Every solar panel gets a score from 0 to 100% built from six factors, and that score maps onto the 5-point rating shown on the site (a 0% score would be 1.5 stars; a perfect score, 5). Each factor is scored against fixed reference points, not against the other products in the list, so adding a new model never moves another model’s rating.
| Factor | Measures | Weight |
|---|---|---|
| Value | price per rated watt | 30% |
| Tested output | measured watts vs. rated | 20% |
| Portability | watts per pound | 15% |
| Durability | water resistance, warranty | 15% |
| Efficiency | claimed conversion efficiency | 10% |
| Features | kickstand, bifacial, USB, wiring | 10% |
Reference points by size
Small panels cost more per watt than large ones, so value is judged per size class. The other factors use the same reference points for every size.
| Size | Price per rated watt scoring 0 → 100 |
|---|---|
| Small, under 150 W | $4.00 → $1.20 |
| Mid-size, 150-299 W | $3.00 → $0.90 |
| Large, 300 W and up | $2.50 → $0.75 |
The factors
Value is the current lowest checked price divided by the rated watts (the front side only, for bifacial panels). Prices are checked by hand and dated on every page; a product with no current price gets the neutral middle score.
Tested output is the highest output independent reviewers measured from the panel in real sun, as a share of its rating. No panel makes its full rating outdoors for long, since the rating assumes lab conditions (see rated vs. real output), so 60% of rated scores zero and 90% scores full marks. When several reviewers have tested a model the best result counts, because a lower one usually says more about that day’s sun than about the panel. Manufacturer claims don’t count here.
Portability is rated watts per pound, so a large panel isn’t penalized for being heavy in absolute terms: 6 W/lb scores zero, 18 W/lb full marks.
Durability combines the water-resistance rating (IP67 and IP68 score full marks, IP65 most of them, no rating none) with the length of the warranty (1 → 3 years).
Efficiency is the conversion efficiency the maker publishes: 19% scores zero, 25% full marks. It carries a small weight because makers quote it inconsistently, some for the bare cells and some for the whole panel, and because efficiency already shows up in weight and size per watt.
Features add up a built-in kickstand, bifacial cells, USB ports for charging devices directly, and a stated ability to wire panels in series or parallel.
Missing data
If a figure isn’t published, that factor gets the neutral middle score (50) and the product page marks it as estimated. That keeps a product from looking worse than one with an average figure, but also from looking better than one with a good figure.
Estimating untested panels
Panels that haven’t been independently tested get an estimated output, also marked as estimated. Every panel falls short of its rating outdoors for the same reasons: heat, sun angle and haze. So what mostly separates one panel’s test result from another’s is how honestly its maker rates it, and that tends to run through a brand’s whole range.
The estimate starts from the median result of every tested panel in this category. It then moves toward the brand’s own results by one step for each of its tested panels, against two steps for the median. So a brand with one test sits a third of the way from the median to that result, and one with four tests sits two-thirds of the way. A brand with no tests gets the median. Until at least three panels in the category have been tested, too few to give a reliable median, untested panels get the neutral score instead. Estimates change as new tests are added, and a real test always replaces the estimate.
Ties and discontinued models
Products are ranked by score within each size. Discontinued models stay listed, since they’re still sold, but rank below every current model and can be hidden with the “Hide discontinued” filter.