Why Sizing Matters
Saunas, hot tubs and cold plunges are power-hungry by nature. A sauna heater warms a small space to 70-90°C. A hot tub maintains water at 38-40°C against Scottish ambient temperatures. A cold plunge chills water to around 5-15°C. Each of these has a heating or cooling element that draws significant electricity — and that draw is the starting point for sizing your solar and battery system.
Get the sizing right and your system captures enough daylight and stores enough energy to run your wellness setup on your schedule. Get it wrong and you will be importing grid electricity more than you need to. That is why we survey before we quote — a proper system is built around your actual equipment, usage patterns and roof, not a one-size-fits-all package.
Understanding Power Demand: Watts, Kilowatts and Kilowatt-Hours
Two measurements matter. Power (kW) is how much electricity your equipment draws at any moment — the heater element switched on. Energy (kWh) is the total amount used over time — the heater running for an hour. Your solar array is sized in kW (how much it can generate at peak). Your battery is sized in kWh (how much it can store). Matching both to your wellness equipment is the core of a useful system.
| Equipment | Typical Power Draw | Energy per Session | Battery Consideration |
|---|---|---|---|
| 2-person infrared sauna | 1.5-3 kW | 1.5-4.5 kWh (30-60 min) | Small to medium battery sufficient for evening use |
| 4-6 person traditional sauna | 4.5-9 kW | 4.5-9 kWh (45-60 min heat-up + session) | Medium to large battery, or schedule during daylight |
| Hot tub (4-6 person) | 3-6 kW heater | 3-10 kWh/day (maintenance + heat-up) | Battery sized for daily heating cycle, not just single use |
| Cold plunge chiller | 0.3-1 kW | 0.5-3 kWh/day (continuous maintenance) | Lower draw, runs continuously — good fit for daytime solar |
| Garden wellness cabin (lighting + small heater) | 1-3 kW | 2-5 kWh/evening | Medium battery covers typical evening use |
These are typical ranges to illustrate the scale of demand. Your actual equipment will have its own specifications — we use those during your survey.
Solar Array Sizing
Your solar array needs to generate enough electricity across the day to cover both your household use and your wellness equipment. In Scotland, a south-facing roof with minimal shading is ideal, but east-west arrays also work well — they spread generation across the day rather than peaking at midday, which can actually suit evening wellness sessions better when paired with a battery.
Scottish daylight hours vary dramatically through the year. In June, much of Scotland gets 17-18 hours of daylight, giving solar panels a very long generation window. In December, that drops to around 6-7 hours. This seasonal swing is exactly why battery storage matters — you capture the surplus from long summer days and use it to offset shorter winter generation. A well-sized system is designed with the full year in mind, not just peak summer.
Scotland's solar advantage: While Scottish winters are dark, summer daylight is exceptionally long — far longer than southern England. A solar array in Inverness in June gets more generation hours than one in London. The challenge is storage and winter backup, not summer generation. That is what your battery and system design address.
Battery Storage Sizing
Battery capacity is the critical piece for wellness setups. Most people want to use their sauna or hot tub in the evening or early morning — precisely when solar panels are not generating. The battery bridges that gap. The question is how much capacity you need.
Start with your equipment. If your sauna heater draws 4.5kW and you run it for an hour, that is 4.5kWh of energy. A battery with 10kWh of usable capacity could run that session and still have half its charge for household use. But if you also run a hot tub heater, cabin lighting and household appliances, you need more. The survey accounts for all of your loads together.
Battery systems are also modular. You can start with a smaller capacity and add more later if your needs grow — for example, if you add a cold plunge or upgrade your sauna. We design the system with expansion in mind where possible.
Running on Stored Solar: How It Works in Practice
During the day, your solar panels generate electricity. That power goes first to anything running in the house — fridge, lighting, devices. Surplus generation charges your battery. Once the battery is full, any further surplus either goes to the grid (depending on your setup) or to immersion diverters if you have one.
In the evening, when you switch on your sauna, the power comes from the battery rather than the grid. If the battery has enough charge, the entire session runs on stored solar. If the battery is partially depleted, you use a mix of stored solar and grid electricity. This is why matching battery capacity to your usage matters — too small and you lean on the grid more than necessary, too large and you have paid for capacity you rarely use.
Smart Scheduling
Modern solar and battery systems include smart management. This can automatically charge the battery during the cheapest grid periods in winter (if you are on a time-of-use tariff), discharge it during expensive periods, and prioritise solar when it is available. For wellness equipment, this means the system can be set to ensure your battery has enough charge for your usual sauna evening or hot tub session, managing the energy flow without you having to think about it.
The Survey and Quote Process
Because every home and every wellness setup is different, we do not publish fixed prices or packages. Instead, we arrange a no-obligation survey. The surveyor assesses your roof orientation and condition, available space for batteries, your existing electrical setup, and the specifications of your sauna, hot tub or cold plunge. From that, you get a written quote for a system sized to your actual needs.
There is 0% VAT on solar panels and battery storage until 31 March 2027, and your quote reflects the current tax position at the time of installation. Loans are available, subject to status, and we can discuss this after your survey.
Ready to find out what your system needs? Use the form below or call us on 0141 230 0198. We will arrange a no-obligation survey and send you a tailored quote — you decide whether to proceed.