VoxSolaris: The Voice of the Sun
Combined Heat & Power

Not quite killing two birds with one stone

At first sight, combined heat and power (CHP) systems kill two birds with one stone. The centerpiece of a CHP system is the generator powered in most cases, by either a gas turbine or an internal combustion (IC) engine depending on the size of the installation. The generator provides electricity while the waste heat from the engine or turbine provides hot water and space heating. Generally electricity is quite a bit more expensive than gas, sometimes to the point where even in the summer when the heat is sent to waste, it is cheaper on an incremental cost basis, to run your own generator. In the winter when both electricity and heat are needed, the benefit of CHP becomes clear.

But the take up of this technology has been surprisingly small. In many cases where it has been installed, the need was for a more reliable power supply rather than a cheaper more benign energy regime. Hospitals needed to generate their own electricity becuase relying on the grid alone would regularly result in a lot of fatalities in the operation theaters and intensive care units. Once the need for a generator opened the door, CHP was an easier sell but even then, many hospitals have not taken this up and instead waste the heat from the generators while burning gas in the boilers. It is not altogether clear why the market has shuned CHP when the savings are there to be had. The stone has hit the two birds but appears to have done little more than ruffle the feathers. Perhaps CHP bores people to tears. By contrast, technologies such as solar voltaic cells have captured the imagination and sold well long before they were economic, even without subsidies.

Off grid and any fuel will do

What we like about CHP is the independence it offers. Without a generator of some description, you cannot have a reliable power supply unless you go for a very large battery. With the usual combination of solar and wind, you can probably ensure a reasonable reliable power supply if you have a battery capable of storing 2 days of power. But you could be shaded and becalmed for 3 days or even a week. What then? Have a battery capable of storing 7 days of power? That with the most established battery still being lead acid, adds up to a lot of money for something you may never use. A generator will cost about the same 10KWhr of storage, for many that is only one day's worth.