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Inspecting used panels

Discussion in 'Off Grid Living' started by timtebow970, Feb 17, 2011.

  1. timtebow970

    timtebow970 Monkey+

    I was wondering what to look for in used panels to see if they would work into a system or not. I got to thinking about it because there are a lot of places in my area that appear to have had solar systems. One place that comes to mind is a set of 4 large panels pointed south with a big beautiful blue spruce tree providing them shade for the bulk of the day literally less than 3' south of here. I figure in the down economy we are in, I could probably offer to pay them a little to remove these eyesores from their property and the short sighted ones would gladly accept. However I don't know much of anything about solar panels, technology advances or how to ascertain their serviceability. I'm a younger guy and buying new is probably not in my financial realm of possibilities. I am an elbow grease kind of guy and have a broad (albeit shallow) knowledge of electricity and most things mechanical, and I believe I could piece together a decent system off old used components. However their would be very little tolerance from the wife for buying useless panels.

    Long question short, how can you tell if old panels are worth a darn?
  2. Nadja

    Nadja RIP 3-11-2013 Forum Leader

    Go to the back of the panel, carefully remove the lid. Then, while the panel is aimed directly at the sun, run your test meter to the different screw terminals on the back. The info on the panel should be about the same as what your meter tells you it is. The main difference is that usually the panel gives you "peak" power and you will be reading actual power. Also, check the front glass surface to make sure there is no cracking of any kind.
  3. TnAndy

    TnAndy Senior Member Founding Member

    First, let's understand there are TWO types of 'solar' panels ( at least ).

    One is a PV panel....photovoltaic, that produces DC electricity when the sun shines on them.

    The other is a solar heating panel, that heats either water ( most common ) for domestic hot water and/or space heating, or uses air, for space heating only. THESE were the most common type of "solar" panels in the past.....lot of them date from the 70's-80's when PV was really a LOT more expensive, and these were the most popular ( and probably STILL the most cost effective use of solar ).

    The procedures for "checking them out" is gonna be entirely different, depending on panel type.

    Since you said you see "4 large panels", my guess is you are looking at a water heating type panel....you don't say...you may not have known before now....

    The way to test them would be to put a pressure gauge on it, and pressurize them with water to probably something low, like 20-30psi....I wouldn't go over that, since most of them are used in a closed loop system with very little pressure.....much below normal household pressure.....and you don't want something to "pop".....then see if they hold pressure for an hour or so without dropping off.

    EDIT: IF it's a closed loop type system, most likely the fluid in it is an antifreeze mix, so be prepared to drain it into something for proper disposal.....don't let the family pets near it, as they will lick it ( it tastes sweet) and can kill them.

    If they hold pressure, they should be fine, internally. You just want to make sure they didn't freeze at some point and bust inside.

    Then examine the glass, and frames for any damage....maybe clean the glass, and they should be good to go. Most of them are made with copper lines soldered to a copper sheet for good heat transfer ( and painted black ), so as long as they don't leak, there's really not much that can be wrong with them.

    Then you'll also find a differential thermostat controller on the system....with a sensor up on the panels, and another on the water storage tank ( and the tank MAY well be the only water heater, with an internal heat exchanger.....so unless you're prepared to buy them a new water heater, you won't be getting that ). The controller measures the water temps at the panel and the tank, and when the panel is higher than the tank, the controller activates a pump ( probably located near the tank ) and circulates water up to the panels to heat. When the tank temp is higher than the panel temps, it shuts the pump down so it doesn't bleed heat away ( like at night or cloudy weather ). To test it, simply warm up the panel sensor more than the tank sensor ( or put some ice on the tank sensor ), and a set of contact in the controller should close, feeding 120vAC to the pump terminals.

    The pump itself will likely be a fractional horsepower ( like 1/20 or 1/12hp )pump, and a good one like a Grundfos bronze or stainless steel model IF you're lucky.....if it runs when you put 120v on it, it's most probably good to go.

    THEN of course, there will be roof patching to do where the panels mounted, and the piping may have penetrated the roof, so IF you get to remove them, you'll probably have to figure that in as well....unless you happen to catch the house when a new roof is going on, and they were removing the system anyway.....ideal situation.

    NOW, if it DOES turn out to be a PV system, write back, and I'll walk ya thru how to test it.

    Edit: Nadja slid in while I was typing. He laid out the basic testing for PV panels......but IF they are taking the whole system out, you also have other components to check.

    But my money is on "they are water heating panels".
    Lot of times, something like a pump or thermostat/controller would go out, and the company that put them in originally is gone, and nobody knows how, or wants to learn, how to repair. Since this was a backup system to the main water heater, the home owner may, or may not even know if it functions.
  4. timtebow970

    timtebow970 Monkey+

    Thank you both for your replies. Once the weather improves and I get the chicken house built, I will go start knocking on doors and inquiring. It sounds like their haven't been any great increases in PV solar panels in the last 50 years. I am worried that if I find some old panels that people are willing to part with, I would have to get six of them mounted to get as much power as 1 new one would give me.
  5. TnAndy

    TnAndy Senior Member Founding Member

    Huh ? Says who ? Efficiencies have gone up and prices have certainly come down.

    Well, AS I SAID ABOVE, most likely you are NOT gonna find "old" PV panels.

    What you ARE gonna find are LOTS of old water heating type panels.......so that whole point is almost moot.....they either leak, or they don't.

    As for old PV panels, I had a chance to test some Arco panels, in service since the early late 70s-early 80's, and they were still above 80% of rated output......so I tend to take that 25-30 year figure most manufacturers put out with a grain of salt.
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