kW vs kWh: the one thing to understand
Almost all the confusion around solar sizing comes from mixing up kW and kWh. They sound similar but measure different things.
- kW (kilowatts) = power. It's the rate at which you use or generate electricity — how much you can run at the same moment. Think of it like the size of a tap: how fast the water can flow.
- kWh (kilowatt-hours) = energy. It's power used over time — the total amount. Think of it like the size of a bucket: how much water you collect.
A quick example: a 1,000-watt (1kW) kettle running for one hour uses 1kWh of energy. Run it for two hours and you've used 2kWh, but the power draw was still 1kW at any moment.
For solar sizing this maps cleanly:
- kW sizes your inverter (how much your home can draw at once) and your panels (how much they generate).
- kWh sizes your battery (how much energy you can store for the night and load-shedding).
Get those two ideas straight and everything else follows.
Step 1: Find your electricity usage
Your municipal electricity bill is the starting point. It shows your consumption in kWh per month — that's how much energy your household gets through. This tells you the scale of system you need to make a meaningful dent in your bill.
As a rough orientation:
- A smaller home or flat might use around 300–600 kWh/month.
- A typical family home often uses 600–1,200 kWh/month.
- A large home with a pool, aircon and electric geysers can use 1,200 kWh/month or more.
Don't worry about precision here — you're just working out which ballpark you're in. The assessment refines it.
Step 2: Decide what you want from the system
Sizing isn't only about your total usage; it's about your goals. There are really two:
Cutting your bill
If your priority is lower electricity costs, you focus on panels and inverter sized to offset your daytime usage. More panels generate more free energy during the day.
Backup for load-shedding
If your priority is staying powered during outages, you focus on battery capacity (kWh) sized to your essential loads — lights, Wi-Fi, fridge, TV, charging. As we cover in our load-shedding setup guide, you rarely need to back up the whole house, just what matters.
Most people want both, which is why a balanced system pairs a sensible inverter and panel array with enough battery to cover the evening.
Step 3: Match to a system size
Here's how the pieces come together for typical homes, using Alumo's real packages as reference points.
Smaller home / essentials — around 3.6kW
A 3.6kW inverter with a ~3.8kWh battery and four panels suits smaller homes or households that mainly want essentials covered and a lower bill. This is Alumo's Bronze package — from R1,911/month or R47,314 outright — giving roughly 3 hours of backup on essentials.
Typical family home — around 5kW
The most common sweet spot is a 5kW inverter with 5kWh+ of battery and six panels. This runs more of the home at once and carries essentials through longer outages. Alumo's Gold package — a 5kW Sunsynk inverter, 5.32kWh battery and six panels — fits here, from R2,423/month or R51,357 outright, with around 5 hours of backup.
Larger home — 5kW+ with added storage
Bigger homes with higher consumption add panels and stack battery capacity for more generation and longer runtime. Because storage is modular, you can start at a sensible size and expand later as your needs grow.
A simple worked example
Say your bill shows about 900 kWh/month and you want your essentials backed up through load-shedding. That usage points to a mid-sized system — a 5kW-class inverter with enough panels to offset a good chunk of your daytime draw, and a 5kWh+ battery to carry lights, Wi-Fi and the fridge through a typical evening outage. That's squarely in Alumo's Gold territory, with the option to add battery capacity if you want to cover longer or back-to-back slots.
Notice what drives the decision: your usage (kWh) points to the system scale, your essential loads set the battery, and your peak simultaneous demand sets the inverter (kW). Three inputs, one right-sized system.
Why oversizing and undersizing both cost you
- Undersize and the system trips or runs out of backup too soon — frustrating, and it undersells solar's benefits.
- Oversize and you've paid for capacity you don't use — money that could have stayed in your pocket.
Correct sizing is the difference between a system that quietly delights you and one that disappoints. It's genuinely worth getting a professional assessment rather than guessing, because the right size depends on details a quick calculation can't capture — your roof orientation, appliance mix, and daily routine.
Get it sized properly
You now know enough to read a quote with confidence: kW for power (inverter and panels), kWh for energy (battery), your bill for scale, and your essential loads for backup. The final step is an assessment that turns those inputs into an exact specification.
SolarGuide is an independent referral partner — we help you understand the options and arrange a free quote. Alumo assesses your home, sizes the system precisely, and supplies, installs and warrants it. Pricing is indicative and subject to that assessment.
Get a free Alumo quote → and have your system sized to your actual home and usage.
Frequently asked questions
What's the difference between kW and kWh?
kW measures power — how much you can run at once — and sizes your inverter and panels. kWh measures energy — how much you use or store over time — and sizes your battery. A 1kW appliance running for one hour uses 1kWh.
How many solar panels do I need?
It depends on your usage and roof space. Alumo's home packages range from four panels (smaller homes) to six or more (family homes), with larger systems adding panels. The right number comes from your assessment.
What size inverter is right for a typical home?
Many family homes are well served by a 5kW inverter, which runs more appliances at once. Smaller homes or essentials-only setups do well on a 3.6kW inverter. Your peak simultaneous demand is what determines this.
Can I start small and expand later?
Yes. Battery storage in particular is modular, so you can begin with a system that fits your budget and add capacity as your needs grow. It's a common and sensible approach.
How do I get an exact size for my home?
Get a free Alumo quote →. A short assessment of your usage, roof and essential loads lets Alumo specify the exact inverter, panel and battery size — with no obligation.
SolarGuide is an independent referral partner. We help you compare options and arrange a free quote — Alumo supplies, installs, finances and warrants the systems. Pricing is indicative, sourced from Alumo’s published catalogue, and subject to a site assessment and credit approval.
