How the Calculator Works
This calculator estimates the solar array size (in kW) and battery capacity (in kWh) you might need to power a sauna, hot tub, or other wellness equipment on stored solar energy in Scotland. It uses your heater wattage, session frequency, session duration, and roof orientation to calculate indicative ranges based on typical Scottish solar yields. The results are ranges, not precise figures — your actual system is sized during a no-obligation survey. For more detail on the methodology, see our costs and sizing guide and sauna heater sizing guide. For solar panel sizing and battery storage, visit our hub.
Understanding Your Results
Suggested Solar Array (kW)
The calculator estimates the total peak capacity of solar panels you might need. This is based on your daily energy demand (weekly demand divided by 7) divided by the typical annual average daily yield per kWp of solar in Scotland (2.5-3.5 kWh/kWp/day), adjusted for your roof direction. South-facing roofs get the full yield; east-west roofs get about 82% of it; north-facing roofs get about 65%. Learn about solar panel sizing on our hub.
Suggested Battery Capacity (kWh)
The battery range is based on storing enough energy for 1.5-2 full sessions, so you can run your sauna or hot tub on stored solar even when panels have not been generating. The lower end covers a single session plus a small buffer; the upper end covers two sessions or a session plus significant household evening use. Learn about battery storage on our hub.
Energy per Session
This is the kWh consumed in a single session — your heater wattage (kW) multiplied by the session duration in hours. A 4.5kW heater running for 45 minutes uses 4.5 × 0.75 = 3.375 kWh. This is the energy your battery needs to deliver for one session.
These are indicative ranges, not a quote. Your actual system is sized precisely during a no-obligation survey, which accounts for your roof structure, shading, existing electrical setup, and all your wellness equipment. Get a tailored quote →
Scottish Solar Yields: The Context
The calculator uses Scottish-specific solar yield assumptions. Scotland's solar potential is often underestimated — the long summer daylight hours (up to 18 hours in June in the north) give panels an extended generation window. The challenge is the winter shortfall, which is why battery storage and correct sizing are essential. For more on this, see our areas covered page which explains regional solar potential across Scotland, and our main site for detailed solar panel information.
Finance and Next Steps
Interest-free credit up to £30,000, subject to status, is available. There is 0% VAT on solar panels and batteries until 31 March 2027. After using the calculator, use our quote form to arrange a no-obligation survey. Read about finance options on our main site. We install through MCS-certified partners and cover all of Scotland.
Last updated: 28 October 2026