# Utilization Factor In solar panels

1. Jan 24, 2010

### bluffreggie

Hey all.

Im currently doing some research into renewable's and have come across a value known as U whose units are kWh/m^2.

The comment next to it simply states it as the utilzation factor. Now i've looked in several books and of course ovia the internet but i cant seem to find a meaning anywhere.

It is in regards to solar power. I need to find out firstly what it is and secondly how it can be calculated. Anyone out there have any idea?

Kind Regards

2. Feb 3, 2011

### d2blake

Where did you come across utilization factor? In regards to solar, I know this as the ratio of DC solar panels to AC inverter rating.
As for KWh/m^2, this is what is used to calculate the efficiency of a solar panel. Every location is different but for testing, 1KWh/m^2 potential solar energy is used. A solar panel is exposed to this quantity of energy and the amount of energy captured, along with the panels size, get its efficiency.
ie: if a solar panel is 1m^2 in size and captures 0.2KW over an hour when exposed to 1kwh/m^2, it is 20% efficient.

3. Feb 3, 2011

### Staff: Mentor

Sorry I missed this thread before: I'm pretty sure utilization factor would be the total amount of solar radiation to hit a spot on earth in a year.

4. Feb 3, 2011

### Topher925

The utilization factor is a ratio of the maximum load to the rated capacity of the solar panels. However, this is a ratio and does not have units of kWh/m^2.

I'm guessing that the author is referring to how much energy is generated by the panels per square meter on an annual basis.

I've always known this to be the capacity factor.

5. Feb 3, 2011

### Staff: Mentor

I was actually looking at the units more than the term (about which we agree). Googling the term doesn't give a lot of relevant hits, so I was thinking it isn't an industry standard term.

Capacity factor on the other hand is a standard term and is what you are describing as utilization factor!
http://en.wikipedia.org/wiki/Capacity_factor

The two would be related, of course. To get kwh/m^2, you multiply the capacity factor by the peak solar radiation.

Last edited: Feb 3, 2011
6. Feb 8, 2011

### thopsy

The utilization factor, U, is a very useful dimensionless parameter for designing solar thermal collectors. It should be dimensionless. Are you sure it was not multiplied by an Irradiation value (i.e. yearly irradiation), to give kWh/m2?

A good reference is Duffie and Beckman's "Solar Engineering of Thermal Processes"