Solar battery: is it really worth it?

From 35% to 80% self-consumption: what a battery actually changes, and how to size one without getting it wrong.

The battery is the most argued-over part of any solar project. Here is the honest calculation, with no dreams sold.

The problem it solves

Solar produces at midday; you mostly use electricity in the morning and the evening. The result without a battery: only 30 to 40% of your production is actually used in your home. The rest goes to the grid for a few cents per kWh — while you buy your evening electricity back at full price.

With a properly sized battery, the midday energy powers your evening and your night: 70 to 80% self-consumption, and a bill that genuinely shrinks.

Why LiFePO4 has won

• Lifespan: several thousand cycles (15 years and more of daily use)
• Safety: stable chemistry, none of the thermal runaway of older types
• Depth of discharge: you can use almost the whole capacity without harming the battery
• Price: down by two thirds in a few years — this is THE change that makes storage pay

Sizing it: the simple rule

Aim to cover your evening and overnight consumption (broadly 40 to 60% of your daily use). For example:

• Household using 8 kWh a day → a battery of about 5 kWh
• Family using 15 kWh a day → 8 to 10 kWh
• All-electric or with an electric car → 15 kWh and above is justified

The part nobody mentions: control

A battery you cannot see into is a black box. The real value comes from control: seeing the state of charge, choosing when to charge and discharge, tracking the cycles. At heliolocal every installation ships with live monitoring on a tablet, fully local and subscription-free — production, battery, grid, house. Your data stays with you, and it works even without an internet connection. See: Monitoring your solar production without the cloud.

The verdict

• Out of the house most of the day? A battery changes everything.
• Heavy evening use (heating, electric car)? Yes, and size it generously.
• At home during the day with a small system? Start without one and add it later — provided you chose a hybrid inverter from the outset.

For a calculation based on your own figures: free calculator or free assessment.