QUESTION: What’s the appeal of solar energy?
JPG: Aside from photography I’m really enthusiastic about renewable energy!
QUESTION: Are you a tree hugger?
JPG: Well I believe the earth should be better looked after and we all need to do our bit to make the best use of earths resources. I’m especially interested in renewable energy; I’d really love a water wheel but I don’t have a stream in my back garden.
QUESTION: So what’s the motivation behind designing and building an alternative energy system?
JPG: In addition to reducing energy bills and mitigating price increases of domestic gas and electricity, I also wanted the reassurance of a hot shower and a hot dinner should energy supplies become intermittent.
QUESTION: Can you outline your design and tell us how effective it’s been?
JPG: Sure. At the heart of the system is a 1000 litre thermal store (TS) — that’s a large hot water tank to you and me. The TS supplies the domestic hot water by means of an efficient heat exchange coil; cold mains-pressure water is fed in and hot mains-pressure water comes out. Great for showers! I like showers! The hot water coming out of the TS is too hot for domestic consumption and so it’s mixed with cold water to prevent scalding.
The radiator system, and there are 13 of them in this 6 bedroom, 3-story house, is also connected to the TS. I have included a diagram to better explain the logical blocks of the system design, the hot water circuit is not shown here but utilises the heat exchange coil located in the top of the TS.

The TS temperatures vary and typically operate as follows:
1. Top third: 60ºC — 75ºC
2. Centre third: 40ºC — 60ºC
A Siemens Logo is used to control the pumps, it monitors temperatures and in situations where the top tank temperature exceeds 83ºC, the radiator circuit is activated to dump excess heat. We don’t tend to run the solid fuel system in the summer so much, and it’s therefore not a problem. In the winter it’s the desired side-effect!
You’ll notice from this diagram that there are 3 heat sources — all feeding into 1 system and all coexist quite happily. Our gas bills have quite frequently been £zero, even in mid-winter. The irony is, we’re more likely to use gas in the summer for cooking as the solid-fuel heat-source is a cooker and oven too and kitchen temperatures could get a little unbearable!
The gas boiler is used as a standby only. Regardless of other heat-sources, the solar-thermal always get busy when the sun shines. Recent refinements have drastically improved the effectiveness of the solar-thermal system:
The solar-thermal pump is activated at mid-TSºC+20ºC. For example, if the mid-tank temperature is 60ºC, the solar-circuit is activated when the solar-array reaches 80ºC. Crucially, the circuit is deactivated at a precise point to prevent TS heat being lost due to over pumping.
The solar array heats at the rate of 0.1ºC/sec on a bright sunny day. So for May, June, July and August I fully expect the solar array to supply most of our hot water, sufficient for 4 adults, 2 washing machines, showers not baths.
QUESTION: Where did you get the design from?
JPG: I made it up! I cannot find any reference to a system like this online.
I will write more about this system at a later date.