Thursday, April 8, 2010

PV Solar - Excess generation payout

Ever wonder what the utility would pay if you generated electricity for them?

In Connecticut where our facility is located, utilities (electric, water, etc) are regulated by the Dept. of Public Utilities (DPUC). Photo-Voltaic generated electricity is considered a Class 1 Renewable Energy Resource, and the DPUC has a ruling on how generators of such energy should be dealt with.

In our region United Illuminating Co. is the electric utility. UI delivers our electricity, and in our case we also purchase our actual electricity from them as a provider (since deregulation, you can also choose to purchase electricity from other providers, re-sellers or aggregators - but everyone must deal with UI who owns the poles, transformers and "grid" infrastructure to deliver the power).

UI has a "Class 1 Renewable Net Energy Rider (NEC1)" to accompany their tarrif schedule and abide by the DPUC ruling. The rider states:
  • Net energy billing shall be performed monthly, and payments for excess sales to the Company shall be made on an annual basis, for the period from April of each year to March of the following year.
  • During the annual period, if energy sold to the Company in any month exceeds energy purchased, the excess sales will first be credited to the customer in the current billing period and any remaining net sales will be carried forward for crediting on a per kwh basis in the next billing period or a subsequent billing period within the annual net energy period.
  • Any excess kwh remaining at the end of an annual period shall be paid at that time according to the Average hourly Connecticut ISO-NE real time locational marginal price (RT-LMP), for the hours 10am-4pm during the annual period.

In plain english: If the array generates more kwh than consumed in a month, the credit kwh carries forward to the future period. If there is a kwh credit at the end of the annual period, the value is paid to the generator. Value is determined by the peak period prices posted by the Regional Transmission Organization (Independent Systems Operator - New England) for our location within their system.

From 2009April till 2010March (billing periods) Our Photo-Voltaic array generated 8480kwh in excess of what was consumed. The ISO-NE RT-LMP for that period is .04663 per kwh. Thus we made $395.42 for the excess power generated. The true value of our PV system is deferring purchase of kwh from the utility.

To put this into relational terms, 8480kwh is approximately 6months of electricity for the typical household.

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