Solar Renewable Energy Credits (SRECs)
SRECs are an additional way to make money from solar installs, that is completely separate from getting paid for the energy. It is the credit for being a renewable energy generator, and there is a market for that because utilities are trying to avoid the fines from not generating enough renewable energy. These have been available for years in other states, and just became available in Virginia due to the Virginia Clean Economy Act.
Solar United Neighbors does a great job describing SRECs.
There are several aggregators who will buy your SRECs, who have good descriptions of SRECs: