In a common PV design, the engineer uses the PSH (peak sun hour) of the place, to estimate the energy from the PV module during a day, month or year. But the PSH obtained from GHI (global horizontal irradiance) in a place, dont take into account the ambient temperature correction, because at a certain irradiance and temperature, the PV module adquire a temperature higher than the STC. If we know a global temperature correction factor to apply in PSH, the calculation for the design must be easier than the value obtained with complex calculations or more reliable than the value obtained with the simplest calculations. If someone knows a previous work related with a global correction factor, please advice me with the refferences to search it. Thanks in advance. I am trying to obtain this factor with measurements and equations if someone is interested in work and share with us, is welcome. Best regards,
The approach that you mention seems rather crude. Why not use a PV system simulation program using actual local irradiance and temperature timeseries?
Jethro, the problem is that in som elocations the data of irradiance doesnt exist with precision and only the mean peak sun hours of the month are available. The problem is that in the basic PV designs (home and commercial applications), the engineer only take into account the PSH to establish the size of the PV system, but the calculation may be wrong by the differences caused by the temperature effect. I am trying to establish this correction factor for this kind of application. I am conscious that in big scale PV application is insane this approximation, because the planning take into account the dairy variations of irradiance, temperature, wind speed, etc. But in small size applications the commercial engineer and design engineer work with the minimun data. Best Regards.
If I understand correctly you are know using an equation like :
E_out= P_nom * PSH * f_tilt * n_inv
with E_out: electrical energy output; P_nom: nominal power output of the modules; f_tilt: tilt factor to account for the irradiance gain of tilting the modules; n_inv the inverter efficiency. You want to multiply the right side of the equation with a temperature factor (f_T) to account for the loss of efficiency for temperatures above the STC-temperature (and gains for temperatures below STC).
f_T will depend on the module type , the way the modules are mounted and the local climate.
I can suggest three approaches:
APPROACH 1
Search the scientic literature with google scholar with the search phrase: "photovoltaic system temperature losses Mexico". Repeat for a country with a similar climate if you do not find anything. f_T will be simply (1-relative temperature loss). Be carefull to use data from the right module and mounting type.
APPROACH 2
If you want to calculate f_T yourself from weather data here is the recipy:
Find a temperature and irradiance timeseries (at least one hr resolution) somewhere in your climate zone. For example from the Baseline Surface Radiation Network (BSRN) database. If you can find windspeed data even better.
- Calculate the module temperature timeseries using for example the simple iNOCT model or more advanced models like Fuentes or Skoplaki.
-Calculate the module efficiency timeseries using the temperature coefficient from the module specs
- Calculate the power output timseries by multiplying the efficiency of the previous step with the tilted irradiance. Integrate to get the energy output e_temp_cor
-Calculate the nominal power output timeseries by multiplying the nominal efficiency with the tilted irradiance. Integrate to get the nominal power output e_nom.
- your correction factor is f_T=e_temp_cor - e_nom
-Hope that f_T is valid for a larger region or, better, calculate it for different locations and see how strongly it varies.
APPROACH 3
Einstein said: Things should be made as simple as possible, but not simpler.
Reconsider proper simulation. Your approach will generally overestimate the yield. Not just because of temperature losses, but the efficiency of the solar panels also depends on the irradiance, the inverter efficiency is also not constant, and depending on the sizing of the inverter some parts of the irradiance will not be used.
Here in Germany PV simulation software is regularly used by PV system installers and financial people, even for small systems. So apprently the little bit of extra work is considered to be worthwhile.
An overview of free irradiance data that you could use as input can be found here:
http://www.soda-is.com/eng/education/other_solar_data.html
and here:
http://photovoltaic-software.com/solar-radiation-database.php
The companies pvgis and 3tier provide worldwide data on a commercial basis.
Good luck,
Thanks you very much, Jethro Betcke. Very clear your explanation.
Dear Martinez,
I find your work very interesting, i would just like to contribute with my Added link to this estimate pv.
http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php
I would like to work on prediction of pvgis and Solar Global Irrdition using ANN in specific regions.
Best regards
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