In this feature
- Start with the timetable, not the roof area
- Three prices belong in three different boxes
- Request a year of half-hourly demand
- Put holidays into the financial model
- Stress-test the PPA against a cheaper grid
- Forward prices are a different form of evidence
- Battery storage needs its own case
- Turn the analysis into a decision record
Start with the timetable, not the roof area
A school considering solar usually begins with two annual numbers: electricity consumption and predicted generation. They are useful, but they do not establish how much generated electricity the school can use when it arrives. The next question is about timing. A kilowatt-hour generated while classrooms, kitchens and equipment are operating can replace an imported kilowatt-hour. The same generation during a quiet holiday afternoon may have a different financial treatment. Leaders need to understand that distinction before turning a promising annual estimate into a long-term commitment.
This is where the electricity market adds useful context. Elexon’s observed Market Index prices vary between half-hour periods. Our initial July–8 October record separates all-hours averages from a weekday 08:00–16:00 UK-time window. That window is a transparent comparison tool, not a measurement of any school’s demand or a solar-weighted revenue forecast. It includes holiday weekdays and cannot describe a particular roof. Its value is to make timing visible and prompt the right evidence request. [elexon]
Three prices belong in three different boxes
Wholesale electricity prices describe a market component. The school’s imported electricity price includes other costs and contractual arrangements. A PPA price is the price agreed for electricity under a particular agreement. They should not be placed next to one another as if they were interchangeable. Ofgem explains that business bills include wholesale, network and environmental costs, with the wholesale share varying. A wholesale index below the school’s unit rate does not establish that a proposed PPA offers the difference as savings. [ofgem]
The useful comparison is the school’s genuinely avoidable cost for the electricity displaced, against the PPA charge and any associated costs. Standing charges may remain. Some network or policy costs may sit within a unit rate, while others follow different charging rules. Ask for the current contract and bill components to be reconciled with the proposed calculation. Establish which charges reduce when imports fall, which remain, and whether the existing supply agreement has any minimum-volume or other relevant conditions. Do not assume every billed penny disappears.
Request a year of half-hourly demand
The practical starting point is a representative year of interval consumption data, where available, with dates and units confirmed. Record school closures, unusual disruption, extended community use, lettings and major changes in equipment. A year affected by building works may not represent the next twenty years. Where interval data is unavailable, record that limitation and seek an appropriate metering or assessment route. Monthly totals can support an initial discussion, but they cannot demonstrate the match between generation and daytime use.
Ask the technical assessment to compare the school’s demand and expected solar output in the same intervals. Each interval should show generation, electricity used onsite and surplus. The calculation should avoid counting the same kilowatt-hour as both a saving from avoided imports and an export receipt. Record who has the right to export revenue under the proposed arrangement. Our dashboard’s weekday proxy can inform questions, but it cannot replace this site-specific matching exercise.
Put holidays into the financial model
Summer offers substantial solar-generation potential, but also includes the longest school closure. That combination deserves explicit treatment. A school with holiday clubs, catering, sports facilities or community lettings may retain meaningful daytime demand. Another may have much lower use. Neither profile should be assumed from the establishment type. Review the actual summer record and discuss planned operational changes. A financial projection should state the resulting annual onsite-consumption share and show how that share was obtained.
NESO’s summer assessment describes periods when lower demand and renewable generation can produce surplus electricity, including sunny and windy weekends. This is a system explanation, not a forecast of a school’s export income. It reinforces the need to test when electricity is produced and consumed. A larger array is not automatically the better financial choice. Compare feasible sizes on usable generation, contractual treatment of surplus and the school’s longer-term estate plans. [summer]
Stress-test the PPA against a cheaper grid
A strong appraisal should survive scrutiny when electricity prices fall. Begin with the school’s avoidable imported unit cost and the proposed starting PPA price. Then test falling, level and rising grid-price scenarios, alongside the actual escalation mechanism proposed for the PPA. A lower starting PPA price can eventually exceed an unchanged grid price if it rises each year. The crossing year matters, but the cumulative and discounted financial effects matter too. A positive first year cannot settle a twenty-year decision.
Our stress test lets leaders change onsite use, annual generation decline, additional annual costs and a discount rate. Its three grid paths are illustrative, not forecasts. It shows both favourable and adverse outcomes. A full project appraisal needs any upfront costs, tax treatment, roof responsibilities, downtime and other relevant cash flows added. Use the tool to identify sensitive assumptions and prepare questions; commission the necessary technical and financial scrutiny before approval.
Forward prices are a different form of evidence
Forward electricity contracts price delivery in a future period. ICE’s UK baseload product covers continuous delivery and offers monthly contracts with quarterly, seasonal and calendar strips. Such a product can help describe market pricing for a specified future period, but its flat delivery profile does not mirror a school’s demand or a solar roof’s generation. A futures quotation also needs a timestamp, contract definition and appropriate usage rights. We have not connected a licensed forward-price feed to this desk. [ice]
When someone presents a future electricity assumption, ask whether it comes from a current forward quotation, an official scenario, an historical average or their own modelling. Those are different evidence categories. Request the delivery period, data date and adjustment used to translate market information into the school’s cost. A twenty-year constant annual increase should be described as an assumption and tested against alternatives. It must not acquire the status of a verified forecast merely because a chart looks precise.
Battery storage needs its own case
Storage may improve the match between generation and consumption, but the benefit depends on the site and the agreement. A battery introduces costs, losses, capacity limits and operational responsibilities. It cannot be added to a solar projection as a free improvement. Establish ownership, replacement assumptions, control of charging, warranties and the treatment of any flexibility income. Check how a battery interacts with the PPA, existing supply contract and the estate’s safety and maintenance arrangements before assuming a combined return.
Keep resilience claims equally specific. Grid-connected solar does not automatically keep the school operating during a power cut. Any backup capability needs a suitable technical design and an agreed operational plan. NESO’s winter outlook concerns national system adequacy, not a particular school’s ability to remain open through a local outage. Distinguish energy-cost reduction, flexibility and continuity in the board paper so each benefit has its own evidence and responsibility. [winter]
Turn the analysis into a decision record
Give finance and estates colleagues a shared evidence pack: interval demand, the proposed generation profile, estate constraints, the avoidable-cost breakdown and the PPA terms. Record the source, date and owner of each input. Ask for a clear explanation of annual onsite use, holiday treatment, export rights, price escalation and retained costs. Governors should see the adverse scenario alongside the preferred one, with unresolved matters assigned to an owner and a review date.
The practical opportunity remains attractive: using suitable school roofs and daytime demand can reduce imported electricity and support a stronger estate. The best projects begin with the school’s actual circumstances. Market intelligence strengthens that process by showing the context and testing assumptions. It earns its place when it helps leaders distinguish a plausible benefit from a demonstrated one, ask more precise questions and make a decision they can explain over the full life of the agreement.
Prepare the evidence, then test the decision
- Finance: obtain interval consumption and reconcile avoidable import costs.
- Estates: commission a site-specific generation and onsite-use assessment.
- Governance: require the adverse scenario, unresolved responsibilities and a review date.
Sources and publication record
Published 9 October 2026. Evidence reviewed 9 October 2026. Practical recommendations are School Connection’s assessment; no supplier is endorsed.
- Elexon
Market Index prices and API
APXMIDP observed half-hourly Market Index price and volume records. Archive extended through 11 October; retrieved 12 October. Initial record was 1 July–8 October 2026. Not a futures curve.
- Ofgem
Managing business energy costs in an uncertain market
31 March 2026. Commodity, network and environmental costs; broad business context is not a school-specific share or current quote.
- NESO
Winter Watch: early view of winter 2026/27
Page reviewed 12 October. Early view: 5.5 GW surplus and 8.8% buffer. Security-of-supply assessment, not a price forecast; fuller assessment awaited on this source page.
- NESO
Summer Outlook: timing and flexibility
14 April 2026. Lower summer demand and local renewable generation can create surplus periods; flexibility is an operational tool.
- ICE Futures Europe
UK Base Electricity Future (Gregorian)
Monthly contracts and quarterly/seasonal/calendar strips; continuous baseload delivery. No licensed forward-price feed has been connected to this desk.