---
title: What size solar system do I need?
description: How to size panels, inverter and battery from your City Power bill, with a worked example and a free one-minute sizing tool.
image: https://cleanvolts.co.za/hubfs/what-size-solar-system-do-i-need-featured.png
---

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# What size solar system do I need?

![Tony Lopes](https://cleanvolts.co.za/hs-fs/hubfs/clean%20volts%20launch%20post.png?width=48&height=48&name=clean%20volts%20launch%20post.png)

 Tony Lopes

November 6, 2026

**Short answer:** Size solar from your bill, not from a package. Divide your monthly kWh by 30 to get daily use, then divide that by about 4.5, the kWh each kWp of panels makes on an average Gauteng day. That gives your panel size. The inverter follows the biggest load you run at once, and the battery follows what you use after dark. Most three-bedroom Joburg homes land on a 5 kW system.

*Last updated November 2026. Rates checked October 2026.*

"What size system do I need?" is the first question almost everyone asks, and the most common answer from a sales rep is a package: 5 kW inverter, 10 kWh battery, ten panels. That package fits a lot of homes, but not all of them, and the wrong size costs you either way. Too small and you keep paying City Power for what you could have made yourself. Too big and you paid for panels or battery you never use. This guide shows you how to size a [solar installation](https://cleanvolts.co.za/new-installations) from your own bill in four steps, with a worked example and a table by household type.

## **What size solar system does a typical Joburg home need?**

A solar system has three parts, and each one is sized for a different job:

| Part | What it's sized for | Measured in |
| --- | --- | --- |
| **Panels** | How much energy you use in a day | kWp (kilowatt peak) |
| **Inverter** | The most power you draw at the same moment | kW |
| **Battery** | What you use after the sun goes down | kWh |

For a typical three-bedroom home using 600 to 900 kWh a month, that usually works out to a 5 kW inverter, about 5 kWp of panels (nine or ten 550 W panels) and a 10 kWh battery. The steps below show how to check whether that's right for your house.

## **How do you size a solar system from your electricity bill?**

1. **Find your monthly use in kWh.** Postpaid bills show it. On prepaid, add up the kWh on your last three months of token slips and average them. If you only know rands, subtract the fixed charge and divide by about R3.80, the middle City Power block rate for 2026/27.
2. **Work out your panel size.** Divide monthly kWh by 30 for daily use, then divide by 4.5. That's the kWp of panels that would make all your daily energy, averaged over the year. Most homes aim for 70 to 100% of that, depending on how much they can use or store.
3. **Size the inverter for your peak load.** Add up what runs at the same time, especially on backup. A kettle, microwave and geyser together can top 6 kW.
4. **Size the battery for the night.** Estimate what you use between about 17:00 and 07:00, then add roughly 10% so the battery isn't drained flat every night.

Why 4.5? A kWp of panels on a north-facing Gauteng roof makes roughly 1,600 to 1,750 kWh a year, according to PVGIS-based estimates. That's about 4.5 to 4.8 kWh a day, less in winter and more in spring. Using 4.5 keeps the estimate on the safe side. If your roof faces east or west, or has shade, your installer will lower it.

If you'd rather skip the arithmetic, the [free sizing guide](https://cleanvolts.co.za/solar-sizing-guide) asks six questions and gives you a starting range.

## **What does a worked example look like?**

Take a three-bedroom house in Joburg on City Power prepaid, spending about R2,800 a month on electricity.

| Step | Working | Result |
| --- | --- | --- |
| Monthly use | (R2,800 − R240 fixed charge) ÷ R3.80 | About 670 kWh |
| Daily use | 670 ÷ 30 | About 22 kWh |
| Panels | 22 ÷ 4.5 | About 5 kWp, or nine 550 W panels |
| Peak load | Kettle 2.2 kW + microwave 1.2 kW + fridge, lights, TV and Wi-Fi 0.6 kW | About 4 kW, so a 5 kW inverter (geyser kept off backup) |
| Night use | About 8 kWh from 17:00 to 07:00, plus 10% | A 10 kWh battery |

That lands on the common 5 kW package, and for this house it fits. But change one fact and the answer changes. Add a pool pump and someone working from home, and use climbs towards 1,000 kWh. Put the geyser on backup and the inverter needs to be 8 kW. That's why the bill comes first and the package comes second.

## **How many solar panels do I need?**

Panel count depends on the panel wattage. Most homes now use panels between 450 W and 600 W. The table uses 550 W panels.

| Household | Typical monthly use | Panels | Inverter | Battery |
| --- | --- | --- | --- | --- |
| 1 to 2 bedroom flat or townhouse | 300 to 450 kWh | 2 to 3 kWp (4 to 6 panels) | 3 to 5 kW | 5 kWh |
| 3 bedroom home | 600 to 900 kWh | 4.5 to 6 kWp (8 to 11 panels) | 5 kW | 10 kWh |
| 4 bedroom home with a pool | 1,000 to 1,500 kWh | 7 to 10 kWp (13 to 18 panels) | 8 kW | 15 kWh |
| Large home, often three-phase | Over 1,500 kWh | 10 kWp or more (18+ panels) | 12 kW or more, three-phase | 20 kWh or more |

Each 550 W panel takes about 2.6 m² of roof, so ten panels need roughly 26 m² of clear, north-facing roof. East and west roofs work too, with about 10 to 15% less output.

## **What size inverter do I need?**

The inverter must handle the most power drawn at once, not the total for the day. These are typical draws:

| Appliance | Typical draw |
| --- | --- |
| Electric geyser | 3 to 4 kW |
| Oven or stove plate | 2 to 3 kW |
| Kettle | 2 to 2.4 kW |
| Microwave | 1 to 1.5 kW |
| Pool pump | 0.75 to 1.1 kW |
| Fridge, lights, TV, Wi-Fi together | About 0.5 to 0.8 kW |

Motors such as pool pumps and borehole pumps draw several times their rated power for a moment when they start, so they need headroom. And size the inverter for the system you expect in three years, not just today. Swapping an inverter later is one of the most common ways people pay for part of a system twice, as our guide to [what solar costs in 2026](https://cleanvolts.co.za/guides/what-solar-costs-2026) explains.

## **How big a battery do I need?**

Size the battery for your evening and overnight use, not your whole day. During the day the panels run the house. After dark, the battery takes over until morning. For most homes that's 6 to 10 kWh, which is why 10 kWh is so common.

Two things push the battery size down. First, a heat pump or a geyser timed to heat in the middle of the day moves the biggest load into sunshine hours. Second, load shedding has stopped, so most homes no longer need days of backup. Batteries were often oversold during the load shedding years. If you're unsure, start smaller with an inverter that can take more battery later. If you can't decide between a grid-tied and a battery system at all, read [hybrid, grid-tied or off-grid](https://cleanvolts.co.za/guides/hybrid-vs-grid-tied-vs-off-grid) first.

## **What sizing mistakes cost homeowners the most?**

- **Sizing from the quote, not the bill.** A package is a starting point. Ask the installer to show the working from your actual use.
- **Too much battery, too few panels.** A battery stores energy but doesn't make it. If the panels can't fill it on a normal day, you charge it from the grid and save very little.
- **An inverter with no room to grow.** If you might add an electric car, a pool or more people, choose an inverter that can take the extra panels and battery.
- **Sizing for summer.** Gauteng winter output is about a fifth lower than the yearly average. A system sized only on December figures will feel small in June.

**Safety First**

- **Sizing is a planning step, not a design.** The final design, cabling and protection must be done by a registered electrician, who issues a Certificate of Compliance.
- **Don't overload the inverter on backup.** Putting the geyser or stove on a small inverter's backup circuit causes trips and early wear.
- **Check the roof before adding panels.** An installer should confirm the roof structure can carry the panels and the mounting.

## **Frequently Asked Questions**

### **How many panels for a 3-bedroom house?**

Usually eight to eleven panels of about 550 W, which is 4.5 to 6 kWp. That covers a household using 600 to 900 kWh a month. A pool, an electric car or someone working from home pushes it higher.

### **What size inverter runs a geyser?**

A geyser draws 3 to 4 kW on its own, so running it alongside the rest of the house needs an 8 kW inverter or bigger. Many homes keep the geyser off the backup circuit and run it on a timer in the middle of the day instead, which lets a 5 kW inverter do the job.

### **How big a battery do I need for the night?**

Add up what you use from about 17:00 to 07:00 and add roughly 10%. For most three-bedroom homes that's 6 to 10 kWh, so a 10 kWh battery covers the night with a margin.

### **Can I start small and add more later?**

Yes, if you choose the inverter for the final system from the start. Panels and batteries can then be added in stages. Our guide to [adding panels or a battery](https://cleanvolts.co.za/guides/add-panels-or-battery) explains what to check.

## **Where We Fit In**

CleanVolts matches homes, businesses and farms with vetted, registered [CleanVolts Approved](https://cleanvolts.co.za/cleanvolts-approved) installers where we have a partner in your area. Your installer starts from your electricity bills and how you use power, shows you the sizing working in writing, and names every component by make and model. You contract the installer directly and they issue the Certificate of Compliance. We never buy or sell hardware, using CleanVolts costs you nothing, and if the installer pays us a referral fee, we tell you up front.

[**Try the free sizing guide**](https://cleanvolts.co.za/solar-sizing-guide) · [Compare solar quotes](https://cleanvolts.co.za/solar-quotes)

*Sources: [European Commission PVGIS solar estimates](https://re.jrc.ec.europa.eu/pvg_tools/en/); [OurPower, Johannesburg solar yield](https://www.ourpower.co.za/solar/johannesburg); [City Power 2026/27 tariffs, as summarised in our tariff guide](https://cleanvolts.co.za/guides/city-power-tariffs-2026-solar).*

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## Keep reading

### [![Thatched bush lodge with a ground-mounted solar array beside it](https://cleanvolts.co.za/hs-fs/hubfs/Featured%20image%20-%20hybrid-vs-grid-tied-vs-off-grid.png?width=1600&height=900&name=Featured%20image%20-%20hybrid-vs-grid-tied-vs-off-grid.png) Hybrid, Grid-Tied or Off-Grid Solar: Which Do You Need?](https://cleanvolts.co.za/guides/hybrid-vs-grid-tied-vs-off-grid)

### [![Technician with a multimeter and checklist inspecting a hybrid inverter and battery in a home garage](https://cleanvolts.co.za/hs-fs/hubfs/Featured%20image%20-%20what-a-solar-health-check-includes.png?width=1600&height=900&name=Featured%20image%20-%20what-a-solar-health-check-includes.png) What a Solar Health Check includes (and what it doesn't)](https://cleanvolts.co.za/guides/what-a-solar-health-check-includes)

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