Proving Round-Trip Efficiency Without a Spreadsheet

The situation

A battery-storage project had a contractual round-trip efficiency it needed to prove - and proving it lived in spreadsheets. Every reporting cycle, someone rebuilt the calculation by hand from exported data. Round-trip efficiency has to be measured at the point of common coupling, adjusting charge energy for losses and excluding imports that have nothing to do with the battery. That is a lot of careful bookkeeping to redo manually, month after month.

The defect

A number you have to reconstruct by hand every month is a number you cannot fully defend. Spreadsheets drift, definitions get remembered slightly differently, and a contractual figure ends up resting on whoever built this month's version. The contract was specific about how efficiency must be measured, but the measurement was not implemented against the meters - it was reassembled after the fact. That is both slow and risky when money and compliance ride on the answer.

What we engineered

• Implemented the contract's exact round-trip efficiency definition directly against metered data at the point of common coupling.
• Adjusted charge energy for losses and excluded unrelated imports, exactly as the contract specifies.
• Removed the monthly spreadsheet rebuild by computing the figure from the source data automatically.
• Added curtailment reporting so lost generation is measured rather than estimated.
• Included incentive-program reporting so the operator can substantiate what it claims.

The result

Round-trip efficiency is now computed the way the contract defines it, straight from the meters, instead of being reassembled in a spreadsheet each month. That makes the number defensible - it traces back to metered data and a fixed definition rather than to this cycle's workbook. With curtailment and incentive reporting alongside it, the operator can stand behind its compliance figures with the receipts to match.