Energy & ROI Modelling

A headline 'six-year payback' means little without the assumptions behind it. We build the model around your actual half-hourly consumption and your current and forecast tariffs. We also factor in a realistic view of self-consumption versus export. Then we layer in maintenance, inverter replacement and panel degradation across the system's life.

The tax position matters too. The real payback is often better than the sticker price suggests. That's because we model it net of the capital allowances that actually apply to solar. Those are the Annual Investment Allowance and, above it, the special rate first-year allowance. We hand you the model, the assumptions and the scenarios, so finance can interrogate every line.

For most commercial buyers, the numbers work like this. The Annual Investment Allowance lets any business deduct up to £1 million a year of qualifying plant and machinery cost against profit. That comfortably covers most single-site solar arrays — provided you haven't used up the allowance elsewhere in the same accounting year.

Solar is 'special rate' expenditure under HMRC's capital allowances rules, not main-rate plant and machinery. So it doesn't qualify for the 100% 'Full Expensing' relief often quoted online. That relief applies only to main-rate assets.

Any spend that falls outside the AIA instead gets the 50% special rate first-year allowance. The remaining balance is then written down at 6% a year in the special rate pool. The 2026 Budget changed the main pool: a new 40% first-year allowance and an 18%-to-14% cut in the main-rate writing-down allowance. That 6% special rate pool rate doesn't move, since the Budget changes apply to a different pool entirely.

Getting that distinction right changes the real, net-of-tax payback. That's exactly what we build into the model. So the figure reflects what you'll actually pay after relief, not the sticker price on the quote.