Monday, September 7, 2020

Solar Farms in Virginia need Stormwater Management Plans

This summer Governor Ralph Northam officially launched Clean Energy Virginia, to push investment into renewable energy and help meet the Commonwealth’s of "100 % of Virginia’s electricity from carbon-free sources" by 2045. The Act requires Virginia’s two largest energy companies to construct 16,100 megawatts of solar and onshore wind power. If we learn from the experience in other locations we can avoid some of the problems they’ve faced and potentially avoid new ones.

In 2018 renewable resources generated less than 7% of Virginia's electricity, so we’ve got a ways to go. Biomass fueled more than 4% of the state's total electricity net generation and hydropower supplied nearly 2%. All renewable biomass sources emit carbon. Virginia does not have any wind-powered utility-scale electricity generation, yet . A test project, Coastal Virginia Offshore Wind, is to come on line this year in federal waters 27 miles off Virginia Beach. Virginia does have some solar power. Although solar PV electrical generation is less than 1%, it doubled in 2018. The largest share of solar PV generation in Virginia is provided by utility-scale facilities built in the last several years. So we will look at those.

An example of utility scale solar facility is the Remington Solar Power Facility developed as a public-private partnership with the Commonwealth of Virginia and Microsoft in 2017. The 20-megawatt project was built on approximately 125 acres of land acquired and owned by Dominion Energy near its Remington Power Station in Fauquier County, Virginia. The 125 acres is covered with almost 236,000 photovoltaic panels that at peak capacity can generate enough electricity to provide power for 5,000 homes.
from Dominion 
Though some of the 16,100 megawatts of solar and onshore wind power will undoubtedly ultimately be wind power, for the moment we will ignore that since only limited number of on shore locations in Virginia had high enough wind potential to support wind turbines. 

Doing a back of the envelop calculation 16,100 megawatts of solar PV generation would require 905,625 acres of land covered with 1,709,820 photovoltaic panels. According to the Farmland Information Center Virginia contains a total of 25,929,900 acres of land much of the land is covered with roads, towns, houses, federal facilities, state parks, and businesses. The only truly open land is agricultural and forested land. There were 8,184,600 agricultural acres in Virginia in 2016; however, 2,812,000 acres of that land was woodland. So that leaves 5,372,600 acres of crops or pastures in Virginia. In the all solar scenario the Commonwealth proposes to cover almost 17% of that land with solar panels (or a lesser amount and a portion in wind turbines). I will leave it to others to estimate the impact to food resources in Virginia instead look at other impacts.

Virginia is a wet state. It averages about 46 inches of rainfall a year, but in the last three rain years we’ve had more than 50 inches each year in Prince William. To a large extent we depend on our groundwater for drinking water supply. More than 25% of all drinking water in Virginia comes from groundwater. A solar farm has hard surface coverage over much of the land and can change the hydrology if the water resources and groundwater recharge are not part of the planning process.

When you convert agricultural field to a solar farm, land that would be open for stormwater infiltration and see minimal disturbance until planting is converted to a site that requires year-round accessibility by machines and workers during construction and operation. Solar arrays need maintenance and snow removal. Solar arrays cause concentrated or sheet flow to develop when it rains, though the hard surfaces may be discontinuous with solar panels arranged in rows; nonetheless the velocity of the stormwater increases. Even when there is vegetated surfaces (post-construction) in the dripline of each row, stormwater management and slowing the flow of the stormwater to encourage infiltration and reduce sediment flow must be planned carefully to maintain site hydrology after installation of a solar project. 

The key issues are the amount of hard surface and change in water infiltration and the amount of stormwater and sediment runoff and subsequent impact on surface waters. In many instances, stormwater management is not required under existing regulations. However, based on others' experience in other wet locations, stormwater management would be required to maintain the health and recharge of the watershed especially during design and construction to account for the changes in stormwater flow. In stressed groundwater basins, increasing hard surface coverage should be carefully considered before damaging the water recharge to our essential aquifers. Let’s not run out of drinking water because we decarbonized the power grid.

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