Using every available solar unit yourself is not always the financially best option. The relevant comparison is the value of an imported unit you avoid versus the export payment you give up, within the actual tariff conditions.

First separate three different numbers

  • Generation: solar electricity produced at a known measurement boundary.
  • Self-use: solar energy genuinely used on site instead of exporting; the calculation depends on system layout and whether a battery is involved.
  • Export: electricity sent to the grid and accepted by the export supplier under its agreement.

Do not assume a high self-consumption percentage means a low bill. Total household demand, time of use, import prices and standing charges still matter.

Compare a genuinely flexible appliance

Suppose, purely to demonstrate the calculation, a household has a necessary appliance cycle that can be shifted into a solar-producing period.

If using an otherwise-exported kWh now avoids importing it later at 27p, but sacrifices 11p in export income, the gross incremental value of shifting that kWh is 16p. This is not a current price quote.

But suppose the same appliance could run using an available off-peak import rate of 7p while solar export earns 11p. Under that narrow scenario, exporting the solar unit and buying an off-peak unit can look better before considering losses, restrictions and all contract terms.

Do not add unnecessary appliance use just to improve an app score. Follow appliance safety instructions, avoid overloading circuits and do not alter protected system settings.

Compare tariffs using a whole-year view

Record your evidenced annual import kWh, its timing by relevant price bands, export kWh recognized for payment, unit rates, standing charges, contract durations and exit conditions.

For each offer, work out:

Imported electricity charge + standing charges − recognized export payment = simplified net annual electricity outlay.

Use the same reasonable usage assumptions for each offer. Change one assumption—such as the export volume or off-peak share—to see whether the apparent winner changes.

The book’s annual worked comparison shows why an offer with a higher export rate can be only marginally better overall, or worse after a change in export volume. That comparison is illustrative, not a promise of savings.

Special cautions

A tariff advertised for solar owners may require a matching import account, a compatible smart meter, an eligible installation, or different treatment of batteries and electricity previously imported from the grid. A time-of-use comparison needs usage in the actual rate periods, not just annual totals.

Check current supplier terms and your exact eligibility before changing contracts. Keep screenshots of the offer and effective dates; supplier terms can change.

Check your bill and the relevant meter readings first, then confirm the export contract and MPAN status. The tariff worksheet and decision method in Solar Panels Installed — Now What? provide a reusable review structure.