You might be forgiven for asking why anyone would want to do this. We live in a country where electricity is readily available. We don’t even worry about power cuts, and rarely seem to get them. The problem is that most of our electricity is generated from coal fired power stations and they’re only 35% efficient. There are different kinds of gas generators and some of them can achieve much higher efficiencies than this. Generating electricity from a CHP unit uses only a fraction of the fuel.
CHP has been around for a long time in industrial buildings. You would need a smaller boiler to provide central heating to a house as an industrial boiler would be too powerful. Domestic boilers are in the range of between 10 and 35 KW and some companies have begun making CHP units of this size that can be used in houses. The CHP produces electricity as long as the central heating is running. This electricity can be used in the house or if there is too much electricity produced (which is quite likely) this can be exported to the national grid.
The Baxi Senertec Dachs uses an internal combustion engine similar to the one in a car. Ordinary car engines are incredibly inefficient but most of the waste energy from a car engine is converted into heat. In a central heating system, heat is what you need. If the engine is producing a lot of heat the gas boiler won’t have to work as hard. So the Baxi system has an overall fuel efficiency of 92%.
The Samad Power Turbo Green Boiler uses a gas turbine similar to a jet engine. This is the kind of gas generator used in power stations and has an efficiency of 75%. In the Samad system the hot gases from the exhaust are used to heat a series of metal plates (heat exchanger) which heat the hot water.
Is CHP a good idea? CHP suffers from intermittency. It can’t generate all your electricity because the heating system isn’t on all the time. When it does come on it might generate far more power than you need at that moment. You can export it to the grid but many people think the government’s Feed In Tariff isn’t all that generous. If we one day develop a cheap and efficient way of storing electricity we’d be able to store the electricity when the central heating came on and use it at any time. The national grid would be used in emergencies – during a hot summer when the heating hadn’t been on for a few days. It might be a really useful way of generating cheap electricity one day.
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