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9.04.2016

After the Storm: Why You Probably Didn't Have Power, Even if You Have Residential Solar

What started as a tropical depression, turned into a category one hurricane named Hermine by the time it made landfall southeast of Tallahassee this week.  Power was out for three days for the majority of customers.  Some are without power on the fourth day.  

Would having photovoltaic panels  have kept the lights on at your home?  In most cases, the answer is 'no.'

The vast majority of all solar systems, regardless of size, are designed to shut down during a utility power outage. Keeping solar power running is dangerous for utility staff working to restore grid power and solar-powered facilities are reconnected to the grid after an outage. Backup batteries or generators help solar-powered homes keep the lights on when grid power goes down, but these are expensive options for homeowners.  This issue can affect relatively larger commercial and municipal solar installations as well as homes with photovoltaic panels. 

Islanding is an option that refers to the ability for a PV system and the loads connected to it to be separated from the utility grid during outages so that no electricity could be fed into the grid and injure utility workers who are trying to repair down lines. If Tallahassee had full “islanding” capability with PV systems, many homes with solar could have remained with power.  If a cluster of solar existed, where residents were able to generate electricity and share it amongst themselves, then a small community could have remained powered up despite the storm [without consideration to potential damage to solar arrays from hurricane force winds or flying debris].

The concept of fully "islandable" PV systems do require specialized inverters along with battery banks that allow them to function off-grid. The battery bank not only provides for functionality at night, but it also establishes proper distribution during the daytime when the grid is down so that AC power can be delivered to a house (or houses). Called “Secure Power Supply,” these inverters can communicate with and draw electricity from the battery bank during a power outage.  Without a battery back-up, there are other inverters which provide small amounts of electricity that would be enough to handle small loads such as charging phones and laptops during the daytime, but not sufficient for air conditioning units or refrigerators.  

For more technical information about varying inverters, see: 
http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/getting-power-solar-equipment-when-grid-down#ixzz4JHxIDK5n

Diagram courtesy of North American Solar Stores
Groups such as the Sustainable Tallahassee Renewable Energy Advocacy Committee have been researching the concept of micorgrids as one way to allow solar panels to keep generating power during a blackout. A microgrid is a localized power grid that can be operated independently of the utility grid. This is an option where ample local power generation resources exist, and where smart inverter devices support switching between locally generated power and the grid.

Right now, in Tallahassee most neighborhoods don’t have enough solar panels or other sources of non-grid electricity to meet basic needs, and thus can’t yet support a microgrid. 

However, given our recent massive utility power grid disruptions caused by Hurricane Hermine, Tallahassee/Leon County may be motivated to install more local generation capacity. Eventually, this might be enough to harness into local microgrids that could keep the lights on when severe weather, wildfires, or other calamities temporarily knock the grid offline.

Realistically, community microgrids probably could combine several power sources in addition to solar photovoltaics with battery backup — especially fuel cells, wind turbines, or conventional generators fueled by natural gas or propane. 

When more solar exists right in a neighborhood, neighbors have more options — not simply to cut utility bills and greenhouse gas emissions, but to keep the lights on! 

Together with the decreases in costs of solar panels, recent changes in home mortgage financing policies through Fannie Mae may incentivize homebuyers to include solar installations, where feasible, at the time of home purchase. [http://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/fannie-mae-s-financing-solar-game-changer] Also, advocates across the US have suggested that community crowdfunding might substantially expand residential solar into rental and low-income housing.

With more homes and businesses with electric generating capacity through solar, the concept of community solar can come into play.  Under this concept, energy can be generated and shared (or sold) to others nearby.  Using the microgrid concept, pockets of neighborhoods that would ordinarily have experienced power outages because they are all tied to the same large grid would not be negatively affected.  

It's important to note that current regulations in Florida prohibit community solar in most locales and in every community serviced by investor owned utilities such as Florida Power & Light, Gulf Power or Duke Energy.  As Tallahassee has its own municipal utility, they are not governed by the same regulation and could amend their policies to allow for community solar in their service area.  It is conceivable that the micro-grid concept could be successfully adopted in Tallahassee and that it would help protect more of its citizens from large scale power outages in the next storm, which is certain to happen.  

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