Most power systems produce at least a small amount of heat during operation. This is a result of inefficiencies in the system as well as friction. Heat generation is the largest energy drain in a home system. So, it stands to reason to couple the systems together. If the overall system is designed well, this “waste” heat can be used.

Most home-sized combined heat and power systems work using Solar Thermal energy as the input. The thermal energy is converted into mechanical and electrical energy by using a heat engine (stirling) or turbine (steam or rankine). Once the engine has used some of the energy, the working fluid will still contain a considerable amount of heat, but the engine will not be able to take advantage of this energy. A water heater can transfer the waste heat from the working fluid of the heat system into hot water for domestic use. A heat based refrigerator could also be used to take advantage of this “extra” energy. In fact, there are countless ways to use heat, from heating our homes to cooling them.

Combined Heat and Power systems have overall efficiencies beyond 60%. This is because the overall system is a combination of two smaller systems. Each of the smaller systems have an overall efficiency of around 20-30% at best. But when combined, each system feeds the other, creating a highly efficient system. Additionally, why should this method be limited to just homes? We believe that this type of system should be introduced into commercial buildings like shopping centres, office blocks, hotels, even airports also. You can picture the smile on the accountants' faces in the Love Money or Big Buck Corp offices as they count up the savings they've made – whilst also being green! These figures mount a serious argument for a movement towards Combined Heat and Power systems being installed in all buildings.

When coupled with solar collectors, the Solar CHP system is far more efficient than solar PV technologies. And instead of using electricity to generate heat, you are using the byproduct of the electrical generation as the heat source. Generating heat with electricity is big energy waster, and for an off-grid system, it is a sin. Use the exhaust from a generator, or better yet, from a solar stirling to heat that water, instead of using costly electricity.

But wait a second, I thought electricity was free in an off-grid homestead. Well, it is and it isn't. It is in that you don't pay for it as you use it, but it isn't free in that you pay for it upfront. You pay for the generator, but rarely the fuel, whereas the grid system pays for the fuel AND the generator, although a little at a time. So, it pays to be conservative, because that up front cost will be a lot less, and using efficient appliances and waste heat is really just common sense, no matter if you are on the grid or not.

The most simple way of using waste heat is for heating water. Sure, you can spend money on a solar water heater, but why do that if you could build it a bit bigger and generate electricity as well as hot water or free refrigeration, or a warm floor in the winter.

Now, some folks will claim that solar thermal systems simple don't work, and that a Solar CHP system is a pipe dream. But, in reality, these same folks are probably using electricity from a similar system, although it might use coal instead of the sun as the initial input. This is because the big businesses that run utilities found out quite a few years ago that there is a relationship between efficiency and cost. The more efficient their systems became, the less fuel they used for the same output, and the less money it cost to run the system. Sounds simple, huh? So, chances are, your grid power is probably using a CHP system, whether it be nuclear that generates heat to run a steam power station, or a coal burning plant or a natural gas burning system, they will all use some of their waste heat for another part of the system.

So, here's our chance to take a lesson from the big guys. Combine part of your power system with part of your heat system, and in turn, you get more of both for less input. This is an important concept in solar systems, because we can only capture a finite amount of the sun's energy. Let's make the most of it!

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