m+ energy

Rooftop solar billing reconciliation and storage case, Ho Chi Minh City

Problem
trace an unexplained extra charge on a Vietnamese manufacturing plant's electricity bill, running rooftop solar under a power purchase agreement, and assess whether storage could reduce it.

Work
  • matched the plant's interval data to the correct utility meter, since an early candidate meter looked plausible from its description but its bill was two orders of magnitude too small, then confirmed the match by reconciling roughly 271,800 kilowatt hours derived from the file against 277,200 kilowatt hours billed for the same period.
  • split the disputed charge into a standard reactive energy charge from low power factor, unrelated to solar, and a separate minimum consumption shortfall fee under the power purchase agreement, then traced the fee to a 75 percent minimum consumption commitment against projected output, against which actual consumption came in at 66.1 percent.
  • derived recoverable solar from two separate inverter monitoring platforms, since the utility's own portal does not expose behind the meter generation, then built a four layer storage revenue stack, time of use shifting, maximum demand reduction, charging from recoverable solar, and additional fee relief, and modelled two system configurations against it.

two charges, not one

the extra charge on the bill was not a single billing error. it was a standard reactive energy charge from low power factor, unrelated to solar, plus a separate minimum consumption shortfall under the power purchase agreement, worth roughly 292 million Vietnamese dong for the year once traced to its source.

Consequence
the dispute was redirected from the bill, which was correct, to what storage could realistically recover. an 800 kW, 800 kilowatt hour system reached roughly 30.7 percent return driven mainly by maximum demand savings, while a larger 1,000 kW, 2,000 kilowatt hour system gave more duration at a lower 13.8 percent. recovering the full consumption shortfall through storage alone needed close to 500 kW, 990 kilowatt hour of usable capacity, and only if the contract recognises stored solar as solar consumption.