5kWh 10kWh 15 kWh

5kWh, 10kWh or 15kWh – How to Choose the Right Residential Energy Storage Capacity

An installer in Spain calls with the same question every week. The customer has a 6 kWp rooftop array, a monthly bill of €140, and no idea whether to buy a 5 kWh, 10 kWh or 15 kWh battery. The installer’s margin depends on getting this right, because a battery that is too small never pays for itself and one that is too large sits half-empty for a decade.

The answer is never a single number. It is a calculation that starts with the household’s actual load curve, not the size of the roof. Get that curve right and the capacity choice almost makes itself.

This article gives you the sizing method, the real numbers for each tier, and the questions to ask a customer before you quote a single kilowatt-hour.

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The Load Profile Is the Whole Game – Read It Before You Size

Capacity is not about how much energy a home uses in a day. It is about how much it uses after the sun stops producing. That gap, measured in kilowatt-hours, is the number the battery has to cover.

Start with the evening-to-morning window. A typical European household draws 4–7 kWh between sunset and sunrise, split across the fridge, lighting, a heat pump or air conditioner, and the always-on electronics. A 5 kWh battery covers the low end of that range and nothing more. A 10 kWh battery covers the full overnight draw for most homes. A 15 kWh battery only earns its keep when the home runs a heat pump, an EV charger, or a pool pump through the night.

Now look at the solar side. A 6 kWp array in southern Europe produces 20–30 kWh on a good summer day and 4–8 kWh on a grey winter day. The battery can only store what the array produces in surplus, so a 15 kWh battery paired with a 3 kWp array is a waste of money for half the year. Match the storage to the 더 작은 of the two numbers: the overnight load or the daily surplus.

The third variable is the tariff. Under a flat feed-in tariff, the battery’s job is self-consumption, and the payback comes from every kilowatt-hour you don’t buy from the grid. Under time-of-use pricing, the battery can also arbitrage – charge cheap at night, discharge at the evening peak – and that changes the ideal size upward, because you now want enough headroom to shift load, not just cover it.

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A drop-shipper sells you a 10 kWh box and moves on. A manufacturer helps you size the box so your installers stop fielding “why is my battery empty by 2 a.m.” calls.

A genuine OEM/ODM partner will give you the discharge curve and the usable-capacity figure, not just the nominal number. A 10 kWh pack with a 90% depth-of-discharge window delivers 9 kWh of usable energy, and that distinction changes the sizing math by a full tier. They will also offer the same enclosure and BMS platform across 5, 10 and 15 kWh, so your installers learn one wiring scheme and one commissioning routine instead of three.

The customisation that matters here is firmware. A partner who can tune the SOC window, the charge current and the grid-export threshold to your market’s tariff structure turns a generic battery into a product that actually fits the local grid code. They will quote MOQs down to 100 units with shared-container options, and they will tell you honestly when a 15 kWh stack is overkill for a market that mostly installs 5 kWh units.

Sizing the Three Tiers Side by Side

Here is how the three common capacities line up against real household profiles, assuming a 48V LFP wall-mount platform with a 90% usable depth of discharge.

용량	Usable energy	Typical overnight load it covers	Best-fit household	Payback signal
5kWh	~4.5 kWh	Fridge, lighting, electronics	Apartment or small home, 3–4 kWp array	Flat feed-in tariff, low evening draw
10kWh	~9 kWh	Full overnight draw, plus heat pump shoulder	4–5 bedroom home, 5–6 kWp array	Self-consumption with moderate evening load
15 kWh	~13.5 kWh	Overnight draw plus EV or heat pump	Large home, EV charger, 8 kWp+ array	Time-of-use arbitrage or high winter load

The payback signal column is the one to watch. A 5 kWh unit pays back fastest in a market with a flat tariff and a small evening load, because every stored kilowatt-hour directly offsets a grid purchase. A 15 kWh unit only justifies its cost when the tariff structure or the load profile gives it a second job to do.