Bad solar advice - what is the real impact?

Submitted: Wednesday, Mar 05, 2008 at 21:49

ThreadID: 55231 Views:4920 Replies:9 FollowUps:13

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Tim Owen

Looks like I've received some bum advice, and I want to understand the real impact.

I have now purchased, and am halfway through installing, 2 Uni-solar 62T panels to mount on the roof of my pop-top troopie camper. I chose this model due to ability to flush mount (no controller box) so I can still get her in the garage, physical dimensions (2 X 64W wouldn't fit on roof), and durability.

But I've since discovered ....

"Uni-Solar’s ES-62t (62 watt) module produces 4.1 amps at 15.0 volts. As with most grid-interactive modules the ES- 62t appeals to motorhome builders as it is readily flush-mounted (i.e. there is no protruding connector box). But that 15.0 volts output is far too low for battery charging (most conventional solar modules produce up to 21 volts)." http://www.caravanandmotorhomebooks.com

I've already drilled some additional holes in the panel frames for mounting purposes, made the mounting rails and attached to the roof. I have only the wiring to complete. So I'm beyond a return.

I'm not particularly happy with the service I've received at present - given Collyns advice above, and if I've made a decision that is really bad, I'll consider taking it up with the retailer despite the holes. If the impacts are moderate, I'll probably just learn the lesson and move on.

So how bad is my situation? The plan was to mount the panels in parallel to aux battery (currently a sealed lead acid). I have an old 'yellow' 39L Engel and a few lights to run. I do want to be able to stay put and be able to keep the Fridge going.

Tim

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Reply By: Robin Miller - Wednesday, Mar 05, 2008 at 21:57

Wednesday, Mar 05, 2008 at 21:57

I don't think you have a serious problem at all Tim.

The 15v is at the peak power and is quite enough to charge the batteries.
You don't state the rest of the system - but typical solar regulators don't loose hardly any voltage drop as they direct excess to ground.

This is note required , but maximum power tracker regulators actually accept any voltage and convert it to optimin.

Robin Miller

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AnswerID: 291028

Follow Up By: Tim Owen - Wednesday, Mar 05, 2008 at 22:14

Wednesday, Mar 05, 2008 at 22:14

Thanks Robin - I don't have a regulator, and am not planning on using one. The panels will not be permanently connected, rather only connected when the fridge is on.

I have done a quick search on those fancy regulators, but I'm not willing to spend that sort of money.

I guess the worry is that the amount of hours in the day that you would actually get the peak 15V output, and how much of the day will the voltage be lower - and below the voltage required to really put any charge into the battery.

"Under charge, most batteries want from around 13.4 to 14.4 volts - quite a bit different than what most panels are designed to put out.

The panel is rated at 75 watts at full sunlight at a particular temperature (25C). If you have a cloudy day, or the temperature is high, you don't get 17 volts. (actually, temperature is the most important factor, as lowered light reduces the AMPS quite a bit, but the voltage only a little, up to a point). At the temperatures seen in many hot climate areas, you might get 15 volts. If you started with 15 volts (as in some of the so-called "self regulating" panels), you are in trouble, as you won't have enough voltage to put a charge into the battery." http://www.mhpower.com.au/

FollowupID: 556451

Follow Up By: Mainey (wa) - Friday, Mar 07, 2008 at 10:42

Friday, Mar 07, 2008 at 10:42

Tim, you NEED a Solar regulator......... ~$200
to protect your battery.

Who or what connects/disconnects the Solar panel from the battery, every day at the correct time when battery is full ??

Only a quality built Solar Regulator will do it.
Even better is a 3 x stage Solar Regulator.

Mainey . . .

FollowupID: 556728

Follow Up By: oldtrack123 - Friday, Mar 07, 2008 at 21:33

Friday, Mar 07, 2008 at 21:33

Hi Robin
Most basic solar regulators DO NOT switch output to ground,they simply open the negative line from the solar panel, cycling on /off as required to maintain charge.
Any solar panel over 20 watts really should have at least a simple solar reg to prevent overcharging batts.

FollowupID: 556851

Reply By: Member - Mike DID - Wednesday, Mar 05, 2008 at 22:16

Wednesday, Mar 05, 2008 at 22:16

Tim - you are reading information out of context.

This page is titled "Grid Interactive modules" using MPPT convertors to 240 volt. This is irrelevant to you - you just want to use it to charge batteries directly which is what it's designed for.

Amorphous cells have different characteristics to polycrystalline panels and even if they do have a lower "maximum power" voltage, they will still put out adequate voltage at lower light levels to keep charging a battery.

You can download the ES62 datasheet and the graphs there show how the voltage knee remains above 15 volts at lower lighting levels. That's all you need to be concerned about for battery charging.

AnswerID: 291040

Follow Up By: Tim Owen - Wednesday, Mar 05, 2008 at 22:24

Wednesday, Mar 05, 2008 at 22:24

Thanks Mike R. I'm feeling much better now.

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Follow Up By: _gmd_pps - Thursday, Mar 06, 2008 at 01:45

Thursday, Mar 06, 2008 at 01:45

what a nonsense..
MPPT converter to 240 volt ... rubbish ...

an MPPT converter is used to optimise the output wattage from several panels (parallel or serial or both depending on size and number) to whatever battery voltage you have (12,24,48).
Most home installations use 48Volts and the panels are serialised to use thinner cables. when you use panels in parallel you need thicker cables because amps are higher and voltage lower. MPPT controllers now optimse the step down of the voltage without burning the excess voltage like cheap solar comtrollers do. but there are limits
for example: I use 2x200W GE panels which put out 32V. A traditional solar controller would not handle that voltage for a 12V system very well, a MPPT controller like my "Outback" can. However I can not serialise the two panels (as I would like) because the resulting 60+ V can not be converted to 12V charge effectively. So I need thicker cables and can only step down to 12 V from 30. If I would have a 24V system it would not be a problem. The lack of MPPT technology in 99% of solar controllers you can buy in Australia is one reason you do not find higher wattage panels than 120 or so, despite the fact that a larger panel is more cost effective. My panels are 150mmx100mm and charge my 440Ah AGM easy. And I am talking RV market not "Home Solar".

have fun
gmd

FollowupID: 556490

Follow Up By: Nomadic Navara - Thursday, Mar 06, 2008 at 10:37

Thursday, Mar 06, 2008 at 10:37

All the MPPTs I know of will only massage the input voltages down. They are not capable of boosting the voltage. If you consider your panels do not have sufficient voltage an MPPT will be of no assistance.

PeterD

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FollowupID: 556514

Reply By: richor - Wednesday, Mar 05, 2008 at 22:43

Reply By: Member - keith P (VIC) - Wednesday, Mar 05, 2008 at 23:26

Reply By: Zodarp - Thursday, Mar 06, 2008 at 05:39

Reply By: chocolate teapot - Thursday, Mar 06, 2008 at 07:34

Reply By: Mainey (wa) - Thursday, Mar 06, 2008 at 08:15

Reply By: Derek from Affordable Batteries & Radiators - Thursday, Mar 06, 2008 at 10:23

Thursday, Mar 06, 2008 at 10:23

Wire them in series and use a 24/12v regulator.

Cheaper then filling holes and I would not recommend using any panel over 20W without a regulator.

I may have a sample lying around you can have.

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Follow Up By: Tim Owen - Thursday, Mar 06, 2008 at 22:45

Thursday, Mar 06, 2008 at 22:45

Thanks for the suggestion Derek, but part of my plan is to be able to remove one of the panels from the roof and plonk in the sun if the troopie is parked in a shady spot (remember the anderson double adaptor debate ....).

I'm getting mixed messages here. Some saying she'll be right, and others (I take it including you) saying that I've definitely bought the wrong product for the application and it won't be acceptable.

I'm not sure what to make of it all.

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Follow Up By: Derek from Affordable Batteries & Radiators - Friday, Mar 07, 2008 at 07:45

Friday, Mar 07, 2008 at 07:45

I would still recommend a regulator even if wired in parallel at 15V.

Do a test on a single panel to see if it puts out at least 14.5V in obscured light. To do this lay a sheet of bubble wrap on the panel and test it in the sun. If the output is low then it can't be used for your application.

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Follow Up By: Mainey (wa) - Friday, Mar 07, 2008 at 10:35

Friday, Mar 07, 2008 at 10:35

Tim, it's not really the 'wrong' Solar panel, even at only ~14.5v this panel will recharge a battery - just a bit slower !!

It's just there are much better *performing* panel choices available, but as you say, you believe they won't fit under your (shed) roof, however the difference in height with these (other) panels and yours is only a few millimetres.

Were you ever advised you can simply remove the "junction box" from a 'normal' 20+ Volt panel and have it mounted remotely ??

Mainey . . .

FollowupID: 556724

Follow Up By: Derek from Affordable Batteries & Radiators - Friday, Mar 07, 2008 at 10:40

Friday, Mar 07, 2008 at 10:40

Mainey,

You are about to make a fool of yourself again.

Better retract your last reply.

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Follow Up By: Mainey (wa) - Friday, Mar 07, 2008 at 10:51

Friday, Mar 07, 2008 at 10:51

Derek, arn't you the guy who posted you have not seen two different Solar panels wired in parallel, I have to do that often when guys have different panels and don't want to go to the expence of getting new panels and 'dumping' their existing 'different' panels !!

I have also remote installed Solar panel Junction box's with-out hassles, that's done so the panel lays flat on a caravan roof !

Mainey . . .

FollowupID: 556730

Follow Up By: Derek from Affordable Batteries & Radiators - Friday, Mar 07, 2008 at 11:03

Friday, Mar 07, 2008 at 11:03

You will VOID the warranty and cause delamination and moisture to enter the cells.

DO NOT REMOVE THE JUNCTION BOX.

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Follow Up By: Mainey (wa) - Friday, Mar 07, 2008 at 11:14

Friday, Mar 07, 2008 at 11:14

Derek,
How many have you removed, obviously none....

Otherwise you would have known delamination CAN'T happen because the rear surface is NOT damaged in the removal process, unless your a TOTAL idiot :-((

Read the post again, I did NOT advise Tim to remove the junction box, I asked if he was given the option of removing it by the supplier to use higher performance Solar panels !!!

Yes, it will void the product Warranty, that is the only hassle, but the product warranty is only for 12 or 24 months anyway.

Performance warranty is 25 years and panel performance is not affected.

Mainey . . .

FollowupID: 556735