CHP boilers – a comprehensive buyer’s guide

    September 17, 2013

The CHP boilers – or domestic micro CHP – is a new type of boiler available for homes. This guide answers all your burning questions and looks at whether these boilers are a worthwhile investment.

Every time we come out of a spell of warm weather and look to heat our homes, we turn to our boilers. Now, there is always that moment of trepidation as I fire up the boiler for the first time as to whether or not the heating system will actually work. Obviously if your system has given you issues in the past or is an older system (10 years old or more) then it may be time for a complete boiler overhaul.

If this is the case you will probably be thinking about replacing the old unit with a like-for-like new condensing unit; however a CHP boiler will provide you with electricity as well as heat, so it may be worth considering. In this blog we look at them in a bit more detail to help you make up your mind.

What is a CHP boiler?

CHP technology is not a new concept, but in the domestic setting, it is something that has only recently become relevant to UK consumers.

We discuss the specific technical aspects of CHP boilers in a bit. Essentially, a CHP boiler will produce your heating requirements just like a normal boiler, but in the process collect the gases to drive an internal generator, creating electricity. The electricity created is then fed back into your property and can power lights and appliances for free as long as enough energy is produced.

Are CHP boilers available for homes?

The answer is yes. Up until now CHP has only really been used in commercial applications. However the introduction of the Stirling engine powered micro-CHP boilers has opened this technology up to households. They are suitable for this operation as they are compact and less noisy than other technological solutions.

There are internal combustion CHP units that operate more efficiently in terms of combustion to electricity generation output; however they tend to be very noisy when operating, large in size, and more suitable for large buildings and commercial spaces.

In addition, fuel cell technology has been used to develop prototypes that may one day become commercialised, but we are probably another 5 years or so from this becoming a viable option.

What size of home is suitable for a micro CHP unit?

The most popular micro-CHP boiler available in the UK today is the Baxi Ecogen, and this wall mounted unit is 950mm tall and 450mm wide. This makes it about a third bigger in size than a traditional regular boiler – but only marginally bigger than a system or combi boiler.

The boiler itself can adjust its heating output to match a heating requirement of 23KW, therefore matching the performance of a regular-sized boiler that would be used to power a 3 bed home. Plus it will produce electricity at the same time!

The Vitali and Viesmann CHP units are probably more suitable for multi dwelling properties.

Financial benefits of a CHP boiler

Since micro-CHP boilers produce electricity, they benefit from the Feed-in Tariff. Check our regularly updated technology pages for current rates of payment.

In addition to earning some income through Feed-in Tariff payments, the CHP unit will also produce electricity whenever it is producing heat (either for heating or hot water). Since people tend to have their heating on when they wake up and when they come home in the evenings, the CHP unit will produce electricity to match peak demand requirements. Therefore this obviously reduces the amount of electricity that needs to be purchased from the National Grid.

Having said that, the micro-CHP unit will also export electricity when you are not using it in the home. So if you like to leave the heating on at night or during the day when you don’t run lights or appliances, the excess will earn you a few extra pennies.

According to the Baxi product specification, their Ecogen product could potentially save £600 off your energy bills per year vs. a G rated boiler (SEDBUK 65% seasonal efficiency) and cut carbon dioxide emissions by as much as 40%.

It is important to remember though that if the boiler isn’t turned on, then you will produce zero electricity.

Current CHP boiler units on the Market

Baxi Ecogen 24/1.0

The Baxi Ecogen has been available in the UK market since 2010 and is an MCS-approved product. The units can now be sourced separately through wholesale companies or specifically ordered and installed with British Gas. The Baxi Ecogen can be powered by both mains gas or LPG. The gas unit retails at c£7,400 (inclusive of VAT) and the LPG unit at c£8,000 – this doesn’t include installation costs, which would have to be undertaken by an MCS accredited installer and a gas safety engineer.

On the other hand, British Gas has been readily installing these units since 2011, so it may be worth giving them a call and finding out if there is a subsidised deal that could potentially bring the cost down.

Vitali Energi

Vitali Energi on the other hand doesn’t have an ‘off-the-shelf’ product as what they manufacture is customised dependent on the size of the property. The units are not cheap and would be more suited to large properties and commercial buildings.

Viesmann CHP

The Vitotwin 300-W is the domestic CHP product developed by Viesamann and currently sold in Germany, but yet to be distributed in the UK. The boiler unit is also a condensing cylinder, allowing it to operate at 96% efficiency.

Whispergen Micro CHP

At the end of 2012, E.ON announced a partnership deal with EHE to potentially launch the Whispergen micro CHP unit in the UK. However soon after this announcement, the plans were shelved (due to the viability of this product for the UK market) and no further plans to launch this product were put in place. Seasonal efficiency figures for the two prototype units produced are still available on the SEDBUK database, even though the models were never distributed en masse to people’s homes.

CHP boilers – are they worth it?

Domestic CHP units like the Baxi Ecogen or the Viesmann Vitotwin 300-W are powered by a stirling engine, which has the capability of producing 1kW of electrical output when the boiler is working at maximum capacity.

In reality this means that the boiler will to some degree help out with electricity consumption during peak load times, for example powering your entertainment system and lights. However as soon as you try and turn on an electricity-guzzling appliance like an oven, tumble dryer or washing machine, the electricity generated will not be enough and the additional requirements will have to be pulled from the grid.

Also when there is little heating demand and in the summer, the boiler in theory will not be generating that much electricity.

According to Baxi, the incremental cost of an Ecogen vs. a current A-rated condensing unit is £3,000. However we think this is slightly underestimated as the unit itself currently retails just under £8,000 excluding installation cost (£8,500 or more including installation cost). A new condensing boiler, install plus parts can be sourced for £2,500, which means that incremental cost is actually over £6,000 with a payback of over 10 years – this means the payback period (5 -6 years) previously quoted in other articles is too generous.

Verdict: if you already have an A or B–rated condensing unit, then the CHP is just not worth it. If, however, you have a fairly big uninsulated house then the CHP could be an option – however it is not as good as an air source heat pump or a biomass boiler, which benefit from the Renewable Heat Incentive.

Installing a CHP boiler – what else do I need to know?

A few things to bear in mind if you have chosen a CHP boiler:

  1. The installation will need to be performed by a qualified MCS installer and a gas safety registered engineer.
  2. The installation surface needs to be uninhibited by other objects.
  3. The wall needs to be able to support the unit weight and when it is filled with water, which will make it slightly heavier
  4. Usually have an electricity generating meter displayed on the unit.
  5. Once the unit is installed you need to notify your electricity supplier so they have somewhere to send the Feed-in Tariff payments!

Installing Micro CHP?

Interested in installing a micro CHP boiler? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

If you would like us to find you a local installer to help install micro CHP in your home, just fill in the form below and we will be in touch shortly!

    Interested in getting a new boiler?

    What kind of boiler are you interested in?

    I would like to be contacted by local installers

    I would like to receive occasional news from TheGreenAge

    Think we missed something? Do you have a different opinion?

    Comment below to get your voice heard…

      CHP Cogeneration – A Comparison of UK to Sweden

    Introduction to combined heat and power

    Sweden Cogeneration plant

    Combined heat and power (CHP) is not a new idea to the UK. Sheffield for example, has a large district heating network which makes considerable carbon savings and the Immingham plant on the Humber is a large industrial example. Yet when one compares the UK to Sweden, UK CHP seems very underdeveloped in comparison. Here I would like to discuss just what makes Swedish CHP so great and what the future holds in the UK for the technology.

    I won’t go into lots of detail on the technical aspects to CHP cogeneration. You can find that on our main technology page here. The principle is simple however; whether on a micro scale or on an industrial scale, power production and industrial processes create a lot of heat, which is effectively wasted energy. CHP cogeneration aims to take this waste heat and make it useful, increasing the efficiency of the installation. Often this will mean piping the heat to nearby buildings to be used for domestic or industrial heating.

    Example of Sweden – wide adoption of combined heat and power technology

    For the best examples of these ideals, Sweden is an excellent place to look. Here, around two thirds of heating requirements are provided through renewables in the form of biofuels, waste materials and sustainably sourced electricity. Additionally, district heating is widely implemented there, and now accounts for 43% of heating consumption. Biomass is considerably more common generally, which makes an excellent low carbon combination with district heating. But what is special about the country to make these technologies so much more widely implemented however?

    Perhaps most importantly, the Nordics have long taken on board the need for action on climate change, and as a result have policies considerably more proactive for carbon reduction than the UK. For example, coal burning is extremely expensive due to the huge taxes levied on power stations burning the fossil fuel – the tax can be as much as twice the cost of the coal. The knock on effect this has is to make renewables much more attractive for electricity production. In some instances this has meant more biofuels, but also geothermal and other renewables are found. Both of these technologies lend themselves well to CHP, due to the large quantities of heat they generate.

    This is not simply a coincidence however. The region has extremely cold winters, and heating is therefore much more important than in milder climes. As a result, many power stations of this type are ‘thermal leading’, meaning their main purpose is to provide heat rather than electricity. Electricity is more the by-product than heating in some instances.

    What does this mean for the UK?

    So are the UK and Sweden similar enough to be able to learn from their example, or are the two so different as to make the comparison irrelevant?

    Even though we are a milder country, the UK spends around £33 billion on heat across the economy per year and it is the number one reason for energy use. It therefore follows that reducing our heating’s contribution to energy use will help cut carbon emissions considerably. Of course, a multifaceted approach to reducing this burden is important. Insulation and energy efficiency are imperative, yet CHP cogeneration could offer a way to tackle this problem at the source. Immingham ConocoPhillips refinery is the largest industrial CHP facilities in Europe, located in the north-east of the UK. Sheffield on the other hand, is a good example of district heating, where its waste to energy plant converts hundreds of thousands of tonnes of waste each year into heat and energy. Running for nearly 25 years, the plant saves around 20,000 tonnes of carbon emissions per year when compared to fossil fuels. The scheme supplies electricity to the grid and helps heat hundreds of the city’s major buildings.

    Sheffield is a great example of CHP working well in an urban environment, yet after a quarter of a century of successful operation, the UK has yet to fully embrace the advantages of CHP as a tool for efficiency and carbon savings.

    The DECC last spring released their ‘Heat Strategy’, which has highlighted areas of improvement for the sector. It confirms the need for a change in Britain’s attitude to heat, looking at both supply and demand to reduce energy consumption. On the demand side it proposes 3 major areas for improvement: insulation, efficiency of heat delivery systems and better heat management. On the supply side, the main areas of focus are: low carbon building level heating systems, changing the content of natural gas in the grid and low carbon heat networks. It also specifically mentions the EU market for heat pumps and how the UK can capitalise on this.

    So is more UK CHP just around the corner?

    Looking at some of the prerequisites for CHP, the UK seems to fulfil them all; the fuel source is there, the technology is already available, the dense urban environments of major cities in the UK lend themselves perfectly to district heating and given the urgent need to new energy solutions, there seems to be an obvious gap in the market for more CHP. Perhaps it is just a cultural barrier that remains. Where northern Europe has embraced the technology long ago, the UK is only now waking up to the fact is needs to rethink its energy and heating policies.

      CHP Cogeneration

    What is cogeneration?

    CHP cogeneration (combined heat and power for industry) follows the same processes and principles as micro CHP boilers, but on a grander scale. When a fossil fuel power station produces electricity, it also produces a lot of waste heat. In fact, 65% of the energy potential contained in the fuel turns to heat and only 35% is actually converted to electricity, which shows that there is a large efficiency gap. The heat produced is in the form of steam, which is used to drive the electricity-producing turbines. When you drive past a power station you will have probably have noticed the large cooling towers releasing this steam into the atmosphere, which highlights the wasted heat.

    The unique point about CHP Cogeneration is that it captures this steam and reuses it for other purposes, such as providing heating for local districts or towns that are close to the plant. In other cases CHP cogeneration plants can fit in tandem with existing industrial processes; for example the production of sugar beet or providing steam to refineries.

    Types of CHP cogeneration

    As mentioned in the CHP boilers section, CHP cogeneration is underpinned by a number of different technological processes. The process that creates the energy required can either be a combustion process or a fuel cell chemical reaction. Both of these processes produce the heat and power to ensure they can be used for the purposes of CHP Cogeneration. A summary of the technological processes is in the sub-section below:

    Combustion CHP Cogeneration

    The structure of CHP cogeneration plants usually takes the form of an external combustion engine, which has been a technology widely used in steam engines. Many fuels can be utilised to produce the heat required including gas, coal, biomass, nuclear and geothermal. The fuel is combusted and this heats water, which is then forced into a pressurised boiler. This heat and pressure feeds the main engine or a turbine, which then rotates. The rotating motion then simply spins a large magnet (main engine) inside a coil of copper wire, known as the generator. This then completes the process of converting mechanical energy into electrical energy.

    The difference with CHP cogeneration and other plants is what happens with the steam and heat generated from the boiler that then leaves the system. If the infrastructure is in place, this heat can be released out of this process and potentially pumped to a nearby facility for a different purpose altogether. Some of the secondary activities that heat can be utilised for are, district heating (as discussed above) and to drive newly built water desalination plants.

    You can also have CHP cogeneration with power plants that are not primarily there to generate electricity but that are there to support additional industrial processes. For example, a bottoming cycle industrial plant produces high temperature heat for an industrial process such as glass furnacing or metal manufacturing. In addition, a waste heat recovery boiler recaptures waste heat from the manufacturing heating process. This waste heat is then used to produce steam that drives a steam turbine to produce electricity. Since fuel is burned first in the production process, no extra fuel is required to produce electricity. In the 1990s British Sugar built a state-of-the-art CHP plant, using excess heat and electricity to support some of its secondary processes – as well as providing district heating.

    Fuel Cell CHP Cogeneration

    An emerging CHP cogeneration technology is the fuel cell, where fuel, such as natural gas, is converted to electricity in a chemical reaction rather than a combustion process. Again, let’s talk a little bit first about this fascinating science. First requirement is to have solid oxide fuel cells (SOFC), which are allowed to operate at high temperatures. The fuel cells then on one side chemically interact with a fuel input (LPG, natural gas, hydrogen for example) and on the other side with air. This combined reaction – using an anode and a cathode – and is then able to produce electricity and heat (up to 1000 degrees centigrade).

    The development of this technology for CHP cogeneration is ongoing, so that one day it can be used as a standard solution for both businesses and homes. Companies such as Mitsubishi Heavy Industries in Japan are looking at ways of introducing this process alongside conventional combustion processes. An example of how this is utilised could be when a company is enhancing existing gas plants with fuel cell technology, to make sure the levels of efficiency increase. As we have already mentioned, the electrochemical process from fuel cells produces heat, and this is then separately captured and used in a secondary process. For example the heat can be used to create steam, which can then feed a combustion system to create secondary electricity. Any excess heat can be recycled further and used to supply district heating or to enable further industrial processes to take place. These processes and recycling heat for multiple uses, increases plant efficiency, which ensures that as little heat as possible is wasted.

    CHP cogeneration industry development

    The principles of CHP cogeneration have been around since the 1960s in the UK. For example the Combined Heat and Power Association (CHPA) was set up in 1966 as the District Heating Authority to highlight benefits of district heating, but now it is there to highlight the benefits of taking an integrated approach to heat and power. Industrial and domestic CHP cogeneration generators of electricity can currently make use of the Renewable Obligation Certificates (ROCs) and Feed-in-Tariffs (FiTs) respectively. More on this in the section below, as well as an explanation of the Renewable Heat Incentive (RHI) in more detail.

    In the UK, the Immingham CHP cogeneration plant (one of our featured case studies), has been in operation since 2004, producing 1.2GW of electricity, making it one of Europe’s largest CHP cogeneration plants. Some of its uses are as follows: providing steam and electricity to the Humber Refinery, steam to a neighbouring refinery, and power back into the grid.

    Now a bit about our neighbours in Europe: CHP cogeneration is already used on a commercial scale in many Scandinavian countries, with 40% of Denmark’s total electricity capacity derived from this source, as is 30% of Finland’s. Germany on the other hand has also made its intentions clear in support of the technology. This signal was made clear since it decided to scale down and decommission the existing civil nuclear power plant project. However other parts of Europe like the UK have a lot of catching up to do to these countries.

    Cogeneration CHP UK public policy

    The DECC policy is to support measures such CHP cogeneration as well as solar commercial power plants, wind farms and nuclear power to ensure that by 2020 the UK is in a good position to meet its emission reduction targets. The main policy areas that cover CHP cogeneration are summarised below:

    Renewable Obligation and Feed-in-Tariffs

    ROCs are available to commercial electricity generators of CHP cogeneration, which are usually ones that are able to demonstrate the production of multiple MWh of electricity production (also considered a metric that symbolises the starting point for mass scale consumption). The level of support varies depending on the CHP cogeneration type. For example, if combusting waste CHP cogeneration, then level of support is 1 ROC per MWh. On the other hand, if you are using dedicated biomass fuel with CHP cogeneration, and can demonstrate sustainable fuel supply, then the entitlement increases to 2 ROCs per MWh.

    FiTs on the other hand are an initiative to support micro generators of renewable electricity. If you are a small business or a community project (and this is your first time involvement in electricity generation), please note to satisfy the FiT criteria, you need to have a declared net capacity greater than 50kW and up to and including 5MW (2MW for micro cogeneration CHP). Income can be earned both from the generation tariff and the export tariff.

    These two policy areas are great incentives if you are looking to invest in renewable CHP cogeneration projects or if you are looking to start up your own renewable CHP cogeneration plant.

    Renewable Heat Incentive

    The RHI is a payment subsidy (pence/kWh), for heat and hot water generated by households or businesses, using an eligible renewable technology, which includes CHP cogeneration.

    District heating

    In March 2012, the DECC set out a roadmap for district heating incentives. This has called on improvements to infrastructure around existing power plants and newly built ones to extract some of the excess heat and provide it for local homes and businesses. An apparent lack of investment in infrastructure is to blame for a lack of district heating incentives in this country. Everything in the UK is dug underground from electricity cables, telephony and natural gas distribution. District heating incentives for example would struggle to compete with existing infrastructure in large conurbations, but there appears to be an opportunity for connecting new out of town developments and/ or areas of the country which are currently off-grid.

    Examples of some of the CHP cogeneration initiatives that could be implemented in the UK are as follows: heat from gas-fired CHP plants, biomass and biogas, heat pumps, energy-from-waste, solar thermal, excess heat from industrial processes and power stations. These processes are very common in Denmark, and as previously mentioned, are enablers used for helping the process of decarbonisation of the economy.

    Installing Micro CHP

    Interested in installing a micro CHP boiler? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

    If you would like us to find you a local installer to help install micro CHP in your home, just fill in the form below and we will be in touch shortly!

      Have a question or would like to find out more?

      What are you enquiring about?

      I would like to be contacted by a local installer/supplier

      I would like to receive occasional news from TheGreenAge

        Sunderland Aquatic Centre – CHP

      Background – Sunderland Aquatic Centre

      The Sunderland Aquatic Centre is a one of a kind facility located in the north-east of England, between Edinburgh and Leeds. It is one of the greenest Swimming centres in the country and also has the lowest carbon footprint amongst its peers. The fitness centre that is housed near the Stadium of Light, Sunderland Football Stadium holds a state of the art 50m Olympics style swimming pool and fitness centre facility. The centre is part of a series of regeneration projects in the area by drawing in both national and internal swimming competitions and improving the health and wellbeing of local residents.

      This sporting facility utilises both energy efficiency measures such as collecting rainwater on the roof and insulation measures to make sure that heating is effectively utilised. In addition and pertinent to this section the facility uses an ENER-G CHP unit that provides both heating and power simultaneously and limits the facility’s reliance on the grid.

      The CHP scheme for which the Aquatics Centre operates under a discounted purchasing scheme with a duration of 10 years. This means that ENER-G installs, finances and generates and then sells the energy back to the Aquatics Centre for a discounted rate.

      Sunderland Aquatic Centre – CHP Unit Details

      The CHP unit that operates on the site is a self-assembled 185kW system. Unlike convention heating and electricity, CHP on site maximises energy effectiveness and minimises heat loss. For example, conventional electricity comes through miles and miles of cabling, which wastes power. The closer the energy source to the demands, the less wastage for the transmission of electricity.

      At the Aquatic Centre, the CHP unit heats the pool and also the building that houses this facility.

      In total, if the unit is running 17 hours per day and utilises the heat produced, this equates to a total of £32k of savings on the energy bills per annum.

      Business Partners Constructing the Sunderland Aquatic Centre

      The project wouldn’t have been successful without the knowledge of business partners who all contributed to their particular area of expertise. Along with ENER-G who supplied the CHP unit, Balfour Beatty constructing timber beams; Laminated Veneer supplied by Wiehag and the main contractor being Arup.

      Sustainability of the Sunderland Aquatic Centre

      From the building design to the materials and power sources, all these inputs ensure that the Aquatic Centre leaves a sustainability legacy in the local area. The rainwater for example, falls on the roof when it rains; then it is harvested and filtered and finally treated for the use in the pool. All of this reduces the overall use of the water supply from the external water company.

      Up to 3 years of operating, the CHP unit in the Aquatics centre has managed to reduce carbon savings of over 500 tonnes of CO2, which is equivalent to planting just over 82k trees. This doesn’t take into account the additional energy efficiency measures talked about such as on insulation, building design, air circulation improvements and harvesting rainwater.

        Immingham Combined Heat and Power

      Background to the Immingham CHP Power Plant

      Combined heat and power technology works well with many existing industrial processes and Immingham CHP plant in the North East of England is no exception. Situated on the North East coast of England, the ConocoPhillips Refinery is one of the largest CHP plants in Europe and together with the refineries that underpin it, employs a large number of people in Grimsby, Hull and Lincoln.

      The ideas and blueprint for the project began in 1998 as ConocoPhilips sought to upgrade the energy supply for its Humber refinery, which essentially needed more steam for its refinery business. In addition, the existing boiler providing the steam was deemed to be out of date and inefficient, increasing the urgency of this project. The ideal solution was to upgrade the existing technology so that both efficiency was increased, as well as reducing the impact on the local environment. Electricity generating capacity was also added, allowing the power plant to be connected to the grid so electricity could be exported and sold.

      Prior to this, the company was relying on the grid to supply electricity as well as processes that failed to provide the quantity of steam required. With uncertainty about gas prices and the capital investment required to undertake a project of this size, Conoco Philips qualified for investment defined under the UK CHP programme and under the EU Cogen Directive, the project got the green light.

      Moreover, the UK Government at the time introduced Enhanced Capital Allowances (ECA’s) and the Climate Change Levy, with Immingham CHP being included in these schemes. These measures related to capital investments and designed to encourage quality CHP. In summary they allow for accelerated depreciation for tax purposes, which means those undertaking the investment like Conoco Phillips benefit from a lower tax bill and keep hold of more cash.

      Key Operational Facts – Immingham CHP Power Plant

      ConocoPhilips ICHP is one of the largest industrial scale CHP plants in Europe. As part of phase 2, the power station now produces 1200MWs of electrical power and has significantly increased its district heating capabilities.

      ICHP Phase 1 began operations in November 2004 and peak output is approximately 735 MW. The Phase 2 Extension is proposed to provide an additional 470 MW, bringing the total to a nominal 1210 MW. Phase 1 ICHP Plant produces electricity for the Humber Refinery and supply to the national grid. The additional capacity was expected to be provided to the national grid and to existing and new third party customers. The proposed fuels used on site were natural gas, distillate fuel oil and refinery off-gas.

      Immingham Power Plant Business Partners

      There are two sites, one that holds the refinery and the other that has the Immingham Combined Heat and Power (ICHP) plant. Crucially, one of the main outputs is steam, which also serves Total’s neighbouring Lindsay Refinery. Therefore ConocoPhilips definitely uses ICHP as a form of investment that will provide benefits to industry surrounding it in the local area.

      Other business partners involved in the project were Foster Wheeler, who were the EPC contractors; Nooter Eriksen providing the Heat Recover Steam Generators (HRSGs) and Franco Tosi Meccanica supplying the steam turbines.

      Environmental Impact Assessment of the Immingham Power Plant

      An Environmental Impact Assessment (EIA) was carried out prior to the project getting the green light, to supplement the commercial business case, which was all about keeping the Humber and Lindsay refineries competitive in the European refining market.

      As an upfront benefit the new ICHP plant reduced utility costs at the Humber Refinery by about 30%. From an environmental perspective it is estimated that the plant, with an overall efficiency of around 70%, will save about three million tonnes of CO2 per year compared with conventional coal fired generation plant. Another key benefit arising from the Immingham CHP is that it contributes to the energy infrastructure on the South Humber Bank which will almost certainly be required for future  industrial development in the area.

        CHP Boilers


      What are CHP boilers?

      Combined heat and power (CHP) boilers produce both heat and electricity in one single process. This process is sometimes referred to as cogeneration and the technology that supports it has been around since the 1970s, but has mainly been confined to industry and large dwellings such as hospitals and sports centres.

      As the price of fuel has increased over the last few years, it now makes economic sense to bring CHP technology into the domestic setting.

      A micro-CHP boiler is defined in the EU Act on Cogeneration as a domestic unit that is limited to 50kW of capacity.

      The different types of CHP boiler

      There are three types of micro-CHP boiler:

      The Stirling engine CHP boiler

      The Stirling engine CHP boiler is a type of external combustion engine, where the combustion engine is heated when the boiler is fired up to produce the hot water. This heats up the fully enclosed working gas within the Stirling engine, causing it to expand. The expansion of the working gas forces a piston to turn up and down between a copper coil, generating an electrical current, which can then be used in the home. The working gas usually used in a Stirling engine is helium, due to its strong heat transfer properties.

      The main limitation of this type of boiler is that it only produces electricity when you have the central heating on, so despite being a very efficient type of boiler, it does not produce an abundance of electricity. A key advantage is that the combustion process involved in a Stirling Engine CHP boiler is much quieter and more efficient than internal combustion engines.

      The internal engine CHP boiler

      This type of CHP boiler is commonly used in large dwellings such as hospitals. It involves using a fuel source to drive a turbine, which is connected to the electricity generator. The waste heat from this combustion process is captured to produce hot water for the space heating and warm water. This is the most common form of CHP boiler found to date. However the process is noisy and you have far less control over the hot water generated, so fuel cell and the Stirling engine CHP boilers are often preferred.

      Fuel cell CHP boiler

      Fuel cell CHP boilers use fuel cells which convert fuel and air directly into power and heat through a quiet, efficient, solid-state electro-chemical reaction. A video demonstration of how a fuel cell CHP boiler operates in the home can be found on the Ceres Power website.

      Fuel cells generate power significantly more efficiently than internal combustion and Stirling engine CHP boilers. This is because fuel cell CHPs convert chemical energy directly to an electrical current, maximising their efficiency.

      This type of CHP boiler is still in development so is not yet commercially available on a wide scale.

      How CHP boilers work in the house

      A home would typically use a boiler to meet its heating and hot water needs only, and then source its electricity from the grid. Central generation wastes a significant proportion of the energy it creates, through heat losses in the power station and in the transmission and distribution network.

      Micro-CHP boilers avoid these losses, and capture the heat for use within the home. This efficiency can save the consumer around 25% of total energy costs (around £600 off your bill if you have a typical 3-bed semi-detached house), and reduce each home’s CO2 emissions by up to 1.5 tonnes per annum. Micro-CHP boilers are designed to generate all of the heating and hot water and a significant percentage of the electricity needed by a typical UK home.

      The CHP boiler can use a variety of fuel options including the gas that is supplied by your current provider, but also hydrogen, LPG & biofuels. Even during the summer when the home’s central heating system is turned off, the heat produced by the micro-CHP boilers when generating electricity can be stored in a back-up hot water cylinder and then used for domestic hot water. Therefore the micro-CHP boilers are capable of operating all year round, maximising energy bill savings 365 days a year.

      Micro-CHP boilers are designed to one day replace your normal condensed boiler, using the same types of connections; they also have similar installation and maintenance requirements. A micro-CHP boiler only requires one connection to the electricity network in the house and it’s ready to go!

      Industry development

      Micro-CHP boilers are an example of a microgeneration product for the home. The UK Government has estimated that microgeneration products (such as micro-CHP boilers) have the potential to supply over 30% of the country’s total electricity needs and help meet its international environmental obligations, such as the 2020 EU carbon emission reduction targets. Owning a micro-CHP boiler is one step in the right direction. Full costs in the UK of a micro-CHP boiler including installation are yet to be made fully transparent; however incremental cost estimated in the region of £2,500 to £3,500 versus a condensing boiler, therefore a full installation is then estimated at between £5,000 to £7,000.

      Research commissioned by the Government has shown that micro-CHP boilers have the potential to become the micro-generation ‘system of choice’, replacing the condensing boiler, which is the standard system in most UK homes today. Commercial experience has also shown that realising the benefits early pays off the most over the long-term.

      Currently only the Stirling engine-type micro-CHP boilers have been made available on the domestic market. For example the Baxi Ecogen product is one of the few available micro-CHP boilers that is commercially viable and available for the home. By the middle-end of this decade, the expectation is that fuel cell models such as the Baxi Gamma 1.0 will be fully available to the UK consumers.

      When fuel cell micro-CHP technology is commercially available, the consumer should see the price of Stirling engine models fall. In addition with the competition in the fuel cell space (Baxi, Ceres Power, etc), this should also make those models commercially competitive. Current evidence suggests that the take-up in UK homes has only been limited, with a lower number of Micro-CHP boilers currently installed in the UK than expected by the government – as opposed to Denmark and Germany where the technology has been more widely adopted.

      CHP Boiler Technology Summary

      The following list is a quick summary of the CHP boiler features:

      Remember micro-CHP boilers are efficient because they generate heat and electricity in one place. They will save you money and help the environment. Currently only the sterling engine type of CHP boilers are available to the residential market (internal engine CHP boilers are available for large properties), but in a few years’ time fuel cell micro-CHPs will also be available. Micro-CHP boilers are a strategic domestic technology for micro-generation that will help homes with their energy needs, but also help the UK (and other EU countries) meet external carbon emission targets.





      Pin It on Pinterest