1. Solar Profiling Interstate Renewable Energy Council presentation to the ERCOT Profiling Working Group Jan. 22, 2008

2. No one solar profile fits Example – customer in a class with a flat profile who averages 5 kW installs solar. Actual daily load shape depends on whether he installs a system with rated capacity of 2 kW (blue), 5 kW (green) or 8 kW (red) In this example, there is no outflow for the 2 kW or 5 kW systems, so using the standard profile with the inflow data would just give a flat line profile. For instance, a 5 kW system would generate 25 kWh in a day. Daily electricity use of 5 kW * 24 hours = 120 kWh would be met by 95 kWh from the grid and 25 kWh from the system. Profile would say customer used a flat 95/24 = 4 kW, which is inaccurate 5 kW 0 kW 6pm6amnoon 4 kW – inaccurate profile for customer with 5 kW system

3. How to fix it Recognize that metered data for inflow minus outflow is only part of customer’s electricity consumption Inflow minus outflow plus generation is total electricity consumption by customer. It is appropriate to use the class profile for this total electricity consumption for the customer It appears that there is problem: we don’t have metered generation data To solve this, estimate generation based on system size. Add that amount to inflow minus outflow and apply the profile, then subtract the estimated generation using a solar profile (like the curves on the last slide) Sounds complicated and hard to automate, but there’s an easy way to get to the same result

4. The Easy Way Apply the standard profile to inflow minus outflow then make an adjustment based on system size, either to the customer’s ID or to a new zero balance ID For instance, from the first slide, the customer with a 5 kW system will reduce load about 25 kWh per day. Instead of seeing metered inflow of 3,600 kWh per month (5 KW * 24 hours * 30 days), metered data will be about 2,850 kWh (30 days * 95 kWh). Apply the daily profile based on that consumption and the daily system totals. The flat profile would come in at around 4 kW. Then apply a solar adjustment (separate ID?) that adds 25 kWh flat and subtracts 25 kWh in the shape of the solar profile. One adjustment methodology for all classes – reasonably accurate, very easy to implement, low cost

5. Step–by–step for 5 kW system Use standard flat profile for metered inflow minus outflow, which will be about 95 kWh - a flat line at just under 4 kW (minimal actual outflow in this example) Add 25 kWh over all hours evenly – adds just over 1 kWh each hour, getting us to daily electricity use from the grid and the system at 5 kW Subtract solar profile for 5 kW system – the green line below 5 kW 0 kW 6pm6amnoon 4 kW – profile based on inflow minus outflow data

6. Step–by–step for 2 kW system Use standard flat profile for metered inflow minus outflow, which will be about 110 kWh - a flat line at about 4.6 kW (no actual outflow in this example) (based on 2 kW times 5 hours equals 10 kWh of generation) Add 10 kWh over all hours evenly – adds about 0.4 kWh each hour, getting us to daily electricity use from the grid and the system at 5 kW Subtract solar profile for 2 kW system – the blue line below 5 kW 0 kW 6pm6amnoon 4.6 kW – profile based on inflow minus outflow data

7. Step–by–step for 8 kW system Use standard flat profile for metered inflow minus outflow, which will be about 80 kWh - a flat line at about 3.3 kW (no actual outflow in this example) (based on 8 kW times 5 hours equals 40 kWh of generation) Add 40 kWh over all hours evenly – adds about 1.7 kWh each hour, getting us to daily electricity use from the grid and the system at 5 kW Subtract solar profile for 8 kW system – the red line below 5 kW 0 kW 6pm6amnoon 3.3 kW – profile based on inflow minus outflow data

8. Conclusion No need for inflow and outflow data – just need the net figure (one meter reading) Use standard profile for that net metered amount Adjust that ID (or make a new ID) to add (system size * 5 hours / 24 hours) to each hour. For 15 minute segments, divide by four and apply to each segment Subtract solar profile times system size