Battery storage is now the most common add-on to a solar panel system — and for good reason. The core problem solar-only systems have is that panels generate most of their power during the middle of the day, when most households are using relatively little. Without storage, that surplus goes to the grid at Smart Export Guarantee rates. With a battery, it stays in your home for use when you actually need it.
This guide explains how to calculate the right battery size for your household, compares SigEnergy and Fox ESS (two of the brands Energy Concerns installs), and explains what you can realistically expect from battery storage in terms of savings and payback.
Step 1: Calculate Your Evening Electricity Use
The battery's job is to cover your household electricity consumption from when solar generation stops (typically late afternoon to sunset) through to when you go to bed — or when the overnight cheap-rate period begins on a time-of-use tariff.
Look at your electricity bill's monthly usage and divide by 30 for a daily figure. Evening use (6pm–11pm) typically accounts for 35–45% of a household's daily total. Here's a rough guide:
| Household type | Daily usage | Evening use | Recommended battery |
|---|---|---|---|
| 1–2 people, 1–2 bed | 5–8 kWh | 2–3 kWh | 5 kWh |
| 3–4 people, 3-bed semi | 8–12 kWh | 3–4.5 kWh | 5–10 kWh |
| 4–5 people, 4-bed detached | 12–16 kWh | 4.5–6 kWh | 10 kWh |
| Family + 1 EV (home charging) | 18–25 kWh | 7–10 kWh | 10–15 kWh |
| Family + 2 EVs / heat pump | 25–35 kWh | 10–15 kWh | 15–20 kWh |
Battery capacity is quoted as usable capacity. Most lithium iron phosphate batteries (LiFePO4) have 90–95% usable capacity versus rated capacity.
Step 2: Match Battery to Your Solar System
Your battery can only store what your solar panels generate in excess of your daytime consumption. A system that's undersized relative to your solar won't fill the battery on sunny days — wasting generation potential. An oversized battery relative to your solar won't charge fully — leaving unused capacity.
A useful rule of thumb: your battery capacity should be roughly 60–80% of your system's peak daily generation in summer. Here's how that works out for common system sizes:
3 kW system
15–20 kWh/day (summer)
Ideal battery size
5–10 kWh
4 kW system
18–24 kWh/day (summer)
Ideal battery size
10 kWh
6 kW system
25–34 kWh/day (summer)
Ideal battery size
10–15 kWh
8 kW system
32–44 kWh/day (summer)
Ideal battery size
15–20 kWh
SigEnergy vs Fox ESS: Which Battery?
Energy Concerns is a certified installer for both SigEnergy and Fox ESS. Both use lithium iron phosphate (LiFePO4) chemistry, which is significantly safer and longer-lasting than older lithium-ion batteries. Here's an honest comparison:
| Feature | SigEnergy | Fox ESS |
|---|---|---|
| Origin | Global manufacturer, UK support | Global manufacturer |
| Chemistry | LiFePO4 | LiFePO4 |
| Available capacities | 5–30kWh (modular) | 5.2, 10.4, 16kWh (modular) |
| Warranty | 15 years | 10 years |
| App & monitoring | SigEnergy app — detailed | Fox ESS Cloud — capable |
| Blackout protection | Yes (islanding) | Yes (islanding) |
| Grid arbitrage | Yes (Agile/Octopus compatible) | Yes |
| Price point | Premium | Mid |
| Best for | Premium all-in-one, EV charging | Value-focused, modular expansion |
Both perform excellently in real-world use. SigEnergy's premium all-in-one design, 15-year warranty and integrated EV charging make it a strong choice for homes that want the best specification and room to expand, while Fox ESS offers excellent value when budget is the primary concern.
What Savings Can You Realistically Expect?
Battery storage savings depend on your household usage pattern, your tariff, and how much solar generation you have to store. Here are realistic annual saving ranges for different household types in the East Midlands:
Solar-only household adding 5kWh battery
Moving self-consumption from ~35% to ~65%
£350–£500/yr
Solar + battery with EV on time-of-use tariff
Combining solar self-consumption and cheap overnight charging
£700–£1,100/yr
Battery-only (no solar, Octopus Go/Agile tariff)
Grid arbitrage: charging at 7–8p/kWh, displacing 24p/kWh imports
£200–£350/yr
Solar + battery + heat pump heating
Full electrification — solar + battery covers heating, hot water, EV, household
£900–£1,500/yr
How Much Battery Storage Do I Need? A Simple Rule of Thumb
The quickest way to size a home battery is from your evening and overnight consumption — the electricity you use after your panels stop generating. For most East Midlands homes that is roughly 40–60% of daily usage. A household using 10kWh a day typically wants a 5–8kWh usable battery; a larger family home on 15–20kWh a day usually sits at 10–15kWh. Going bigger than your evening load rarely pays back, because the extra capacity sits unused most nights.
Two adjustments change the answer: an electric vehicle or heat pump pushes you towards the top of the range (or a modular system such as Sigenergy that you can expand later), and a time-of-use tariff can justify a little extra capacity because you charge it cheaply overnight and discharge through the expensive peak. Battery pricing in 2026 sits around £400–£700 per usable kWh installed, and the solar-and-battery element carries 0% VAT until 31 March 2027.
We size every system from a year of your actual usage rather than a template — see battery storage installation across Leicestershire, or request a free quotation and we will model your home specifically.
Frequently Asked Questions
What size battery storage do I need with solar panels?
For a typical 3–4 bed home with a 4kW solar system, a 5–10kWh battery is the most practical range. A 5kWh battery covers evening consumption for most households without EV charging. Match battery capacity to your average evening electricity use after solar generation stops.
Is a 5kWh battery enough for a house?
A 5kWh battery is sufficient for most 2–3 bedroom homes without an EV. The average UK household uses 2.5–3.5kWh in the evening (6pm–11pm), so a fully charged 5kWh battery covers most evenings comfortably. Larger families should consider 10kWh.
Can I get battery storage without solar panels?
Yes. A battery can be charged from the grid on time-of-use tariffs (Octopus Go or Agile), storing cheap overnight electricity for use during peak hours. Without solar, savings are smaller but typically £200–£400 per year. Battery storage works best when combined with solar panels.
Get a Battery Storage Quote
Energy Concerns designs and installs SigEnergy and Fox ESS battery storage systems across Leicester, Leicestershire, and the East Midlands. We model your actual usage against your solar system's generation to recommend the right capacity — no guesswork, no upselling.
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