The llamas are horrified. Their field behind our house in the Derbyshire Peak District looks like a scene from the Great War. Two 100m trenches, almost as deep as a man is tall, stretch away up the hill. Everywhere are mountains of earth, and car-sized rocks. 200 tonnes of sand arriving in lorries. A digger is working, finishing the second trench, and loaders are shunting sand back and forth.
I feel seasick, nursing my abused cheque book, comforted only by the knowledge that in a week’s time the field will be returned to its former aspect — save for two long strips of bare earth where trenching has been filled in again. I can reseed them.
But deep beneath the surface will lie an invisible skein of black plastic piping, encased (against sharp rocks) in a core of sand. And the piping will converge on two valves beneath a manhole, from which will run two big conduits, leading through the wall of our holiday cottage into the utility room. Here will sit, humming softly, a machine about the size of a fridge-freezer. One conduit will bring “brine” (water laced with antifreeze) from beneath the field where it has been gently warmed by the soil, into the machine. The other will carry away the brine, refrigerated by the machine, to rewarm beneath the field. The machine will provide us with copious hot water for central heating and domestic use.
This is the first and biggest step in the plan I set out on this page last year, to make our property in Derbyshire self-sufficient, using “green” energy. Few householders are as lucky: I have fields, woods, my own water supply, sewage system and reed-beds. But I hope to learn — and pass on — lessons from this project. At its core is something called “ground-source energy”: a means of home-heating that other European countries have been readier to adopt than us. But if the experience of the Sheffield company supplying my heat pump is typical, Britain is fast waking up to the idea.
In Switzerland every third new building is equipped with a heat pump. In Sweden seven out of ten new builds rely on this technology. In Germany, too, it is catching on. Because the installation makes a huge mess inside and around a house, the technology is most obviously applicable to new construction. My stone buildings are centuries old; but I have decided to brave the cost and inconvenience. If the system works in the large holiday cottage beside our house, we will adopt it throughout.
Perhaps because the concept of heat pumps stumps and mystifies people, the invention has never attracted the band of true believers that (say) wind turbines, or “hot rocks” (geothermal) energy, or even nuclear fusion or fission, have. The whole idea seems counter-intuitive. How can a simple compressor pump suck heat out of seemingly nowhere? How can you turn something cold into something warmer without putting energy in?
But it works; and on inspection the mystery dissolves. Did you know that the standard kitchen fridge is a heat pump in reverse? Your fridge cools its interior and dumps the heat outside: into your kitchen through the grill behind the back. My kind of heat pump will dump the cool and keep the heat. Indulge me — no physicist — in 500 words of explanation, for this idea may prove a big component of Europe’s future energy philosophy.
Unlike combustion, heat pumps do not create heat: they move it from one place to another. “Fair enough,” you say, “but how come the place you heat gets hotter than the place you got the heat from? Isn’t this something for nothing?”
No. Put a hot teaspoon into a bucket of cold water. The spoon will be cooled a lot, the water warmed just a little. Overall, you have not gained or lost heat by this move: you have simply transferred it, spreading out the heat from a small mass of hot material, into a large, cooler mass that it will slightly warm. Well, how about doing this in reverse and ending up with a hot teaspoon and a slightly cooler bucket?
This is essentially what a ground-source heat pump does: it collects a lot of low-level heat from one place and “concentrates” it into a little high-level heat in another. It slightly refrigerates a waste of stuff that doesn’t matter — the soil around the house — and greatly heats a little of something that does — your hot water tank and central-heating system.
How? Consider two everyday examples. When you use a bicycle pump the nozzle heats up. And after a long blast with an aerosol spray, the nozzle gets cold. This is because when you compress a gas (or condense it into a liquid) it gets hot; and when you evaporate a liquid into a gas (or decompress the gas) it gets cold. So to pump heat from one place to another, we make a closed loop and pump gas around it, compressing and liquefying where we want heat delivered, then decompressing and evaporating where we want it to capture its next load of heat. This does use energy, but not much: the electricity to drive the compressor/circulator pump.
A ground-source heat pump gathers heat into a hot water tank for your house — and captures it from a much larger body of water (“brine”) which is being pumped round a huge circulatory system running in pipes hundreds of metres long, beneath your land. Here the refrigerated fluid warms up again, to be reused, bringing the heat back to the heat pump and its gas-filled loop. The whole system will deliver about four times as much energy (in the form of heat) as it consumes (in the form of the electricity).
The ultimate energy source is sunshine — but a metre or so down, soil temperatures do not fluctuate wildly with sunrise, sunset and the seasons, but level out, varying gently around 10C. This unlimited supply of low-level heat at a fairly steady temperature is ideal for the delicately balanced gas-circulation system of the machine.
Other heat-pump systems use the air, not the soil, for heat collection. Or you can take it from rivers or wells. And for ground-source you can go vertically down, putting pipes into bore holes if you are short of space. But I have chosen to use my field.
I wondered last year whether the Peak District National Park (our local planning authority) would prove a stumbling block. Quite the reverse. It seemed enthusiastic about green-energy schemes and a young officer came to talk to me about mine. He was positive. Before Christmas I went to see a new ground-source scheme in successful operation at a farm near Tideswell, and since then the owner has received planning permission for a small wind turbine too. This is on my list also, but not yet.
My only problem with bureaucracy has been that the earthworks for ground-source require planning permission. “If permission is finally refused,” the lady in the office warned me, “you may be required to put everything back to how it was before.”
“I’m doing that anyway,” I said: “I’m digging a trench then filling it in again.” So I went ahead regardless.
David Cameron’s new and greener Opposition should look again at planning laws. Perhaps for a range of defined green energy applications there should be a presumption in favour of permission, shifting the onus on to the planning authority to demonstrate exceptional reasons why it should be refused.
That aside, the National Park authority seems encouraging and interested. People around me share the curiosity, and a stream of visitors has come to take a look. Coincidentally, in nearby Youlgreave a group has formed to develop ways of making the whole village more energy self-sufficient. A tide is turning in public attitudes and public interest.
Oh dear. We’re going to have to move the llamas. Their horror has turned to fascination, and there could be a horrible accident with a digger. But I’ll keep you posted on progress — and, in time, with how the economics work out. What fun, to be a pioneer.
Matthew Parris
