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Panel output
By acapulco, Section Solar Posted on Tue Aug 12th, 2008 at 04:17:03 AM MST
Is it normal to have lower than rated output even at peak sun condition?

hey,
I have 4 x 60w solarex panels probably around 10-12 years old maybe more.
I recently reconfigured to 24volt system and have 2 strings of 2panels.
today i checked with a MM what output was going into batteries(no reg,direct wire)
I checked it right at 12pm but it is tail end of winter here(australia, Sunshine Coast)
Anyways, I only read 5.7amps(24volt config) where as the panels (according to rating for powermax: on back) should be giving 7.5 amps configured for 24 volt. Is this normal?
I mean, I expect the ratings on back to be optimistic but is this a reasonable out put?
The wire run is about 10-12 metres using 4.58mm squared wire.
Is there a better way to test output than MM from + wire to battery + ?
tia

Panel output | 10 comments (10 topical, 0 editorial)

Re: Panel output (3.00 / 0) (#1)
by ghurd on Mon Aug 11th, 2008 at 11:07:46 PM MST
(User Info)

Seems reasonable to me.
Humidity, etc, reduce the output.
Age can too.

The powermax rating is under perfect conditions, and perfect conditions are rare.
G-

Re: Panel output (3.00 / 0) (#2)
by Flux on Tue Aug 12th, 2008 at 01:25:15 AM MST
(User Info)

I agree that you are seeing a reasonable output. The 7.5A is the peak current at the maximum power point for a new panel under test conditions ( 1kW/M^2). You will never see the 60W per panel as the peak power point is at about 17v.

Few places see the test energy conditions and they are based on a panel temperature of 25 or so degrees so on the days when you might see that level your panels are likely to be reasonably warm and that will bring you below the knee of the curve.

Not sure how much they drop with age but you seem to be doing fairly well. If this is winter and the ambient temperature is low, you may not be able to get this output on hot summer days.

Flux

[ Parent ]

Re: Panel output (3.00 / 0) (#9)
by acapulco (thatskankystuff{at}hotmail) on Thu Aug 14th, 2008 at 01:12:39 AM MST
(User Info)

ok,

thanks all for input. saved me climbing up on roof and fretting ;p
SE QLD AUSTRALIA.*OFF-GRID*.RE:2x4xT105@24v./450Ah@24v IN:240w.PV,backup:Genset/charger24v@10amp cont. OUT:Mod.Sine Inverters: 1500w/4500w/2000w & 350w.
[ Parent ]

Re: Panel output (3.00 / 0) (#10)
by ghurd on Thu Aug 14th, 2008 at 08:19:56 AM MST
(User Info)

You want several inches between the roof and panel.
I go 6" minimum at the low side. The high side may end up 18" or more.

If the panels are just sitting parallel with the roof angle, that will not help because the panels are not catching as much sun as the should.
The panels should be about the same angle as the latitude, plus 10 degrees or a bit more.

Panels don't like to be too hot. They can 'burn' and really reduce the output, for ever. They can be totally ruined by burning.

So get some space under them for circulation, and get the angle right.
G-

[ Parent ]

Re: Panel output (3.00 / 0) (#3)
by Chuck on Tue Aug 12th, 2008 at 12:10:10 PM MST
(User Info) http://www.greeleynet.com/~cmorrison

I also have some older solex panels. They exhibit the same results, but so do my Siemens and Photowatt panels. I have around 1600 watts of rated power but have only seen 1300 watts max coming from the panels.

As Flux said, the rated power in amps is at a specific voltage (17vdc). Unless you are using an mppt type charger, you will not be getting anywhere close to the 17vdc you need to hit the rated output (34vdc for two in series). 30% under rated power is a pretty standard result and the mppt charger makers say you'll get that back with their units.

There is another issue that frustrates our ability to easily determine power output, which is the state of the batteries and what stage the charger is in. Unless you have a properly sized diversion load, What you see is what the charger is allowing into the battery, not what the panels can produce.

Re: Panel output (3.00 / 0) (#4)
by Ungrounded Lightning Rod on Tue Aug 12th, 2008 at 08:49:39 PM MST
(User Info)

I seem to recall a previous posting pointing out that there are government requirements on how solar panel power is measured and that these measurements significantly overstate the power output for a battery-charging application (where the panel voltage is clamped below the peak power point voltage by the battery voltage.)

Re: Panel output (3.00 / 0) (#5)
by fishfarm on Wed Aug 13th, 2008 at 03:25:17 AM MST
(User Info)

I just completed a year of operation with 6 190-watt panels. Based on the MX60 charge controller data, the panels averaged 33.2 kWh per week. Using an NREL number of 5.47 average hours of sun per day for my location, the rated output would have been 43.65 kWh per week, so my results were 76% of rated.

Re: Panel output (3.00 / 0) (#6)
by wpowokal on Wed Aug 13th, 2008 at 06:17:04 AM MST
(User Info)

I have 10 second hand BP panels that have had a hard life previously and they make around rated output.

I purchased 6 Shell 140 watt pannels new and they struggle to make rated output, after taking into account all that others have said. It may be that the hang in for the long term, only 4 years into their life so can't comment on that.

allan down under
A life lived in fear is a life half lived.

Re: Panel output (3.00 / 0) (#7)
by tecker on Wed Aug 13th, 2008 at 11:19:56 AM MST
(User Info)

The substate expands

Re: Panel output (3.00 / 0) (#8)
by tecker on Wed Aug 13th, 2008 at 11:27:50 AM MST
(User Info)

I mean in direct sun they expand and voltage falls off . Tracking to temp is something I'd lke to try,atleast at midday .

[ Parent ]

Panel output | 10 comments (10 topical, 0 editorial)

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