Combined heat and power, also known as co-generation, is a well-established technology at the utility and industrial scale. Now, some manufacturers see potential for home-scaled combined heat and power systems.
Co-generation makes use of heat that is typically not utilized. A typical power plant generates electricity by burning natural gas, biofuels, oil, coal, or other fuels, which powers an electrical generator. The process of combustion generates excess heat, in the range of 40 to 67 per cent of the energy contained in the fuel. That waste heat can be captured and used for space heating and hot water. More advanced systems can also incorporate cooling.
The technology can be scaled down for home use. Honda has been producing and selling small-scale, or micro combined heat and power systems, since 2003 and says it has sold and installed more than 100,000 units. Marathon Engine Systems manufactures the Ecopower Micro CHP and received a 2011 ENERGY STAR Emerging Technology Award for the system. The company says its system is appropriate for houses larger than 230 square metres.
More recently, several converging factors have been driving the development of the systems. Natural disasters such as the Fukushima earthquake, for example, led Honda to produce small systems designed to be used as a backup energy source in the event of power outage. A small gas engine powers a generator, while the waste heat powers a water heater.
Off-grid homes and other buildings are obvious choices for combined heat and power systems. If the home is accessible to fuel delivery, the systems can provide most and sometimes all of the electricity, hot water, and space heating needed. Solar systems can be incorporated as well, reducing the amount of fuel burned.
Increased adoption of grid-tied home energy production is a factor as well. Net-metering pricing schemes make home energy production of all types more cost effective and attractive to homeowners. As home photovoltaic systems become cheaper and more popular each year, more people see the potential in producing some or all of the energy they use. Since 2011, two-thirds of new solar capacity has gone to distributed (non-utility) installations, including individual homes.
Solar photovoltaic systems are the most popular grid-tied option, but micro combined heat and power systems will also work. A new development in micro combined heat and power systems is currently undergoing testing and regulatory approval. The Nirvana Power Stick uses a Stirling engine, fueled by propane, to produce one to four kilowatts of electrical power, and 15 kilowatts of thermal power, with system efficiency over 90 per cent. The company claims the cost will be comparable to a new boiler, with a similar physical size, as well. Added benefits include system payback in two to three years and lower CO2 emissions.
While the Australian market has not seen much adoption of micro combined heat and power so far, that could change as the technology matures and is proven.
A report by Energia, Personal Power Stations: The Australian Market for Micro-Combined Heat and Power to 2021, offers a potentially brighter future for the technology. The report cites the technology’s efficiency and carbon footprint as benefits.
“Personal power plant technology could cost effectively provide most of Australia’s gas connected residential premises with all of their electricity and hot water heating needs at 23% to 39% of the carbon emissions of today,“ the report states.