Micro combined heat and power, micro-CHP, μCHP or mCHP is an extension of the idea of cogeneration to the single/multi family home or small office building in the range of up to 50 kW.
The most common systems use natural gas as their primary energy source and emit carbon dioxide; nevertheless the effective efficiency of CHP heat production is much higher than of a condensing boiler, and thus reducing emissions and fuel costs.
When used primarily for heating, micro-CHP systems may generate more electricity than is instantaneously being demanded; the surplus is then fed into the grid.
The PEMFC fuel cell mCHP operates at low temperatures (50 to 100 °C) and needs high purity hydrogen.
[13] A 2013 UK report from Ecuity Consulting stated that MCHP is the most cost-effective method of utilizing gas to generate energy at the domestic level.
The energy sources with the lowest emissions of particulates and net-carbon dioxide include solar power, hydrogen, biomass (with two-stage gasification into biogas), and natural gas.
Due to the high efficiency of the CHP process, cogeneration has still lower carbon emissions compared to energy transformation in fossil driven boilers or thermal power plants.
However, since reciprocating internal combustion engines have the ability to modulate their power output by changing their operating speed and fuel input, micro-CHP systems based on these engines can have varying electrical and thermal output designed to meet changing demand.
Other possibilities include the Organic Rankine cycle, which operates at lower temperatures and pressures using low-grade heat sources.
The primary advantage to this is that the equipment is essentially an air-conditioning or refrigeration unit operating as an engine, whereby the piping and other components need not be designed for extreme temperatures and pressures, reducing cost and complexity.
The future of combined heat and power, particularly for homes and small businesses, will continue to be affected by the price of fuel, including natural gas.
The advantages for a stationary fuel cell application over stirling CHP are no moving parts, less maintenance, and quieter operation.
For PEM fuel cell units, which shut down at night, this equates to an estimated lifetime of between ten and fifteen years.
[25] United States Department of Energy (DOE) Technical Targets: 1–10 kW residential combined heat and power fuel cells operating on natural gas.
Thermoelectric generators operating on the Seebeck Effect show promise due to their total absence of moving parts.
[28] Sopogy produces a micro concentrated solar power (microCSP) system based on parabolic trough which can be installed above building or homes, the heat can be used for water heating or solar air conditioning, a steam turbine can also be installed to produce electricity.
The recent development of small scale CHP systems has provided the opportunity for in-house power backup of residential-scale photovoltaic (PV) arrays.
[29] In some regions, in order to reduce waste from excess heat, an absorption chiller has been proposed to utilize the CHP-produced thermal energy for cooling of PV-CHP system.
A "generate-and-resell" or net metering model supports this, as home-generated power exceeding the instantaneous in-home needs is sold back to the electrical utility.
When turning on an oven or space heater, about the same amount of electricity is drawn from the grid as a home generator puts out.
The largest deployment of micro-CHP is in Japan in 2009 with over 90,000 units in place,[17] with the vast majority being of Honda's[31] "ECO-WILL" type.
[35] 20,000 units were sold in 2012 overall within the Ene Farm project making an estimated total of 50,000 PEMFC and up to 5,000 SOFC installations.
[25] The ENE FARM project will pass 100.000 systems in 2014, 34.213 PEMFC and 2.224 SOFC were installed in the period 2012–2014, 30,000 units on LNG and 6,000 on LPG.
Manufactured by Honda using their single cylinder EXlink engine capable of burning natural gas or propane.
[50] Quota systems favor large, vertically integrated generators and multinational electric utilities, if only because certificates are generally denominated in units of one megawatt-hour.
[85][87] Through a pilot program scheduled for mid-2009 in the Canadian province of Ontario, the Freewatt system is being offered by home builder Eden Oak[89] with support from ECR International,[90] Enbridge Gas Distribution and National Grid.
This study found that the devices resulted in average carbon savings of 9% for houses with heat demand over 54 GJ/year.
The results showed that the nominally 1 kWe state-of-the-art micro-CHP system operated at an electrical and total efficiency (LHV based) of 23.4 and 74.4%, respectively.
[87] The most popular 7 kWe home backup generator (not CHP) operated at an electrical efficiency (LHV based) of 21.5%.
[96][97] 12 project teams have been selected to develop a 1 kWe mCHP technology that can achieve 40% electrical efficiency, have a 10-year system life, and cost under $3000.