Is there a way of getting the PTC if not listed on CSI?

[coachpete]

Interested in a new thin film solar pv module from Germany. The panel is not yet listed on the CSI approval page. Also their data (Cut) sheets do not have their PTC listed. Is there another source for finding the PTC on a module that has applied and is waiting to be included in the CSI????

[Mike90250]

PTC can be derived from STC. I don't know the exact formula . It might be -10% of the STC or something. Find a couple of other panels, and see what the ratio is.

[Sunking]

PTC can be derived from STC. I don't know the exact formula . It might be -10% of the STC or something. Find a couple of other panels, and see what the ratio is.

I was about to say the same thing. PTC is in the range of 80 to 90% of STC. Use 85% and you should be close.

[coachpete]

A little confused

Hey Guys,

Thanks for your imput... However I am a little confused by your responses.

STC stands for Standard Test Conditions which are 1,000 watts per square meter solar irradiance, 1.5 Air Mass and 25 degrees C. cell temperature. STC are indoor factory test conditions. ?

Whereas PTC stands for PV USA Test Conditions which were developed at the PV USA test site at Davis, California. PTC are 1,000 watts per square meter solar irradiance, 1.5 Air Mass, and 20 degrees C. ambient temperature at 10 meters above ground level and wind speed of 1 meter per second.

When I am doing my Efficiency calculations on a module I need the accurate PTC for the module. I then divide the PTC by the Sq.Ft. of the panel and this gives me a 100% accurate efficiency rating.

The PTC is not a percentage of the STC. It is a calc! ???? I am a little confused... Help me out... Thanks in advance.

[coachpete]

Hey guys,

Since I am right down the road from Cal Davis I delved a little deeper into thier PTC calcs that are available to me.... this is what I found: Now I understand... THANKS...

A big smile to you.

"PTC is more like "real-world" conditions but does not factor in dust and dirt, module mismatch, DC and AC wire losses, actual inverter efficiency, and electric storage efficiency if you have batteries.

The higher the cell temperature which is perfectly normal in the real world results in the lower power. Silicon crystal cells average about 30 degrees C. above ambient temperature in the real world and cell voltage drops as temperature increases (amps change very little). Volts times amps equal watts which is power. Thus, a module's power output in the real world is lower than its power when measured in the factory where cell temperature is controlled to 77 degree F. (25 C). A rough rule of thumb is deduct 10% from STC for single crystal PV, 12% for polycrystalline PV and 5% for amorphous silicon PV. For example, a 150-watt polycrystalline solar module in bright sun may only put out 132 watts DC and 120 watts AC.

Real-world AC factors in solar array temperature loss (5% to 12%), dust and dirt (2% to 4%), module mismatch (2%), DC and AC wire losses (2% to 3%), real inverter loss (5% to 15%) and electric storage loss if you have batteries (15%). Well designed batteryless PV systems usually have a DC STC-to-real-AC conversion efficiency of 75% to 80%. Well designed battery PV systems usually have a DC STC-to-real-AC conversion efficiency of 65%."

[Mike90250]

Well designed battery PV systems usually have a DC STC-to-real-AC conversion efficiency of 65%."

I think that 50% - 55% is closer to real life, when using flooded batteries.

[Sunking]

Real-world AC factors in solar array temperature loss (5% to 12%), dust and dirt (2% to 4%), module mismatch (2%), DC and AC wire losses (2% to 3%), real inverter loss (5% to 15%) and electric storage loss if you have batteries (15%). Well designed batteryless PV systems usually have a DC STC-to-real-AC conversion efficiency of 75% to 80%. Well designed battery PV systems usually have a DC STC-to-real-AC conversion efficiency of 65%."

Pete I think you are getting things a bit mixed up.

For grid tied systems the efficiency is around 77 to 80%, for a stand alone battery system using a PWM or shunt controller around 50%, and 65% if using an MPPT controller.

For example lets say you are going to build a stand alone battery system using a MPPT controller and you need 1000 wh per day, and winter insolation is 2 hours. You would take 1000 wh and divide by .66 so 1000 wh / .6 = 1500 wh. To find th esolar panel wattage divide the adjusted number by the sun hours so 1500 wh / 2 h = 750 watts. You would now know what size solar panel array to use. Really not much more to it than that.

Pro designers will fine tune it a bit more once the know distances and actual equipment specifications, but from a DIY POV that is as close as your going to get.

[coachpete]

Dereck,

Thanks... My above post came from CAL DAVIS...

IN a nutshell I simply needed the CALCS in finding a modules PTC

Your information however valuable, had nothing to do whatsoever with what I AM TRYING to ascertain... However I do appreciate and Thank your for your imput.

"And we wonder why a complex product like solar technology, with a two-year decision-making cycle that requires re-search, financing, permitting, and lengthy application forms, inevitably leads to consumer inertia and fall out!"

[DaveC]

PTC ratings changed last July. Instead of being a measured figure based on irradiance, temp, etc., it is now a calculated figure using the nominal operating cell temperature and the module's temp coefficient of voltage. Solar Professional Magazine (www.solarprofessional.com) had an article on this in their Oct/Nov '09 issue.