Solar Sources and Calculation Methodology

Solar estimates are only useful when the inputs are visible. This page explains the evidence hierarchy and calculation choices used across Here4Solar.

Units used

kWp

The rated peak capacity of the solar array under standard test conditions.

kWh

A unit of energy used for electricity consumption, generation and export.

kWh per kWp

A yield factor that links system size to expected annual generation for a location and roof.

Self-consumption

The share of solar generation used in the home rather than exported.

Generation method

A simple annual estimate multiplies array size by a regional or location-specific yield, then adjusts for roof orientation, pitch, shading and system losses. The on-site calculator can use postcode-based PVGIS output where available. An installer should provide a property-specific generation estimate and explain the dataset and losses used.

Financial method

First-year benefit is the value of solar electricity used in the home plus income from electricity exported. A basic simple-payback figure divides installed cost by that annual benefit. It does not automatically include finance interest, inverter replacement, maintenance, tariff changes, degradation or the time value of money, so those limitations are stated beside the result.

Cost evidence

National averages are used only as orientation. Quotes should be compared using system size, panel and inverter models, battery usable capacity, scaffolding, electrical work, monitoring, warranties, VAT treatment and paperwork. A cheaper total may describe a smaller system or omit work.

Policy and regulatory evidence

Grant, tax, planning and export pages link to GOV.UK, Ofgem or the relevant scheme administrator. UK nations can have different planning and funding rules, so a page must state its territorial scope. Live supplier rates are not treated as permanent.

Quality checks

• One clear page purpose and one H1.
• A unique title and useful search description.
• Canonical URL, crawlable internal links and inclusion in the XML sitemap.
• Primary citations close to the claim they support.
• Affiliate links labelled sponsored or nofollow.
• Mobile rendering, image alt text and structured-data validation.

Evidence records and version control

A dated claim should retain enough context to be checked later. For tariff and policy research we record the source owner, source URL, checked date, territorial scope, numeric value, unit and any visible eligibility conditions. If the source does not answer a field, we use “not stated”. If an official public rate cannot be located, we preserve the supplier as a source-gap record instead of filling it from an uncited comparison table.

Material datasets use versioned filenames and retain earlier releases. Reports use their own version numbers because a clarification can change the interpretation without changing the underlying numeric rows. The July 2026 export tariff dataset and version 1.1 transparency report show the live method, archived files, reuse licence and correction trail.

What an editorial check date means

A check date means the cited evidence and important page conclusions were reviewed on that date. It is not an automatic freshness label. Supplier prices, grants, VAT rules and consultations can change afterwards, so readers should open the linked authority and confirm the current position before acting. Where two first-party pages disagree, the tariff information label, written supplier confirmation, signed contract or responsible public authority takes precedence over a general marketing page.

Reproducible research

Where practical, we publish structured CSV or JSON beside a readable page, document field definitions and provide a citation and reuse licence. This lets a journalist, researcher or reader reproduce a headline finding instead of trusting a chart alone. Corrections should preserve the original evidence and explain what changed.