Testing a solar panel

[Topcat47]

I keep a pair of cheap Maplin panels on the boat just to maintain the charge no my service and starting batteries. they don't push enough watts to sustain the service battery at sea, so I have recently bought a bigger panel. This one has a lamp on it that shows it is working but the battery to which it is attached doesn't appear to be benefitting. nominaly it's a 5w panel with a 15.6v max output. How can I test it with a simple multimeter? If I get a voltage reading how do I know it's pushing out the amps? (up to 300mA).

 

[RichardS]

You can just connect a multimeter set to volts across the two cables from the panel and see what voltage it is producing in full direct sun. Then disconnect and switch the multimeter to the 1A range and reconnect and get an amp reading.

These open panel readings won't be the same as the panel output when it is in circuit but are close enough such that you should see if there is a problem.

I'm a bit confused though ..... if your new larger panel is only 5W, what size are the smaller panels?

5W would be very small for a modest house bank and virtually make no impression on a bank in use.

Richard

 

[Topcat47]

Thanks. I'll give it a go and report back once I find my multimeter. The bigger panel wasn't intended to provide full house power, just push enough amps to extend the life for an hour or so rather than run the engine to recharge batteries when daysailing. (It was originally bought too top up an electric fence battery).

 

[dovekie]

Agree with Richard. 5 Watts is a pretty small panel for significant battery charging. In full sun, at the right angle, it will take more than 3 hours to put 1 amp hour into the batteries. What's the size of the battery(s) it is trying to charge? If it's a fairly typical 100 amp hour battery your 5 watt panel will have only a small effect even on a sunny day.

 

[macd]

This one has a lamp on it that shows it is working but the battery to which it is attached doesn't appear to be benefitting. nominaly it's a 5w panel with a 15.6v max output.

Richard has described how to test it, but a panel peaking at a mere 15.6V is going to spend a lot of time putting out fewer volts than that. (Most panels used on boats have an open circuit peak of 20+V.) Obviously if the output is at less volts than the battery, no charging can occur. It may be that the lamp you mention will light at 12V or less, which isn't enough to put anything into a healthy battery. Some panel controllers can take almost any voltage and increase it to a useful figure, but they cost far more than any 5W panel.

 

[William_H]

I have not ever seen a panel with a lamp built in to indicate that it is working. Indeed a simple LED in series will drop something over 2.5 volts so will seriously waste power (voltage) when charging a 12v battery and this may be why you are seeing no effect.
I would suggest if you can bypass or remove the lamp. (bypass if it is in series ie short it out) it will help.
If the lamp is in parallel then it will light with no battery connection. If in series it will only light when connected to a battery. Anyway if you can get a measurement at the panel itself. It hopefully with no load connected produce much more than15.6v. As said hopefully nearer 18v+. A typical 5w panel will produce 250ma in max sun. Test as said with an amp meter across the output leads not connected to a battery. If mounted at a suitable angle in lots of sun it should be possible to measure with amp meter in series with battery some charge like 100 to 250ma and this should be useful for at least keeping a battery happy when not in use. (I have a 5w panel on my boat as only source of power but then at 35degrees south lots of sun) olewill

 

[Topcat47]

OK I now have a follow on from my previous post.

I have my 1.5 and supposedly 5w panels in the garden. I have just checked the output as described in the posts. At 1400 today, the 1.5 watt panel was pushing out 18.6V and 76mA, pretty close to the max spec for the panel. My 5w Panel was pushing 15.6v (it's nominal max) but only 200mA, 130mA below max. Had it been performing as well as the smaller one, I would have expected ~300mA. Am I missing something crucial, here. I keep a couple of 2.5w panels on the boat to maintain battery condition and they've never let me down, the 1.5 was to keep our second car battery up as we don't use it very often and again it copes with the alarm drain well. The 5w was supposed to extend the operation of a 110V leisure battery powering an electric fence, but experience has shown it has very little effect on the battery duration, if any.

Any sparks out there care to comment? Am I unreasonable in my expectations? should I return the 5w Panel as unfit for purpose?

 

[jakeroyd]

Have a look at the back of the panel.
The maximum current expected at peak should be given.
Due to inefficiencies etc. it may be less than 300ma.

 

[dom]

I have my 1.5 and supposedly 5w panels in the garden. I have just checked the output as described in the posts. At 1400 today, the 1.5 watt panel was pushing out 18.6V and 76mA, pretty close to the max spec for the panel. My 5w Panel was pushing 15.6v (it's nominal max) but only 200mA, 130mA below max. Had it been performing as well as the smaller one, I would have expected ~300mA. Am I missing something crucial, here.

The 5w was supposed to extend the operation of a 110V leisure battery powering an electric fence, but experience has shown it has very little effect on the battery duration, if any.

Am I unreasonable in my expectations? should I return the 5w Panel as unfit for purpose?

To be honest a back of the envelope calculation, assuming panel was vaguely tilted towards full sun, would suggest that the 5W does not appear to be doing very well. As a matter of interest, are the Isc and Voc quoted in the 5W panel spec?

As a general comment, don't forget that the Vmp/Imp (max power) are not the Voc and Isc respectively.
Pmp = Vmp * Imp and MPPT controllers are designed to track this dynamically. But also a 5W panel to try and extend the duration of an electric fence seems small -- though I've no idea what the inherent losses might be or how many times the livestock activate it

...assuming that is what we are talking about

 

[Topcat47]

Hi Dom, I've not idea what the TLAs you are quoting (Voc/Isc) actually mean. The specs say:- Pmax (W) 5; Vmax (V) 15.6: and Imp(mA) 330. The led flashes when the panel is not connected but the sun is out. The voltage was on the button, but the current was ~ 200mA less than 2/3 the Imp, whereas the older 1.5w Maplin Panel was kicking out nearly 90% of it's design max current.

 

[dom]

Fair point Topcat I had to Google 'TLA'! It's really only the lingo that's complicated. You get out your panel and measure the voltage when it's open circuit (Voc) and driving nothing. You then short circuit the thing through your ammeter to measure the amps (Isc).

Finally you connect it to a battery, whereupon the voltage will settle a little below Voc and the amps a little below Isc. In there is a sweet spot, i.e. a voltage amp combination that produces max power (mp).

So what you have there is: Power max (Pmax) of 5W; Voltage max (Vmax) of 15.6V, which I'm guessing is Voc; Amps at max power (Imp) of 330mA. What they haven't given you is the Vmp, which one could back of an envelope to be 15.1V (5W/0.330).

Basically I don't think the the spec is fully inclusive and if you can't get an Ioc of more than 200mA on a sunny day then I'd say send the panel back. Incidentally you'd probably need to go to 20-30W panel to observe anything worthwhile in terms of reduced charging need when sailing.

 

[Topcat47]

Hi Dom, that sounds good to me. I'll return it for a refund and may look for something a bit more powerful. The smaller Maplin panels I have on the boat (2.5w) are good to maintain the voltage of the house and service batteries and have even been known to recharge them in high summer while I was away on "holiday". but that's all I wanted from them, really. Something meatier would be nice, if only to extend the time before having to run the engine to top up the service battery. A "fag packet" calc told me that the panel would extend the time between charges of the electric fence battery from ~15 days (forecast by the provider of the trembler) to around three weeks. In practise, while we were away in Canada, the battery was flat in 14 days. The woman helping with the horse swapped to my 85aH service battery which I"d left there ae a back-up. When we got back, that was completely flat, too. So Flat I had to put my "intelligent" bike charger on it for over a week to recover it.

 

[thesaintlyone]

I had a 25w panel on my 21ft jouster and that kept the house battery topped up running lights, depth, 12v phone/handheld vhf charging

Just fitted a 100w to the Longbow cause I expect to have a few more guests.


TBH stop wasting time going to Maplin prices are way better for panels on ebay and get yourself a solar controller with display i paid about £15 all very easy to set up.

 

[Topcat47]

That's where I found the one I have problems with. The Maplin ones were cheap when i bought them.

 

[PaulRainbow]

That's where I found the one I have problems with. The Maplin ones were cheap when i bought them.

IMO solar panels are a long term investment, i currently have a pair that are 15 years old. I'd rather fit quality than cheap Chinese crap. I've just fitted a pair of 100w back contact panels from Photonic Universe and they are producing more power than i'm using at the moment, staying aboard.

 

[dom]

IMO solar panels are a long term investment, i currently have a pair that are 15 years old. I'd rather fit quality than cheap Chinese crap.

Lol !!!

"Between 2008 and 2013, China’s fledgling solar-electric panel industry dropped world prices by 80 percent, a stunning achievement in a fiercely competitive high-tech market."
https://www.scientificamerican.com/article/why-china-is-dominating-the-solar-industry/

Thank goodness they're just a bunch of clueless, slipshod eastern folk without say $103 billion of raw cash to invest in renewables during 2015 alone.
https://www.scientificamerican.com/article/what-4-million-solar-panels-look-like-from-space/

Makes one pause for breath ....no?

 

[PaulRainbow]

Lol !!!

"Between 2008 and 2013, China’s fledgling solar-electric panel industry dropped world prices by 80 percent, a stunning achievement in a fiercely competitive high-tech market."
https://www.scientificamerican.com/article/why-china-is-dominating-the-solar-industry/

Thank goodness they're just a bunch of clueless, slipshod eastern folk without say $103 billion of raw cash to invest in renewables during 2015 alone.
https://www.scientificamerican.com/article/what-4-million-solar-panels-look-like-from-space/

Makes one pause for breath ....no?

Indeed. It's good that they've pushed the price of quality panels down

You really think everything produced in China is good quality ? Or perhaps some of the cheap stuff on Ebay really is crap ?