Solar or Grid: Which Should Charge the Battery?
Compare a solar-first charging strategy against grid-only charging using the battery energy required, available solar, charging losses and the economic opportunity cost of solar.
Why charge source changes storage economics
The physical source of charging energy is only part of the decision. Grid energy has a direct price, while solar energy may have an opportunity cost based on export value or another useful application.
Why charging losses are included
The source must supply more energy than ultimately reaches the battery when charging losses occur. The tool therefore calculates source energy separately for the solar-first and grid-only paths.
When grid charging can be useful
Grid charging can make sense under favorable time-of-use periods or when maintaining backup energy is strategically important, subject to the operating rules that apply to the system.
What is outside this comparison
The model does not include demand charges, fixed charges, dynamic dispatch, taxes or inverter standby consumption. Those can be layered into a larger financial model.
FAQs
Is solar charging always cheaper?
No. It depends on solar opportunity cost and grid price.
Why use solar opportunity cost?
Because solar energy used for the battery cannot simultaneously be used for another economic purpose.
Can I use an off-peak grid tariff?
Yes. Enter the actual price applicable to the charging period.
Does this include discharge losses?
No. This tool isolates the charging-source comparison.