Equation that calculate output power

System

Dear all,
I want to find equation that calculate power from the solar cell dependent on the temperature and insulation
Thanks in advance.

BB.

Re: Equation that calculate output power

Using data from this source:

Nominal Operating Cell Temperature: 45ºC±2ºC
Temperature Coefficient of Pmax: -0.34 %/ºC
Temperature Coefficient of Voc: -0.48 %/ºC
Temperature Coefficient of Isc: 0.017 %/ºC

Assume Ratings:

Standard Air temperature: 25ºC
Standard Solar Irradiation: 1,000 W/sq.meter
Panel Rating: 200 Watts

Ambient Air Temperature: Tamb
Solar Irradiation: Si

The equation below should work as an approximation. You can substitute your measured values (actual panel rating, cell temp measured vs ambient, etc.). Note the signs are important (-*-=+).

Power = 200 Watts * (1 + (25ºC-Tamb)*(-0.34 %/ºC)) * (Si/1,000 W/sq.m.)

-Bill

TnAndy

Re: Equation that calculate output power

BB:

Is there a meter to measure irradiation that doesn't cost an arm and leg ? I've often been curious as to "how good a solar day is today"....but I wouldn't want to sink a WHOLE lot in knowing....

thanks...

BB.

Re: Equation that calculate output power

There are several ways of getting an answer...

One is there are several moderately priced weather stations (LaCrosse and others) out there that have optional solar irradiance meters. Many come with a USB to PC interface for data downloads

Or, just get a small solar panel that is the same type as your "main panels" (i.e., silicon mono or poly crystalline) and measure the output current with a DVM (short the output with your amp meter). The output current is pretty porportional to the irradiance (over time and temperature).

In this thread "Jeff Fendison" offered on his website information on how to build your own irradiance meter (basically short the output of a small solar cell with a current sense resistor and a panel DVM)--and he also sells kits that will log the data over months just using a 9 volt battery and a usb dump to a PC.

http://www.microcircuitlabs.com/SIM.htm

I have not used any of his equipment or had any discussions with Jeff, but his kit/turnkey logger looks very reasonable.

In the end--you (TnAndy) have a Grid Tied Power system--and as long as everything is working OK--your system pretty much is logging the solar irradiance + temperature coefficient to a reasonably accurate number.

If you have logging software for your system--can it log Solar Array Current? That will be a much more accurate representation of Solar Irradiance vs the Array Power reading:

Temperature Coefficient of Pmax: -0.34 %/ºC
Temperature Coefficient of Isc: 0.017 %/ºC

A 10C (18F temperature offset) will affect Pmax by -3.4%. The same offset will only affect Isc (~Imp) by +0.17%

Both numbers are probably more accurate than you can expect from a "garden variety" GT Inverter's data panel readings (many systems seem to be off in the +5-+10% range--read more power than is really generated--The Xantrex, from what others have said, is probably closer to the +/- 1-2% accuracy range--"Nobody is unhappy when their system produces more power than nameplate" :roll: ).

Don't get too mired in the data and assume that you have better than ~10% accuracy unless you have done some calibration/conformations.

-Bill

System2

Re: Equation that calculate output power

hello,
i'm doing the research about the solar energy conversion.
where do you got this formula.
i'm trying to find power output from the solar cell from the internet, but can't find one.

BB.

Re: Equation that calculate output power

Can you give us more information on what you need?

The formula I provided is just a first approximation written in linear form based on how temperature of a solar cell affects its output power by using a temperature conversion factor from the panel manufacturer based on standard temperature and solar radiation levels.

It will break down at lower illumination levels--there is a parasitic resistor that becomes significant at lower power levels.

-Bill

RCinFLA

Re: Equation that calculate output power

See if this is of help.

http://www.pvresources.com/en/solarcells.php

System2

Re: Equation that calculate output power

i need the equation that have power as output and solar irradiance with temperature as input. diode voltage is not needed. it is the power output directly from the sun.

BB.

Re: Equation that calculate output power

This equation should work OK as a first approximation down to the point at where the tare energy requirement of the inverter will take 100% of the panel's energy to run the electronics (for my 3kW inverter and 3.5kW array, that is around 50 watts of panel output):

• Power = 200 Watts * (1 + (25ºC-Tamb)*(-0.34 %/ºC)) * (Si/1,000 W/sq.m.)

Just substitue the values for your panels (the above just plugged in 200 watts and -0.34 %/ºC for temperature. Assumed standard was 1,000 watts per sq.meter of "sunlight").

If you want real PSPICE Models (for electrical simulation)--those are available too. Just Google around for them.

-Bill

System2

Re: Equation that calculate output power

BB. wrote: »

Using data from this source:



Assume Ratings:

Standard Air temperature: 25ºC
Standard Solar Irradiation: 1,000 W/sq.meter
Panel Rating: 200 Watts

Ambient Air Temperature: Tamb
Solar Irradiation: Si

The equation below should work as an approximation. You can substitute your measured values (actual panel rating, cell temp measured vs ambient, etc.). Note the signs are important (-*-=+).

Power = 200 Watts * (1 + (25ºC-Tamb)*(-0.34 %/ºC)) * (Si/1,000 W/sq.m.)

-Bill

Hi there!

I am working on a master thesis in energy and i need to calculate the power from the PV, it doesn't matter what panel i use as long its a commercial panel that exist in the market. I have the data from a local weather station that gives the solar insulation (SI) and the air temperature, but what about the Tamb? you said that Tamb is the temperature of the cells vs ambien. since i don't have any actual panel i wouldn't know Tamb? Can I somehow calculate it only based on the air temperature? And if (25ºC-Tamb) give a positive value then (25ºC-Tamb)*(-0.34 %/ºC) give negative value and if the value is grater then 1 => the power will be negative. This cant be right!

Power = 200 Watts * (1 + (25ºC-Tamb)*(-0.34 %/ºC)) * (Si/1,000 W/sq.m.)

BB.

Re: Equation that calculate output power

The maximum rated operating temperature of a solar cell is usually around 80C (180F)...

• -0.0034 * (25C-80C) = -0.187

(note: 0.34% is 0.0034

So 1-0.187 = 0.793 or ~80% of STC (standard test conditions) rated power. This will not go negative as long as you are in the operating range of the solar cell... If the cell goes above rated temperature, it will fail at some point.

The assumed worst case cell temperature rise is ~35C over ambient (full sun, no wind, panel mounted against roof so poor air circulation on rear of panel).

I am sure you could model the cell temperature based on Watts/sqmeter of sun falling on panel if you need too (obviously, temperature rise is not 35C in the morning and evening times).

A quick way of measuring cell temperature is to use an IR gun (assuming glass panel is near cell temperature). Take a sample solar panel, short its output and measure the current (shorted output current is linear with respect to watts/sqmeter to within 5% without any other corrections-there is a smaller positive temperature correction for output current of a solar panel--if you want a bit better accuracy). And measure the ambient temperature, panel temperature during the day (once an hour?) and the panel current ((Imeasured/Ishortcircuit * 1,000w/sqm=~measured sunlight). You can curve fit a typical temperature rise based on w/sqm of sunlight for your needs/installation (or go through the physics of radiation on a flat surface and convective/radiative cooling).

Make sense?

-Bill