Stirling engines become more and more used and promoted among alternative energy circles. The interesting fact with them is that they can be fueled by any source of heat, and the cleaner the source is, the better the stirling engine does to the environment.
A Boulder, CO – based startup company, Cool Energy, has developed a CHP system that doesn’t use biogas or any other “fuel” to produce energy, but the solar power. The efficient stirling engine approach could make their device compete with other sources of energy in cold and darker climates, usually found in northern countries.
This system’s efficiency comes from the fact that during summer months it works both as a water heater and as an electricity provider, by using the excess heat that is normally lost in other water heating systems. The electricity is generated by using the innovative stirling engine. During colder seasons, the tubes that collect heat make better use of diffuse light than standard photovoltaic panels do, and heat up water and the home’s interior, something hard to accomplish by other more active means.
The system is not a self-sufficient electricity generator, because it merely produces 1.5 kW of electricity, not having enough juice to satisfy most homes. Still, if you use energy wisely, the charged batteries may support higher peaks of electricity demand for reasonable times – it all depends on how much energy you’re using during the day and how charged are your batteries at night, when you use electricity most.
We’ve seen efficient heaters before, but the Cool Energy’s strong point is the stirling engine. Ordinary stirling engines run at temperatures of above 500°C – theirs only requires 200°C, and that makes it so suitable for use in conjunction with a water heater.
The observation that led to their stirling engine’s efficiency was that conventional engines are made of metals, that conduct both electricity and heat. Making the stirling engine work at lower temperatures, metals aren’t required anymore, since plastics and ceramics can also do a good job and not melt. Through metals, an important amount of heat is lost, but through ceramics, the losses are lowered by a significant number. And they’re also cheaper than their metal versions, don’t require oiling, and are more reliable.
Cool Energy says their stirling engine system can recover the initial investment twice as quickly as conventional photovoltaic systems. That remains to be seen – the company is testing their third prototype and hope to release it soon on the market at convenient costs.