Solar Module Tolerances
Solar modules are rated using STC, Standard Test Conditions, and PTC, PV Utility Scale Application Test Conditions.
Most module manufacturers include their STC rating right in their part number.
For example, a BP SX3195 has an STC rating of 195. But BP also states in their literature that it has a +-9% tolerance.
What BP is saying is their 195 module may be a 195 -9% = 177.4 watt module.
Would you pay that much for a 177.4 module. Of course not. That is why they don't advertise it as a 177.4 watt module.
An interesting fact is that BP can't sell their +-9 modules under the German incentive programs or even under the California New Solar Homes Program. Since they can't sell them in some of the best markets, they are dumping them in markets with deceptive marketing.
Buyer Beware. Check your tolerances so you know what you are really buying.
