One year cannot establish whether the estimate was right — below P50 has roughly a 50% probability by construction. It can establish whether the plant works as built, which is what year-one monitoring is actually for.
Operational performance depends on both equipment and repeatable human routines; for a separate workplace-management perspective, see self-reporting bias.
Performance ratio is the one number that separates weather from equipment, because it corrects for the irradiance actually received. Typical values sit in the high seventies to mid eighties, and the absolute figure matters less than comparison against the design prediction and against itself over time.
Five causes produce the same shortfall chart: the weather, an optimistic model, a build that differs from the design, a fault, and an operating omission. Separating them starts with getting the actual irradiance, which is the step everybody skips and without which every later step is guesswork.
For additional context on photovoltaic operation, maintenance and sector developments, consult CleanTechnica.
Monitoring has four blind spots. It reports inverter output rather than plant output, compares against nothing, uses modelled irradiance where it uses any, and cannot show gradual decline. A disconnected string appears as a slightly worse day, not as a fault.
Maintenance is low, not absent. Monthly numbers, an annual visual and thermographic inspection, connection checks, inverter housekeeping and vegetation control return more than they cost. Frequent cleaning in a wet climate frequently does not, and the two-month measurement settles it.
And inverter replacement is a capital event mid-life that most projections omit entirely.
The section also covers what a warranty claim needs and why claims fail on evidence and deadlines rather than on merit, the four ways to read your own production data and which finds problems earliest, and when adding capacity is cheaper than restoring it.
Cleaning
A cleaning contract is sold on recovered yield that is rarely measured. How to find out whether yours recovers anything.
Expand or Repair
Adding capacity is sometimes cheaper than restoring it. Four situations where that holds, and the constraints that stop it.
When Actual Falls Short
Five causes produce the same chart. A decision procedure that separates weather from model from plant, in order of cost.
Inverter Replacement
The capital event in the middle of the plant's life that most projections omit. When it arrives and what decides the cost.
Maintenance That Matters
Solar plants are low-maintenance, not no-maintenance. Six items that return more than they cost, and three that usually do not.
Making a Claim
Claims fail on evidence and deadlines more often than on merit. What to gather, in what order, and which counterparty to approach.
What Monitoring Misses
A dashboard showing green is not evidence the plant is healthy. Four blind spots, and the one check that reveals them.
Reading Your Own Data
Four views of the same data answer four different questions. What each reveals, and the one that finds problems earliest.
Performance Ratio
The one number that separates weather from equipment. What a normal value looks like, and what a declining one is telling you.
Year One
One year is a single draw from a distribution. What it can establish, what it cannot, and the four numbers to record.