The Term-Time Problem: Does Your School Solar Need a Battery?

The problem no other building has

A school’s electricity demand is unlike any other building, and it creates a genuine puzzle for solar. Picture the mismatch: a school’s solar array generates hardest in July and August — the longest, sunniest days of the year — precisely when the six-week summer holiday means the building is empty. Add every weekend, half-term and INSET day, and a large share of a school’s annual generation lands when almost no one is there to use it. A warehouse runs a flat weekday baseload; a school’s roof over-generates exactly when the building sleeps.

This is the term-time problem, and it is the single most important thing to understand before sizing a school system. It doesn’t mean solar is a bad fit for schools — far from it — but it does mean a school array has to be designed around its demand curve, not just its roof area. This guide explains the problem honestly, then sets out the two answers: a battery, and the Smart Export Guarantee.

Self-consumption: the number that matters

The key metric is self-consumption — the share of the electricity your panels generate that you actually use on site, rather than exporting to the grid. Self-consumed energy is worth far more than exported energy, because it displaces power you would otherwise buy at full retail price (often 25–35p/kWh), whereas exported energy earns only the export rate (4–15p/kWh).

For a typical term-time-only, non-boarding school, self-consumption is usually only 35–55%. In plain terms: roughly half of what the roof generates over the year is used on site, and roughly half is exported — much of it during the summer holiday and weekends at the low export rate. That is a real drag on the economics compared with a business that self-consumes 70–80%.

Not every school suffers equally:

• Primary and secondary day schools — the classic term-time profile, self-consumption toward the lower end (35–50%).
• Boarding independent schools — a 24/7 residential baseload means self-consumption is the strongest of any school type, often well above 60%. Boarding bucks the term-time problem entirely.
• Special schools — often more year-round occupancy (holiday clubs, specialist provision), giving better self-consumption than a day-only primary.

It is worth being precise about why this matters financially, because the intuition trips people up. A unit of solar you use on site is worth the full retail price you didn’t have to pay — call it 30p. A unit you export is worth only the export rate — call it 8p. So the same kilowatt-hour is worth nearly four times as much when self-consumed as when exported. Two schools with identical roofs and identical annual generation can therefore have very different economics purely because one uses more of its own power. Raising self-consumption is not a technicality; it is the single biggest lever on a school array’s payback, which is why it deserves proper design attention rather than an afterthought.

The point of understanding self-consumption isn’t to be discouraged — it is to size the system and choose the extras correctly. Which brings us to the battery.

When a battery pays

A battery (typically 50–150 kWh for a school) solves the term-time problem by storing generation when the building is empty and releasing it when it isn’t. Concretely, a battery:

• Shifts weekend generation into Monday–Friday use — Saturday and Sunday sun is banked and spent during the school week.
• Captures early-morning and late-afternoon generation for use outside peak daylight, when a day school’s demand actually sits.
• Lifts overall self-consumption, often from the 35–55% range toward 70% and above, which is where a day school’s economics genuinely improve.

But a battery is not automatic, and honest advice matters here. A battery adds capital cost, so it only pays when it displaces enough expensive imported electricity to justify itself. The battery case is strongest when:

• Your self-consumption without one is low (a classic term-time day school).
• Your imported electricity is expensive (most schools, post-2021).
• You have significant weekend or shoulder-season generation to bank.
• You can access interest-free Salix funding, which spreads the battery’s cost painlessly.

The battery case is weakest for boarding schools that already self-consume most of their generation — there’s little surplus left to store. This is exactly why sizing must come from data, not a rule of thumb. We model the battery’s return from your half-hourly meter data, including a holiday period, and only recommend one where it genuinely pays. For the numbers behind battery-and-panel economics, see our cost guide.

The Smart Export Guarantee: monetising the surplus

Whatever you don’t self-consume or store, you export — and export is not wasted. The Smart Export Guarantee (SEG) pays for every kilowatt-hour a school sends to the grid, at rates of 4–15p/kWh as of 2026. For a term-time school exporting heavily across the summer holiday, SEG income is a meaningful line in the business case — it turns the “empty building in August” problem into a revenue stream rather than a loss.

The rate you get varies by supplier, and the best non-domestic export tariffs are worth shopping for. SEG never funds the install, but it materially improves the lifetime economics of a school array, and it matters more for term-time-only schools than for almost any other building type — precisely because they export so much. A well-designed school project stacks all three: self-consumption first (most valuable), battery-shifted consumption second, and SEG export on the surplus third.

It is also worth noting that export tariffs are not fixed for the life of the system. A school signs up to whatever SEG tariff its supplier offers, and can switch as better rates appear — the export meter and MCS certification that make you eligible don’t change. Over a 20-year system life, a school that periodically reviews its export tariff can capture meaningfully more than one that signs up once and forgets. We flag the leading non-domestic export tariffs at handover and suggest a review whenever the market moves, so the surplus keeps earning its keep long after the panels are up.

Battery or no battery: the honest decision

Putting it together, the decision comes down to your school’s profile:

• Day school, low self-consumption, expensive electricity, Salix funding available → a 50–150 kWh battery usually pays and sharpens the case considerably.
• Boarding independent school with strong 24/7 baseload → often no battery needed; self-consumption is already high, so spend the capital on more panels instead.
• Special school with year-round occupancy → somewhere in between; model it from data.
• Any school → the export surplus earns SEG income regardless, so no generation is truly lost.

The wrong approach is to bolt on a battery because it sounds thorough, or to skip one because it sounds expensive. Both are guesses. The right approach is to size the whole system — panels and any battery — from at least 12 months of half-hourly meter data that includes a holiday period, so the design matches your real demand curve.

Get the sizing right for your school

The term-time problem is solvable — it just has to be designed for, not ignored. The schools that get the best economics are the ones that sized the array, the battery and the export strategy together, from real data, rather than filling the roof and hoping. See our pages for primary schools and independent schools for how the profile differs by type, and our FAQs for the questions governors raise about holiday generation.

To find out whether your school needs a battery — and how big — request a free feasibility. We will model your self-consumption from your own half-hourly data, including a holiday period, and tell you plainly whether a battery pays on your roof or whether your capital is better spent elsewhere.