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Approximately 2 years ago I designed and built an alternative energy system for my folks. They live in a large Victorian house; 6 bedrooms, 3 floors. The gas bill for the past 12 months which includes the coldest winter for 100 years was £3.60. Needless to say the gas supplier has inspected the meter, no doubt checking for foul play!

The challenges

1. Reduce heating bills
2. Overcome the issue of poor hot water supply to top floor
3. Introduce the possibility of cooking on solid fuel

Reducing the bills

Owing to a plentiful supply of free wood the aspiration to reduce heating bills was more than a theoretical possibility.

Increasing hot water supply pressure

The old hot water tank was replaced with a Gledhill 400 litre Thermal Store (TS). And this cunning plan enabled mains pressure hot water in one easy step.

No longer cooking on gas

Compared to the cost of heating a large home, cooking on gas is not a large consideration — even at today's gas prices it's still cheap. However, it's no bad thing to have the option of cooking on solid fuel or gas and if the solid fuel range is used for cooking it's heating the water and the house too. We installed one of these: http://www.fireplaceproducts.co.uk/Stoves-Cookers/Sideros-Desiree-860-Idro-Wo... (Not the same name but it is the same unit).

My design

It's a bit too complex to explain in detail, I'll let the drawing do that. Suffice to say, the domestic hot water and central heating are supplied by any combination of 3 heat sources.

1. Evacuated tubes on a south facing roof
2. Solid fuel
3. Gas

If the sun shines the tubes get busy and preheat the water but, to be honest, I don't think they've been worth the investment.

The gas boiler is hydraulically common with the TS and heating system but heats the TS by means of an indirect coil. The boiler will not fire if there's no load i.e. if the water temperature is above a preset TS temperature.

The solid fuel boiler heats the 400L TS to a maximum of 85ºC. Above this temperature an overheat condition triggered and hot water is pumped to the radiators to bring the operating temperature back to safe levels.

Schematic

Net result

I have just completed a version 2 redesign followed by a system rebuild and reprogramming of the Siemens LOGO! PLC. All seems to be working well so far.

If the wind will not serve, take to the oars — Latin proverb