How utilities can leverage their grids to integrate solar faster and cheaper
Starting at the rooftop is backwards, Clean Coalition says. Utilities must consider the entire system.
While death spiral predictions run rampant, and power companies across the country bicker with solar installers over rate design, a whole new way for utilities to get the most out of distributed energy resources is taking shape in California.
Clean Coalition’s Community Microgrid Initiative could be what utilities want for themselves, their ratepayers and their communities. Southern California Edison, Pacific Gas & Electric, Public Service Electric & Gas, and the City of Palo Alto Municipal Utility are already on board.
The way DERs are done today is backwards because it starts with a single resident or business that wants to install distributed generation, explained Clean Coalition Programs Director Greg Thomson.
“If a utility wants to move to the Utility 2.0 utility-of-the-future model,” he said, “it looks at the distribution grid as an asset and the local generation as an opportunity to shift from mostly centralized technologies to 25% to 30% local renewables. To do that, the utility looks at the system rather than a bunch of one-offs.”
The Community Microgrid Initiative begins with a DER survey of the local renewables potential. It is combined with input about the utility’s distribution system to identify the highest level of distributed generation that can be readily interconnected without disrupting the power flow or requiring equipment upgrades. Finally, the renewable energy nonprofit performs a financial analysis that optimizes for costs and benefits.
“That makes it possible to get the maximum level of DG into a community that makes sense operationally and financially,” Thomson said. “Storage can be added as needed.”
The test case
Clean Coalition pioneered the concept and methodology for its Community Microgrid Initiative on a single PG&E substation area in San Francisco's Hunters Point community.
“We got 25% of the energy in the model from 50 MW of new local solar without any voltage issues or back-feeding because our Solar Siting Survey allowed us to find the optimal locations for solar, the best rooftops and parking lots, based on the local grid characteristics,” Thomson said.
Clean Coalition projected benefits over the hypothetical 20 year life of the 50 MW of new PV and concluded it would be cost competitive on a per-MWh basis with a comparable addition of natural gas capacity. But, it would keep $260 million otherwise spent for the plant and fuel in the community and avoid $80 million in transmission costs and $30 million in power interruptions.
It would also save San Franciscans 15 million gallons of water per year and offer $200 million in community economic impacts, $10 million for site leases, and $100 million in local wages for 1,700 job-years of local employment, according to Clean Coalition.
Taking it to the city
More recently, SCE asked Clean Coalition to do a survey of its two substation Preferred Resources Pilot (PRP) area. It is, SCE reported, a transmission‐constrained area of the utility’s service territory “directly influenced by the closure of the San Onofre Nuclear Generating Station in 2013.”
The multi‐year pilot is aimed at exploring the use of “preferred resources” — energy efficiency, demand response, renewables, and energy storage — to meet load and reduce the need for new conventional generation. It also targets, according to the utility, “informing the development of the grid of the future.”
Clean Coalition was asked to identify commercial-industrial sites suitable for solar arrays of 500 kilowatts or more.
They did a rigorous assessment of rooftops in the area, using Google Earth so they could “see the roofs from the top,” Thomson said. It was a deliberate, block by block study. Google Earth tools allowed them to calculate the square footage of each roof.
“We looked at the size, shape, and clutter of each rooftop and parking lot in the area and characterized them as capable of hosting a high, medium, or low density of solar panels,” Thomson said.
They double checked with local solar developers on assumptions like watts per square foot for the different types of roofs, Thomson explained, because software tools like Helioscope and SolView, designed to streamline such assessments, “are not there yet” for this purpose.
SCE provided an overlay of its feeder system in the area so they could estimate feeder proximity at each site. That is very important, Thomson explained, because if a location’s feeder access is complicated the cost and time of obtaining an interconnection goes up.
They identified more than 160 MW of new solar PV technical potential on rooftops, parking garages, and parking lots in the PRP area. SCE published the findings to allow developers to see where the best opportunities are.
SCE did not ask for the DER optimization or the cost-benefit analysis that would normally follow the Solar Siting Survey, Thomson said. And the utility also did not ask for the local potential of other DERs. “Solar will always be a part of it but every community is going to have a different local DG mix,” Thompson said.
Optimization would include consideration of the local load, its shape, and its peaks.
“We marry that grid profile with the DG opportunity to get to how much DG can be supported with little cost," he said.
When possible, Clean Coalition’s assessment would also include not only feeder proximity but available feeder capacity. That information strongly influences which sites are selected as optimal.
SCE asked what PPA rates would attract developers, Thomson said, and that comes down to how easy it is to connect the site to the grid.
“If a high potential solar site’s feeder is at capacity, it will be harder to add,” he explained. “The interconnection process can be costly in dollars and in time so any project that looks easy will get pursued first.”
The cost for Clean Coalition’s analyses depends on the area the utility wants surveyed and the level of detail it wants. “The methodology is very specific and there is no guesswork,” Thomson said. “What drives the cost is what area we are looking at and how deep we are going.”
The benefits for utilities
Utilities can use this kind of analysis to drive renewables growth in their communities, to develop their own systems and sites, or to build community shared solar, Thomson said. Clean Coalition recently worked with the City of Palo Alto’s municipal utility to identify viable sites for solar on city-owned parking structures and helped structure their RFP.
“That kind of community benefit is a small example of what a utility can and should do,” he said.
About 30 MW of the commercial-industrial solar in the Hunters Point system was interconnected at the PG&E substation so the generation could be shared with other customers on other feeders that also connected at that substation.
“It is a community solar model done from the broader system view and from the utility view,” Thomson said. “Any local Target or Wal-Mart or storage facility or shopping center could benefit immensely from participating in a solar program and sharing that generation locally. Imagine the marketing potential.”