How does net metering affect solar system sizing?

Net metering is one of the most important policy factors in solar project economics because it determines what happens when your solar panels produce more electricity than your building consumes at any given moment.

Under traditional net metering, excess energy exported to the grid earns credits at the full retail rate — essentially spinning your meter backward. In this scenario, oversizing your solar system (within your roof's capacity) can still make financial sense, because every kWh exported has the same value as every kWh consumed on-site.

Under net billing or successor tariffs (like California's NEM 3.0), exported energy is compensated at a lower rate than consumed energy — sometimes significantly lower. This changes the sizing calculus. Once your system produces more than your building uses, the marginal return on each additional panel drops sharply. In these markets, the optimal system size is typically one that keeps the building from becoming a net exporter of energy over the course of a year.

This "net metering limit" is a key constraint in solar system sizing. It caps the array at the point where annual solar production roughly equals annual consumption, preventing the building owner from being in a position where they're exporting energy at a financial loss relative to what they paid to generate it.

The takeaway: before sizing a system, always understand your local net metering or net billing policy. It directly affects the maximum system size that makes economic sense, and it's one of the reasons two identical buildings in different utility territories can have very different optimal system sizes and financial returns.