1. What is the minimum warranted power rating of the solar panels that the dealer/installer is trying to sell you ?

Many manufacturers claim that they offer high efficiency solar panels. A few relatively new manufacturers even claim that they offer the highest efficiency solar panels on the market, but some of them fail to emphasize how much power their panels are actually guaranteed to produce.

A solar panel manufacturer's claim of having a high efficiency rating can be worthless if the solar panel has a poor minimum warranted power rating.

Most consumers are not aware of the fact that the power rating or "name plate rating" of a solar panel may not match the actual power that the solar panel will produce. In other words you could for instance be paying for 215 Watt solar panels and only be getting 197.8 Watt solar panels !

The discrepancy is known as "peak power tolerance", "minimum power max", "minimum warranted power" or "negative tolerance rating". When shopping for solar panels, what you want to look for is the highest minimum warranted power rating or the lowest negative tolerance rating.

What all this means is that the solar panel manufacturer offers a warranty that states that their solar panel's actual power rating will not be less than a certain amount out of the box. So if a 215 Watt solar panel has a negative tolerance rating of 8% then their 215 watt panel is guaranteed not to have a power rating of less than 197.8 Watts right out of the box. In our opinion 10% or even 8% is not so great when you consider that other solar panel manufacturers have a negative tolerance rating of only 5% (A lower negative tolerance percentage rating is better)

Here's an example that's easier to understand:

Car manufacturer A. (A relatively new company) claims that they manufacture the highest fuel economy car on the market at 80 miles per gallon and costs $25,000.00, but in their fine print they only guaranty that their car will get 72 miles per gallon (A 10% discrepancy). 

Car manufacturer B. (a well established company) claims that their car offers 78 miles per gallon and costs $22,000.00 but guarantees that their car will get no less that 74.1 miles per gallon. (A 5% discrepancy).

Obviously car manufacturer B offers the better buy with better guaranteed mileage at a lower price. 

Smart Tip ! When shopping for a solar electric system, never allow a salesperson to simply quote you their solar panel's minimum warranted power rating. Always insist on seeing the solar panel's factory printed specification sheet and look for the minimum warranted power rating, because that's all the power that you're guaranteed to produce. If the solar panel's specification sheet doesn't list the panel's minimum warranted power, be very, very cautious. The manufacturer may be trying to hide something ! Click here for more information on warranted minimum power.