Heat or Dirt

Gazz

Hello,
In the UK we have had very unusual Easter weather (hot and sunny).

Late summer last year when I had just had the system installed I could see bursts of 3.0kw on a good day although we did not have a particular good summer (sporadic sun). But this year all I am getting is a maximum of about 2.3kw although I am getting it for a number of hours solid.

I can only think that either the panels are getting hotter because of the prolonged sun or they are dirty as it has not rained for a number of weeks and they are looking a bit dusty although they are high on the roof so it is a bit hard to tell.
My systems is 12x240 Sanyo (2.9kw)

Any advice as I cannot find any information on what would be a realistic loss in output in hot weather, or should I get on the roof and clean them.
Thanks
Gary

blackswan555

Re: Heat or Dirt

Keeping them clean will help and you are correct, They do lose performance as they get hotter,
But I think what you are seeing is a result of lower "sun power" ( insolation http://en.wikipedia.org/wiki/Insolation) due to the season,
The standard "Spec" for panels is at 1000w of insolation, Even down more south here in Spain, We are only getting > 850w ish at this time of year,

Have a good one
Tim

Gazz

Re: Heat or Dirt

blackswan555 wrote: »

Keeping them clean will help and you are correct, They do lose performance as they get hotter,
But I think what you are seeing is a result of lower "sun power" ( insolation http://en.wikipedia.org/wiki/Insolation) due to the season,
The standard "Spec" for panels is at 1000w of insolation, Even down more south here in Spain, We are only getting > 850w ish at this time of year,

Have a good one
Tim

That is what I would have thought, but last summer I saw 3.0kw so I know they can do it, may need to wait until June/July. But I think I will clean them anyway.

Thanks
Gary

Cariboocoot

Re: Heat or Dirt

3.0 kW from a 2.9 kW array is an aberration. Panels rarely produce their nameplate rating. Odd weather occurrences such as cold snaps or edge-of-cloud events can cause this. 2.3 kW output is more like the expected averaged output.

BB.

Re: Heat or Dirt

There is also a chance that you have a problem with the panels or their wiring.

Is this a Grid Tie installation?

Can you check the voltage and output current of each panel (basically Isc--short circuit current. Set an Amp Meter to 10 amps full scale--assuming that Isc is less than 10 amps for the panels). Check each string/panel for open circuit voltage and current and see if you can find one or more poor performance.

It could be a failed panel (if Sanyo HIT, not likely) or it could be a failing electrical connection.

The panels should all match pretty closely in output current and voltage. If you can get a DC Current Clamp Meter, it would make comparing each panel string against another much easier.

It is very difficult to see/measure a 10% reduction in output--A 50% reduction is pretty obvious. It sounds like something may not be correct.

-Bill

Gazz

Re: Heat or Dirt

Cariboocoot wrote: »

3.0 kW from a 2.9 kW array is an aberration. Panels rarely produce their nameplate rating. Odd weather occurrences such as cold snaps or edge-of-cloud events can cause this. 2.3 kW output is more like the expected averaged output.

I have seen 3.0kW. I'll try to find a picture on the sunny beam. I had a problem with some shading so I had two panels moved so I was taking photos of the output, and was monitoring it closely.

Gazz

Re: Heat or Dirt

BB. wrote: »

There is also a chance that you have a problem with the panels or their wiring.

Is this a Grid Tie installation?

Can you check the voltage and output current of each panel (basically Isc--short circuit current. Set an Amp Meter to 10 amps full scale--assuming that Isc is less than 10 amps for the panels). Check each string/panel for open circuit voltage and current and see if you can find one or more poor performance.

It could be a failed panel (if Sanyo HIT, not likely) or it could be a failing electrical connection.

The panels should all match pretty closely in output current and voltage. If you can get a DC Current Clamp Meter, it would make comparing each panel string against another much easier.

It is very difficult to see/measure a 10% reduction in output--A 50% reduction is pretty obvious. It sounds like something may not be correct.

-Bill

I have had two panels moved because of shading. Is there a way of seeing if that was all done OK from the inverter. They are on a high roof, not easy to get to. I suppose if I get just one high (2.7-3.0kW) then I suppose they are cabled correctly.

BB.

Re: Heat or Dirt

Did you bring down several sets of wires from the array down to your inverter/accessible combiner box, or just one set of wires?

You can also monitor array voltage at the inverter... In general, the array voltage is affected by the temperature of the array and the current is affected by the amount of sun light.

The problem with guessing about the amount of sunlight/current is that our eyes are not very good at estimating how much total solar energy is hitting the ground/panels. There have been some 1/2 hazy days here that have sent my inverter to peak output... And sunny clear looking days that have not.

One way would be to make your own solar irradiation monitor... Basically a small solar panel that you measure Isc (short circuit current with). You can use a shunt resistor and sensitive DC panel meter (across the resistor) or use a panel with a DMM amp meter... More or less, the Isc is proportional to solar radiation hitting the panel. Mount the sensing panel at the same angle as the solar array and you will have something to compare your other array with).

From another thread, Jeff Fedison posted a link to his small company's web site to show how you can build or buy his version of a 5% accuracy solar irradiance meter--basically a small shunt resistor and DVM panel instrument--for much less (I have never done anything with this website--but somebody else here said that they are good to work with).

If you are looking for longer term automated measurement--He also has a battery powered data logger for, what seems to be, a nice price.

-Bill

Gazz

Re: Heat or Dirt

BB. wrote: »

Did you bring down several sets of wires from the array down to your inverter/accessible combiner box, or just one set of wires?

You can also monitor array voltage at the inverter... In general, the array voltage is affected by the temperature of the array and the current is affected by the amount of sun light.

The problem with guessing about the amount of sunlight/current is that our eyes are not very good at estimating how much total solar energy is hitting the ground/panels. There have been some 1/2 hazy days here that have sent my inverter to peak output... And sunny clear looking days that have not.

One way would be to make your own solar irradiation monitor... Basically a small solar panel that you measure Isc (short circuit current with). You can use a shunt resistor and sensitive DC panel meter (across the resistor) or use a panel with a DMM amp meter... More or less, the Isc is proportional to solar radiation hitting the panel. Mount the sensing panel at the same angle as the solar array and you will have something to compare your other array with).

From another thread, Jeff Fedison posted a link to his small company's web site to show how you can build or buy his version of a 5% accuracy solar irradiance meter--basically a small shunt resistor and DVM panel instrument--for much less (I have never done anything with this website--but somebody else here said that they are good to work with).

If you are looking for longer term automated measurement--He also has a battery powered data logger for, what seems to be, a nice price.

-Bill

Thanks for all the advice, I will keep monitoring.

RandomJoe

Re: Heat or Dirt

When you say you "have seen" 3kW, do you mean for minutes at a time, or just that the peak power produced was at some point 3kW?

If you are just seeing occasional peaks to 3kW, you are probably seeing cloud-edge effects, your description of "sporadic sun" last year made me think of that. As the sun goes behind or comes out from behind a cloud, there is a "lensing" effect at the edge of the cloud that will briefly produce a much stronger sunbeam, thus producing a brief (seconds long) spike in power.

Gazz

Re: Heat or Dirt

RandomJoe wrote: »

When you say you "have seen" 3kW, do you mean for minutes at a time, or just that the peak power produced was at some point 3kW?

If you are just seeing occasional peaks to 3kW, you are probably seeing cloud-edge effects, your description of "sporadic sun" last year made me think of that. As the sun goes behind or comes out from behind a cloud, there is a "lensing" effect at the edge of the cloud that will briefly produce a much stronger sunbeam, thus producing a brief (seconds long) spike in power.

I can't remember for sure but I think it was for more than a few seconds more like minutes, I will look into it a bit more, but I do appreciate the information. Its all abut learning.

System2

Re: Heat or Dirt

Yes, I think the rated power is MAX ie theoritcal,

not typical expected levels under any amount of light

Peter_V

Re: Heat or Dirt

freeenergythinker wrote: »

Yes, I think the rated power is MAX ie theoritcal,

not typical expected levels under any amount of light

I've seen panels produce MORE than their rated output, on a clear day during winter when the temps are low.

As for the Gazz's question, my bet is that there are two factors at work.
The panels are probably oriented so they point closer to the sun during the summer and the below mentioned "edge of cloud effect"


Gazz didn't mention the inclination angle, but being 20 degrees off from pointing directly at the sun can drop production by almost 10%, the further off you are the faster the power drops off (it's a sine function basically)

Gazz

Re: Heat or Dirt

freeenergythinker wrote: »

Yes, I think the rated power is MAX ie theoritcal,

not typical expected levels under any amount of light

Getting near to Max today, looks about 2.8kW system is 2.9kW, and it only 1st May.

Still not sure if its Heat or Dirt, cleaned the panels on Friday but today is also a few degrees cooler (18C) and there is a breeze, but not that much different. On for a record day.

Be interesting to see what happens in June. Might see some 3kW. Need a sunny but cool summer.

Attachment not found.

Gazz