---
title: Is Your Solar System Underperforming? How to Check
description: How to tell whether your solar system is producing what it should, the checks you can do yourself from the app, and when it is worth getting it looked at.
image: https://cleanvolts.co.za/hubfs/Imported%20sitepage%20images/0001-8043948169462701930.jpg
---

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# Is your solar system underperforming?

![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

September 28, 2026

Most solar systems in Johannesburg are never measured against anything. The app shows a number every day, the number looks reasonable, and nobody asks whether it should be bigger.

Often it should be. A system can lose a fifth of its output to dust, a tripped string or a setting left over from load shedding, and still look fine on the app. The inverter doesn't send you a message saying it made less than it could have. It just makes less, and your bill comes down less than it should.

Here's how to work out what your system should produce, three checks you can do yourself from the app, and when it's worth getting it looked at.

## What Your System Should Produce

You need two numbers.

**The size of your array, in kWp (kilowatt-peak).** It's on the installer's quote or invoice. If it isn't, multiply the number of panels by the wattage of one panel. Twelve 455 W panels make 5.46 kWp.

**What it produced over the last 12 months, in kWh.** Most inverter apps show this under yearly or total production.

Divide the second by the first and you have your system's yield per kWp. Then compare it with what a system facing the same way should produce in Johannesburg:

| **Which way the panels face** | **Expected per kWp per year** | **Average per kWp per day** |
| --- | --- | --- |
| North | About 1,600 kWh | About 4.4 kWh |
| East or west | 1,350 to 1,500 kWh | 3.7 to 4.1 kWh |
| South | 1,000 to 1,400 kWh | 2.7 to 3.8 kWh |

So a 5 kWp array facing north should make roughly 8,000 kWh a year, or about 22 kWh on an average day. A clear spring day will beat that. A stormy summer afternoon or a short winter day won't.

Two cautions. Use a full 12 months, because a single month tells you more about the season than the system. And a south-facing array making less than a north-facing one isn't faulty. That's where it points, and it's a different conversation.

## Three Checks You Can Do From the App

### 1. The yearly check

Take your yield per kWp from above. If it's within about 10% of the figure for your orientation, the system is doing its job. If it's more than 15% below, something is costing you output and it's worth finding out what.

### 2. The year-on-year check

Compare this October with last October, or any month with the same month a year earlier. Panels lose around half a percent of their output a year as they age, so a small drop is normal. A drop of 10% or more, in a month with similar weather, isn't age.

### 3. The shape of a sunny day

Open the production graph for a clear, cloudless day. It should look like a smooth hill: rising from sunrise, peaking around midday, falling towards sunset. Other shapes tell you things:

- **A flat top around midday.** Something is capping the output. Either the inverter is smaller than the array, which installers sometimes do by design, or the system has nowhere to put the power. More on that below.
- **A lopsided hill, or a line that drops at the same time every day.** Shade. Often from a tree that has grown since the system went in, or a neighbour's new second storey.
- **Sudden drops to zero, or a jagged line under a clear sky.** The inverter may be tripping and restarting. Check the app's alarm or fault log.
- **A smooth hill, but much lower than a similar day last month.** Dirt, a string that has stopped working, or a fault.

If the app shows two PV inputs (often labelled PV1 and PV2), compare them. Two strings with the same panels, facing the same way, should produce nearly the same. If one is well below the other, something on that string needs attention.

## The Most Common Cause in Joburg: Nowhere to Put the Power

This one surprises people. Many systems here are set up not to export any power to the grid, often because they aren't registered with City Power. Once the battery is full and the house is using less than the panels can make, the inverter turns the panels down. The panels are fine. The sunshine just goes to waste, and the app records less production.

The signs are a battery that's full by late morning and a flat top on the midday graph. There's a simple test. On a sunny morning, with the battery full, switch on the kettle, the oven or the geyser and watch the solar figure in the app. If it jumps straight up, the panels were being held back.

The fix is rarely new hardware. It's usually running the geyser, pool pump and dishwasher in the middle of the day, changing how the battery is used, or registering the system so that it's allowed to export. The system isn't broken. It's [mis-tuned](https://cleanvolts.co.za/tariff-optimisation). Changes to export and grid settings are a job for a registered person, and they depend on your registration with City Power.

## Other Common Causes

- **Dirt.** Highveld dust, bird droppings and spring pollen build up over a dry winter with no rain to rinse them off, and panels at a low tilt hold more of it. Light dust costs a few percent. A heavily soiled array can lose far more.
- **New shade.** Trees grow. Neighbours build. A satellite dish goes up.
- **A string that has stopped working.** A failed connector or a tripped isolator can take a whole string of panels out. It shows up as one PV input at or near zero.
- **Heat.** Panels make less power when they're hot. Panels mounted with little or no gap behind them run hotter and can lose several percent over a year.
- **Damaged panels.** Cracks, brown or yellow discolouration, and hotspots all cost output, and some are a safety concern.
- **The monitoring, not the system.** Sometimes the Wi-Fi dongle has dropped off the network and the app simply stopped recording. Check the data is up to date before assuming the worst.

## What Not to Do

- **Don't go onto the roof** to inspect or clean the panels. Falls are the biggest risk in the whole job. Cold water on hot glass can crack a panel, and the wrong brush or detergent can damage the coating.
- **Don't open the inverter, isolators, battery or any junction box.** The DC side, between the panels and the inverter, is live whenever there's daylight and can't be switched off.
- **Don't change export or grid settings** in the app.

If you see scorch marks, melted plastic or a swollen battery case, or you smell burning or hear buzzing, stop. Don't touch anything, and get it looked at quickly.

## When to Get It Looked At

- Your yearly yield is more than 15% below the figure for your orientation
- One PV input is well below the other
- The fault log shows the same alarm again and again
- Output has dropped by more than the weather explains
- The system hasn't been cleaned or checked since it was installed
- You've never had the login to your app, so nobody has been watching it

## Where We Fit In

A [Solar Health Check](https://cleanvolts.co.za/health-check) by a CleanVolts Approved installer answers the question this guide asks: it compares what your system produces with what it should, reads your inverter history and checks the rest of the system, with a written report ranking every finding. What happens next depends on the cause: a setting problem is a [re-optimisation](https://cleanvolts.co.za/tariff-optimisation), dirt is a [clean](https://cleanvolts.co.za/solar-panel-cleaning), and a fault is [repaired](https://cleanvolts.co.za/remediation) by the registered contractor you contract directly. Approved partners cover every province.

[**Book a Health Check**](https://cleanvolts.co.za/health-check) · [Free checklist: is your solar legal and safe?](https://cleanvolts.co.za/checklist)

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### [![How to choose a solar installer you can trust](https://cleanvolts.co.za/hs-fs/hubfs/Featured%20image%20-%20choosing-a-solar-installer.png?width=1600&height=900&name=Featured%20image%20-%20choosing-a-solar-installer.png) How to choose a solar installer you can trust](https://cleanvolts.co.za/guides/choosing-a-solar-installer)

### [![Rent, finance or buy solar?](https://cleanvolts.co.za/hs-fs/hubfs/Featured%20image%20-%20rent-finance-or-buy-solar.png?width=1600&height=900&name=Featured%20image%20-%20rent-finance-or-buy-solar.png) Rent, finance or buy solar? How to choose in 2026](https://cleanvolts.co.za/guides/rent-finance-or-buy-solar)

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