Solar is not automatically “free” if exported electricity would otherwise earn a payment.
The Short Answer
Use the lower-value energy source after considering export income, import prices and battery losses. In some tariff combinations it can be financially better to export solar and charge the battery from a cheaper night rate.
The hidden cost of solar charging
If your supplier pays you for exported solar, putting that solar into the battery means giving up the export payment. That forgone payment is the opportunity cost of charging from solar.
Compare like with like
Compare the value of exporting one kWh of solar with the effective cost of buying and storing one kWh from the grid. Include round-trip efficiency when comparing stored energy.
Seasonal strategy
In summer there may be abundant solar and limited need for overnight charging. In winter, solar output falls and cheap grid charging may do most of the work.
Use a blended strategy
The best setup is often not solar-only or grid-only. Battery schedules can change by season and respond to weather, expected demand and tariff prices.
Key Takeaway
Battery economics depend on the complete energy flow: what electricity costs when you charge, what it would cost when you discharge, what solar export is worth, and how efficiently the battery is used.
Frequently Asked Questions
Is solar energy free once the panels are installed?
It has no additional fuel cost, but exported solar can have a cash value, so using it in the battery can carry an opportunity cost.
What if my export rate is higher than my night rate?
That can favour exporting solar and buying cheaper electricity later, subject to battery losses and tariff rules.
Should the strategy change through the year?
Yes. Solar availability and household load profiles change substantially between summer and winter.
Optimise My Charging Strategy
Compare solar export value with the real cost of night-time battery charging.
Tariffs, supplier terms and export payments change. Check the current plan details before making a purchasing or settings decision.