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Solar Installer GuildUnited States · independent

After it is on the roof

My solar system is producing less than promised. What now?

The short answer

First establish what was actually promised and on what basis: a production estimate is a model, and a shortfall can mean a fault, a shading assumption that was wrong, or an optimistic model. Gather a full year of monitoring data, compare it against the estimate in the contract, and raise it in writing with the specific numbers.

Work through it in order

  1. Find the production estimate in the contract and note what it assumed: system size, orientation, shading, and whether it was stated as a guarantee or an estimate.
  2. Gather at least twelve months of monitoring data. Seasonal comparison is the only fair one.
  3. Check the monitoring for individual panels or strings producing nothing, which points at a hardware fault rather than a modelling problem.
  4. Check what has changed: a tree that has grown, a new building, a soiled array, a failed optimiser.
  5. Raise it in writing with the numbers and the contract clause, rather than by phone.

Estimate and guarantee are different things

Some contracts include a production guarantee with a defined remedy; most contain an estimate with a disclaimer. Which one you have determines whether you have a claim or a conversation, and it is worth finding out before you start either.

Silent failures are common. A single failed microinverter or optimiser, or a tripped isolator, can go unnoticed for months if nobody looks at the monitoring — which is why the monthly check is worth more than any of this.

Also asked

Is some degradation normal?

Yes. Panels lose a small proportion of output per year, which is what the performance warranty describes. Gradual decline over years is expected; a step change is a fault, and the monitoring data distinguishes them clearly.

The long version

After the installation

Permission to operate, monitoring, what a workmanship warranty covers, and what happens if your installer disappears.

General information about solar and about hiring, not advice about your roof or your tax affairs. Incentives, net metering and contractor licensing are set federally, by state, and by your utility, and all of them change. The authority that publishes the rule is the current answer.