Solar PV & Home Batteries

At the time of writing, the methodology for EPC assessments of existing dwellings is RDSAP 9.94. This updates to RDSAP 10 on 15th June 2025 and a significant methodology overhaul from RDSAP to the Home Energy Model (HEM) is proposed for 2026. In addition, government consulations indicate future changes to the format of EPCs and minimum rating levels required for priate rental properties. Methods for improving EPC ratings may therefore change in the future.

Solar photovoltaic (PV) panels capture the sun's energy and convert it into electrical power.

This provides a source of 'free', renewable, 'clean' electricity which you can use towards powering appliances in your home, therefore reducing the amount of electricity you draw from the National Grid.

In addition, any excess power can be stored in a Home Battery, or exported out to the National Grid for a finacial return.

The presence of these panels and associated equipment in a dewlling will help improve the EPC rating, and due to falling prices and increased product performance over recent years are fast becoming a popular energy upgrade.

By definition, solar panels are useful for capturing power during the day when the sun shines, and more so in the Summer compared to Winter.

This contrasts to wind as a source of electricity generation which is more constant, and is plentiful in the Winter compared to the Summer, although rarely used in a domestic environment.

Together, these two sources of power are now contributing significantly to electricity generation at a national level, as can be see on the historical graphs of the GB Energy Dashboard here: https://www.energydashboard.co.uk/. This has enabled us to move away from less green fuel sources such as coal.

(Ratcliffe-on-Soar, the last remaining coal-fired power station in the UK, closed on September 30, 2024, marking the end of a 142-year history of coal-powered electricity generation in the UK).

This page is about Solar Photovoltaic panels, but there is another type of Solar panel that you may occasionally come across called Solar Thermal panels..

Solar Thermal panels contain pipes in which water is heated by the sun and circulated to heat up water stored in a Hot Water Cylinder for use in baths, showers, basins and sinks in the home.

Solar Thermal panels have fallen out of favour in recent years, with preference now generally given to Solar PV panels instead due to the flexibility of use of the generated electricity and the reduction in costs of solar panels in recent years.

By way of example, the photo above is a property I walk past four times a day during school drop-offs and pick-ups.

In the centre of the roof is a solar thermal panel. You would normally only see one or two of these in such an installation.

The two blocks of three panels, located either side, are solar photovoltaic panels. Often, these may cover all of the available space on a roof.

In this case of this particular installation, they have been limited in size by the presence of the Solar Thermal panel and the two other rectangles on the roof, which are 'Velux' style windows.

It's much more common for retrofit installations to take up as much of the roofspace as possible, and this next picture shows three bungalows owned by a housing association that have had significant solar capacity added recently, and their EPC ratings are now over 100 SAP points each: 

Solar Photovoltaic panels are often listed as a recommendation on domestic EPCs as an improvement measure, and the gains can be fairly significant.

In order to be listed as an improvement measure on an EPC, the following conditions need to be met:

• The property needs to be a House or a Bungalow
• The property must not have a thatched roof
• There must be no photovoltaics currently present at the property

If Solar PV is displayed on an EPC as a recommendation then 2.5kWp is the level used for the indicated EPC rating improvement, although you can install as much as your property can accommodate.

Solar PV panels don't have to be accommodated on the roof, and there are various ground and wall mounting solutions available which may widen the range of properties where they are approriate.

When an energy assessor records the presence of Solar PV at your property they ideally like to see the MCS Certificate which would have been provided at the time of installation.

Most solar PV installers will be registered with the Microgeneration Certification Scheme (MCS), and will have provided a certificate to the customer on completion of an installation.

The MCS website indicates that in order for an MCS certificate to be made available, an installation must:

•     Be commissioned by an MCS certified Installation Company
•     Include an MCS certified product
•     Have a commissioning date after 15th July 2009

An MCS certificate is actually not a mandatory or legal requirement for a solar installation, but it is normally a pre-requisite for Smart Export Guarantee (SEG) eligibility where you get paid for any excess generation that you send into the national grid. Therefore most people seeking installtion of solar PV will want to use an installer registered with MCS.

Aditionally, the MCS certificate provides a level of proof that your installation has been designed, installed & commissioned to a high standard using MCS certified products.

If an MCS certificate is available at the time of an EPC assesment, it serves as a very useful form of documentary evidence which declares the capacity of the solar installation, measured in kWp. It also indicates the orientation and the elevation of the panels, ie which direction they face and at what angle they are mounted. The energy assessor will take a photograph of this document to support the assessment as well as the roof and panels. The only other data entry that's required is an estimate of the level of overshading (none/little, modest, significant or heavy).

If an MCS certificate is not available then the Energy Assessor can instead simply enter the proportion (%) of the roof area that is covered with solar panels, but that is the only data entry field available using that method. As a result, assessment of the capacity of the installation will not be as accurate (read: likey it will be lower) as that which could have been recorded had the MCS certificate been available. This could become ever more noticeable as the capacities of newer panels increase as technological advances are made over time, although some alteration of the solar pv calculation methodology is due in RDSAP10 scheduled from 15th June 2025.

If you have Solar PV panels installed, take time in advance of an EPC assessment to locate your MCS certificate so that you can present it to the energy assessor when they arrive. This will ensure the capacity of the panels can be fully recognised within the assessment.

The assessor will also need to record the fact that the solar PV system is connected to the property's electrical supply. If the panels are part of an 'off-grid' setup then they won't be recorded in the assessment.

Solar Diverters enable the use of excess power generation from solar pv panels to heat up water stored in a cylinder, rather than be exported back to the national grid.

This means your hot water cylinder will need less power from your boiler or immersion heater in order to heat up the water within it, thus saving energy and costing you less money.

The myenrgi eddi is a well known example of a solar diverter:

At the time of writing, under RDSAP 9.94, the presence of a solar diverter cannot be recorded in an EPC for an existing dwelling.

However, this will change from 15th June 2025 when the assessment methodology for EPCs of existing dwellings changes to RDSAP 10, and solar diverters will then become recordable in the assessment.

Let's take a look at what difference Solar PV makes to my property, a 1950s mid-terraced 3-bed house with a gas condensing boiler, no cavity wall insulation, and 200mm loft insulation (We cover this property in our Case Study 2).

The base EPC rating is 68D, and I don't have any solar panels currently.

This table includes 6 options for solar panels with capacities specified as if an MCS certificate was available. These include panels with 'none or little' overshading and an inclination of 45 degrees.

This is followed by 4 options where the 'percentage of roof' method is used to estimate the solar capacity instead: 

Solar PV clearly makes a considerable difference to the EPC rating for this property, particularly if the panels are South facing.

Considering this is a bordeline band D/C property, even with only 2.5kWp on a South facing roof, an increase to a 81B would be a significant increase compared to that available from other measures.

Just to demonstrate that EPC ratings with a SAP score of more than 100 are possible, one line in the table is for 9.0kWp split 50% North and South, and for this I would an EPC rating of 105A.

SAP scores above 100 indicate that a property generates more energy than it consumes.

The capacity of solar PV panels is increasing all the time and costs are coming down due to improvements in technoogy and manufacturing, so Solar PV will become ever more affordable going forwards. 

Any gain in EPC rating will be dependant on various aspects of a property, so always consult an energy assessor before fitting Solar PV as a measure to increase your EPC rating.

Home batteries allow you to store electrical energy, and then use that energy at a different time of the day.

This could be electricity you have generated from your solar panels, or it could be electrcity drawn from the national grid at night time when you have cheap rate electricity available.

You can choose when to consume the stored electrical energy, and this would usually be when it's more costly to have drawn it from the national grid instead.

Any spare power in the Home Battery could also be exported back to the National Grid for a finaical return, depending on your tariff.

Home batteries are often fitted in combination with solar photovoltaic panels , but they can also be fitted on their own and used simply for load shifting.

Unfortunately, at the time of writing (April 2025), home batteries cannot be included within an RDSAP EPC at all - this is the type of EPC conducted on an existing dwelling, rather than a new build.

However, a methodology update is due on the 15th June 2025, known as RDSAP 10. This will then support the recording of Home Batteries but only in conjunction with solar PV panels.

Even under RDSAP 10, if you have a Home Battery installed on its own, ie without solar, then unfortunately you will still not be able to include it in the EPC assessment.

In the slightly longer future, advertised for 2026 onwards, the Home Energy Model (HEM) will replace RdSAP/SAP completely and we will need to see what provision is made available under that new methodology.

If you are able to include your home battery under RdSAP 10 (because you also have solar), then the home battery should improve the rating of your EPC. By how much we will have to wait and see.

Click here to return to our 'Improve Your EPC' main page, and see if there is another way you could improve your EPC rating.