Reference

Default assumptions

Every default value used anywhere on this site lives in a single registry. This is that registry, printed in full, with the reasoning and source behind each entry.

What default values does SnapEnergyLab use, and can they be changed?

There are 13 defaults covering electricity price, battery behaviour, inverter and charging efficiency, heat pump performance and solar system losses. Every one of them is editable at the point of use, and changing it recalculates the result immediately. Defaults exist so a page can answer a question before you have typed anything — they are starting points, not claims about your home.

The full registry

Registry version defaults-1.0.0. Every value below is editable wherever it is used.
Default	Value	Why this value	Source	Revised
Electricity rate	0.18 $/kWh	Round-number stand-in close to the US residential average. Always editable — your own tariff overrides it.	US EIA residential average electricity price (rounded)	2026-01
Currency	USD	V1 launches with a single currency; the data layer supports more.	Product decision	2026-01
Inverter efficiency	0.92 fraction	Typical round-trip DC→AC conversion efficiency for residential hybrid inverters at partial load.	Manufacturer datasheet range 90–95%, conservative midpoint	2026-01
Usable depth of discharge	0.9 fraction	Most residential LFP systems allow 90–100% depth of discharge; 90% is a conservative planning figure.	Residential LFP system specifications	2026-01
System reserve	0 fraction	Extra energy held back for the end of an outage. Zero unless you set one.	Product decision	2026-01
AC charging loss	0.1 fraction	Onboard charger and thermal losses mean roughly 10% more energy leaves the wall than reaches the pack.	Published AC charging efficiency measurements (85–93%)	2026-01
Vehicle efficiency	3.5 mi/kWh	Mid-size battery-electric car in mixed driving.	EPA combined ratings, typical mid-size BEV	2026-01
Heat pump seasonal performance (SCOP)	3	Season-average performance for an air-source heat pump in a mixed climate — not a nameplate COP.	Seasonal performance ranges for air-source heat pumps	2026-01
Resistance heater efficiency	1	Electric resistance heating converts essentially all input electricity to heat.	Physics — conservation of energy	2026-01
Solar system losses	0.14 fraction	Soiling, wiring, mismatch, inverter, connections, availability. PVWatts uses 14% as its default.	NREL PVWatts default loss factor	2026-01
Array tilt	20 degrees	Typical residential roof pitch.	Common residential roof geometry	2026-01
Array azimuth	180 degrees	Due south in the northern hemisphere gives peak annual yield.	Solar geometry	2026-01
Panel rating	400 W	Common residential module size currently sold.	Residential module market	2026-01

How defaults are chosen

Where a published reference value exists — the PVWatts 14% loss factor, for example — it is used directly and cited. Where the honest answer is a range, the default sits at a conservative point inside it rather than at the flattering end, so a result is more likely to understate a benefit than overstate one. Where no meaningful average exists, the default is a round number chosen for legibility and clearly labelled as a stand-in you should replace.

Two defaults deserve particular attention because they move results more than the rest. The electricity rate scales every cost figure linearly, so entering your own tariff is the single most valuable correction you can make. The heat pump seasonal performance figure dominates every heating comparison and varies enormously with climate and system design.

What is not assumed

There is no assumed tariff structure with time-of-use bands, no assumed standing charge, no assumed tax treatment, and no assumed incentive or rebate. These vary too much between suppliers and jurisdictions for a default to be useful, and inventing one would manufacture precision the calculation does not have.