“Why do you monitor the BTU’s on the consumption side?”
“Dr. Ben, why do you monitor the BTU’s on the consumption side of the system rather than the capture (solar) side of the system?”
– Steve Edlund
The answer is more philosophical than technical. We think the only honest thing to do is measure the energy that actually goes into the load. When we bill people for the energy used, they expect to pay for the energy that went into their system.
Measuring the energy collected doesn’t tell us whether that energy went onto the load. If the delivery system is low efficiency, for example, it has a lot of heat lost through poor insulation, incorrectly sized heat exchanger, etc, then the customer is not getting their money’s worth.
The counter argument is based on the utility model of selling gas/oil/electricity to a customer. The customer pays for the gas/oil/electricity as it comes off the street, regardless of the efficiency of the boiler, or device using the energy.
The flaw in that argument, as I see it, is that the gas/electricity/oil costs ongoing money to produce, or capture, and deliver it to the customer, so they have to pay that cost. That is a continuing cost of production. Solar, on the other hand is a fixed, one time expense (ignoring maintenance), so the production cost is not relevant here. Actually, the customer does pay the electric bill to run the equipment, which could be considered the production cost.
Also, the oil/gas/electric energy devices are a century old and well defined. Solar is more like the wild wild west, with variable quality in design, engineering and installation. We have seen systems where the energy captured was billed and the energy delivered was a fraction of that energy.
We don’t believe the production model of conventional energy is the relevant model for solar, so we only measure and sell the actual energy used in the application.
I hope this answers your question.