This is probably one of the most difficult case to understand. In theory, we have to subtract the solar kWh produced from the post-retrofit data.
Remember, Baseline represents how much energy “would have been used” if there was no ESP. I understand solar PV was part of the ESP, but for our calculations here, the ESCO did not want to include solar PV production. So, we need to pretend that solar PV was installed but was not part of the ESP. This would be as if the client had installed the solar during the performance period (see Case 4).
This is a little convoluted, but the Baseline then represents how much energy “would have been used” minus the Solar Produced (as the solar was going to be installed anyway).
We take the pre-retrofit bills that did not use solar and do a regression on these bills. To account for the fact that they are producing solar, we have to add a baseline modification for solar:
Baseline kWh = Fit line of Bill kWh – Solar Produced kWh
Solar production reduces energy drawn from the grid, therefore it should be negative.
The Actual data is also tricky. We want usage minus the Solar Produced, which is Bill kWh:
Bill kWh = Building kWh – Solar Produced kWh
Actual kWh = Bill kWh
kWh Savings = Baseline kWh – Actual kWh
kWh Savings = (Fit line kWh – Solar Produced kWh) – Bill kWh
This is just like the client installed solar during the performance period (Case 4). But this time the solar went online at the same time the performance period started.
To do this in Metrix or Option C
- Do a regression of base year Bill kWh
- Enter a baseline modification for Solar Produced. Make sure the solar kWh are negative in the baseline modification.
- For post retrofit bills, enter in NET kWh supplied by utility to the building. That means kWh provided by utility minus kWh provided by solar system. I define this as Bill kWh.
In this example, we are given 2 days of usage in a month. In day 1, the solar produces more than the building uses. In day 2, the building uses more than the solar produces.
|Day||Fit line of Bill kWh||Solar Produced Modification
(Fit line – Modification)
|Solar Produced kWh||Total Building Usage
|Net kWh Supplied to Building
|ESP Savings NOT Including Solar
Given the numbers in this table, we want our savings results to match the last column, or 25 kWh.
Savings = Baseline kWh – Actual kWh
Savings = (Fit line of Bill kWh – Solar Produced kWh) – Bill kWh
Savings = 185 kWh – 120 kWh – 40 kWh = 25 kWh
How to Handle Demand
You would treat demand exactly as you treat energy. So:
Savings = Baseline kW – Actual kW
Savings = (Fit line of Bill kW – Solar Produced kW) – Bill kW