Solar PV Efficiency

[Robert9]

Hi,
I have a 1.9KW PV array, but even with the sun at midday, and at 90 degrees above the panels in mid-summer, I only record outputs of around 1600-1650 Watt. Is this normal, or should I be getting my full 1900 Watt?
Robert

[Paul Haese]

Yep that is normal. You can expect something like 85% efficiency on good days. Sometimes it might go a bit higher to around 1700 or 1800. My PV system at Clayton gets similar numbers.

[Robert9]

Thanks for your confirmation Paul. But I really don't understand why or how we can be sold a system of a given rating which has no meaning in real life. Sounds like a con. Certainly I was not told by the salemen of a number of companies, of whom I had a few prior to choosing one, that the rating was meaningless. It was my understanding that these cells were guaranteed to deliver their rated output for so many years. For my panels the specs. are at 10 years down to 90% and 25 years 80%. Surely new panels must be 100%, otherwise its all a take. Or am I being too niaive?
Robert

[clive milne]

Robert...
You may be using an inverter with significant internal losses.
They vary between 85% to 97% efficiency.

[Robert9]

I don't think the inverter is involved at this stage as I am measuring the output power from the array. Measured array voltage times current gives the same value of power as shown on the inverter display.

[Exfso]

Robert, there are losses associated with any system, distance from inverter to panels, heat losses through power generated and as others have said the efficiency of the panels and inverter. I have a 4.5kw system and mid summer 90deg and no cloud plus temp below 35deg C, I get around 4kw, so the numbers you are getting sound good. I have noticed that as the temp gets above 35deg C, the efficiency does drop a few percent. My next door neighbor has a 7kw system and he is getting identical output percentages to me. The guy that sold me the system said I would be doing well if I averaged 80% of the rated output. I have checked this carefully since it was installed and when cloud is not around and the sun is at zenith my panels are delivering approx 85% in mid summer, this obviously drops off as the sun migrates to the northern lattitudes so to speak, and that is expected. My best day since I have had the system installed in July was 34kw generated by my panels, obviously that was on a coolish clear day mid summer, now I am getting around the 28-30kw mark on clear cool days, this will obviously continue to drop off now as the days get shorter. As I said in another thread, I now no longer have to pay monster power bills of over $500 / quarter, and I get money back from the power company for the excess power I export back into the grid, which in the last quarter was around 1600kw. Since that reading on 30 Dec I have exported 840kw back to the grid. I think that corresponds to around 20kw per day exported, so I am happy with that.
Granted I still use power from the grid when the PV's are not operating, but that is only about 40% of what I used to use.:thumbsup:

[BPO]

Hi. My array at a relatively high altitude in NZ's alpine region usually outputs as rated, and in cold conditions it exceeds the manufacturer's specs. My guess is that, for you Australians, heat is likely to be the biggest cause of reduced PV output on clear days.

[Robert9]

Hi, Thanks for all your input. You have restored some faith in my system and it's supplier. There are certainly a number of factors involved. Temperature effect is certainly one, the other may well be losses because of atmoshpheric pollution or just overall absorbsion. I note even the lightest of cloud cover causes a drop in output. BPO's experience at higher altitude in NZ seems to support this.
With regard to temperature, the specs. on my panels show an efficiency voltage loss of 0.35% per degree. My bank of 10 panels shows a voltage drop-off of about 45V (12% down from 375V) from 8am to midday,and the current rises from 1.5A to 5A in the same time. At 0.35% per degree, the panels must be at about 35 degrees above ambient to record such a voltage loss, which I guess, is possible. Perhaps I need to put water-cooling on the panels. :screwy:
Wouldn't it be nice if companies told prospective customers what they should expect from their systems?
Robert

[BPO]

Altitude/elevation generally means lower temperatures and higher insolation (even in NZ), ideal for PV systems, which is why arrays tend to perform so well on, say, a mountaintop. But one disadvantage of lower temps is that you lose battery capacity, unless your battery bank is well insulated or in a heated environment. Not much of an issue for anyone on the grid and in a hot locale such as Australia, but something to be aware of if you're not.