Solar Panels with Battery Storage: The Modern Standard

When export rates were 5p/kWh and import was 14p/kWh, batteries struggled to make economic sense. Now that export rates are 8-15p/kWh and import is 28-32p/kWh, the gap between selling exported solar and avoiding imported electricity is wide enough that batteries pay back in 8-10 years on most homes.

Octopus Flux, Intelligent Go and similar tariffs let you charge the battery from cheap overnight grid power and export at peak rates — a further £100-£300 annual saving on top of solar.

The rule of thumb is to size battery capacity to roughly your average evening + overnight consumption. For a typical South East home that's 5-10 kWh; for EV-charging households 10-15 kWh; for heat-pump households 15-20 kWh. Oversizing wastes money — undersizing forces you to import at peak rates from 4pm onwards.

Modular brands (Fox ESS, Pylontech, Sigenergy) let you start moderate and scale up later without replacing what you've got. Fixed-capacity brands (Tesla Powerwall 3, GivEnergy AIO) require committing to your size at install time.

If you already have solar (often from a Feed-in Tariff install 2012-2019), adding a battery is straightforward via an AC-coupled retrofit. Installation typically takes one day, doesn't disturb the existing solar inverter, and most importantly preserves your FiT payments — which are based on generation, not export.

Typical retrofit cost for a 10 kWh battery is £5,500-£8,500 fitted, and most older-FiT homes see annual savings of £600-£1,000 from the battery alone because their existing solar has been heavily exporting at near-zero value.

Most modern batteries include Emergency Power Supply (EPS) — automatic switchover to battery power for a set of essential circuits (typically fridge, lights, broadband, a couple of sockets) during a grid outage. Whole-home backup is a paid upgrade requiring additional switching hardware (£600-£1,500) and is most valuable in rural Kent, Sussex, Hampshire and the Isle of Wight where outages are more frequent.

Choose solar-only if: you're at home most daylight hours, your bills are under £1,200/year, and you don't have an EV or heat pump on the horizon. Payback 8-11 years.

Choose solar + battery if: you work away from home, your bills are over £1,500/year, you have or plan an EV, or you want backup during outages. Payback 8-12 years with materially higher lifetime savings.