Net energy metering — the policy that has allowed distributed solar to flourish across the country — is under threat as utilities push lawmakers and public service commissions to rethink how distributed generators should be compensated.

Once a little-known policy that allowed a few customers to earn back a portion of the their investment in distributed generation technologies like rooftop solar, it is now the backbone of a fast-growing multi-billion dollar industry.

At its core, net metering allows customers to send power they generate, but don’t need, to the grid in return for credits to lower their electric bills when they do need power. In effect, it means a distributed generation customer is able to sell power at the full retail price, well above what any traditional generator receives.

As the distributed solar industry has grown, utilities have increasingly voiced concerns that the policy offers distributed generators too much value per kWh, resulting in cost shifts to customers without solar. But distributed solar supporters say the policy is crucial to adding new emissions-free solar PV to the grid and reducing environmental impacts. They also argue solar PV reduces the need for new utility infrastructure investments.

In state after state, policymakers, utilities, the solar industry and consumers are arguing over whether the policy should be changed or eliminated. While most states still support net metering, some have eliminated it and others are considering alternatives.