What is Cogeneration?

Most electricity is generated by large central power stations using big steam turbines which spin alternators that produce the alternating current (AC) electricity we use at home. The steam is produced in a large boiler fired by coal, oil, natural gas or a nuclear reaction. Not advertised widely is the fact that this process is very inefficient. Only 30-40% of the thermal energy is converted to electricity. The rest is lost as heat. This is typically lost to the atmosphere using a cooling tower, or warms up the local river, lake or sea water from which the cooling water is drawn. To make matters worse, about 8% of the electricity produced is lost in transporting it to your home. With the exception of nuclear power (which has a few problems of its own), the amount of greenhouse gases produced to produce all this heat which is wasted is enormous.  

















But, it gets worse. On a cold day, whilst the power station is busily heating up the local river or whatever with vast quantities of heat, your house is stone cold. So what do you do? Burn some more fossil fuel of course. So at the expense of even more greenhouse gas emissions you burn up energy, typically in the form of natural gas, to heat your home.

So what is the answer? What if every house was equipped with its own small power station? Then the heat produced as a by-product of the generation of electricity would heat your home rather than the river. You would not need to burn additional fuel to keep your house warm. The energy savings are enormous. A 35% saving is quite achievable, as the picture above shows. So are the reductions in greenhouse gas emissions - in fact a household can save several tonnes of CO2 in a year. This process is called co-generation. The name refers to the combined generation of two useful things at simultaneously, heat and electricity. It is sometimes also called Combined Heat and Power (CHP). This process has been used in industry for decades, where heat is required for factory processes and the electricity powers the machines. Household size systems (less than 10kW electrical, and more typically 1-3kW electrical) are called micro cogeneration or micro CHP systems. They are still rare, but we are changing that.


How it works in your home