Case 4: Solar was installed by the client during the performance period of the ESP. Solar PV kWh are used at the building and the remainder goes to the grid. Utility Buys and Sells kWh at the Same Rate.

Remember, the adjusted baseline represents how much energy would have been used if there had been no ESP.  If the ESP had never been implemented, the client would still have had a reduction in energy due to the solar project.  Therefore, the adjusted baseline would have been reduced by the kWh produced by the solar project.  To achieve this reduction, a baseline modification will have to be created to handle the reduction in energy usage due to the solar project.

Baseline kWh is calculated using the regression model of base year bills, before the solar was installed, which is what the building was drawing from the grid.

However, this Baseline is going to need a baseline modification to account for the solar PV system.  The modification would be the metered solar kWh produced. So:

Baseline kWh = Fit line of Bill kWh – Solar kWh

Actual kWh is the net amount that the grid is providing to the building, or as defined above, Bill kWh:

kWh Savings = Baseline kWh – Actual kWh

kWh Savings = (Fit line of Bill kWh – Solar kWh) – Bill kWh

To do this in Metrix or Option C

  1. Do a regression of base year bills.
  2. Enter a baseline modification for Solar Produced. Make sure the solar kWh are negative in the baseline modification.
  3. 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 defined it as Bill kWh.

Example Calculations

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.

Baseline Actual Savings
Day Fit line kWh Solar Produced kWh Total Building Usage

(Bldg kWh)

Net kWh Supplied to Building

(Bill kWh)

ESP Savings NOT Including Solar


Day 1 95 100 80 -20 15
Day 2 90 20 80 60 10
Total 185 120 160 40 25


Given the numbers in this table, we want our savings results to match the “ESP Savings Not Including Solar” 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