The BBC reports today on the commencement of a Geothermal Energy project in Newcastle. The academic in charge, the esteemed Paul Younger, says that ‘geothermal energy operates 24/7’ and the reporter happily parrots the factoid that in July the borehole will produce ‘water with a temperature of 80 ºC’. And as I listened and read, I searched for the fact that would change this from PR for Newcastle University into reporting. The reporter should have asked ‘How much?’. As in:
- How much water will be produced at 80 ºC each day?
My suspicion – and please forgive me for being suspicious – is ‘not much’. I can boil water with a magnifying glass on a sunny day, but not much! In order to make sense, such a scheme needs to capture not just hot water, but lots of it!
What is your point Michael?: Now I think this is a great research project and I am glad that we collectively are funding it. But except in a rather small number of locations, the amount of heat rising up through the Earth per unit area of Earth’s surface is tiny: somewhere close to 0.1 watts per square metre. In the UK the average is less than this, excluding Cornwall the measured values are in the range 0.058 ± 0.016 watts per square metre. So to produce an output of (say) 100 kW(thermal power) requires the collection of the heat from an area around 1 kilometre x 1 kilometre. This either requires a complex arrangement of boreholes, or the exploitation of water seepage through natural cracks in the rock. All in all it amounts to a complex engineering structure and it does not run itself. Water must be pumped, cleaned, and returned or disposed off. If the thermal output were 100 kW at 80 ºC this would involve the production of 400 millilitres of water per second, or around 34 cubic metres of water per day.
Cost: My (optimistic) guess is that such a piece of infrastructure might cost on the order of £1million to construct. It could replace the heating of 33 standard 3kW immersion heaters (Capital Cost ≈ £500) or around 5 standard domestic gas boilers (Capital Cost ≈ £15000). I can’t guess the running the cost of the geothermal project, but if we imagine that the £1million must be repaid at 0% interest over say 10 years the cost is ≈£100,000 per year. If we imagine we need to maintain the facility or manage it in some way or pay for the pumps then the cost would be more than this. For immersion heaters, the running cost is £175,000 per year assuming one pays 20 p per kWh. And for gas boilers the running cost is £40,000 per year assuming one pays 4 p per kWh. So the capital costs of a geothermal project are enormous, and the running costs are similar or higher than conventional options. If a council said it was going to take £1million of its residents’ money to invest in such a project, but that there would be no financial benefit to the residents, then I think we all know what would happen to the council.
So what?: Now the carbon costs of the geothermal project are difficult to estimate – drilling through rock is amongst the most energy intensive activities conceivable! – but I have gone through this analysis to make one simple point.
- However much we might like geothermal energy to be implemented, it will not happen until it makes economic sense.
And it won’t make economic sense until energy prices rise way beyond current levels.
- PDF version of a presentation by Paul Younger and colleagues on a previous project. I found it very hard to work out how much power they extracted from their boreholes.
Tags: Geothermal Energy