Renewable Energy for Your Self-Build

Self-building is becoming increasingly popular in the UK and the potential to create an energy efficient home has become an important factor in this.  

There has never been a better time than now to invest in carbon neutral technologies with renewable energy prices falling and incentives to go green. This is particularly true for self-build projects which are achieving the greatest results.

It is also worth bearing in mind that the UK government has ruled that gas boilers will be banned in all new homes built after 2025. The government’s “future homes standard” will require all new builds to have low-carbon systems, such as electric heat pumps. Any new homes built from this year on are expected to achieve a 31% reduction in carbon emissions to ensure industry is ready to meet the new standards by 2025.

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It’s invariably cheaper to merge renewables into a new build project than trying to retrofit into an older house. You have the advantage of being able to include renewable energy in your initial self-build planning.  This means that you can install renewable energy systems that complement each other without running into restrictions as well as being able to choose the best options available without the need to compromise.

In order to build a sustainable home, you will need to consider what types of renewable energy systems you can use to power your home. Though most people want to save money, many will put a greater priority on cutting their emissions and lowering their carbon footprint. Fortunately, there are several renewable energy systems available which can both reduce your carbon emissions and cut your energy costs.

As heating accounts for most of our home’s energy demand and carbon emissions let’s start by looking at renewable heating options. 

Air Source Heat Pumps

The most popular type of air source heat pump (ASHP) in the UK is the air-to water model which absorbs heat from the outside air into a liquid refrigerant at a low temperature. Using electricity, the pump compresses the liquid to increase its temperature. It then condenses back into a liquid to release its stored heat. They distribute heat via a wet central heating system and work much more efficiently at a lower temperature than a standard boiler system would. For this reason, they are more suitable for underfloor heating systems or larger radiators, which give out heat at lower temperatures over longer periods of time. ASHPs can still extract heat when air temperatures are as low as -15°Celcius!

The perfect place for an air source heat pump is outside either at the back or side of your property, ideally in a sunny spot. They require good air flow in order to work at their most efficient as they draw air in through the sides and the back of the unit and then allow cold air to exit from the front once the heat has been extracted. You will also need to bear in mind the space you require indoors for the compressor and a hot water cylinder.

On average the supply and installation of an air source heat pump will cost in the region of £8,000-£14,000. This is more expensive than many traditional heating systems, but the benefit to the environment is considerable and they are currently highly incentivised.

In 2011, the UK government launched the Renewable Heat Incentive (RHI), a scheme aimed at encouraging the uptake of renewable heat technologies amongst householders, through financial incentives.

To be eligible for RHI payments all renewable technologies must be:

  • listed as a Microgeneration Certification Scheme (MCS) certified product
  • issued with a MCS certificate

Technologies that are covered by the domestic RHI are:

  • biomass (wood fuelled) boilers*
  • biomass pellet stoves with integrated boilers providing space heating*
  • ground to water heat pumps
  • air to water heat pumps
  • solar thermal panels (flat plate or evacuated tube only) providing hot water for your home
  • water source heat pumps can potentially be eligible for the Domestic RHI – they are included in the definition of a ground source heat pump.
  • certain cooker stoves and high temperature heat pumps may also be eligible

If you are eligible, you’ll receive RHI cash payments quarterly over seven years. The amount you receive will depend on a few factors, including the technology you install, the latest tariffs available for each technology and in some cases metering. After seven years of receiving RHI payments, a combination of these plus savings on your heating bills should see you making back a good chunk or in some cases all the initial investment.

Though ASHPs run on electricity they are cheaper to run than traditional heating sources as they should use less electrical energy than the heat they produce. They are generally very efficient and are known for their reliability and consistency. The efficiency of a heat pump is measured by their Coefficient of Performance (COP). That is the ratio of heat produced per unit of electricity consumed when pumping the heat. A COP value of 3 means that you get 3kWh of heat output for every 1kWh of electricity used to run the pump. The average annual heat demand for most homes in the UK is at 12,000 kWh. If you divide the annual heat demand by 3 kWh, the heat production per unit of electricity, your heat pump would use 4,000 kWh of electricity. The average price of a kWh in the UK is around 14.37p. The cheapest price per kWh is around 12p and the most expensive is 24p. Say your electricity was priced at £0.13p per unit your annual heating costs would be around £520.

When calculating the size of heat pump that you require for your self-build the general principle is the bigger the house, the bigger the heat pump you will need.  A 100 sq. m house may require a 5kW air source heat pump. This will double to 10kW for 200 sq. m houses. You have the advantage of being able to ensure that your self-build is properly insulated which is vital if you are to enjoy the full benefit of an air source heat pump.  

In order to reduce the cost of running your heat pump as well as your carbon emissions you can generate your own electricity by installing solar panels on your roof. The number of solar panels that you can install on your roof will determine the amount of electricity you can generate. More on solar panels to follow.

Another type of heat pump is the air-to-air model. While the system works to produce warm air that is then circulated by fans in order to keep your home nice and warm, it cannot heat your water at the same time. They can generally only be used for one function at a time. Air-to-air heat pumps are also not eligible for the UK government’s Renewable Heat Incentive (RHI).

Ground Source Heat Pumps

A ground source heat pump system (GSHP) harnesses naturally occurring heat from deep underground by pumping water through it in pipes. The heat pump increases the temperature and the heat produced is used to heat homes or hot water. Ground source heat pump systems are made up of a ground loop (a network of water pipes buried underground) and a heat pump at ground level. A mixture of water and anti-freeze is pumped around the ground loop and absorbs the naturally occurring heat stored in the ground.  The water mixture is compressed and goes through a heat exchanger, which extracts the heat and transfers it to the heat pump. The heat is then transferred to your home heating & hot water system. A ground source heat pump can increase the temperature from the ground to around 50°C.

Installing a ground source heat pump system is perfect for self-builds as it involves a lot of soil upheaval in your garden or drilling deep down into the earth. Plenty of room is required for digging machinery and the installation process can be quite disruptive. How big the ground loop needs to be will depend on how big your self-build is and how much heat you need. The ground array for a GSHP can be either a horizontal grid of pipes which should be 1.2m below ground level or two or three vertical boreholes which are likely to be more than 70m deep.

Like ASHPs, GSHPs run on electricity, but they are even more efficient than air source heat pumps. For every unit of electricity used by the heat pump, three to four units of heat are captured and transferred. This means that a well installed ground source heat pump can be 300-400% efficient in terms of its use of electricity. Installing a GSHP can lower your fuel bills especially if you are replacing conventional electric heating or an old oil or LPG boiler. 

We are all aware that currently electricity is one of the more expensive fuels particularly when you compare it to gas and oil. However, the highly efficient performance of GSHPs means they can convert electricity into 2-4 times as much heat. To give an example if you were paying 14.4/kWh of electricity, each thermal kWh of heat produced by a GSHP with a SCoP of 4 will cost 3.6/kWh. Because gas boilers aren’t 100% efficient this is potentially cheaper than gas. The reason for this is that average gas prices stand at 4.17p/kWh so for a gas boiler with an efficiency of 93% to deliver a full thermal kWh it would cost 4.46p/kWh which is more than a heat pump.

It isn’t cheap to install a GSHP, typically around £18,000 to £30,000 for a horizontal ground array or £25,000 to £40,000 for a borehole system depending on the size of system you choose. However, GSHPs are an attractive choice for self-builds because after you’ve made the initial outlay, the Renewable Heat Incentive payments are higher for GSHPs compared to ASHPs, meaning you will save more in the long term when opting for a ground source heat pump. 

To create an energy efficient home, it is essential to ensure it is well-insulated as this will affect the performance of either an ASHP or a GSHP.

Solar PV

Solar panels also known as photovoltaics (PV), use the sun’s energy to create electricity and only require daylight not direct sunlight to work. They generally work better on a south facing roof at a pitch angle of about 30 or 40 degrees. You can fit panels on a flat roof, or on a frame on the ground but a sloping roof is usually the easiest. Though south facing is optimum, anywhere between east and west is possible. When designing your self-build, it’s important to ensure that your solar panel system is not going to be overshadowed by trees or other buildings as this will have a negative impact on the performance of your system. Space is a key consideration. A 4kW solar PV system, usually consists of 10 to 16 panels, and requires around 25m²-30 m² of roof space.

Solar PV is far more affordable today and can be paired with air source heat pumps or used as a standalone system to generate electricity for your household. A typical solar panel system supply and installation with 30m2 of panels will cost between £4,500 and £6,500 and is getting cheaper. If you include a renewable battery in the package the cost will rise to between £7,000 and £10,000. In recent years, the price of installing panels has decreased by 70%.

To make the most of the electricity generated while the sun is shining you would ideally be at home during the day to use appliances such as washing machines and dishwashers etc though you can of course set your appliances to come on during the day when you’re out and about. If you’re generating more electricity than you need during the day the surplus will be fed back to the National Grid for someone else to use. If you want to avoid having to use electricity from the Grid during the night you can invest in a special renewable battery system in order to store any unused energy generated during the day.

Alternatively, you can take advantage of the Smart Export Guarantee (SEG) a government scheme devised so that energy suppliers pay their customers for the renewable energy that they export to the grid. You will need to sign up to a SEG tariff with a company, otherwise you won’t get paid for your excess electricity and will export any you generate but don’t use to the National Grid for free.

Currently the cost of domestic solar electricity is around 8p per kWh which is a lot less than the 14.7p average domestic import cost from the grid which means you will definitely save money on your electricity bills. This cost has increased by an average 4.75% each year over the past decade. Just taking this fact into consideration will make installing solar PV extremely worthwhile as you will be protecting yourself against future increases in the cost of importing power from the grid.

Solar Thermal

The sun is an infinite renewable energy source which can also be used to heat your hot water using solar thermal systems. Solar thermal panels are ideal for a self-build project. They work by transferring the sun’s heat within special pipes on your roof via copper wires inside. There are two types of solar thermal, Flat plate collectors and Evacuated tubes. Flat plate collectors are heavier, take up more room, and can be cumbersome to install on certain roofs while Evacuated tubes tend to have lighter components which tend to be more fragile but are easier to manage on the roof.  Solar thermal systems work best when sited on a roof facing between southeast and southwest, with little to no shading. The optimal angle for solar thermal is quite steep to maximise their performance throughout spring and autumn,

To decide if installing solar thermal is suitable for your build, you’ll need to consider how many occupants will be living in the property. Roughly speaking, you’ll need one metre squared of panel per person, but larger families who use more hot water than single occupants are likely to get the most benefit.

The installation of a typical domestic solar hot water system, with 4m2-6 m2 of panels will cost you between £2,500 – £5,000.

Solar thermal systems are eligible for RHI which means you will be able to get some of your initial layout paid back over 7 years.

In the summer, they should provide all the hot water you require for your home. In the winter, it’s a lot less, however over the course of a whole year, roughly 60% of your hot water needs could be provided by your solar thermal install.

Other than the initial installation cost and a little maintenance, there are no running costs with a solar water heating system as it’s free energy. Solar thermal systems are very low maintenance. Aside from an annual check by you, your system should only need professional servicing every 3-5 years.

Basically, the world is your oyster with a self-build project. You have a range of options to look at, some of which we’ve covered here, but none of the considerations of existing systems you would have with a traditional home.

A final consideration to take into account when making your self-build more sustainable is that your house value will ultimately rise too. With a super energy efficiency rating, your home will be more attractive to potential buyers, especially knowing that they won’t have to go through a ‘transition’ to clean energy later on as the work is already done. That means renewable energy is a true investment into your present and future wealth.