Sources, assumptions and limits
The live tool is a transparent planning model. It is designed to help you compare cooling demand with solar availability, not replace an installer's heat-load calculation or solar design.
Hourly air temperature and cloud cover come from the MET Norway Locationforecast API ↗. Town forecasts use rounded town-centre coordinates. Postcode forecasts use approximate coordinates returned by OpenStreetMap Nominatim after you submit the form. Forecast responses are cached for six hours.
The default outlook models one air conditioner drawing 0.9 kW whenever the forecast temperature is at least 24°C. Energy for each forecast interval is power multiplied by time. It does not model solar gain through windows, humidity, thermostat cycling, internal heat or building fabric.
The forecast model estimates the sun's position from time, latitude and longitude, then applies cloud attenuation and a general system performance factor to a 3.5 kWp array. The model does not know your roof direction, tilt, horizon, shade, inverter clipping or panel temperature. Solar contribution in each interval is capped at the cooling load, so the tool does not count unrelated exports as cooling savings.
Persistent local figures come from the European Commission Joint Research Centre PVGIS tool ↗. We model 1 kWp, south facing, at 35 degrees with 14% system loss. Annual and July yield scale that result by array size. Climate figures use the PVGIS typical meteorological year, which represents typical conditions rather than a forecast or a record for one specific year.
Local dataset refreshed: 9 August 2026
The default rate is 26.11p/kWh, the Ofgem average capped electricity unit rate for 1 July to 30 September 2026. Standing charges are excluded because cooling does not create an extra daily standing charge. The personal plan and running-cost calculator separate avoided grid imports from export income forgone. Net energy cost is remaining grid cost plus the export payment given up on solar used for cooling.
Scheme summaries link to GOV.UK, Ofgem, Home Energy Scotland, the Welsh Government or the Northern Ireland Housing Executive. Warm Homes: Local Grant allocations use the government's published successful-authority list, including named consortium members. An allocation belongs to a delivery programme and is not the amount available to an individual household.
Bundle starting figures are early planning estimates, not local market averages or offers. Equipment, room load, roof access, scaffolding, cable routes, planning constraints and electrical work can change the price. Only a named installer's written quotation creates a price for your property.
The room model estimates fabric gain from room volume and the selected insulation level, then adds glazing gain by direction and shade, top-floor roof gain, occupants and equipment. It applies a room-use factor and 10% contingency, then displays a range 20% either side of the central estimate. Electrical draw uses a nominal cooling efficiency ratio of 3.2. This is a transparent screening model, not the installer's room-by-room design.
Quote submissions are held for review and only approved records enter the aggregate. We publish no raw quote, postcode district or group with fewer than five records. Published medians and lower and upper quartiles are rounded to the nearest £25. The result describes submitted scopes, not a controlled market survey.
A scheduled collector saves MET Norway temperature forecasts at 1, 24, 48 and 72-hour lead times for 12 UK airport reference stations. It later matches them with public AviationWeather.gov METAR observations. Mean absolute error reports the average size of the miss. Bias is forecast minus observed. Airport measurements can differ from conditions in nearby streets and buildings.
The multi-room planner applies the same screening load model to each room, then adds the displayed ranges as though all selected rooms peak together. Its system-route text is a comparison prompt, not an outdoor-unit selection. Manual plans stay in local browser storage. The native companion converts Apple RoomPlan walls, floors, windows, doors and openings into a small geometry-only JSON document. Imported files are parsed locally by the browser and are not uploaded.
RoomPlan geometry cannot determine insulation, glazing performance, shade, air leakage, occupancy, pipe routes or electrical constraints. Users must confirm the thermal inputs and an installer must verify the design.
Send the page, figure and source through the contact form. We would rather correct a useful model than defend a stale number.
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