Clear assumptions, better decisions

Terms & methodology

These proposals provide indicative solar and storage estimates, not guaranteed performance, financial advice or a certified installation design. Contact the business that issued your proposal for its quotation, business terms and contact details.

Solar generation

For Google-based estimates, roof-generation data comes from Google Maps Solar API. We use the reference configuration matching the selected panel count, or linearly interpolate between neighbouring configurations. We scale its annual DC energy by your selected panel wattage divided by Google's reference wattage, then apply the stated system-loss percentage.

When a visual roof layout is selected, it replaces count-based interpolation: we sample 81 points across each panel footprint in Google's annual sunlight raster, multiply the mean DC yield by the selected panel capacity, sum the panels and apply the stated system losses. Panel width is across the roof slope and height down the slope; pitch shortens the top-down footprint only. Sunlight already reflects Google's modelled roof, so no additional pitch cosine is applied to generation.

Panel positions, dimensions, pitch, per-panel yields and fixed aerial/annual-sunlight images are retained in a visual proposal. Overlap, off-roof samples and missing sunlight prevent saving, but the mask may include adjoining buildings. It does not certify ownership, setbacks, mounting gaps, roof loading or usable area. Monthly heatmaps show relative, annual-equivalent sunlight, not monthly electricity generation. These are 2D planning views, not a 3D or hourly-shading simulation.

Reference layout limits refer to Google's panel dimensions, not necessarily your chosen Jinko module. Panel fit, shading, usable roof area and installation suitability require a site survey. Inverter AC rating is shown for design checking; clipping, hourly generation and export constraints are not simulated.

Independent-survey estimates use panel count × panel watts / 1000 × the supplied annual DC yield in kWh/kWp, followed by the stated system losses. The source notes are shown on the proposal. These estimates are not Google Solar data.

Battery energy balance

Direct use is generation × the assumed direct-use percentage, capped at household annual demand. Usable battery capacity is module count × nominal capacity × usable percentage.

Annual charging is capped by all three of: surplus solar, remaining household demand divided by round-trip efficiency, and usable capacity × 365 × assumed daily cycles. Battery energy delivered equals charging × round-trip efficiency. Remaining surplus is exported and unmet demand is imported.

This annual model can overstate achievable storage use because it does not resolve winter shortages, summer surpluses, hourly demand or battery/inverter power limits. Battery capacity does not increase solar generation. No grid charging, time-of-use arbitrage, backup reserve or battery degradation is modelled.

Financial results

Annual bill benefit is avoided grid imports at the selected import rate plus export income at the selected export rate. Extra battery benefit compares that figure with the same solar system without a battery, accounting for battery losses and lost export income; it can be negative.

Simple payback divides net installed cost by annual benefit, without financing, maintenance, replacements, degradation, price escalation or discounting. A zero cost means payback is not quoted. Grant eligibility and export agreements must be checked separately. Default rates and equipment values are editable examples, not current prices or certified datasheets.

Prices, grants and long-term outlook

New proposals itemise the installed package and additional items, less issuer-entered grants, to calculate the net customer price. Entered prices include applicable taxes; the application does not calculate VAT or determine grant eligibility. Grants are provisional deductions, not approved entitlements. Their eligibility, approval and payment arrangements must be checked with the scheme provider. A zero gross price means pricing is not set. A fully grant-funded net price of zero is shown accurately, but investment ratios and payback are not quoted.

The expanded bill comparison adds a fixed daily standing charge to both before/after totals and deducts export income. A negative net bill represents estimated export credit. Monthly bill figures are annual averages, not seasonal predictions. Standing charges cancel from the annual benefit.

The long-term outlook defaults to 20 years, zero annual tariff change, 0.4% annual PV degradation after the first year, and a 3% discount rate. These are editable scenario assumptions, not forecasts or manufacturer guarantees. Each subsequent year reuses the annual energy-balance model with compounded PV degradation and the same percentage change applied to import and export tariffs. Demand, battery capacity and standing charges remain constant. Maintenance and a single replacement allowance are entered as fixed nominal costs; no unspecified replacement is automatically included.

Cash flow starts with the net installed price at year zero and counts each year's avoided imports plus export income, less maintenance and any replacement. Net present value discounts year-end cash flows at the selected rate. Discounted payback is the final sustained break-even crossing, interpolated within its year; a later replacement can undo an earlier recovery. Return on total costs is total net benefit divided by total installation, maintenance and replacement costs. These metrics require a positive net installed price. Financing, taxes on income, residual value, general inflation and battery degradation are excluded. Existing saved proposals retain their original calculations and do not gain retroactive assumptions.

Deposit and balance are based on the net price after grants. Quote validity runs from preparation for the entered number of days. Warranty, service and payment text is supplied by the issuer, not independently certified by this site. Viewing a proposal does not accept a contract, submit a grant application or make a payment.

Saved proposals and Google data

A customer-requested, address-specific commercial proposal is saved as a fixed snapshot. Changes require a new proposal. Google supplies the roof-generation data only and does not endorse the equipment, battery calculations or financial estimates.

Google Maps content is subject to the Google Maps / Google Earth Additional Terms of Service and Google Privacy Policy.