Updated  July  2017

Solar modules lose energy when hot. They lose 4% to 5% for every 100 C rise from little above freezing, but not the 250 C that most believe. Here’s why. The evidence is from the industry’s own data. 

The solar industry’s Standard Operating Conditions (SOC) are not encountered in real life. They are akin to solar modules facing directly into the sun at 12 noon. And, furthermore, atop an equatorial mountain. On a cold mid-winter day.

There is no issue, as such, with the SOC standard for design and development. BUT that SOC output is used also for promotion and marketing.

Solar modules lose energy when hot

That SOC power output is at a claimed 250 C. That, at first seems reasonable, however not made clear is that 250 C is not ambient air temperature. It is the temperature of glass covered solar cells under a hot sun.  At 250 C ambient, those cells are at 470-490 C. As solar modules lose energy with heat, they have, as a consequence, already lost about 10% output.

Solar modules lose energy when hot – NOCT reflects typical usage

The solar industry does reveal that heat loss (and other losses). It is in the so-called Nominal Operating Cell Temperature (NOCT) specifications – that reflect typical usage. That NOCT, however, is only in the full technical specifications. And sometimes on the rear of the module.

Despite NOCT, most resellers and installers claim that 250 C relates to ambient temperature. (The proof that it relates to cell temperature is shown below.)

solar kyocera sign

                        The data panel of an actual ‘120 watt’  Kyocera module. Column 3 shows NOCT output as 87 watts. The cells are at 47 0 C. Pic: successfulsolarbooks.com

Solar reality – what it really is 

Typical solar module output in temperate climates is about 71% of that seemingly claimed. If used via a genuine MPPT solar regulator, however, it is likely to about 78%-80%. 

The solar industry justifies all this as ‘traditional trade practice’. So, nevertheless, it can be argued, is thieving in the burglary trade.

Solar reality – amorphous modules

So-called amorphous solar modules are far less affected by heat. Most are, however, less electrically efficient, They are consequently larger per watt. Some are available in flexible form. This is handy for mounting onto curved roofs etc. 

For those interested fuller details are included in my (ongoingly updated) books Solar SuccessSolar That Really Works! and Caravan & Motorhome Electrics

Every aspect of solar for homes and properties is covered in my constantly updated Solar Success. That for boats, cabins and TVs is covered in Solar That Really Works!Caravan and Motorhome Electrics is also used in training courses and by auto electricians. 

Please see also our associated website: caravanandmotorhomebooks.com.  It has over 80 RV-related articles.

This article is copyright (2017) successfulsolarbooks.com