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 2026Lithium vs lead-acid solar batteries: which is right for you?
Lead-acid looks cheaper on the quote. Over the life of the system, the answer is often different. Here is how to compare them fairly.
The battery is often the most expensive part of a home solar system, so the choice between lithium and lead-acid matters. The sticker price does not tell the whole story, so this guide shows you how to compare them on what they actually deliver.
The two types in plain terms
- Lead-acid (flooded, AGM and gel) is the older technology. It is familiar, widely available and cheaper to buy.
- Lithium iron phosphate (LiFePO4, often written LFP) is the chemistry most home solar batteries now use. It costs more upfront and lasts a lot longer.
Other lithium chemistries exist, but LFP is popular for homes because it is considered more thermally stable than some alternatives.
Side by side
| Lead-acid | Lithium (LiFePO4) | |
|---|---|---|
| Usable share of capacity | Often kept to about 50% | Typically 80% to 90% or more |
| Typical cycle life | Hundreds to around a thousand or more, depending on type and care | Commonly several thousand |
| Upfront cost | Lower | Higher |
| Maintenance | Flooded types need topping up and ventilation | Usually none |
| Weight and size | Heavy and bulky | Lighter and more compact |
| Battery management | Basic or none | Built-in battery management system (BMS) |
These are typical ranges. Always check the datasheet and warranty for the exact product, because quality varies widely between brands.
Why the cheaper battery can cost more
Two things make lead-acid look better than it is:
- You cannot use all of it. Draining lead-acid deeply every day shortens its life sharply, so you plan to use about half. A "10 kWh" lead-acid bank may give you only 5 kWh a day.
- It wears out sooner. Fewer cycles means replacing it sooner.
A fair comparison is cost per kWh actually delivered over its life:
Cost per kWh delivered = battery price ÷ (usable kWh per cycle × number of cycles)
Illustrative example (ratios, not a price quote): suppose a lithium battery costs twice as much as an equivalent lead-acid bank. If lead-acid gives you 0.5 usable per cycle for 1,000 cycles, and lithium gives 0.9 usable for 4,000 cycles, then:
- Lead-acid: 1 ÷ (0.5 × 1,000) = 0.0020
- Lithium: 2 ÷ (0.9 × 4,000) = 0.0006
In this example lithium delivers each kWh for roughly a third of the cost, even though it was twice the price at the till. Your real numbers will differ, so plug in the figures from each quote.
When lead-acid can still make sense
- A very tight budget now, with the plan to upgrade later.
- Occasional backup use, where the battery sits mostly full and cycles rarely.
- A system where the inverter only supports lead-acid voltage and settings.
What to check on any battery
- Usable capacity in kWh, not just the rated figure.
- Warranty in both years and throughput (for example, years and total kWh or cycles), and what state of health it guarantees at the end.
- Compatibility with your inverter, including voltage and communication, so the two work together properly.
- Operating temperature range. Batteries in hot garages or cold outbuildings age faster.
- Certification and installer support. Who services it if something goes wrong?
- Safe installation. Correct cabling, protection and ventilation are essential.
How much battery do you need?
That depends on how much of your day you want to cover. Our sizing guide shows how to work it out, or try the load calculator and compare backup options. If you want to see where the battery fits in the system, read how a solar system works.
This article is general information, not electrical advice. Always confirm product specifications and warranty terms with the supplier and your installer.