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“There are cheap panels which flat-out lie about power output.”
Photo Credit: iStock
A solar DIYer on Reddit thinks they may have spotted a red flag in the bargain-panel market.
Some low-cost solar panels appear to match their advertised wattage only when two test numbers are multiplied together — not when the panel is producing usable power.
For households hoping to cut utility bills with solar, inflated specifications can turn a money-saving upgrade into an expensive disappointment.
Using Victron controllers and dedicated panel watt meters, the original poster compared open-circuit voltage with short-circuit current during a solar-noon check under clear skies.
In a discussion on r/SolarDIY, the poster said the product of those readings matched the number printed on the panels.
“I just did a voc and short circuit current test and multiplied those two numbers and that answer is exactly the wattage they claim these panels are,” they wrote.
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That led the poster to question whether some off-brand manufacturers can simply print whatever output they want on the label.
In a follow-up, the poster argued, “No name brands use voc and short circuit current to generate the claims of their wattage output.”
Several replies steered the discussion toward the standardized conditions used for panel ratings rather than the OP’s theory alone. While acknowledging that poor-quality panels do exist, commenters said official specs are based on controlled testing.
“Panel ratings are established at STC (standard test conditions) which are 1kW/m2 irradiance, 25 degree C cell temp, and 1.5 atmospheric rating,” one commenter explained.
Another added, “The panel must deliver its rated power when the panel is at 25 C and it is illuminated at 1000 W/square meter.”
Outdoor solar performance can vary with panel temperature, sun angle, shade, and system configuration. One commenter said spec-sheet wattage often assumes a quick test at 77 degrees Fahrenheit (25 degrees Celsius), before heat buildup starts pulling output lower. Another said a panel can lose “.35% power per degree C” above that benchmark.
That means a 400-watt panel in hot conditions may reasonably produce less than 400 watts outdoors, even if nothing is wrong with it. At the same time, shoppers can still get burned by junk equipment that never had a realistic chance of meeting its labeled output in the first place.
The OP shared one painful example, writing, “The absolute max power i got out of that kit was 60 watts, and i bought several of them before i realized i got shafted.”
If a buyer pays for a 100-watt panel and only gets 60 watts, that amounts to a 40% shortfall.
Underperforming gear can lengthen the payback period and reduce monthly savings.
Most commenters said a quick Voc-times-Isc test, by itself, does not prove fraud and that judging a panel’s performance requires more than comparing it with marketing claims.
Datasheets, independent testing or flash-test results, and unusually cheap listings are areas to scrutinize. Even a small mismatch can add up quickly: If a four-panel system is 10% under spec, that is the equivalent of losing nearly half a panel’s worth of output.
As one commenter put it, “There are cheap panels which flat-out lie about power output.”
Multiple factors can influence a solar panel’s performance outside of discrepancies between advertised figures.
• EnergySage says interconnected factors shape what homeowners actually pay for solar installations.
• A solar expert said one persistent myth still distorts expectations about modern panel performance.
• Homeowners often learn the biggest myth about bill-slashing panels is simpler than advertised.
• Palmetto experts say misinformation about leasing keeps confusing buyers weighing rooftop solar deals.
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© 2025 THE COOL DOWN COMPANY. All Rights Reserved. Do not sell or share my personal information. Reach us at hello@thecooldown.com.

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