Getting to high levels of PV usage is desirable, given all the benefits that solar offers, but it also presents challenges.
Those challenges are not insurmountable, however; upgrades to technology and updates to how electricity is bought and sold can help make increasing levels of solar penetration possible.
One challenge for rooftop solar is that having power flowing from customers, instead of to them, is a relatively new situation for utilities. Neighborhoods where many homes have adopted solar can approach a point at which the rooftop systems can produce more than the neighborhood can use during the day. Yet “feeder” lines that serve such neighborhoods customers may not be ready to handle flows of electricity in the opposite direction.
Large-scale PV projects face their own challenges in that they can be located far away from urban centers, often requiring transmission lines to carry the electricity to where it will actually be used. This requires investment in building the lines themselves and results in “line losses” as some of the energy is converted into heat and lost.
The variability of solar generation associated with PV at both scales presents new challenges because grid operators cannot control the output of these systems with the flip of a switch like they can with many non-renewable power plants. The amount of generation from PV systems depends on the amount of sunshine at any given time. When clouds block the sun, generation from a solar array can drop suddenly.
Conversely, on particularly sunny days with high amounts of solar on the grid, if the output from non-renewable energy power plants is not reduced to allow for the solar generation, electricity supplies could exceed demand. Both situations can lead to instability on the grid.
But the issues associated with adding more PV to the grid are eminently solvable. Fixes to the transmission and feeder issues are largely economic, not technical. And variability challenges are well understood in part because grid operators already manage fluctuations caused by constantly changing electricity demand and drops in electricity supplies when large power plants or transmission lines unexpectedly fail.
Much of the variability inherent in solar generation is also predictable and manageable, and can be handled in several ways including:
Overall, renewable energy sources including solar help to stabilize and make the electricity system more resilient, both economically and environmentally.
Original Arctle: Union of Concerned Scientists: http://www.ucsusa.org/clean-energy/renewable-energy/