Guide · Equipment

What battery size for my house?

The simplest way to answer is to follow a real house. Take a four-person villa in Casablanca: two to three hours of evening air conditioning, TV, lighting, a fridge running continuously, phone charging. The family mainly wants the house to stay liveable in the evening on solar stored during the day, and to get through an outage without thinking about it. Let's see what battery capacity that corresponds to, in usable kWh, and why.

Step 1 — how much energy in the evening and at night?

Everything starts from what the house consumes once the sun sets, since that's exactly what the battery will have to cover. For our Casablanca family, we roughly add up: evening living room air conditioning, the fridge overnight, lighting and TV, plus small appliances. Depending on lifestyle, this nighttime need most often falls between 6 and 12 kWh in a house like this. Let's say 10 kWh to fix ideas.

It's this figure — the energy actually drawn between sunset and sunrise — that sizes the battery, not the day's total consumption. During the day, the house runs directly on the panels.

Step 2 — from need to usable capacity

Our family is therefore aiming for a battery that returns about 10 kWh every evening. This is a usable capacity: what the battery really delivers, not the figure printed on the label. To place this need against market offerings, it helps to think in tiers:

• Backup only (~5–10 kWh usable). Keeping lighting, a few outlets and the router running during an outage, without aiming for extended autonomy. The most modest sizing and often the most profitable entry point.
• Evening self-consumption (~10–20 kWh usable). The battery absorbs the day's surplus and returns it in the evening. This is where our Casablanca villa falls, and the tier that makes the most sense for a home whose peaks arrive after sunset.
• Near-autonomy (20 kWh usable and up). Covering almost all nighttime needs, including in a low-sun winter. Relevant for demanding profiles or areas with frequent, extended outages.

Our family therefore lands on a battery of about 10 to 12 usable kWh. What remains is translating that usable need into nominal capacity — the step many quotes skip.

Step 3 — nominal vs. usable: the margin not to forget

The figure shown on a battery is its nominal capacity. That's not what you draw day to day. Depth of Discharge (DoD) indicates what fraction is usable without damaging the battery.

For lithium iron phosphate (LFP) batteries, the technology we recommend for Moroccan homes, DoD reaches 80 to 95 %. A 10 kWh nominal battery at 90 % therefore delivers 9 usable kWh. For lead-acid (AGM/GEL), usual DoD is only about 50 %: that same 10 nominal kWh gives only 5 usable kWh, and the battery lasts far less long under the Moroccan sun.

For our family wanting 10 to 12 usable kWh, this means targeting about 12 to 14 nominal kWh in LFP. With lead, you'd need more than double the nominal capacity for the same service — hence the rule that holds for everyone: compare offers in usable kWh, never in nominal kWh. A "10 kWh LFP" spec sheet and a "10 kWh AGM" one don't deliver the same service, not in real capacity, not in lifespan, not against heat.

Storing rather than exporting: what Law 82-21 says

Our family might wonder whether a bigger battery or selling the surplus to the grid is better. Since 9 June 2026, Law 82-21 (Decree 2-25-100) authorises selling the surplus, but within a framework that makes exporting far less attractive than storing:

• Injection cap: 20 % of annual production. The share resold to the grid is limited to one-fifth of what your panels produce over the year.
• Buy-back tariff: 0.18–0.21 DH/kWh — but for MT/HT. The price at which ONEE buys back the surplus (tariff set by ANRE decision 04/26, off-peak / peak hours) is published for medium and high voltage. The residential low-voltage tariff (< 11 kW, declaration regime — our villa's case) is not yet published. Meanwhile you buy grid electricity between 0.90 and 1.66 DH/kWh depending on your bracket — that figure, at least, is known.

As long as the LV tariff isn't published, we can't say exactly how much an exported kWh will earn our villa — only that it will be a buy-back tariff well below the purchase price (for reference, MT/HT sits at 0.18–0.21 DH). The same kWh stored and consumed in the evening, by contrast, avoids buying a kWh at the marginal tariff — a known gain already clearly higher than what exporting would bring. It's this ratio that justifies storing rather than reselling, regardless of the upcoming LV figure.

The value order to remember

With Law 82-21 as the framework, the hierarchy runs from most to least profitable:

1. Consume during the day (direct). Electricity from the panels feeds appliances directly, with no conversion loss or extra hardware. The most advantageous scenario: shift the washing machine, water heater or air conditioning to broad daylight when possible.
2. Store for the evening. The day's surplus charges the battery and feeds the house after sunset, at the value of your avoided tariff, well above the grid buy-back rate.
3. Export the remaining 20 %. What can neither be consumed nor stored goes to the grid within the legal cap, at the buy-back tariff. A real gain, but the weakest of the three.

The consequence for our family, as for most households: you don't oversize a battery to export more, since the law caps exports and the buy-back is low. You size for real nighttime consumption. A villa with a different profile — more people, a pool, a heat pump — will shift these figures, and that's exactly what an hour-by-hour consumption reading lets us calibrate precisely.