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Our research shows that over 18,000 solar panel owners could face a £100 fine from HMRC if they don’t check their energy statements and submit their self-assessment tax return before Friday, 31 October.
After a record-breaking year for installations in 2025, 1.6m UK households now have solar panels, and hundreds of thousands of Brits are earning money by selling unused electricity back to the grid.
While households can make over £300 a year through the Smart Export Guarantee (SEG), these payments can quickly tip some people over HMRC’s £1,000 tax-free trading allowance, creating a requirement to declare the income.
With 39% of Brits side hustling in 2025, an estimated 624,000 solar panel owners could therefore unknowingly be earning more than the £1,000 trading allowance. And with HMRC figures showing that 2.89% of self-employed taxpayers still use paper-based tax returns, this means an estimated 18,033 solar panel owners could be facing a £100 fine if they miss Friday October 31st self-assessment postal deadline.
Faced with this predicament, it’s crucial that solar panel homeowners check, before it’s too late, how much they’re earning – including any additional income from their SEG payments. If the total exceeds £1,000 made between April 2024 and April 2025, solar panel homeowners could be at risk of being fined by HMRC.
Review your latest statements from your energy supplier as soon as possible. These show exactly how much income you’ve earned from selling power back to the grid, which is crucial in working out whether you may have surpassed your £1000 allowance.
If this extra income, plus any further additional income you may earn from other side hustles surpasses £1,000 between the April 2024 to April 2025 tax year, you must declare this with HMRC.
While paper tax returns close on Friday 31st October, filing online extends your deadline to 31 January 2026. That gives you three extra months to get everything right and avoid a £100 fine.
To file online, head to the government’s online self assessment tool. The tool is quick and simple to use, which also helps reduce errors, ensuring your tax return is processed faster.
Completing your self assessment tax return online can mean you are more exposed to scams, with HMRC stating over 170,000 scam reports were brought to their attention in the past year. Homeowners must be extra vigilant, as the average HMRC-related scam costs victims an average of £1,730 according to National Trading Standards.
Always use official government websites and never click links in unexpected emails or text messages. Doing so could expose your financial information and leave you vulnerable to a costly scam.
If you’ve received a notice to file a tax return, you must complete it, even if you believe your solar income is below the £1,000 threshold, as ignoring it can still lead to fines.
Failing to submit a return after being asked by HMRC triggers an immediate £100 penalty, regardless of whether any tax is owed. If the return remains unfiled, additional charges quickly mount: after three months, daily penalties of £10 can apply for up to 90 days (adding up to £900), followed by a £300 fine or 5% of the tax due after six months, and the same again after twelve months.
These fines can escalate rapidly, so even if you think your solar income doesn’t need to be reported, it’s always safer to triple-check and complete your return on time.
Notes to editors
To estimate how many solar panel owners could miss the paper-based Self Assessment deadline, The Solar Co applied the UK’s 39% side hustle rate to the 1.6m households with solar panels, suggesting around 624,000 may earn additional income that pushes them over the £1,000 trading allowance. Using National Trading Standards data, which shows 2.89% of taxpayers still file by post, this equates to approximately 18,033 solar panel owners who could be at risk of missing the 31 October postal deadline.
About George Penny
Based in Bromley, George Penny is the Director of The Solar Co. He has a passion for leading the UK’s transition to efficient and reliable renewable solutions for households and businesses alike.
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