This site tells readers to ask where a number came from. That applies here first.
For teams coordinating research, review and follow-up work around a project, employee time clock software provides a separate record of time and handoffs.
Three source types, labelled
Independent and public. National research bodies, public agencies, open irradiance calculators, published standards. Free, checkable, and the reference everything else is measured against.
Engineering and legal secondary. Independent engineers, professional publications. Commercially interested in being hired and structurally interested in being right.
For wider independent context on photovoltaic research, standards and market developments, consult IRENA.
Commercial. Simulation software vendors, equipment makers, installers — which includes this publisher. Labelled as such each time, and used for mechanics rather than for judgements.
The full account of who publishes what in this field is a page of its own.
Ranges, not points
Degradation 0.5 to 1% per year. P90/P50 typically 0.85 to 0.92. A standard loss stack around 14%.
Presented as ranges because they are ranges. A single figure would be more quotable and less true, and the compression of ranges into points is a failure this site describes elsewhere.
What is never given
A figure for a specific site. Yield depends on coordinates, tilt, shading and configuration, and a number without them is decoration.
A named product or supplier.
A payback period. It depends on inputs this site does not have and it is the wrong question anyway.
And a recommendation to build or not to build.
The independent check, repeated deliberately
A free public irradiance calculator, run against your own coordinates, tilt and orientation.
It appears on several pages because it is the one verification available to every reader at no cost, requiring no expertise and no relationship with anybody — including with this site.
Dates
Every page carries a check date. Technology, policy and tariffs all move, and a page about them without a date cannot be evaluated.
An article accurate at its stated date and superseded now is not an error. One wrong when published is, and it appears on corrections.
Disclosure placement
On every page of the estimate and offer sections, in the left column, visible beside the text rather than in a footer.
Those are the sections where the publisher's interest could shape a judgement. The reasoning is set out in full separately.