In the latest heatwave, you might be wishing more than ever you had solar panels. Why not make 2025 the year you make that leap?
As energy prices continue to soar, more people are investing in solar PV systems to generate their own electricity. But pairing solar panels with a battery storage system is where you really benefit.
A battery allows you to store excess energy produced during the day, so you can use it at night, or during outages.
Yet one of the biggest questions homeowners ask is: how much battery storage do I actually need? The answer depends on your household’s energy habits, the size of your solar PV system, and how independent from the grid you want to be. In this blog, Jem Energy explores this in more detail.
How Big Should Your Battery Be?
Battery storage capacity is measured in kilowatt-hours (kWh). Here’s a simple way to think about the size of a battery:
Look at how much energy you use per day. Most UK homes use between 8–12 kWh per day, though this varies with lifestyle and the size of your household.
Estimate how much of that you’d like to store. Many households aim to cover their evening and overnight consumption, which typically ranges from 4–6 kWh.
Match it with your solar generation. Your solar PV system will only charge the battery if it produces a surplus. So if your panels can generate, say, 10 kWh per day on average, you might reasonably store 4–6 kWh to cover the night-time hours.
For many homes in Southeast England, a battery sized between 5–10 kWh hits the sweet spot. This balances a meaningful amount of self-sufficiency while keeping installation costs reasonable.
Factors That Affect the Size of a Battery
Let’s look more at what affects your ideal battery storage size:
Your Household and Lifestyle
Bigger households with more appliances, lighting and the need for more heating will naturally use more energy. If you run devices like electric ovens, tumble dryers or work from home, you may benefit from a larger battery.
The Size of Your Solar PV System
A bigger solar PV array will produce more excess energy to store. If you have a 4kWp system versus a 6kWp system, the amount of surplus power available for charging batteries will differ.
The Time You Use Energy
Some energy providers in the UK offer tariffs with cheaper overnight rates. In these cases, you might choose a larger battery to store cheap off-peak electricity for later use, in addition to your solar-generated power.
Backup Power
Want your battery to run essentials during a power cut? You’ll need to size it for critical loads. This might include lighting, a fridge or even an air source heat pump for heating.
Prepare for the Future
Planning to get an EV charger or add an air source heat pump later? Consider sizing up the battery slightly to handle higher future energy demand.
Is Bigger Always Better?
Not necessarily. Batteries are still a great investment, and oversizing one without a good reason can tie up money you might prefer to spend on more solar panels, or on energy efficiency measures.
At Jem Energy, we advise customers to balance their battery size with their realistic evening and overnight demand. A battery that is too large might not get fully charged often enough, meaning you won’t see the payback you expect.
A Typical Example for Southeast England
Let’s look at an example. A family of four in Kent has a 5kWp solar PV system, which generates around 4,500 kWh annually (roughly 12 kWh per day averaged across the year). In the evening, their consumption averages 5 kWh.
A 5–8 kWh battery would likely:
capture their excess solar generation most days
provide enough storage to power their home through the night
still be small enough to keep costs manageable
That size range gives them independence for routine power cuts and reduces grid electricity bills, without overinvesting.
Integrating Other Technologies
If you’re also considering an air source heat pump or an EV charger, it’s even more crucial to pick the right size.
Heating with a heat pump adds significant demand in winter. Meanwhile, charging an electric vehicle will add to your energy consumption. In these cases, a 10–15 kWh battery may be appropriate. It depends on how much you want to rely on stored solar or cheaper overnight tariffs.
Jem Energy can help you design a system that works harmoniously, so your solar PV, battery storage, EV charger, and even your heat pump are optimised together. If you have any more questions, we’re always happy to help.
Find out more about our solar PV panels. Or simply contact our team today.