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 20267 things to check before you sign a solar quote
Two quotes can look similar and hide very different systems. Use this checklist to compare them like for like.
A solar quote can be a single page of numbers. Two quotes with the same total can describe very different systems, so before you sign, work through these seven checks.
1. Is the system sized for your actual loads?
A good quote starts from your energy use, not a standard package. Ask:
- What daily kWh did they design for?
- What peak load and surge did they allow for?
- Which sun-hours figure did they use, summer or winter?
If they cannot explain it, ask for the working. Compare it with your own numbers from the load calculator and our sizing guide.
2. Is the equipment named?
"5 kW inverter and lithium battery" is not enough. A proper quote lists the brand, model and quantity of:
- Panels (and their watt rating)
- Inverter (and whether it is hybrid or off-grid)
- Batteries (and their usable kWh, not only the rated capacity)
- Mounting, cabling and protection devices
Without model numbers you cannot check datasheets, warranties or whether the parts work together.
3. What do the warranties really cover?
Look for separate warranties on panels, inverter, battery and workmanship. For each, ask:
- How many years, and who honours it (the installer, the importer or the manufacturer)?
- For batteries, is there also a cycle or throughput limit?
- What happens if the installer closes down?
4. Will you get a Certificate of Compliance?
Under South African electrical installation regulations, a Certificate of Compliance (CoC) is required for new electrical installations and alterations, and it must be issued by a registered person. Ask:
- Who is the registered person signing it off?
- Is the CoC included in the price?
- Will you receive the documents for your insurer?
The industry also has a voluntary quality standard for PV installers. Ask whether the company follows it and what training their installers have.
5. Is anything left out?
Compare what is in and out of the price:
| Item | Included? |
|---|---|
| Mounting structure and roof work | |
| DB board changes and surge protection | |
| Earthing and isolators | |
| Cabling and trunking | |
| Monitoring app and set-up | |
| Certificate of Compliance | |
| Municipal paperwork (if grid-tied) | |
| VAT |
Fill this in for each quote. Gaps are where "cheap" quotes often become expensive.
6. What about the grid and your municipality?
If your system connects to the grid, your municipality may require registration or approval, and the rules differ between municipalities. Ask who handles the application, and never feed power back to the grid without approval. If you are fully off-grid or only using a backup setup that does not export, ask the installer to confirm what applies.
Also tell your insurer about the installation, because it can affect your cover.
7. Are the payment terms fair?
Be careful of large upfront deposits. A fairer structure ties payments to milestones, such as delivery of equipment, completion of installation and handover of the certificate. Check cancellation terms and what happens if equipment prices change before delivery.
Bonus: ask how it will perform in winter
Ask what the system is expected to produce in your worst month, and how many days of backup the battery gives without the sun. A confident installer will answer clearly. If you are unsure what to ask for, the load calculator gives you a sized system and indicative price to compare against.
Where to go next
- Understand each component in how a solar system works
- Compare battery types in lithium vs lead-acid
- Browse all our guides
This article is general information, not legal or electrical advice. Regulations and municipal rules change, so confirm requirements with a registered electrician and your municipality.