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Peak Shaving with PV

Researchers:  Richard Perez

One of the perceived problems of the solar resource (as well as other natural resource) is that the resource is not controllable/dispatchable as, say, a gas turbine would be. Therefore in places such as New York Sate where cloudy days are not infrequent, the resource is commonly perceived as having no capacity credit. Capacity characterizes the resource's contribution to an electric utility's reserve. For instance, if a 100 MW hydro power plant is built, this will add close to 100 MW of new generating capacity on the grid that a utility can count on for deployment. For PV without capacity credit, deploying 100 MW of PV would be perceived as adding zero new generating capacity for the grid.

It turns out however, that, because in some places, peak electrical demand is driven commercial air-conditioning demand, itself driven by [sunny] heat waves, the effective capacity of PV can be very significant. In fact, the metropolitan eastern seaboard including the New York metro area is one of the places in the country where this effective capacity is the highest, approaching 70% of nameplate rating.

This new finding was made possible because we had access to site/time specific satellite data allowing us to analyze coincident time/specific load demand and solar availability data. We analyzed a large number of electric utilities in the country and were able to derive a photovoltaic effective capacity map. Note, for instance that despite a lesser climatic solar energy resource in New York than in Florida, the effective capacity of PV is markedly higher in New York.

The economic implications of this finding are not trivial. Combined with the high retail value of electrical power (energy and demand) in the northeast, the high effective capacity of PV makes this region one of the most promising grid connected PV markets in the country almost on par with California and Hawaii.

At present, we are focusing our investigations on localized grid PV interaction and rising occurrences of power blackout situations caused by high demand and inability of grid operators to deliver localized power. We observe that the availability of photovoltaic power during instances of high grid stress leading to power outages is consistently very high, confirming the contention that a dispersed peak shaving PV resource would be very beneficial to the grid.

In a parallel effort, peak shaving PV investigations led to the development of the concept of solar load control (SLC) and to the development of a prototype SLC application. The SLC works in tandem with PV generation to guarantee the equivalent of 100% firm peak time system availability.

It does so by acting on end-use settings (e.g. building temperature set points) to make up for any PV output deficit (e.g., caused by clouds or sunset) at time of critical peak demand. The amount of end-use discomfort necessary to guarantee firm PV capacity is very small - for instance guarantying 100% peak time PV capacity in New York with 10% PV penetration on the City's grid could be achieved with a total end=use discomfort of 15-degree hours for the entire cooling season, with a maximum one-day burden of 5 degree-hours. SLC beta prototypes are currently being tested in Albany and Ithaca in collaboration with AWS Scientific and Powerlight and under funding from NYSERDA and USDOE/NREL.