Establish the baseline
Name the responsible body and project sponsor. Attach dated bills, interval data, surveys, roof programme, generation design and an explanation of which costs are avoided. List missing evidence with an owner.
Published 10 October 2026 / Practical appraisal
From solar proposal to defensible school decision
A worked appraisal, proposal comparison and evidence checklist for school and trust leaders assessing long-term solar agreements.
A credible proposal joins demand, design, price, responsibilities and an achievable approval route. The worked example below is invented for teaching the arithmetic. It is not a school case study, market quote or prediction.
One illustrative school, several possible outcomes
Start with 100,000kWh of year-one solar generation, of which 70,000kWh is consumed onsite. The remaining 30,000kWh is surplus. The school pays 15p/kWh only for onsite energy, avoids 22p/kWh of imported costs, retains no export income and incurs £500 of additional annual costs plus £1,000 at the outset.
| Component | Calculation | Amount |
|---|---|---|
| Avoided import cost | 70,000kWh × 22p | £15,400 |
| PPA electricity payment | 70,000kWh × 15p | £10,500 |
| Gross difference | Avoided cost less PPA payment | £4,900 |
| Additional annual school cost | Entered allowance | £500 |
| Year-one operating difference | Gross difference less annual cost | £4,400 |
| Initial school cost | Time-zero cash flow, deducted separately | £1,000 |
The 22p input excludes charges that the school still pays. Do not replace it with a whole-bill average unless the avoided components have been checked. Prices and costs use one consistent tax basis; actual VAT recoverability and other tax treatment need to be resolved in the school’s own appraisal.
Why the contract’s purchase obligation matters
If the school must pay 15p for every generated kilowatt-hour, the year-one PPA payment becomes £15,000. With the same onsite use, retained costs and no export income, the operating difference becomes -£100. If onsite consumption instead falls to 50% while payment remains for onsite energy only, the operating difference becomes £3,000. These are different contractual and demand assumptions, not arguments that every PPA has those terms.
Look across the term
The following three paths assume 0.5% annual generation decline, constant onsite share, 2% annual PPA escalation, fixed £500 annual school costs and a 3.5% discount rate. All are illustrative nominal assumptions, not official recommended values. Cash flows are year-end; the initial £1,000 is at time zero. Export prices, if entered in the interactive tool, remain constant.
| Avoidable grid-price path | Year-one operating difference | Final-year operating difference | Undiscounted total | Discounted difference | PPA unit price above grid |
|---|---|---|---|---|---|
| Falling grid prices | £4,400 | -£6,558 | -£29,043 | -£11,628 | Year 9 |
| Level grid prices | £4,400 | -£406 | £40,240 | £32,374 | Not within term |
| Rising grid prices | £4,400 | £10,144 | £139,235 | £93,831 | Not within term |
The discounted difference is not a complete investment valuation. Add actual roof-work timing, downtime, changing demand, variable fees, tax effects, financing and end-of-term costs. A favourable total does not remove annual affordability or contractual risk. A unit-price crossing year alone does not capture payment for surplus energy.
Four kinds of price evidence
| Evidence | What it tells you | What it cannot establish |
|---|---|---|
| Observed wholesale index | Dated short-term market conditions; £/MWh ÷ 10 converts to p/kWh. | A school’s delivered bill, solar capture price or future tariff. |
| Forward market quotation | A price for a defined future delivery period, product and quote time. | A guaranteed realised price or a school-specific supply offer. |
| School supply/PPA quotation | Terms offered to the school, with profile, charges, validity and tax basis. | Savings without usable generation, retained-cost and full-term analysis. |
| Illustrative scenario | Sensitivity to explicitly chosen price paths. | A forecast, probability or claim about the market’s expected direction. |
The electricity desk has a dated Elexon archive and refresh path. A licensed forward-price feed is not connected. We will not populate a forward curve from historical observations or present the calculator’s 25p grid / 15p PPA defaults as available offers.
When forward information is supplied, record quotation time and timezone, delivery dates, baseload or peak profile, currency/unit, settlement versus bid/offer, source, usage rights and stale-data policy. A baseload strip supplies every hour; a school’s load and a rooftop’s solar output do not. Procurement margins, hedging and non-commodity costs need a separate bridge to the school quote.
The weekday 08:00–16:00 chart includes holidays. To assess solar’s value, match generation and school demand interval by interval: onsite use equals the smaller of the two, surplus is accounted for separately, and financial treatment follows the actual contract. Avoid applying a single national wholesale average to every generated kilowatt-hour.
ICE’s UK baseload product definition · Elexon’s observed Market Index · Ofgem’s business-bill context
Compare the whole proposal
Use the same site, demand record, generation method and comparison period for every proposal. Ask suppliers to identify assumptions and exclusions rather than filling unknowns with optimistic numbers. The worksheet is a record of questions, not a substitute for technical, procurement or legal advice.
| Area | Evidence request | Question to resolve |
|---|---|---|
| Demand and design | A year of half-hourly demand, holiday/lettings calendar, proposed generation profile and the effect of planned efficiency works. | A large roof or annual electricity total alone cannot establish usable solar. |
| Roof and electrical works | Condition and structural surveys, remaining roof life, asbestos assessment where relevant, electrical capacity, access and connection responsibilities. | Who pays for roof repairs, isolation, removal and reinstatement during the term? |
| Consents and procurement | Landowner/responsible-body authority, applicable school-land approvals, planning and connection route, and a documented procurement/value-for-money assessment. | A registration or expression of interest is not permission to sign. |
| Price and purchased energy | Starting tariff, indexation formula/caps, invoice basis and whether payment covers onsite use or all generated energy. | Who pays for surplus generation and who receives export revenue? |
| Performance and maintenance | Expected yield, monitoring access, fault response, maintenance scope, warranties, exclusions and any enforceable performance commitments. | A forecast yield is not a contractual guarantee. |
| School’s retained costs | Metering, network/supply charges, insurance changes, surveys, professional fees, tax treatment and any annual service payments. | Only demonstrably avoidable import costs belong in the savings input. |
| Change and exit | School closure/expansion, academy transfer, counterparty failure, assignment, termination payments and funder rights. | Ask advisers to examine the actual drafted clauses and adverse circumstances. |
| End of term | Ownership transfer or removal, roof reinstatement, residual value and treatment of equipment reaching end of life. | Do not assume ownership transfers free of cost. |
| Battery and resilience | Separate storage cost, replacement, losses, control and income allocation; explicit backup capability if proposed. | Solar generation alone does not establish power-cut resilience. |
| Evidence and educational use | Metered generation/import/export, dated baseline, tariff reconciliation, pupil activities and a named monitoring owner. | Evaluate educational benefits separately from cash savings; do not monetise them without evidence. |
A board paper that survives the adverse case
Show the alternative
Compare the PPA with doing nothing and feasible alternatives, including demand reduction and a funded/capital route where available. Grant-funded programme returns do not establish the return from a school’s proposed PPA.
Explain the downside
Show lower onsite use, cheaper imported power, reduced yield, additional school costs and the actual obligations for surplus generation. Discuss cash flow, termination and roof works across the agreement.
Define the decision
Separate permission to investigate from authority to commit. Record reviewer conclusions, procurement/consent status, unresolved conditions and when the board will revisit the proposal.
After installation, assign an operating owner for meter reconciliation, fault reporting, performance review and educational use. A saving is stronger evidence when another reviewer can reproduce it from generation, imports, exports, invoices and the documented baseline.
Evidence update register
| Evidence item | This review | Next evidence needed |
|---|---|---|
| Programme counts | Separated funded installations, planned expansion and private-finance pilot. | A later official school-by-school completion record. |
| Case studies | Added published project tables, participant accounts and delivery lessons. | Matched bills and metered results before claiming audited solar-only savings. |
| Pricing | Retained observed data / forward quotes / school quotes / scenarios distinction. | Licensed timestamped forward source and genuine school quotations. |
| Appraisal | Aligned default inputs; added upfront cost, export rights and purchase obligation to stress test. | School-specific technical and contractual inputs with consistent tax treatment. |
| DfE template | Published guidance checked; final approved templates still awaited on that source. | Official publication and confirmation of resumed approvals. |
Evidence reviewed 2026-10-10. Original interviews and unpublished partner claims have not been invented. Public-source interpretation is School Connection’s assessment. Any future commercial participation must remain separately disclosed.
Examine the participating-school evidenceReturn to the programmeFrom interest to operation
Understand the delivery stages, responsibilities and first-year evidence.
From interest to switch-on, and the first year afterwardsEnergy pressure and school budgets
Dated spending evidence, participating school leaders’ experiences and practical choices across efficiency, procurement and solar.
School energy bills: the pressure, the choices and what leaders can control