What is Micro CHP?

Micro combined heat and power (micro-CHP) (Micro-cogeneration) is a technology that converts heat and electricity from the same source into individual houses or buildings.

Micro-CHP systems generate most of their output in the form of heat, with a modest amount of electricity generation, at an average ratio of 6:1 for domestic appliances.

Once warmed up, a typical domestic system will produce up to 1 kW of power. The quantity produced each year is contingent on how long the system can operate.

How Does Combined Heat And Power Work?

Many of these systems are built around a central heat pump, which powers fans to extract heat from inside the home.

The main energy source is mains gas or liquefied petroleum gas (LPG), although some models now operate on oil or bio-liquids, including biodiesel.

Despite the fact that gas and LPG are fossil fuels rather than renewable energy sources, the technology is considered low carbon because it can produce more power than burning fossil fuels for heat and obtaining electricity from the grid.

Micro-CHP systems are similar in size and shape to standard domestic boilers. They can be mounted on a wall or can stand on the floor.

The primary distinction between a micro-CHP system and a regular boiler is that a micro-CHP system can produce electricity while heating water, whereas a boiler cannot.

Combined Heat And Power Benefits

Here are the benefits of having a micro-CHP system:

  • You can save money on your energy bills.
  • You can reduce your carbon emissions.
  • You can receive payments for the electricity you generate.
  • You can be less reliant on energy from the grid.

Reduce your energy bills

The electricity that you generate using your micro-CHP system is free. This is because the heat that would otherwise be wasted is used to generate electricity.

You can use this electricity to power your home and any surplus can be sold back to the grid. This means that you could see a reduction in your energy bills of up to 15%.

Reduce your carbon emissions

Micro-CHP systems produce less carbon dioxide (CO2) than traditional heating and electricity systems.

This is because the heat that would otherwise be wasted is used to generate electricity. As a result, you could see a reduction in your carbon emissions of up to 1.5 tonnes per year.

Receive payments for the electricity you generate

You can receive payments for the electricity you generate through the government’s Smart Export Guarantee (SEG) (previously called the Feed-in Tariff) (FIT).

The SEG pays you for every kilowatt-hour (kWh) of electricity you generate. The amount you receive will depend on the tariff that your energy supplier offers.

Be less reliant on energy from the grid

If you have a micro-CHP system, you will be less reliant on energy from the grid. This is because you will be generating your own electricity.

As a result, you could see a reduction in your energy bills and you will be less affected by power cuts.

What Are The Disadvantages Of Combined Heat And Power?

  • Micro-CHP systems are capital intensive.
  • A CHP energy center is required which takes up room.
  • It is difficult to install an underground hot water system because of the requirement for huge diameter, well-insulated metal piping.
  • The ground is typically cooler than the air around it, which causes heat to be lost.
  • You’ll also have to budget for the cost of operating and maintaining the system’s “energy center” over its entire lifetime.

Capital intensive

The biggest initial disadvantage of a combined heat and power system is that it is costly to build, and because it is primarily fueled by natural gas, it isn’t considered a “real” sustainable energy source until it can be used with biogas produced from AD plants or hydrogen.

Takes up room

Another disadvantage of CHP plants is that they are quite large and require a significant amount of space.

This can be a disadvantage if you are trying to install a micro-CHP system in a small house.

Difficult to install underground

Combined heat and power systems are also difficult to install underground, due to the need for large diameter, well-insulated metal piping.

Heat loss

Another disadvantage of CHP systems is that they rely on the ground being cooler than the air around it, which can lead to heat loss.

Operating and maintenance costs

You will also need to budget for the cost of operating and maintaining the system’s “energy center” over its entire lifetime.

How Do I Get Started With Combined Heat And Power?

Micro combined heat and power system for households

If you’re interested in generating your own electricity and heat for your home, you’ll need to install a combined heat and power system.

You can either buy a micro-CHP system or you can build your own. If you decide to buy a micro-CHP system, you’ll need to find a supplier that offers the right type of system for your needs.

If you decide to build your own, you’ll need to purchase a heat pump, a generator, and an inverter.

You’ll also need to install piping and wiring to connect the system to your home’s electrical and water systems.

CHP boiler (cogeneration boiler)

Combined heat and power boilers, also known as CHP units, are meant to create heat as well as electricity at the same time.

These machines are built to operate on a big-scale commercial premise.

The CHP unit works in tandem with a boiler on the heating side, providing a backup source of heat in the event of a boiler failure or power outage.

Fuel cell CHP boiler

Fuel cells are a type of CHP boiler that uses chemical reactions to generate electricity.

Fuel cells are often used in micro-CHP systems because they are small and efficient. However, fuel cells are very expensive, so they are not always the best option for large-scale CHP systems.

Wind turbine CHP

Wind turbines can also be used to generate electricity for CHP systems.

Wind turbine CHP systems are usually only used in large-scale commercial or industrial applications.

Solar photovoltaic (PV) CHP

Solar photovoltaic (PV) panels can also be used to generate electricity for CHP systems.

Solar PV CHP systems are usually only used in large-scale commercial or industrial applications.

A History of Micro CHP

Since the 1960s, Micro CHPs have been used in the industrial sector to increase energy output when burning fuel to generate electricity, but it has been adapted for domestic heat and power use through technological progress.

It’s a method of collecting carbon emissions from your home that’s been dubbed the future of domestic carbon reduction, and it may be something we’re all quite familiar with in the not-too-distant future.

Types Of Micro CHP And CHP Technology:

The primary mover, the engine that generates mechanical power, the electric generator, and the heat recovery unit are all basic elements of most combined heat and power systems.

From here, many different technologies have been produced and engineered.

These include fuel cell mCHP units that create electricity and heat by extracting energy from fuel at a chemical level, to Stirling engine generators that utilize conventional combustion methods to drive an engine.

The Different Generators

  • Fuel cell micro-CHP generators
  • Stirling engine micro-CHP generators
  • Gas Turbine CHP Generators
  • Steam Turbine CHP Generators
  • ORC – Organic Rankine Cycles CHP

Fuel cell micro-CHP generators

What is micro-CHP fuel cell technology?

A hydrogen-powered fuel cell is a type of electrochemical device that converts hydrogen to electricity and heat using only hydrogen as a source.

A catalyst, such as a transition metal or an acid solution, can help speed up this process.

Fuel cells at high temperatures (greater than 600°C) do not require catalysts because they create DC power directly.

These types of systems are more expensive than Stirling engine systems, but they have far superior electrical efficiencies of around 55%, owing to the fact that they run via a clean electrochemical reaction rather than combustion.

Stirling engine micro-CHP generators

What is micro-CHP Stirling engine technology?

External combustion is used in the Stirling engine, which means that all of the machine’s heat goes in and out through its wall.

The engine is encased in a sealed container of constantly gaseous fluid such as helium or air.

This happens when the hot and cold gases are expanded and contracted, generating a mechanical cycle using two pistons:

Although electric power is cleaner than gas, it has its drawbacks. Internal combustion engines have greater efficiency and are more reliable, but the current systems available are inefficient at around 6-8%.

This may end up causing CO2 increases in the UK if they are used to replace a high-efficiency condensing boiler.

Gas Turbine CHP Generators

Compressed, high-velocity air drives the turbine and generator using these engines. This air is expanded down to exhaust pressure as it drives the turbine.

It’s by utilizing this shaft coupled to the generator and compressor that creates both compressive and mechanical rotation for the alternator for electricity by driving it with hot air.

The heat exchanger uses the turbine exhaust’s thermal energy to provide warmth or hot water.

These types of systems are used in large-scale applications, as they are expensive and have a low electrical efficiency of around 20-25%.

Steam Turbine CHP Generators

The steam is generated in a boiler and used to drive the turbine. When the steam is condensed and returned to the boiler as hot water close to the boiling point, it is most efficient.

The Rankine cycle, named after its developer William John Macquorn Rankine, is the thermodynamic cycle.

The electrical efficiency of industrial-scale fully-condensing steam turbines in power plants (both nuclear and fossil fuel) is approximately 36-38%. However, in CHP applications (where steam extraction lowers their electrical output), they have average electrical efficiencies of 10-12%.

ORC – Organic Rankine Cycles CHP

The fundamental principle of an ORG CHP system is the same as that of a steam turbine, however, it employs a higher (or lower) boiling fluid to do so.

The technology works by using low-grade heat to produce extra power.

These may be fueled by waste heat from traditional CHP or ordinary boilers.

If the heat from a boiler-driven ORC is directed for use, it isn’t considered CHP.

This term only applies if the ORC is driven by a traditional CHP and some of the heat obtained before being sent to the ORC. This is classified as CHP.

It is not easy to eliminate the heat produced by an ORC cycle. Because the condenser temperature is around 20°C, it would be difficult in many situations to remove heat from the ORC cycle itself.

Recovering heat between turbine stages would make a process already plagued with low efficiency even worse.

Micro CHP Boiler Cost/price

There are Micro CHP systems that function as a logical substitute for a wall-mounted boiler and are suitable for almost all households in the UK. If you buy them now, they will be eligible to take advantage of the micro CHP feed-in rate and generation rate for ten years, as mandated by the government.

They also generate electricity and heat, so they are a more eco-friendly way to utilize the fuel you pay for. With this in mind, it’s possible to claim that the money you save on energy bills may be used to partially or entirely cover the initial investment, giving the units a suggested payback time.

The efficiency of the energy production process will most likely decrease your family’s carbon emissions. Some new mCHP boilers that are still in development and not yet deployed have reported efficiency rates as high as 92%, which may save up to 2.6 tonnes of CO2 each year!


What is the maximum efficiency of a micro-CHP unit?

Efficient, clean, and natural gas combined heat and power (CHP) systems typically achieve total system efficiencies of 60 to 80 percent, as opposed to 50 percent for conventional energy generation and heat harvesting.

How do I know if a micro-CHP system is right for my home?

A variety of factors will affect whether a CHP system is the best option for your home, including the local climate, fuel costs, electric rates, and incentives.


Main image: TEDOM a.s.CC BY-SA 4.0, via Wikimedia Commons

About the Author

Passionate about helping households transition to sustainable energy with helpful information and resources.

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