Reference

Data sources

Which datasets sit behind the calculators, where each one comes from, how current it is, and what it cannot tell you.

Where does SnapEnergyLab's data come from?

Four bundled datasets feed the engines: an appliance dataset of 10 household loads with typical power, ranges and duty cycles; a backup load catalogue of 13 items with startup surge figures; a coarse latitude-band solar yield table; and the default registry covering rates and efficiencies. All of them are versioned and ship with the site. One calculator also consults an external source: the solar output calculator queries PVGIS, the European Commission’s Joint Research Centre solar-resource service, for long-term production at your coordinate, and falls back to the bundled latitude-band table — clearly labelled as such — whenever that service is unavailable.

Dataset inventory

Datasets shipped with the site, plus the external sources used by the solar output calculator.
Dataset	What it contains	Basis	Version	Update cadence
Appliance dataset	10 appliances: typical watts, realistic range, duty cycle, standby draw, usage hours	Published appliance energy labels, manufacturer specifications and metered usage studies, reconciled to a typical value with an explicit range	appliances-1.0.0	Reviewed as efficiency standards and typical products change
Backup load catalogue	13 common outage loads with running power, duty cycle and startup surge	Motor and appliance specifications; surge figures reflect typical direct-on-line starting	backupLoads-1.0.0	Reviewed alongside the appliance dataset
PVGIS (external, primary for solar output)	Long-term monthly and annual PV production for a specific coordinate, plus interannual standard deviation	European Commission, Joint Research Centre. Radiation database and reference period are returned per request (typically PVGIS-SARAH3 or PVGIS-ERA5, 2005–2023) and are shown with each result	API v5.3 (/PVcalc)	Maintained by the JRC; results cached for up to 90 days
OpenStreetMap Nominatim (external, geocoding)	City or postal code to latitude and longitude	OpenStreetMap data, © OpenStreetMap contributors, Open Database License	Public Nominatim service	Continuously updated by contributors; lookups cached for up to 90 days
Latitude-band solar yield (fallback only)	Annual kWh per installed kWp by latitude band, plus a hemisphere-aware seasonal shape	Coarse bands derived from published long-term yield ranges. Used only when the location-specific source cannot be reached, carries a SnapEnergyLab fallback uncertainty estimate of ±25% (our own judgement, not a measured interval), and reflects latitude and hemisphere rather than local climate	solarData-1.1.0	Stable; irradiance climatology changes slowly
Default registry	Electricity rate, efficiencies, depth of discharge, losses, panel size	Cited references where they exist, otherwise conservative points within a published range	defaults-1.0.0	Rate-sensitive entries reviewed as published averages move

Why the data is bundled rather than fetched

Every dataset ships as versioned code inside the site. A calculator therefore works instantly, works identically for every visitor, and cannot silently change its answer because an upstream API returned something different today. It also means the numbers you see are reproducible: the engine version and dataset version together pin the exact result.

The cost of that choice is currency. A bundled electricity price does not track your supplier’s latest tariff, which is precisely why the rate is editable on every page and why entering your own figure is the first thing each calculator invites you to do.

Known limitations

Appliance values are typical, not yours. A twenty-year-old chest freezer and a current model with the same capacity can differ by a factor of two. Where the spread is wide, the range is shown alongside the typical figure.

Solar yield ignores your roof. Regional yield cannot see your shading, your exact pitch and orientation, or your local microclimate. Treat it as a planning band, not a production guarantee.

Surge figures are indicative. Actual inrush depends on the specific motor, its age, its load at the moment of starting and whether a soft starter is fitted.

Nothing here is tariff-aware. Time-of-use bands, demand charges, standing charges and export rates are not modelled, so a flat rate is applied throughout.

If a value looks wrong

Every calculator lets you override the dataset value with your own measurement, and a plug-in energy monitor will beat any published typical figure for your specific appliance. Where your number and ours disagree, use yours.