What size solar system do I need? A simple way to work it out
Daily energy, peak load, sun hours and backup time. Four numbers decide your panels, inverter and battery, and you can work them out yourself.
Read article 16 Oct 2026
Learn it once
From sunlight to your plug, in five steps
Tap each stage to see what it does, what to watch out for and what it means for your budget.
Step 1 of 5
Sunlight is the fuel, and South Africa has plenty of it
Solar systems do not need heat, they need light. What matters is how much solar energy lands on each square metre of roof, measured in kWh per day.
Installers talk about "peak sun hours": the number of hours per day the sun delivers its full-strength equivalent. Most of South Africa sits well above many countries in Europe, but winter and weather still matter, which is why we size for your worst months, not your best.
- Rule of thumbMost of the country gets roughly 4.5 to 6.5 kWh of sunlight per square metre per day, depending on region and season.
- Why it mattersThe Western Cape has a big summer-winter swing. Gauteng and the Northern Cape stay steadier through the year.
- AimNorth-facing roofs perform best in the southern hemisphere.
Step 2 of 5
Panels turn light into direct current (DC)
Each panel is a grid of silicon cells. When light knocks electrons loose inside them, a current flows. This is the photovoltaic effect and it has no moving parts, which is why panels last decades.
Panels are wired in "strings". More panels in series raises the voltage, more strings in parallel raises the current. The wiring plan is matched to what the inverter can accept.
- Typical sizeModern residential panels are rated in the region of 400 to 600 W each.
- Heat hurtsOutput falls slightly as panels get hotter, so airflow behind the panels helps.
- ShadeEven partial shade on one panel can drag down a whole string unless optimisers or microinverters are used.
Step 3 of 5
The inverter is the brain of the system
Your home runs on 230 V alternating current (AC). Panels and batteries give DC. The inverter converts one into the other and, in a hybrid unit, decides every moment whether your house should draw from the sun, the battery or the grid.
Built-in MPPT trackers constantly adjust to pull the most power out of the panels as the light changes.
- Three kindsGrid-tied (no battery, switches off in a power cut), hybrid (battery and grid together) and off-grid (no grid at all).
- Size it for peaksKettles, geysers and motors draw far more at start-up than while running, so the inverter must handle the peak, not just the average.
- TipA bigger inverter than you need costs more but leaves room to add panels and batteries later.
Step 4 of 5
Batteries move sunshine into the evening
Sun is strongest at midday, but most homes use the most power at breakfast and after dark. A battery stores the surplus and gives it back when you need it, and keeps the lights on during load-shedding.
Capacity is measured in kWh. Only part of it is usable: lithium iron phosphate (LiFePO4) batteries typically allow deep daily discharge, while lead-acid is usually kept shallower to protect its life.
- Quick mathsA 5 kWh battery can run a 500 W load (fridge, TV, lights, router) for roughly ten hours.
- ChemistryLithium costs more upfront but usually gives many more cycles and more usable energy per rand over its life.
- ProtectionA battery management system (BMS) guards against over-charge, over-discharge and overheating.
Step 5 of 5
Your distribution board, wired for safety
Power reaches your home through the distribution (DB) board. Good designs put essential circuits (lights, fridge, plugs, router) on the backed-up side and keep heavy loads such as the geyser, stove and pool pump on the grid side or on a smart timer.
Earthing, surge protection, isolators and a Certificate of Compliance from a registered electrician are not optional extras. They protect your family, your insurance and your resale value.
- Efficiency firstEvery watt you do not use is a watt you do not have to buy panels and batteries for. LEDs and a heat-pump or solar geyser pay back fastest.
- ComplianceInstallations should be done by qualified, registered people, and grid-tied systems may need municipal approval.
- MonitoringApp monitoring shows where your energy goes, so you can fine-tune over time.
About Solar-Rescue
The place to learn solar before you buy it
Solar is one of the biggest purchases a household or business will make, and it is surrounded by jargon and pushy sales talk. Solar-Rescue exists to change that: independent, in-depth explanations first, then tools to size your system, then trusted people to build it.
Knowledge firstPlain-language guides on how every part works and why it costs what it does.
Vetted providersQuotes are delivered by approved installers and suppliers who meet our standards.
Numbers you can checkOur calculator shows its assumptions so you can see exactly how your estimate is built.
What we can help with
Whatever you need to keep running
From a single fridge during load-shedding to a farm that has to run entirely off the grid.
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