EPC guide 11
Solar panels and your EPC
Fitting panels changes what an assessor records about your home, and on a cost-based rating that generally works in your favour. How much it helps depends on the roof, the array and the assumptions built into the model – not on the sales pitch.
How generation appears on a certificate
The headline band on an EPC is driven by a modelled energy cost rather than by carbon alone, and certainly not by your actual bills. Electricity produced on site reduces the amount of grid electricity the model assumes the property needs to buy, so a photovoltaic array generally pushes the rating in the right direction. The size of that shift varies a great deal from one property to another, and because the rating is cost-based, the cost and carbon outcomes of a measure do not always move together.
An existing home is assessed using RdSAP by an accredited Domestic Energy Assessor, who records the array among the features listed in the written part of the certificate. Where no array is present, solar is one of the measures that can appear in the recommendations instead. Our guide to reading an EPC explains how those sections fit together, and if you are weighing panels against other work the wider view in our guide to improving your EPC rating is worth reading first, because the cheapest gains are often in insulation and controls.
The factors that actually matter
An assessment of a photovoltaic system turns on a short list of inputs: the installed capacity of the array in kilowatts peak, the compass direction it faces, the pitch of the roof plane it sits on, how badly it is overshadowed by trees, chimneys or neighbouring buildings, and the region the property sits in. A broadly south-facing array on a moderate pitch with an open aspect is modelled most favourably.
Split east and west arrays, shallow or very steep pitches and heavy overshading all reduce the modelled contribution. The assessor records these things by observation and from whatever documentation you provide. They do not test the system, take a meter reading or measure output on the day, so what is written down is a description of the installation rather than a measurement of its performance.
Standard assumptions, not your meter
The methodology behind an EPC uses standardised occupancy, standardised patterns of use and regional weather data. Two identical arrays on two identical houses will produce the same modelled result even if one household is out all day and the other runs the washing machine at noon. That consistency is the whole point: it lets one property be compared with another on the same basis.
It also means the figures on the certificate will not match your inverter app or your electricity bill, and they are not meant to. Treat any promise of a specific band jump made before an assessment has taken place as a guess. Nobody can commit to a result until an accredited assessor has surveyed the property and lodged the certificate on the national register.
Check these before you install
- Roof condition and remaining life. If the covering is near the end of its service, re-roofing later means removing and refitting the array.
- Structural capacity for the extra load, which the installer should confirm in writing.
- Permissions. Many domestic installations fall within permitted development, but conditions apply and listed buildings, conservation areas and flats are treated differently. The position for a listed building is not automatic in either direction, so check the current guidance on gov.uk and with your local planning authority before ordering.
- Leasehold arrangements, including whether the roof is demised to you and whether the freeholder’s consent is needed – our guide to EPCs for flats and leasehold covers the usual complications.
- Installer certification. MCS registration or an equivalent scheme is normally required to access export payment arrangements.
- Notification to the local network operator, which the installer usually handles.
- Warranties, monitoring and who is responsible for servicing or replacing the inverter.
Batteries and self-consumption
A battery stores generation you cannot use at the moment it is produced, raising the share consumed on site rather than exported. Whether that pays depends on your tariff, your daily routine and the price you were quoted, so it is a question to work through with figures specific to your household rather than a general rule. This guide is general information about how EPCs work, not financial advice.
How storage is credited within the assessment methodology is a separate question from how it affects your bills, and the methodology is revised periodically. Be cautious with any claim that adding a battery will lift your band. Ask the installer to make the case on running costs and resilience, and treat the effect on a rating as unknown until a new certificate exists.
Keep the paperwork
When the system is commissioned you should receive a handover pack. Keep the MCS certificate, the commissioning and handover documents, the panel and inverter specifications, the total installed capacity and the network operator notification together with your deeds and warranties. Photographing the finished roof from the ground is a sensible addition.
This matters because an assessor works from evidence. Where documentation is missing they follow the conventions of the methodology, which can mean a more cautious assumption than the installation deserves. Producing the certificate and the capacity figure at the visit is the simplest way to make sure the array is recorded as it was actually built.
Your existing certificate will not update itself
An EPC is a snapshot taken on the day of the assessment and lodged on the national register, and a domestic certificate is valid for ten years. Installing panels does not alter the entry already on the register. The only way to have generation reflected is to commission a fresh assessment, which produces a new certificate alongside the old one.
If you are selling or letting, time that visit sensibly. Wait until the system is commissioned and any other planned work is finished, so a single assessment captures everything. Fees are not fixed: they vary with the property, the location and the assessor, and commonly fall somewhere in the region of £60 to £120. Our guide to getting an EPC covers how to book one and what the assessor will want to see.
Where you are in the UK matters
Energy performance is a devolved matter, so the rules, the certificate format and the enforcement regime are not identical across the UK. Scotland and Northern Ireland run their own systems and their own registers, and planning rules for solar installations also differ, which is worth checking before you apply anything you have read about England and Wales to a property elsewhere. Our guide to EPCs across the UK sets out the main differences.
For landlords in England and Wales, the minimum standard has since 1 April 2020 prevented the letting of a property with a rating below band E unless a valid exemption is registered. Proposals to raise the minimum to band C have been consulted on but are not settled law, and no date for them should be treated as fixed. Our guide to EPC rules for landlords covers the current position. EPC Checker is a research aid over public data; it is not an assessment, survey, or professional, legal or financial advice.