. First one sets a maximum flow temperature for the system – this is the temperature of the hot water as it enters the radiators.

Heat pumps typically use weather compensation, which means that when the weather is cold, the heat pump increases the temperature of the water flowing in the radiators. For a heat pump the maximum flow temperature required in the coldest weather should ideally be below 50 °C.

Click on image for a larger version. This tab allows users to see how the area of radiators, and the type of radiators affect the performance of the heating system.

The table above shows – for the heat pump size calculated on the previous tab – what combinations of total radiator area and types of radiator will be able to heat the dwelling adequately.

For heat pumps to work at their very best, the temperature of the water flowing in the radiators should be as low as possible while still allowing the dwelling to be adequately heated.

In the example above the heat pump needs to transfer 5,296 watts of heating power to the dwelling.

• The table shows that this would require 9 square metres of single-panel/single-fin (Type 11) radiators, but the same heating could be done with just 5 square metres of double-panel/double-fin (Type 22) radiators.
• Alternatively one might use 9 square metres of double-panel/double-fin (Type 22) radiators because this would require a flow temperature in the radiators 39. 8°C rather than 49.2 °C – and this reduced flow temperature would result in increased heat pump efficiency, and lower running costs.

Sheet 5: More Radiators

Click on image for a larger version. This tab allows users to see how the number, size and type of radiators in their dwelling affect the performance of the heating system.

The previous tab allowed users to see in general terms how the area of radiators, and the type of radiators affect the performance of the heating system. On this tab a user can input the size (width and height) and type of their existing radiators and see whether – for the flow temperature set on the previous tab – they can release enough heat into their dwelling.

Click on image for a larger version. This TAB allows users to see how the area of radiators, and the type of radiators affect the performance of the heating system.

By putting in data on their existing radiators – the radiator type is input via a drop-down menu – the heating power of each radiator is calculated at the maximum allowed flow temperature. The heating power of each radiator is then summed up to see if the assemblage of radiators in the dwelling is capable of providing enough heating power to keep the dwelling warm on a cold day. This is shown as a percentage on a bar chart.

If a figure of 100% cannot be reached with existing radiators, then users can see whether 100% can be achieved by either adding radiators, or replacing radiators with larger ones, or radiators with more panels and fins.

Sheet 6: Summary

Click on image for a larger version. This tab summarises the results from the previous tabs and compares the cost and carbon dioxide emissions of systems using a gas boiler or alternatively, a heat pump.

Nearly finished! This summary tab collects together the conclusions from the previous spreadsheets. If a user enters the cost of their electricity and gas, the spreadsheet will then estimate the likely running costs of a gas boiler and a comparable heat pump.

The annual costs of the gas installation are estimated based on the users estimate of their own gas consumption. The running costs of the heat pump installation are based on an estimated seasonal coefficient of performance (SCOP).

The coefficient of performance (COP) of a heat pump is a measure of the efficiency of a heat pump measured over a period of typically an hour, a day or a week. In mild weather, the COP will be high (perhaps 4) and in cold weather the COP will be low (perhaps 2.5). SCOP measures the efficiency of a heat pump averaged over a whole year.

If a user experiments with different flow temperatures they will find that the lower the maximum flow temperature they plan for, the higher the achievable SCOP and the lower will be their running costs. Typically users will find that with the relative costs of electricity and gas as they are now (April 2023) at a ratio of roughly 3 to 1, a heat pump installation will commonly be a little bit cheaper to run than a gas boiler, but the difference is not very large compared with the capital cost of the installation.

Click on image for a larger version. This tab summarises the results from the previous tabs and compares the cost and carbon dioxide emissions of systems using a gas boiler or alternatively, a heat pump.

And finally – and this is the point of the entire endeavour – the spreadsheet makes a comparison of the carbon dioxide emissions from a dwelling heated either with a heat pump or a gas boiler. It is here that the entire point of running a heat pump becomes clear: carbon dioxide emissions from a heat pump installation are generally around 75% lower than an equivalent gas boiler. And that’s why this matters.

Click on image for a larger version. Graph showing the annual emissions of carbon dioxide from a gas boiler and an equivalent heat pump installations.

The Gas Man Cometh… for the last time

Friends, today was a special day for me. Today, the gas man came and disconnected my house from the gas grid. We haven’t used any gas for a year now – but being physically disconnected from the grid just feels sooooo good.

The gas grid

The gas grid is an international network of pumps and pipes constructed on a scale which is hard to grasp. In extent, it sprawls across Europe – take a look at this astonishing map. And locally, it extends into most individual dwellings in the UK.

When I consider the astonishing magnitude of the decades-long endeavour required to construct such a network, two thoughts occur to me: one depressing and the other uplifting.

Depressing thought

Depressingly, the people who have invested in this network will fight tooth and nail to keep extracting ‘value’ from it.  To these people – which probably includes my pension fund – the fact that the toxic gas they transport is leading to climate change is of no interest. In their perception, Climate Change is indeed an existential threat, but not because it is a threat to humanity. Instead they see Climate Change as an existential threat to their business model. They have no corporate interest in humanity.

The businesses that operate on this grid extract value from shipping stuff through it. And if governments restrict their right to sell methane – so-called ‘natural’ gas – because of its climate impacts, then they will see shipping hydrogen as an opportunity, despite its unsuitability for domestic heating.

Because they take no responsibility for the climate impacts of their business, they will use their power to lobby on behalf of using hydrogen or hydrogen-blended with methane. This is just an insidious attempt to try to continue to extract ‘value’ from their network: it is not based on rapidly reducing carbon dioxide emissions. Rather their aim is to prolong methane extraction which they will process, at a cost, to produce hydrogen.

The uplifting thought

The uplifting thought is that the colossal gas grid was constructed over decades, one project at a time. And this gives me hope. Because every new wind or solar farm, every new battery storage plant, every new electricity grid interconnection is another step in the construction of the infrastructure for renewable energy.

I believe that eventually we will look back with horror at the idea of delivering toxic, asphyxiant, explosive gas directly into people’s homes. Gas which people burned for cooking, emitting toxic irritant combustion products directly into their kitchens. And we will be appalled at the idea that we ever thought it acceptable to allow the average UK dwelling to emit more than  two tonnes of carbon dioxide every year: TWO TONNES of a gas which is changing the climate of Earth.

Friends, the future is coming, one gas-meter-removal at a time.

The privilege of being allowed to speak

On stage at the Emmanuel Centre.

Friends, I had a busy day last Thursday.

Despite forgetting there was a train strike, I managed to make it into London to speak to roughly 600 sixth formers in the morning. And then I loitered in central London before travelling to Hampstead in the evening to speak to the Hampstead Scientific Society. Eventually, I arrived home at a quarter to midnight. By my retirement standards, it was a busy day.

Morning 

The morning talk (similar to this one) was for Physics in Action. The first part of the talk clarified the fundamental reason why carbon dioxide emissions affect the climate, and the second part emphasised the opportunities that the energy transformation offers us. And in particular – the opportunities for young people to engage in meaningful and noble activities throughout their lives.

I thought it went well. I broke at half-time to take questions – and there were a couple of interesting points raised. And I finished on time – especially important when one is sharing with other speakers.

And then students queued up to ask questions. And it was at this point – as students spoke to me personally that I realised that they had listened to me, synthesised what I said with their own understanding, and were actively processing the ideas I had put forward. One student in particular spoke movingly and coherently about the unfairness of some the steps required to minimise the extent of climate change, pointing out the impact could be to make life worse for the poorest in our society.

After I had spoken, I sat quietly at the back of the Emmanuel Centre listening to the next talk and reflecting on the diverse lives and backgrounds of each one of these students.  Including my previous talks for Physics in Action last December, I have probably addressed almost 2,000 young people and their teachers. And as I sat there recovering, I reflected on the privilege of having been invited to address them. In this special educational context, they had allowed my words to enter their minds and – I hope – frame some of the things they are learning and the decisions they will make. It maybe that I overestimated the impact of the talk, but the responsibility felt overwhelming.

Perhaps teachers feel this all the time. Or perhaps they feel it in quieter moments, if indeed teachers have any quieter moments left.

Evening  

After the talk, I wandered past the Houses of Parliament and then along the Southbank in awe of the magnitude of the edifices that the wealth of the Empire had once created.

Amongst the throng of people on the Southbank were gangs of – I presume – criminals playing 3-cup tricks and a man blowing gigantic bubbles for no apparent reason.

In the evening I headed up to Hampstead to give a similar – but extended talk – to a much older audience in the crypt of St John’s Church: it was not as spooky as it sounds!

This was a much smaller and more combative group. Most people acknowledged the basic physical reality of Climate Change, but there was no end of questions on all kinds of peripheral topics and the evening was lively and pleasant. But the nature of some of the questions made me appreciate just how pernicious and effective are the efforts of fossil fuel lobby groups.

I say this because when talking about heat pumps there were the perennial questions about heat pump noise and the superiority of ground-source heat pumps over air-source heat pumps. When talking about solar panels and batteries there was concern expressed about the embodied carbon and about the imminent arrival of fusion power which would solve all our problems.

In general terms, all these questions are perfectly legitimate. But these ideas have been planted in people’s minds to spread Fear, Uncertainty, and Doubt (FUD). As this week’s IPCC summary report makes clear: we need to act urgently. Spreading FUD creates delays, and every year of delay in implementing practical solutions which cut fossil-fuel use is another year in which fossil-fuel companies continue to pollute our atmosphere and to make profits: their raison d’etre.

A younger me might have said to present-day me “Oh Michael, you are being too cynical“. But present-day me no longer thinks so. We live in a world where right-wing papers claim that heat pumps don’t work; or that they don’t work in older properties; or that the current high prices of electricity and gas are somehow the fault of renewable energy providers. Or that nuclear fusion is a realistic possibility.

Home  

As I travelled home my head was buzzing and I reflected again on the privilege of being asked to talk to both groups: youngsters who will live through changes in climate that humans have never experienced, and oldsters who are struggling to understand what they can do to effect change.

If you would like me to speak to a group to which you belong, and I can get there by public transport from Teddington, I would be honoured to oblige.

Assessing Powerwall battery degradation: End of Winter of 22/23

Friends, three months ago in December 2022, I wrote about my technique for estimating the degradation of the capacity of my Tesla Powerwall 2 battery (Link).

The idea was to consider data from days in which the battery is charged to 100% capacity at night, and then discharges fully to 0% during the day. This only happens in winter when household demand is high and solar PV generation is low. After correcting for any solar generation one can make a reasonable estimate for the practical working capacity of the battery.

Click on diagram for a larger version. Illustration of day in which the Powerwall fully discharged.

We have now had another 60 days during which the battery discharged fully and using the same technique I described previously, I have re-evaluated the degradation of battery capacity. The results are shown below in two graphs: it’s the same data in both graphs they are just plotted on different times scales.

Taking all the data into account, the trend line suggests that battery capacity is degrading at roughly 2.6% per year. Since the battery has a nominal capacity of 13.5 kWh, this corresponds to a loss of capacity of 0.35 kWh/year.

Click on image for a larger version. Full discharge capacity plotted versus date. The blue dots show all the data and the dots surrounded with a pink circle show data with solar contribution during the day. The trend line suggests capacity is being lost at 2.6%/year.

The Powerwall was installed in March 2021 and if the degradation were to continue at 2.6%/year in future years then the battery would lose 10% of its capacity by the winter of 2024, and 20% of its capacity by the winter of 2028.

Click on image for a larger version. Full discharge capacity plotted versus date. The blue dots show all the data and the dots surrounded with a pink circle show data with solar contribution during the day. The trend line suggests capacity is being lost at 2.6%/year.

What to do?

Nobody wants their £10,000 battery to be losing capacity. But there is very little I can do about it! It’s inherent in the nature of the batteries and of the charge/discharge cycles they experience.

One option would be to prevent the battery from fully discharging by forcing it to retain, say, 1 kWh in reserve. However, while this might reduce the rate of degradation, it would deprive me of the battery capacity that I was hoping to preserve!

So my plan is to do nothing. If the degradation continues at this rate I will still have a 10 kWh battery in 2031 – and that’s still a very useful size of battery.

If I feel the need for more storage, my thought is that it would probably eventually make sense to upgrade one of my solar PV inverters to be a hybrid inverter, and then add extra battery capacity in the loft. These batteries will have the Lithium Iron Phosphate chemistry that is supposed have very low degradation. This option would likely cost much less than buying a replacement – or additional – Powerwall.

Of course, by the time this becomes important Powerwalls may have fallen in price and be readily available (!). Or the use of batteries in vehicles for domestic storage may have become commonplace.

In short, this is tomorrow’s problem.

 

Tariff Calculation Spreadsheet

Friends, as you may or may not know, Saturday night is the night of week I like spend documenting large spreadsheets. Lucky me!

In this article I will be describing how to use the spreadsheet I have developed over the last couple of weeks and used in the last couple of articles. The spreadsheet allows one to estimate the likely costs of using particular electricity tariffs – the Octopus GO, FLUX and COSY tariffs – if your dwelling has a domestic battery and solar PV panels. My hope is that it will help people make rational choices about which option is best for them.

Download

The Excel spreadsheet can be downloaded from this link [link updated to v3.2 on 23/3/2023], If you are downloading this macro-enabled file on a Windows computer, then the macros will probably be blocked by default. To change this you may need to first close the file in Excel, then right-click on the file’s icon and select the ‘Properties’ pane. Here you should see a tick box labelled “unblock”. If you unblock the file then it should work correctly.

Please note, the spreadsheet comes with no guarantee of anything at all, and it can at times be very slow to re-calculate.

Structure

The spreadsheet consists of two parts.

• At the top are several boxes that set the parameters of the simulation, and which show the results. I think of this as a ‘dashboard’
• Below this are 8,760 rows, one for each hour of the year. The spreadsheet proceeds through the year hour-by-hour simulating the flows of electricity from solar PV panels and the grid, into and out of batteries and your dwelling.

Throughout the spreadsheet, cells which are ‘inputs’ i.e. cells that you might reasonably want to change, have a yellow background with red text. Cells which are ‘outputs’ i.e. which contain the results of calculations have a red background with white or yellow text.

Click on image for a larger version. The visual appearance of ‘inputs’ and ‘outputs’.

The Dashboard: Overview

Click on image for a larger version.

The dashboard has controls in four regions.

• Regions 1 & 2 are about the tariff being simulated and the prices of the tariffs in each of their cheap, medium and high periods.
• Region 3 sets the parameters of the battery and the charging strategy, the amount of solar PV generation, and the likely household load.
• Region 4 contains the results of the simulation.

The Dashboard: Tariff Section

Click on image for a larger version.

After selecting the tariff to be investigated in the drop down menu, the selected tariff will appear in the box on the far right.

The prices of the different tariff stages can be changed if you desire.

The timings of the tariffs cannot be changed on the spreadsheet. They are set in a Visual Basic macro with the code below. If you understand this sort of thing then you can see how you could adapt the spreadsheet to a different set of tariff timings.

Click on image for a larger version.

The Dashboard: Main Settings

Click on image for a larger version.

The settings for the simulation have four main parts.

The Battery Settings are as follows

• Battery capacity describes the amount of electrical energy the battery can store.
• Round trip efficiency accounts for the energy lost as electricity is stored in the battery and then later drawn from the battery.
• Charge Rate is the rate at which battery charges. This limits how much electricity can be stored in the battery over a given period.
• The initial state of charge is the assumed state of charge at midnight on the 1st January.

Click on image for a larger version.

The cells referring to summer and winter should really be in the neighbouring box about charging strategy [Edit: they have now been moved]. Why are they there? For some systems, it can be sensible to switch between different charging strategies through the year, depending on the amount of solar energy available. For my own system:

• In winter I charge the battery at night using cheap rate electricity and the battery then runs down during the day.
• In summer, there is no need to charge at night because the battery is charged for free during the day by solar PV electricity.

The two boxes allow one to choose the days of the year on which to switch strategy.

In the ‘Grid Charging Strategy‘ box one can choose between charging when electricity is cheap, and/or charging in the hour before electricity becomes expensive. Either option can be chosen to be active in summer, winter or both.

In the solar factor box, one can set the expected amount of solar generation expected. This is generated by scaling the hour-by-hour solar data by the factor shown in the box.

Note that selecting a target amount will give an accurate result if the average solar generation from 2005 to 2016 is selected in the drop down menu at the bottom of the box. If one selects solar data from a particular year then the amount of generation will vary in line with that years variable output.

Click on image for a larger version.

The final box simulates how electricity demand from the household changes through the year.

Click on Image for a larger version.

Demand consists of two components: a steady consumption every day, and a component which peaks in mid-winter simulating the use of a heat pump.

The length of winter depends on a setting from 1 to 5 as shown in the figure below.

Click on Image for a larger version.

How the simulation works.

Each row of the spreadsheet from row 48 downwards calculates the state of charge of the battery, the household demand, and the solar PV according to the settings on the dashboard.

The simulation works row-by-row proceeding hour-by-hour through the year. The columns are as follows

• A: Index
• B: The day of the year expressed as a decimal day.
• C: The hour of the day, used for calculating the appropriate tariff
• D: The season of the year WINTER or SUMMER according to dashboard settings
• E: The Tariff Rate (cheap, medium, or high) determined by the Visual Basic code described above.
• F: G: & H: The hourly background & variable consumption – and their total.
• I: The daily average of the demand
• J: The time of day expressed as a fraction of a whole day
• K: Blank
• L: The 3-day running average of solar generation (used for plotting)
• M: The hour-by-hour solar data selected in the drop down menu in the SOLAR box. This is looked up from the data table in columns AE to AQ
• N: Modified demand: this is the difference between current demand and the amount of solar PV currently being generated.
• O: The amount of energy delivered to the battery (if positive) or drawn from the battery (if negative). This is calculated according to the current state of charge of the battery.
• P: The amount of energy drawn from the grid (if positive) or sent to the grid (if negative). This is calculated according to the current state of charge of the battery.
• Q, R, S, & T : Imports: If column P indicates that electricity has been imported, columns R, S and T list the amount of it in each tariff charging rate: these columns are then totalised at the top to calculate the annual amount to be paid.
• U, V, W, & X : Exports: If column P indicates that electricity has been exported, columns U, W and X list the amount of it in each tariff charging rate: these columns are then totalised at the top to calculate the annual amount of revenue accrued.
• Y: Hourly cost of grid imports
• Z: Hourly amount due from grid exports
• AA: Depending on the charging strategy this is when the battery charges from the grid. Household consumption is also met by the grid during these periods.
• AB: The amount of electrical energy sent to the battery.
• AC: The current state of charge of the battery.
• AD: Blank
• AE to AQ. Hourly solar data for the years 2005 to 2012 downloaded for the EU Sunshine database for my 4,000 kWh/year solar system in Teddington.

Graphs

Click on Image for a larger version.

Scrolling down  the spreadsheet will show four graphs which can be helpful in understanding what is happening.

The first graph shows three quantities charted across each day of the year:

• The 3-day average of the selected solar data
• The daily household demand
• The capacity of the battery

The second graph shows the state of charge of the battery charted across each day of the year.

The third and fourth graphs show the state of charge of the battery during a typical summer and a typical winter day.