Solar PV & Home Batteries

At the time of writing, the methodology for EPC assessments of existing dwellings is RDSAP 10. Some of the information in this page refers also to RDSAP 9.94, and clarity is given in each case. Note that 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, and reducing the cost of your electricity bill.

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

The presence of photovoltaic panels on a dewlling will help improve your EPC rating, and due to falling installation costs and increased product performance over recent years they are 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 comparitively more consistant over a day, 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 30th September 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 3 panels located either side, are solar photovoltaic panels.

In the 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 new installations to take up as much of the roof-space as possible, and this next picture shows three bungalows owned by a housing association that have had significant solar capacity added recently. Their EPC ratings are now over 100 SAP points each, indicating that they financially generate more energy than they consume: 

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 however 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 like to see documentation that confirms the capacity of the installation, specified in kWp. This enables the full capacity of the installation to be recorded.

Assessors have to abide by Convention 9.05 which describes the rules about recording Solar PV in an EPC assessment, and in this regard, it advises:

"When photovoltaics are present the peak power (kWp) of the PV array is required. Potential sources include the system specification documents or the shematic wiring diagram (possibly adjacent to the electricity meter or the consumer unit). If the peak power (kWp) cannot be found, the declared net capacity (DNC) stated on the MCS certificate may be used instead."

Mention is made at the end of that paragraph of an MCS Certificate, which would have been provided at the time of most installations.

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 regarded by energy suppliers as the 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 installation of solar PV will use an installer registered with MCS.

If documentation of the kWp capacity of an installation is available at the time of an EPC assessment, it serves as a very useful form of documentary evidence which helps the assessor record the full capacity of the installation.

The assessor needs to record the following information about each solar array on the dwelling, up to a maximum of three arrays:

• The capacity of the array - measured in kWp
• The orientation - ie the direction in which the array faces
• The elevation of the panels - that angle they sit at, relative to horizontal
• Level of overshading - None or little / Modest / Significant / Heavy
• Whether the array is connected to the dwelling's electricity meter

For reference, the following table indicates the overshading factor that is applied to the number of generated kW hours, depending on the overshading option chosen above:

This is Table H2 from the SAP10.2 documentation (for RDSAP 10) available on the Building Research Establishment (BRE) website.

The energy assessor will take a photograph of any documentation to support the assessment and photos of the roof and panels. They will also want to photograph a generation meter, and possibly further visually evidence that the installation is connected to the electricity meter of the dwelling.

Since the 15th June 2025 they will also want to determine whether the meter is a smart meter, and whether it is export capable. Although it does not make a difference to the EPC rating whether the meter is smart capable, it does make a difference if it is not export capable. We'll touch on this later as we progress on to home batteries.

If suitable documentary evidence of the kW peak capacity of the solar installation is not available then the Energy Assessor can instead simply enter the proportion (%) of the roof area that is covered with solar panels.

When using this method, this percentage figure is the only data-entry field the assessor has available. The methodology calculates a contribution from the panels by calculating their area (m2) via the roof percentage, and using a default panel power (per meter squared). It also assumes South facing panels with a pitch of 30 degrees and Modest overshading.

The documentation for both the previous and current versions of the RDSAP methodology indicate a default figure of 120 Wp per square meter of solar panel (ie 0.12 kWp/m2) is used to calculate the capacity of the whole installation.

I think that's quite a low value compared to the performance of modern panels. Modern panels are now commonly 450W each (June 2025) and are about 2m2 each, whereas it wasn't too long ago that 285W was typical.

Looking briefly on the City Plumbing website (June 2025) and taking a nominal solar panel at random (DMEGC Solar 450WP Full Black N-type Bifacial PV Module - DM450M10RT-B54HBB), this has a capacity of 450Wp and a physical size of 1134 x 1762mm. I calculate that as 225W/m2. That's quite a lot more than the 120W/m2 that the methodology needs to assume when the % of roof method is used.

As a result, for modern installations, assessment of the capacity of the installation will not be as accurate via this method, compared to that which could have been recorded had documentaton such as an MCS certificate been available. This could become ever more noticeable in the future as capacities of new panels get ever greater as technological advances are made over time.

I think the default panel power is likely this low because we wouldn't want an assessment to overestimate the capacity of an older installation, but on the other hand if you had a modern installation without any documentation, you wouldn't want it to be unnecessarily under-estimated either. 

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

If you cannot locate any documentation, see what you can do to obtain copies of it. Perhaps contact the original installer if they are still around. Perhaps contact MCS themselves. If you are buying a property with solar panels already installed make sure you get documentation from the previous owners, and make sure the panels are owned by the vendors, rather than being leased.

Let's take a look at the improvement to my EPC rating if I were to install Solar photovoltaic panels on my house. This is 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 page).

My base EPC rating under RDSAP 9.94 is 68D, and I don't have any solar panels currently. This methodology has now been upgraded to RDSAP 10, and I have not re-calculated the figures, but they should be pretty much the same as presented here.

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. These figures were produced under the RDSAP 9.94 methodology: 

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. This is likely to be a far more cost effective option compared to other measures such as floor insulation, although in the future the proposed changes to EPC metrics will require a different approach.

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 get 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 is likely to 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.

Under the previous EPC methodology for existing dwellings (RDSAP 9.94), there was no option in the EPC assessment to record whether an electricity meter was export capable or not. The methodology simply assumed it was, and the full benefit of a solar PV installation would be experienced simply by declaring  presence of it in the assessment.

Under the newer RDSAP 10 methodology, introduced on the 15th June 2025, the energy assessor now has to expressly declare whether the connected electricity meter is export capable, or not.

Let's take a look at the effect of this assessment option in action, with another example, the property we covered in our Case Study 1 page which I have modelled under the new RDSAP 10 methodology.

Here I model the house without solar PV, then with solar PV with and without an export capable electricity meter:

(Here, the solar installation is declared with 30-degree elevation, South facing, no/little overshading, and 'Connected' to the electric meter. 'EPC Rating' is the main cost-based headline rating on the certificate, and 'EI rating' is the Environmental Impact rating which is related to CO2 emissions)

There are two aspects of these results which interest me. Firstly, we can now separately identify the benefit to the EPC rating of self-used solar power in the house, versus the exported excess solar generation.

In this example the increase from 74C to 79C represents the financial benefit of the self-consumed solar generation. This is the generated electricity that we have consumed within the house straightaway. Any excess generation is ignored because it could not be exported to the grid. The increase here is 5 SAP points.

Then, the increase that occurs from 79C to 87B represents the additional financial benefit where excess PV generation can be exported to the grid because the meter is export capable. That’s a difference in this particular example of 8 SAP points.

I use the word ‘financial’ in these paragraphs because of course, EPC ratings for domestic dwellings are currently a cost-based metric.

However, the second reason for my interest is that in this example, 8 SAP points is over the audit error failure threshold of 5 SAP points. So, if the EPC ever came up for audit by the accreditation scheme and the assessor had accidentally forgotten to declare that the electricity meter was export capable, and perhaps a photograph or other evidence suggests that it was, then this might be a problem for the assessor.

There are two sets of fuel prices (fuel costs) used by the domestic EPC assessment methodologies.

One set is used during the calculation of the headline EPC rating, and the other is used for calculation of the indicated running costs shown on the EPC, and also the improvement figures for EPC recommendations.

The first set of fuel costs are static and are rarely changed, perhaps only when a significant methodology update occurs. The second set however are updated every 6 months in order to remain representative.

We're going to look at that first set of fuel costs in this section, and from this paragraph onwards I will simply call them 'fuel costs', and not distinguish them from the second set of costs described above.

We also need to bear in mind as we progress that there are two assessment methodologies used in EPCs for domestic properties:

• SAP (Standard Assessment Procedure) is the assessment methodology used for new-build dwellings.
• RDSAP (Reduced Dataset Standard Assessment Procedure) is the assessment methodology used for existing dwellings.

SAP EPCs are based on detailed performance data of materials used at the time of construction.

RDSAP uses the underlying SAP calculation methodology, but gathers a reduced set of information about a property at the time of the assessment, and uses standardised assumptions of certain aspects of the property. For example, some building fabric performance is based on the minimum building regulations requirements at the time of constuction.

The previous version of the SAP methodology was SAP 2012, and this was updated in 2022 to the current version SAP 10 (SAP 10.2 currently). At that time, the fuel costs in the methodology were updated.

RDSAP was not updated in 2022 when SAP moved to version 10. RDSAP instead remained in use at version 9.94 (based on SAP 2012) until 15th June 2025, as which time RDSAP was finally updated to RDSAP 10 (based on SAP 10.2). However, the fuel costs in RDSAP 10 were kept the same as they were in RDSAP 9.94 (based on SAP 2012), and were not updated to those currently used in SAP 10.2.

This followed lengthy delibertation by key decision makers at the time whilst the update was delayed for various reasons including a general election.

For reference, the fuel costs can be viewed in:

• Table 12 of the SAP 2012 documentation on the BRE website. These fuel costs were used by SAP 2012 and RDSAP 9.94.
• Table 12 of the SAP 10.2 documentation. These are the fuel costs used by SAP 10.2
• Table 31 of the RDSAP 10 Specification document. These are the fuel costs for the current version of RDSAP.

Let's take a quick look at these fuel costs.

Here are the main relevant electricity prices for single rate electricity, dual rate electricity and electricity exported to the grid.

To keep the table simple, I have omitted other, lesser used, electricity tariffs and information about standing charges etc.:

You'll notice overall that the unit rates are rather low compared to actual electricity costs in 2025, particularly for RDSAP.

For example, typical unit prices for single rate electricity in 2025 are probably around 24 p/kWh, so 13.19 and 16.49 are rather less than that, but in itself this is not too important.

There is however an overall difference in fuel costs between the two methodologies and this could contribute to a disparity in ratings between them.

Importanty (for home batteries particularly), notice in the table that for RDSAP 10, excess electricity exported to the grid from solar is still valued equally with electricity imported from the grid on a single rate tariff (13.19p/kWh).

In comparison, notice the value of excess electricity exported to the grid from solar in SAP 10.2 (at 5.59 p/kWh), is much lower compared to the single rate import unit price (of 16.49 p'kWh).

Just to complete the picture in relation to solar and home batteries, the methodologies both consider self-consumed electricity from solar generation as having the same value as electricity drawn from the grid. This is the single tariff rate when a single rate meter is present or a weighted average of the low and peak rates when a dual rate meter is used.

Looking back at that decision to keep the fuel costs the same from RDSAP 9.94 through to RDSAP 10, this choice will have contributed significantly to maintaining the consistency of EPC ratings of existing dwellings when new EPCs are conducted (subject to other changes in methodology of course).

This is because the EPC rating for domestic properties is cost-based. This is in contrast to that for non-domestic (ie commercial) buildings where the ratings produced by the SBEM methodology are based on CO2 emissions.

That decision however also likely baked-in the effect that we will discuss next where home batteries, which are now recordable under RDSAP 10, are unlikely to improve your EPC rating unless your electricity meter is not export capable.

Home batteries allow you to store electrical energy, and then consume it at a different time.

This could be excess electricity generated by your solar panels, which you choose to store rather than export to the grid. You can then use that stored electricity later when your solar generation is less than your household load.

Alternatively it could be electricity drawn from the national grid during the night when you have cheap rate electricity available. You can then consume that stored electrical energy during the day when it would be more costly to have drawn it from the national grid instead.

It's also possible for any spare power in the home battery to be exported back to the National Grid for financial reward.

Home batteries are often fitted in combination with solar photovoltaic panels , but they can be fitted on their own and used simply for load shifting (i.e. charging at night and consuming during the day).

The EPC assessment methodology for existing dwellings (RDSAP) did not support the recording of home batteries until 15th June 2025 when RDSAP 10 was introduced.

Since then, home batteries are now recordable, but there are some significant limitations.

Firstly, let's look at the guidance in RDSAP 10 Convention 9.05, which instructs energy assessors that:

"For PV batteries, photographic or written evidence of manufacturer and model of battery unit used, and usable capacity (kWh) is required. If this cannot be obtained, use a default of 5kWh per battery."

On it's own this shouldn't be too much of a problem because most systems would be easily identifiable, and information should be easily available online. Also, the maximum recordable size of a battery is 5kW, but assessors are allowed to record multiple batteries to match the capacity of a single larger battery. An example would be 5 + 5 + 3.5 to represent a 13.5 kWh battery such as the GivEnergy All-in-one.

However, only a maximum of four batteries can be recorded in an assessment, and the maximum combined total recordable capacity is 15kWh. For most installations this is likely to be fine, but many people have installations greater than 15kWh.

Next, the following two assessment 'Addenda' are related to solar and battery storage. Energy assessors must select these yes/no options in the associated situation, and they have the following effect on the final EPC:

Addenda 15 - PV recommended - This has to be manually selected (currently) by the assessor if the EPC which is about to be produced has a recommendation on it for Solar Photovoltaics. This results in the following text being added to the final EPC: "When considering the PV installation consider installing PV battery and a PV diverter for water heating."

Addenda 16 - PV-independent battery storage present - This has to be manually selected (currently) by the assessor if home battery storage is present at the property, but solar PV is not. This results in the following text being added to the final EPC: "The assessment does not include PV-independent battery storage"

The text related to that latter Addenda indicate the EPC assessment will ignore the presence of home batteries in the absence of solar PV. In reality a home battery in this situation could help save energy costs by charging from the grid during the night when low cost electricity is available and allowing the house to consume that electricity during the day when it would be more expensive to draw from the grid instead.

Lastly, searching through the SAP 10.2 document from the BRE, information is present about how the methodology uses the capacity of a home battery to calculate an increassed self-use factor for solar generated electricity.

Adding to the previous point above however, there is no indication of 'load shifting' being considered, even when solar PV is present.

The RDSAP 10 Specification document lists a new EPC recommendation as being available for a home battery. This is present in table 33 of that document:

• This recommendation will be considered when the dwelling currently has solar PV present
• This will be recommended if the dwelling has solar PV present but not battery storage.
• The recommendation will suggest the installation of a single 5kWh battery

Supporting information advises that a recommendation is made on an EPC only if it increases the SAP rating by at least 1 (one) SAP point, or 0.5 SAP points in the case of cylinder insulation, draughtproofing and Low Energy Lighting (LEL).

I'm interested in what EPC rating improvement I could expect on my Case Study 1 property with a home battery added.

Firstly, we discovered earlier that home batteries are only considered in the RDSAP methodology if solar PV is also present. Therefore if you don't have solar PV present, fitting a home battery will not improve the EPC rating.

We added solar to this property earlier, and just to recall, here were the results we observed:

Let's now also add a home battery and see what rating we get.

I'll add a 15kWh battery, and we'll declare the electricity meter as export capable as that is what you would expect in almost all cases of a solar installation, and it is currently a single rate electricity meter:

So, my rating doesn't change at all which would be mildy inconvenient if I'd just purchased a home battery expecting an increase.

This property has a single rate meter, but I do notice that if I were to select a dual rate meter instead, I would get a single SAP point increase in rating to 88B.

So why do I not get an increase in my EPC rating?

Well, we touched earlier on the electricity costs used in the RDSAP methodology and we noticed that it treats electricity exported to the grid from excess solar generation as having the same financial value as electricity imported from the grid.

This is certainly true where a single rate electricity meter is present, and I think it's pretty close to being true for dual rate meters too. In the case of a dual rate meter, the import cost used in the solar calculations is a weighted average taken of the low and high rate costs, and I believe this works out to be very close to but not exactly that of the single import rate, perhaps resulting in the single SAP point improvement referred to above.

As a result it effectively makes no (or little) comparative financial difference within the RDSAP methodology whether excess solar is stored in a home battery and then consumed onsite when the sun goes down, or whether it is instead exported to the grid and drawn back from the grid later when needed by the dwelling.

The EI rating also indicates no difference in CO2 either.

However, let's now consider the case where the electricity meter is again single rate but is not export capable:

In the unlikely situation where solar PV is present but the electricity meter is not export capable, then presence of the battery clearly does make a significant difference, ensuring a greater proportion of the solar generation is self-used.

In this case however it does not bring the rating fully up to the level it would have been had the meter been export capable.

In summary, at the moment, addding a home battery will only really improve the EPC rating if you also have solar PV present, and your electricity meter is not export capable.

On the face of things, that might come across as a very strange statement to make because you'd rightly expect all properties that have solar installations to also have export capable electricity meters as standard, and you'd also expect the presence of a home battery to provide a financial benefit to the property that would be reflected in the EPC rating beyond just having the solar installation on its own.

It is however an unfortunate behaviour produced by the methodology as a result of having electricity unit prices for exported excess solar being comparable to the rate for imported electricity.

Referring back to the section above where we looked at those electricity prices, you'll recall the situation was different under the latest version of SAP, for new builds.

SAP uses a figure for exported excess solar which is much lower that that for electricity imported from the grid, so the presence of a home battery should make a difference to the EPC rating on new-build properties.

It's possible however that the initial gain from having the solar installation in the first place might be less than that experienced under the previous methodology.

Unfortunatley, I'll not be fitting a home battery anytime soon with the sole intention of improving my EPC rating. In my opinion this is a shame and a missed opportunty to encurage more widespread uptake of this technology.

Home batteries do in reality result in financial cost savings in the long term, either used on their own for load shifting or when used in conjunction with solar PV for storing excess generation, or even a combination of both of those strategies.

Solar PV installations though can provide a significant improvement in EPC rating, although EPC metrics and methodologies are likely to change in the near future, thus changing approaches required for rating improvement.

The Home Energy Model (HEM) will eventually replace the RdSAP/SAP methodologies. This is advertised to start in the latter part of 2026 but the indication currently is that HEM may run alongside SAP/RDSAP for a while before a component similar to the current Reduced Dataset facility we use today becomes available for assessing existing dwellings.

Hopefully HEM might favour home batteries for existing dwellings and help encourage the uptake of this technology.

I always recommend that you contact a local energy assessor to find out how the EPC rating could be improved for your specific property. It is important to do this before undertaking any measures and will ensure you have certainty in your outcome.

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