# calculating loses

Discussion in 'Photovoltaics' started by David Lesher, Jul 16, 2010.

1. ### David LesherGuest

So I have a demand of 1.6 KWh/day, and insolation is 5.5 kwh/M^2day.

If the world was perfect, I'd just divide to get panel area.

It's not, so I assume there are other factors I must
include; the panel efficiency of course, and some electrical
losses. [It's a DC pump motor, so that eliminates one,
conversion losses..]

Where do I go for more data on this aspect?

2. ### David LesherGuest

{STC vs PTC, temp derate, aging}

Thanks. I was also hoping for some writeups on how much each
factor deserves, etc.
....
And unlike one vender's bid: by keeping the supply voltage up.
[The SqFlex series will run from 30-300V, and run well above 120V.]
Nope, we're storing energy the rational way: Ug = mgh
No oxides of lead or such needed, and very low losses.
We shall all wear out before G*{m_1*m_2}/{r^2} does.
I figure we have 40-60 DAYS worth of water storage, so a few
cloudy days won't cause grief.

Further, there's some balancing factors. Rainy season has less
sun, but the well level will likely be 75-125 ft higher, using
less power. And the panels will be cooler.
Well, I've got a handle on everything save the panel issues.

3. ### Martin RiddleGuest

Include Panel dust too.

I believe the efficiency turns out to be somwhere around 75% of the
72% if you want to be exact for a grid tie.

I think someone here , with the same question, was seeing values in this
range.

cheers

4. ### Martin RiddleGuest

Include Panel dust too.

I believe the efficiency turns out to be somwhere around 75% of the
72% if you want to be exact for a grid tie.

I think someone here , with the same question, was seeing values in this
range.

cheers

5. ### Martin RiddleGuest

Panel dust and atmospheric dust (eg dirt, smog) has an effect. Depends
upon location as to the amount. I have some info somewhere, if I
remember correctly its in the 3% range.

Something associated with Global Dimming 1Kwm some think is
unrealistic. And conservativly use 800wm instead.

I have some info somewhere, I'll try to dig it up tonight, got something
to do before this heavy wall of rain hits NY.

Cheers

6. ### Martin RiddleGuest

I have notes that indicate 900wm^2 is a realistic value to use in
calculations.
Inverter effeciency 94%
Wiring loss 2%
Dust and wire connections 10% loss.

..9 x .94 x. 98 x .9 = 74.6% system efficiency.

Cheers

7. ### Martin RiddleGuest

The PVwatts system is a good system, heres a list of derating factors.
<http://www.nrel.gov/rredc/pvwatts/changing_parameters.html>

Dust, or Soiling (as it is listed) Does vary with location.

But generally, the system efficiency is ~75%

Cheers