Michael Jacobs, of the Union of Concerned Scientists, explains the advantages of clean energy microgrids — and the obstacles to making them more common.
This is the season in the Northeast U.S. for power outages. Severe weather caused widespread damage to the electric power system during Hurricane Sandy in 2012, and early snow caused significant problems in October 2011. Grid resilience and mitigation of power outages have been significant topics since these events. The Union of Concerned Scientists just released a report documenting how electricity infrastructure along the East and Gulf coasts is highly exposed to storm surge and coastal flooding from a major storm today, and how rising sea levels due to climate change mean the risks of power outages from storms are also rising.
The significant impacts of power outages are driving interest and technology innovation to provide electric power in a sustainable manner, even when the grid is damaged. An approach that’s growing in popularity and is becoming increasingly cost-effective is to combine solar plus storage to provide this added layer of reliability. While creating a redundant electricity supply is an expensive undertaking, it may be that microgrids built for reliability are a key step in deploying energy storage for the electricity distribution system.
Hybrid grids, like hybrid cars
I described in an earlier blog post the greater complexity of powering a home or set of buildings in a microgrid compared to adding batteries to a hybrid or all-electric car. Continuing the analogy of cars to resilience for electric power systems, every car has a battery in it to start the car, and support the electronics. The battery has a small, though important role in running the car. In a house, the analogy might be the batteries in flashlights, cellphones, and laptops. These things will work in their own limited way, for a limited time if the main power supply for the neighborhood is knocked out.
A hybrid car puts a larger battery into the drivetrain, making additional power available to supplement the primary gas-powered engine. At my house, and at three-quarters of a million of others, a set of solar panels makes additional power available to supplement the primary supply from the central grid. As with the original hybrid cars that don’t operate in electric-only mode, the supplemental power won’t run my house on solar when the grid is down.
Setting up a microgrid for the house, or a small campus of buildings, to run when the grid is down requires a lot more planning. Just as we have seen earlier and wider use of hybrids before all-electric cars started to become popular, there are obstacles that must be overcome to set up a microgrid using solar plus storage.
Solar has advantages
The advantages of a back-up power system using solar plus storage come from the advantages of solar over diesel or gasoline.
First, there is the challenge of fuel delivery. In the aftermath of Sandy, fuel deliveries to emergency generators were inadequate. The disaster hit so many at once, the contractors for fuel deliveries could not meet the demand. Storm damage flooded fuel tanks and interfered with fuel pumping, and even ships coming to the harbor with deliveries of bulk fuel. Reportedly, over 50 percent of diesel generators failed to start during the Sandy storm.
Second, because the marginal cost and pollution to run solar panels is zero (unlike diesel generators), the equipment can be used every day. The savings on energy costs from using the solar or the solar-plus-storage can pay for that equipment. Clean Energy Group recently released a study of this, describing the resilience benefits as a free or near-free addition to apartment buildings that have installed solar plus storage.
In those examples, the buildings remain connected to the broader electricity grid, and amortize their investments through the collection of grid-based revenue streams. When the centralized grid goes down, these buildings will rely on specialized inverters and energy storage to facilitate “islanding” from, or running in parallel to, the main grid.
That approach of using the solar plus storage everyday, while the grid is still functioning, is what sets this apart, and offers a path to both wider adoption of solar-plus-storage, and microgrids for resilience.
Still, there are complications
Where this all gets tricky is designing how to allocate the limited power supplied in an emergency. A microgrid has to contain enough energy supply to provide for the demand on that grid. When a house runs on an emergency generator, there is a selected subset of the electric circuits and uses that are going to be powered by the emergency generator. Same is true for a solar-plus-storage arrangement. Same is true for a microgrid supporting a fire station or water plants and an adjacent town building serving as an emergency shelter.
To make microgrids based on solar more common, the non-profit Clean Coalition is providing education and engineering on specific projects that will serve as models for enhancing resilience, increasing renewable energy use, and speeding the adoption of storage on the distribution system. As these slides illustrate, the deployment of microgrids requires an owner to determine the goals and scope of a microgrid, and define what additional assets need to be included, and then design an economic and functional deployment. The Clean Coalition seeks to standardize and simplify microgrid deployments.
We are at the stage where microgrid development can provide grid resilience to communities, but microgrid deployment is not so easy that we can say resilience is the“killer app” for solar-plus-storage.
This article first appeared in the Union of Concerned Scientists’ blog, The Equation. Author Michael Jacobs is a UCS senior energy analyst.