Net metering is a billing arrangement between a utility and a solar energy system owner where excess electricity generated by the solar panels is sent back to the grid and credited to the owner's account. This allows solar energy system owners to reduce their electricity bills by using the grid as a virtual battery.

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In a residential or commercial solar energy system, net metering works by installing a bi-directional meter that can measure both the amount of electricity the solar panels generate and the amount of electricity the property consumes. When the solar panels generate more electricity than is being used, the excess electricity flows back to the grid, and the bi-directional meter credits the owner's account.

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The payment for overproduction during net metering varies depending on the utility and state regulations. Some utilities may pay the solar energy system owner at the end of the year at the wholesale rate of electricity, while others may credit the owner's account at the retail rate.

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The true-up period refers to the annual reconciliation of a solar energy system owner's electricity bill at the end of the 12-month billing cycle. During this period, any net excess generation (NEG) or net surplus generation (NSG) is either carried over as a credit or purchased by the utility. The exact details of the true-up period can vary depending on the utility and state regulations.

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In the case of PPL Electric, which serves customers in Pennsylvania, the true-up period occurs in May of each year. During this period, any remaining credits from the previous year will be paid out to the customer at the current retail rate for electricity. If the customer still has a credit balance, the credits will be carried over to the next billing cycle.

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It's worth noting that net metering policies and regulations can vary by state and utility, so it's important to check with the local utility to understand the specific rules and requirements for net metering in a particular area.