Adding more clean power to the grid will require utilities to redesign the network that delivers solar electricity locally. Utility Southern California Edison on laid out plans Monday to make its distribution grid more responsive to the fluctuating infusion of solar electricity throughout the day.
Specifically, SCE is investigating new inverter and distribution circuit designs that will help it incorporate more solar electricity, said Mike Montoya, director of grid advancement at SCE. An inverter is a critical component of a solar electric system that converts the direct current from the solar panels into alternating current, which is necessary for feeding the grid or for using the electricity on-site (appliances run on AC power). A circuit is a distribution line for connecting homes and businesses to the nearest substation, which receives electricity from power plants and modifies its voltage before sending it to customers. Each circuit serves 2,000 to 2,500 customers.
One of the big problems with solar electricity is that the amount of solar power produced fluctuates throughout the day, depending on time of day, amount of clouds in the sky, and location. These changes can cause significant voltage fluctuations that are run counter to a utility trying to run a grid smoothly.
Figuring out how to accommodate more solar electricity into the grid is a big challenge for utilities, particularly when many states require their utilities to add more renewable electricity into their power supply. California recently mandated that 33 percent of the electricity supply needs to come from clean power by 2020. Although renewable energy can come from wind, biomass, geothermal and others, solar is emerging to be a major source because it can be deployed in a variety of locations, from giant power plants in the desert to small systems on the rooftops of homes and businesses. California also runs an incentive program that encourage home and business owners to add solar.
SCE is carrying out a 500 MW solar program that will split solar generation evenly between systems owned and operated by SCE and those by independent power producers, who will sell the electricity to SCE. The utility on Monday said four new projects that fall under the utility-owned category have been completed. SCE leased the rooftop space of industrial buildings owned by Prologis to install four systems, which total 7 MW. SCE has built 15 projects, totaling 28.75 MW so far.
The growing installation of rooftop solar electric systems in cities also adds complexity to running the grid. A distribution network, made up of many circuits, has historically been designed for one-way transferring of power (from fossil fuel power plants to homes and businesses). With rooftop solar, the electricity that isn’t used onsite will flow from many spots at the termination points of the distribution network.
“The distribution has been around for 100 years. In a future with photovoltaics, we will need power going bi-directionally, with the power going back to the substation,” Montoya said.
What SCE – and other utilities – want to do is to make their distribution networks more responsive to voltage and other changes as more solar electricity enters the grid. One way to tackle this challenge is to design inverters so that the inverters can adjust the voltages more quickly, Montoya said. Inverter companies have told SCE that they can make it happen by changing the software that runs the inverters, Montoya said.
The SCE wants to make this voltage-response to feature a standard and is participating in technical standards-setting organizations such as IEEE and IEC. Adding a new standard generally takes a few years at least, however. Since the utility will see more solar energy installations in the meantime, it’s working with inverter makers to make the change for systems that will be installed in the SCE territory, Montoya said.
SCE engineers also are working on new circuit designs that will be more responsive to the flow of solar electricity. One project is looking at using capacitors that will act more like dimmer switches than on/off switches, said Gil Alexander, a SCE spokesman. Another project will look at connecting the circuits and sectioning them in ways that will make it possible for SCE to better monitor voltage changes, identify problems, and fix those problems without causing service interruptions to many customers, Montoya said.
Photo courtesy of Southern California Edison