What factors influence solar array specification for new-build developments

Building regulations, site location, orientation, roof design/shape and integration with other renewable technologies are the key factors that influence solar array specification for new-build developments.

New-build developments must produce dwellings that comply with the energy saving requirements of building regulations. Choosing a solar array as part of a residential dwelling provides a way to lower carbon emissions by producing energy from a renewable source. This helps the dwelling to meet its energy performance requirements calculated by using the government approved Standard Assessment Procedure (SAP).

Once a solar array is specified, its placement and size will be determined by the site’s location, roof orientation, shape and design. The available power that can be generated by a solar array will vary depending on the pitch and orientation of the roof and number of solar panels as well as the available sunlight in that specific geographical area, taking into account any potential shading factors

When a solar panel specification is drawn up, it can form part of a wider strategy to maximise the benefits of the technology. Storing the electrical power produced by a solar array in solar batteries can make more financial sense that selling back to the grid at a much lower amount than you will pay directly from your electrical provider, this minimises the wastage of power that goes unused during the day when the house may be unoccupied.
Use of a PV diverter uses renewable energy to power the production of domestic hot water, reducing the energy demand on the dwelling’s boiler or heat pump.

How do building regulations influence solar array specification in new-build developments?

The current version of Approved Document L is Part L 2021. This uses version 10.2 of SAP and solar panel specification can be influential in helping developers achieve regulatory compliance. Specifying renewable technologies such as solar, generates power for a dwelling bringing energy efficiency and carbon reduction benefits that are reflected in the SAP calculation.

There are of course many other factors, such as the thermal performance of the building fabric, the dwelling’s air permeability and the efficiency of heating systems, that contribute to the overall energy performance of a dwelling. However, the specification of solar systems provides an efficient and cost-effective way for developers to achieve compliance with current regulations. A new build property that incorporates a gas boiler the use of solar panels will be mandatory to achieve compliance with Part L.

The next change to those regulations is due in 2025 in the form of the Future Homes Standard (FHS) that aims to bring buildings closer to being net zero in line with government targets for the UK. One of the biggest changes in the FHS is that it will not be possible to achieve compliance if fossil fuels are specified as the main power source. This switch to electricity is designed to help homes eventually become net zero carbon when the grid becomes fully decarbonised [1]  – this is due to be completed by 2035.

Whilst the final details of the FHS are yet to be revealed, the consultation [2]  released in December 2023 gave the industry an indication of the governments preferences on ways the new regulations would seek to reduce carbon emissions and conserve energy. The consultation acknowledged the positive contribution that solar arrays could bring through:

• Decreased carbon emissions
• Reduced energy bills for households
• Offsetting some of the electrical power demand on the grid
• Helping to decarbonise the grid when feeding unwanted renewable energy back into the grid

The consultation also expressed the view that, when compared to low carbon heating, solar arrays gave a relatively small contribution to carbon savings. However, it would be a strange decision if net zero homes built under the FHS did not take advantage of the benefits of solar panel specification especially as the energy generated by the solar array will offset the increased electrical demand and cost on the property and give households security from fluctuations in wholesale electricity prices.

How do site related factors influence solar array specifications for new build developments?

The specification of solar arrays for residential new-build developments will need to adapt to the specific characteristics of the site to optimise their performance. There are several key factors.

Pitch

The best pitch or angle of roof slope for solar arrays is anywhere between 30 and 45 degrees in the northern hemisphere but it will depend on your exact latitude. Therefore, the optimum angle for PV arrays on a site in Scotland will be different from a site on the south coast of England.

Orientation

In the UK the best orientation for solar arrays is to be south facing, as it maximises the panels exposure to sunlight throughout the day. While south-facing panels provide the highest energy generation, they are not the only viable option, depending on shading factors Solar PV systems on east-and west-facing roofs can still generate significant energy and value. Actually, having panels on East and West facing roofs is very beneficial as you will capture the sun throughout the whole day, generating power as the sun rises in the east and sets in the west.

Shading

Shading can have a significant effect on the actual on-site performance of an installed solar array; therefore, the positioning of solar panels should be carefully considered in order to optimise their final energy output.

Consideration to shading from neighbouring buildings, trees or roof projections, such as dormer roofs or chimney sacks should be accounted for during the specification. The MCS solar PV installation standard [3] highlights the importance of establishing a shading factor (SF) for an array. The shading factor is used, along with pitch and orientation data to determine expected annual output of the solar array in kWh.

This can be a particular issue for flat roof specifications where gaps need to be left between rows of solar panels. However, on pitched roofs, the solar panels are all fixed on the same plane, in line with the slope of the roof. Therefore, they do not cast a shadow on neighbouring panels and are placed close together to maximise available roof space and power generation.

How does an integrated approach to renewables influence solar array specification for new build developments?

Current regulations and the proposals within the upcoming FHS encourage residential specifiers to take a holistic and integrated approach to help deliver modern homes that will be net zero ready. Low carbon technologies are increasingly linked together to maximise their ability to reduce carbon emissions and lower the energy demand of the dwelling.

The specification of solar batteries in conjunction with solar arrays was incorporated into the changes in SAP 10.2, allowing their benefits to be recognised by current building regulations. This can be extremely beneficial if you have got a complicated roof design incorporating hips, valleys, or dormer projections and the roof area is not sufficient in size to reach the kWp needed with solar panels alone.

As well as storing energy generated by solar arrays, solar batteries can be charged using off-peak electricity supplied at a lower cost by the grid. The stored electricity can then be used the next day to help power the home in the normal way or for cost effective charging of electric vehicles. As an additional feature, many solar batteries can supply a dwelling with power during a power outage.

Another way to utilise the power generated from solar arrays is through a PV diverter. This technology diverts the renewable electricity generated to heat hot water using an electric immersion heater. This saves energy by reducing the hot water demand placed upon the dwelling’s boiler or heat pump system.

This integration of a solar array with complementary technologies presents developers with the opportunity to deliver modern, sustainable, low energy homes that comply with regulations. In addition, it adds appeal for modern householders. This is backed up by research from Legal and General in 2022 that showed buyers will pay up to a 20% premium for energy efficient low carbon homes [4].

How can I find out more information about solar array specification for new build developments?

Marley has extensive experience gained by supplying individual products needed to capture and store solar energy, including our Marley SolarTile®, solar inverter, solar storage battery and EV charger.

When asked why customers are confident to specify Marley systems, Kevin Taylor, Marley’s Training and Technical Support Manager commented: “We carefully select and thoroughly test the components within the complete Marley renewable energy system. Our customers know that by specifying Marley they are choosing a proven and reliable solar array solution for their project”.

If you are looking for technical support and advice when specifying solar arrays for your next project, please contact us at Marley Technical Services and we will be happy to help.

References

[1]https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1033990/net-zero-strategy-beis.pdf

[2] https://www.gov.uk/government/consultations/the-future-homes-and-buildings-standards-2023-consultation/the-future-homes-and-buildings-standards-2023-consultation#legislative-changes-to-the-energy-efficiency-requirements

[3] https://mcscertified.com/wp-content/uploads/2023/05/MIS-3002_Solar-PV-Systems-V5.0-Final-for-publication.pdf

[4] https://group.legalandgeneral.com/en/newsroom/press-releases/legal-general-research-shows-buyers-will-pay-up-to-20-premium-for-low-carbon-homes