Solar Panel Efficiency Ratings

Solar panel efficiency is vitally important if you live in an area like Ontario, Canada where long, sometimes harsh winters are the norm. You want to generate the most power you can during the hours of daylight.

But, you NEED TO KNOW the 3 rating systems that are explained in this article to be sure of getting solar panels with the best efficiency ratings.


Choosing High Efficiency PV Panels

Installer Testing For Solar Panel EfficiencyInstaller Testing for Solar Panel Efficiency
(Source ©123rf.com/Temistocle Lucarelli)

You might even be wondering whether photovoltaic (PV) panels are practical for your house location. Days or weeks of cloudy weather and snow flurries hardly seem compatible with an electrical power system that relies on sunlight for its power.

However, PV panels have benefited from much innovation and progress in solar technology during the past decade, and solar panel efficiency has increased.

A modern, high efficiency solar panel can easily generate electricity even on cloudy, rainy, or snowy days, even in a northern country like Canada. Harvesting energy from sunlight IS practical for your home!

How Solar Panels Are Rated

You might want to read the following information twice, as you need to be crystal clear on the subject of solar panel ratings when shopping for PV panels. The rating advertised by the manufacturer might not be the most stringent one by which to judge a panel's performance.

There are 3 rating systems you need to consider when choosing a high efficiency solar panel:

1. PTC Rating

The PTC rating system measures PV (photovoltaic) output under specific conditions such as amount of direct sunlight, air temperature, wind speed, and elevation, so that solar panel efficiency can be accurately measured and compared.

PTC is a standardized rating system that was developed as part of the PVUSA (Photovoltaics for Utility Scale Applications) project to create standardized test conditions for comparing photovoltaic system performance.

2. STC Rating

STC (Standard Test Conditions) is a rating system that's often used by solar panel manufacturers to describe their product. While STC uses the same variables as the PTC rating system, such as amount of direct sunlight, air temperature, wind speed, and elevation, it uses slightly different numbers in its formula.

STC ratings tend to be higher than PTC ratings and are considered to be less representative of the panel's actual performance.

3. Minimum Warranted Power Rating

Though PV panels are manufactured to produce a given number of Watts (a measurement of how much electrical power is available for use), they can never deliver 100% of their advertised power because of unpreventable power losses.

Such power losses result from naturally occurring factors such as electrical resistance caused by transmission through the wires and inverters, extremes of temperature, and the effects of dust, dirt, and snow on the panel's surface.

After these types of losses are factored into a panel's performance, the manufacturer will advertise the Minimum Warranted Power Rating that they will guarantee for the solar panel.

How to Compare Solar Panels

PTC versus STC Ratings:

Use the PTC rating as your standard for comparing solar panels. Do NOT compare PTC values with STC values; that would be like comparing apples to oranges. A solar panel's PTC rating is generally lower than its STC rating because PTC factors are more stringent (lower air temperature, and so on).

As a comparison example, a 185 Watt solar panel manufactured by Brand A might have a PTC rating of 165.9, and a similar PV panel manufactured by Brand B might have a PTC rating of 163.7. Brand A could be expected to have a slightly better performance than Brand B. The difference might not seem large, but in an array of 50 PV panels it could be significant.

So, when comparing solar panels, use the PTC rating, the higher the better, and consider the manufacturer's Minimum Warranted Power Rating, the higher the better.

If neither of these efficiency classifications appears in the manufacturer's advertising, request the manufacturer's specification sheets to make sure you are getting the best solar panel efficiency for your hard-earned money.

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