A PV question

[Capt Slog]

I've just received my second solar panel, another 80W mono to give me 160W

In the middle of summer I'll be producing more electricity than I need.  I have a dump controller so this isn't a problem apart from throwing away good power as heat, but I'd like to know the answer to this question.

Is it better for a panel to switch it out of the system or to keep connected and just dump the power?

A third alternative is to switch it out AND shade it.

I just want to know which of these gives the best longevity.

Thanks

[electronbaby]

what equipment does your system use? do you have a wind turbine also?

If there is no wind involved, and its just PV, then a conventional PWM charge controller will do just fine. This allows the PV module to go open circuit when the batteries are satisfied. If you want to get fancy, you could add MPPT to squeeze a little more power out of the array, but with 160w, it does not pay to do that just yet.

PV can be shorted and open with no damage to them so I dont think you should be concerned with the longevity issue there. I would be concerned with the longevity of your batteries by use of a dump controller.

BUT, if there is no wind turbine, then there is no use for a dump controller.

Again, if you are using just PV, stick with a PWM charge controller. You will be fine.

[richhagen]

In general, it does little harm to the panel to dump the power.  When in Fiji, where the climate is harsh with many more sun hours, salt water in the air, ect. I was able to observe aging defects on older panels, Arco's and such from the 80's and 90's.  The Plastic (maybe tedlar?) backing would crack, exposing the EVA, and in some cases that would exhibit cracks as well.  Additionally corrosion around exposed junctions on old panels was a problem, especially to the frames where mounted and to exposed junctions.  Wear and tear from panels leaned against something and moving around without a permanent mount was also problematic as it allowed for scratches and damage which the weather could exacerbate.  Some of the panels put out significantly less than there rated amperage.  Some of my panels here in Chicago are old Arco's from the 80's and put out fairly close to there rated outputs, however I do not know their exact history prior to my acquisition of them, they have plastic over steel on the backing.  I am meaning to clean and coat the few locations where there is damage to that plastic but it is still on my list of things to do. :-(  If I live long enough I may get proper maintenance done - although not in a timely manner.  

My thinking is that in general it probably isn't worth the risk of moving and handling the panel to store it for the summer unless your climate/use is extremely harsh physically on the panel.  In a residential setting physical damage is likely the biggest risk to the continued functioning of your panel when compared to the sun exposure or lightning.  Just my opinion, others may disagree.  Rich

[ghurd]

Hey Capt,

Sounds like you need more LEDs!  Gotta find a way to use that power.

You are using a 'ghurd' controller?

Simply add another IRFZ44N, and add a heavy duty blocking diode.

PV positive to the fet drain, and the diode.  Out of the diode to the battery positive.

PV negative to the fet source, and battery negative.

Fet gate connected to the other fet gates and controller.

When the controller dumps, the fet turns on, the amps from the new PV are shorted through the fet.

The blocking diode stops current coming from the battery (so the fet won't short unlimited battery amps)

The new PV's amps don't go into the battery or dump load when the circuit is dumping.

The dump load does not need expanded, or changed at all.

I have sketches.

I recall at least Dr Dave and Independent posted stories doing it this way (solar with no dump load).

http://www.fieldlines.com/story/2008/5/4/41311/92374

http://www.fieldlines.com/story/2008/6/22/21540/7547

No reason to shade it at all.  I don't believe it would hurt the PV.  I am too lazy to be bothered doing it.

Automatic is good.  :-)

G-

[Ungrounded Lightning Rod]

Leaving the panel driving a load results in less heating of the panel than either opening or shorting it.  The power that would drive a load heats the panel instead in either of the don't-drive cases.

Since the power to the load is about 15% or so of the total sunpower absorbed by the panel - and all the rest heats it, too - it doesn't make a lot of difference.

So since you've already got a dump load hooked up I'd say leave the panel driving the load and let it run slightly cooler.