The sunniest six weeks of the year, and nobody's home

There's a quiet inefficiency sitting on school roofs all over the UK, and once you see it you can't unsee it.

Thousands of schools have done exactly the right thing. They've put solar on the roof. Some funded it themselves, some through community schemes, and a growing number through the Great British Energy programme that's now covering hundreds of schools. A typical install runs anywhere from 30kWp on a primary school to 250kWp on a large secondary.

Here's the problem. A school consumes energy on weekdays, in term time, roughly 39 weeks a year. Solar generates most in exactly the periods a school is empty. Weekends. Long summer evenings won't save you, but long summer days matter, and then the big one: six weeks of summer holiday landing precisely in the highest yield weeks of the year.

And unlike a house, a school often can't just export the surplus and get paid fairly for it. Many sites sit behind constrained grid connections. Their G99 agreement caps what they can push back to the network, sometimes at zero. Others can export but at a rate that would make you wince. So the choice on an August Saturday is: curtail the generation and waste it, or export it for pennies.

Run the numbers on a fairly ordinary 50kWp school array on the south coast and the scale of it becomes obvious. On a sunny June day it produces something like 200kWh beyond what an empty building needs. That's four or five full EV charges, every day, through the holidays. Even a grey December day usually leaves enough surplus for a decent top up. Multiply that across a multi academy trust with dozens of sites and you're looking at a genuinely useful community energy resource that currently evaporates.

So here's the thought experiment we've been working through.

What if the surplus became bookable? A portal reads the solar forecast for a site and opens exactly as many charging slots as the surplus can support. A sunny Saturday in July shows five slots. A grey Tuesday in January shows one, or none. You book, you turn up, you plug in, and the energy is spare sunshine the site couldn't use anyway. Because a car charging on site is self consumption, it never touches the export limit. The school stays inside its grid agreement, the driver charges on genuine surplus, and the site turns a wasted asset into a community story.

There are real questions to answer before anyone should build this at scale, and I'll be honest about what they are. Who operates it and carries the liability. What the site's insurer says. How you handle the winter months when the sun barely clears the rooftops. Whether the regulations treat a community scheme as a public charge point. None of these are trivial, and some of the adjacent attempts at community charging have found the economics brutal. The graveyard of peer to peer charging apps is well populated.

But the physics is not in question, the grant landscape is unusually favourable right now (schools can currently get 75 percent towards charge point hardware, a scheme that ends in March 2027), and as far as we can tell nobody has built the piece that matters: availability that honestly follows the sun.

So we're starting with the simplest possible thing. We're building a free calculator. Any school, trust or workplace will be able to enter their postcode, their array size and their export limit, and get back a straight answer: this is how much of your generation goes to waste, and this is how many free EV charges a week it could fund, month by month, in a one page summary you can put in front of your governors or your board.

Before we release it, I'd like to hear from people who live with this every day.

If you manage a school, trust or workplace estate with solar on the roof: do you know how much of your generation you actually use? Is your site export limited?

If you work in community energy or EV charging: what would make you take a scheme like this seriously, and what makes you roll your eyes?

And if you think the whole thing falls over somewhere, tell me where. That's the most useful comment you can leave.

Craig Lewis MBCS is co-founder of LDS Consulting, where we build practical tools for the energy transition.