One side plans to deliver. The other expects to draw. On the ground the difference is absorbed by margin, and nobody looks. On a surface where every watt arrived at launch cost, the difference is the whole commercial question, and the first time anyone looks at it is the first time it fails.
A headline efficiency figure has the same defect. It is only useful when the system boundary, the operating conditions, and the treatment of uncertainty are stated with it, and they usually are not. A number without those three is not a measurement, it is a claim in the shape of a measurement.
It is not only the numbers. There is no conformance scheme for a lunar power interface either. The governing interface document states that the physical interfaces between loads and power systems are not defined, and describes its own procedures as suggested. So two parties can both comply with it and still fail to connect, and there is no test anyone can point at to find that out before the hardware is on a surface.
So a power business on the Moon has a sequencing problem that nobody has solved. You cannot write a supply agreement against delivered energy until delivered energy is measurable. You cannot arbitrate a dispute between a provider and a consumer without a party who measured and has no stake in the result. And you cannot price energy at all until there is a verified quantity to price.
The instrument is the product. The power is what the instrument makes sellable.