Solar Fraction of a PV system?

[bernard]

Hello,
I am puzzled by something:
In thermal solar systems, a ratio of the system output and required energy is called: Solar fraction.

I was wondering, why doesn't the same name exist in Photovoltaics systems?

For example a house requires 10 000 kWh per year. A house has a PV system which produces 3000 kWh per year.
So the ratio of a PV system output and required energy:
3000/10 000 = 0.3 (30%).

What is the name of this 30% ratio? Is it called a Solar Fraction in Photovoltaics systems, the way it is called in Thermal solar systems too?

Thank you for the reply.

[Naptown]

The term would apply but because thermal systems are tested to a specific set of parameters. Based on a set mumber of gallons per day of use and water draws are timed throuoight the day SRCC determines the solar fraction based on inlet temp outlet temp etc.

[bernard]

Thank you for the reply Naptown.
But I am not sure I understand you.

[Naptown]

Go to the SRCC site and they will explain the test in more detail.
However the solar fraction is never correct in that mo two systems even if identical and next to eaxh other will produce the same fraction if the gallon per day use is different.

[bernard]

Thank you Naptown.

The SRCC deals with definition of Solar Fraction in solar thermal domain and those uncertainties related with its calculation you mentioned.

But that is not my question.

I wanted to know whether a similar term exists in the domain of Photovoltaics.
The term which defines the ratio of the system output and required energy.

In Solar thermal systems, we call it: Solar fraction.

How do we call it in Photovoltaics systems?

[Naptown]

In short percentage of offset.
Same thing only a lot more accurate.
You use 10000 kwh houes a year
You produce 7000 kwh per uear you offset 70%
So a 70% solar fraction
This is not a term widely used in the industry.

[foo1bar]

In Solar thermal systems, we call it: Solar fraction.

How do we call it in Photovoltaics systems?

I believe it's not a number that is useful to a user or designer, so it doesn't really need a name.

Useful numbers/terms for designers and users are
* DC KW size
* AC KW size
* estimated annual kwh production
* estimated kwh production for Jan, Feb, March, etc.

And then on the cost side of things - system cost, system maintenance costs, and life of system. And POCO $/kwh.

[sensij]

"Solar fraction" as described in this thread is not a useful term in PV because it depends on the power company providing full net metering retail credit for it to have even close to the same meaning as it does with solar thermal. Those deals exist today, but not for too much longer.

"Total solar resource fraction" is sometimes used as a way to describe the amount of insolation that an array will capture, relative to what an optimally oriented, unshaded array would capture in the same location.

[bernard]

Thank you Naptown, foo1bar and sensij.