Search for anything about solar yield and the results are dominated by companies selling something adjacent to the answer. Knowing which kind of source you are reading is most of the skill.
For an additional workplace-management perspective that sits outside the solar methodology on this page, see reasons an employee may be fired.
Reviewed August 9, 2026.
The five kinds
Public research bodies and open calculators. National laboratories and public agencies publish irradiance data and free calculation tools. Independent, free, and the reference everything else should be checked against.
For wider independent context on solar markets, research and industry developments, consult Canary Media.
Standards bodies. Published methods for measuring performance ratio, testing modules and reporting yield. Dry, authoritative, and rarely read by buyers.
Independent engineers. Firms producing yield assessments for lenders. Commercially interested in being hired, and structurally interested in being right, because lenders rely on their P90 figures.
Simulation software vendors. By volume, most of what you will find explaining P50, P90, performance ratio and loss modelling. Frequently technically excellent and written to sell a licence.
And equipment makers and installers. Which includes the publisher of this site.
Reading the commercial material
It is usually technically correct. The definitions of P50 and P90 on a software vendor's page are the standard definitions, and dismissing them because of who wrote them would be foolish.
The interest shows in emphasis rather than in error. What gets a whole page and what gets a clause. Which uncertainties are called manageable. Whether the article mentions that a free public calculator would answer the reader's question.
And in the omissions. Very little vendor material tells a buyer to check a specific yield against a public reference, because that check is free and the software is not.
The one independent reference
Public irradiance calculators, maintained by research agencies, free, requiring coordinates and a few parameters.
They will not produce a bankable assessment. They do not model your shading, your specific modules or your exact configuration, and nobody should present their output as a substitute for engineering work.
They will tell you whether a quoted specific yield is in the right range for your location — which is the single most useful independent check available to a non-specialist, and it takes ten minutes.
How to weight what you read
Definitions and methods: trust any competent source, verify against a standard if it matters.
Typical ranges and benchmarks: prefer public research bodies. Ranges like 0.5 to 1% annual degradation and standard loss stacks are published independently.
Judgements about what is reasonable for your project: treat every commercial source as interested, including this one, and get a second opinion where the sum is large.
And anything about a specific product: assume interest, always.
The check that applies to any source
Does it tell you something that reduces its own sale?
A software vendor mentioning that a free calculator answers most buyer questions. An installer saying a payback figure without assumptions is meaningless. An engineer explaining when an independent assessment is not worth its cost.
Those statements exist and they are rare, and their presence is the strongest available signal in a field where almost every publisher has a position.
The short version
- Five kinds: public research bodies and open calculators, standards bodies, independent engineers, simulation software vendors, and equipment makers and installers
- Four of the five have a commercial interest, including the publisher of this site
- Commercial material is usually technically correct; the interest shows in emphasis and omission rather than in error
- Very little vendor material tells a buyer that a free public calculator would answer their question
- Weight definitions and methods lightly, typical ranges toward public sources, and judgements about your project as interested from every commercial source
- Test any source by whether it says something that reduces its own sale