(4) 300w solar panels MPPT controller and 24v battery bank from golf cart batteries

[BLOWN93LX]

First I would like to say hello and thanks for all the amazing information available on this site. I have been lingering for a while and decided it was time to register and ask some questions before I blow something up (kidding).

While on a recent vacation, I was able to pick up (4) 300w solar panels from a company in Indiana who manufactures them on site. I want to set up a 24v battery bank in my class A motor home with an MPPT controller. I bought 4 panels which should be 1200w which may be over kill but since I picked them up I had no freight charge.

http://www.ebay.com/itm/320-Watt-Semi-Flexible-Frameless-Solar-Panel-24-Volt-Made-in-USA-MonoCrystalline-/272329685331?hash=item3f681d3953:g:uXgAAOSwhOdXoihJ

Next I need to pick up a MPPT controller and some golf cart batteries. After that I will begin the wiring process.

What do you think of the quality of the panels? Did I make a mistake?

Any information, suggestions or comments are always greatly appreciated.

[littleharbor]

You have to wonder why they are selling these at 27 cents a watt. Granted the modules are frameless and haven't got junction boxes attached yet. Is the reason for this that they failed flash testing to the point that it isn't worth finishing assembly? The most involved and costly part of manufacture is in actually making the monocrystalline cells and assembly....soldering and vacuum laminating. An aluminum frame and j box aren't much more costly in large quantity. If it hasn't been disclosed to you what the reason for such a low price point is I would be wary.

These modules aren't necessarily "flexible panels" they just weren't finished for some reason. They would need frames for rigidity and the junction boxes will need to be mounted which may involve soldering and , hopefully, a weather tight seal on the j box.

[BLOWN93LX]

Thanks for taking the time to reply. I am unfamiliar with the economics behind solar panel manufacturing but since this is my first attempt at off grid living, I wasn't too concerned. At around $100 a panel, it's an inexpensive way to get started.

To mount them, I bought these clamps. I hadn't given much thought to clamping before purchase and after the purchase I realized almost nothing existed on the market.

http://www.ebay.com/itm/Frameless-or-Thin-Film-Solar-Panel-Mounting-brackets-/182232756994?hash=item2a6deb3302:g:~gsAAOSwXeJXfazG

[BLOWN93LX]

With these (4) 300 watt solar panels, can someone help me to understand how many amp MPPT charge controller is sufficient? I want the battery bank to be 24v by using (8) 6v Sams club golf cart batteries.

I included the wrong link before, these are actually the panels I bought. These are 60 cell, not 72 like the other link. 300w not 320w

http://www.ebay.com/itm/New-300-Watt-Semi-Flexible-Frameless-Solar-Panel-24V-Volts-300W-Made-In-USA-/262486922417?hash=item3d1d7094b1%3Ag%3AT5cAAOSwKfVXI75L&nma=true&si=Dv3JZbAj8r%252FxcYkR0fuCzHwab6E%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

[SunEagle]

Ok. I still haven't seen the 300 watt models . That last one had 305 watt 72 cell panels. But I presume they are close to the 72 cell 320 watt ones.

If you have 4 x 300 watt panels then you have 1200 watts total. If your battery system is going to be 24volts then you will need a 50A MPPT CC ( 1200 watt / 24V = 50A).

But again at that low price I find it a little too good to be true so you may not have a product that is Grade A or they may be having a fire sale.

[BLOWN93LX]

Ok. I still haven't seen the 300 watt models . That last one had 305 watt 72 cell panels. But I presume they are close to the 72 cell 320 watt ones.

If you have 4 x 300 watt panels then you have 1200 watts total. If your battery system is going to be 24volts then you will need a 50A MPPT CC ( 1200 watt / 24V = 50A).

But again at that low price I find it a little too good to be true so you may not have a product that is Grade A or they may be having a fire sale.

I genuinely appreciate the comments and concern that the panels may be sub-par. Knowing nothing about solar, my assumption was that there were three issues driving down the cost. One was that they were manufactured in house, two was they were not UL listed and couldn't be grid tie and three they can't easily be shipped requiring freight companies to deliver them.

Either way, I am happy to give them a try and am inquisitive enough to notice when something is going wrong.

In the future, I would like to discuss SERIES and PARALLEL options for the four panels and discuss which is best for my system.

Just to confirm, these were indeed the panels I picked up.

http://www.ebay.com/itm/New-300-Watt...p2047675.l2557

• STC DC Watts Maximum Power Pmax: 300 W
• Module Efficiency: 18.4%
• Maximum Power Voltage Vmp (V): 33.67V
• Maximum Power Current Imp (A): 8.96A
• Open Circuit Voltage Voc (V): 40.0V
• Short Circuit Current Isc (A): 9.35A
• Maximum system voltage: 600V UL, 1000V IEC
• Maximum reverse current: 20A
• Power Tolerance 0 +3 watts
• Cells per module: 60
• Glass: Low iron tempered with Anti-Reflective Coating
• Dimensions: 65.95 x 39.4 x .29 inches (33mm)
• Weight: 39.7 lbs

Thank you all for the replies
Nick

[BLOWN93LX]

Quick question: On an MPPT controller, if the battery bank is 24v, what will the DC light output be? Will it still be 12 volt? Or will the light output terminals match the battery bank?

[Wy_White_Wolf]

It will match the battery bank.

WWW

[Mike90250]

300w x 4 = 1200w
1200 x .8 = 960 w expected output / 24v = 40A max. So a 40A or larger MPPT controller would be the ticket
the specs from your link

• Module Efficiency: 18.4%
• Maximum Power Voltage Vmp (V): 33.67V
• Maximum Power Current Imp (A): 8.96A
• Open Circuit Voltage Voc (V): 40.0V
• Short Circuit Current Isc (A): 9.35A
• Maximum system voltage: 600V UL, 1000V IEC
• Maximum reverse current: 20A
• Power Tolerance 0 +3 watts
• Cells per module: 60

So, I'd wire 2 in series, and then parallel 2 of the series strings, giving you close to a 66v array @ 18A to run to the charge controller. You can wire 2 strings n parallel without needing fuses or breakers. It's nice to have a breaker on the PV and Battery sides of the Charge controller, for ease of shutting it down.
Most reliable MPPT controllers will self-limit to operate in a safe region even if overpaneled

[Mike90250]

Quick question: On an MPPT controller, if the battery bank is 24v, what will the DC light output be? Will it still be 12 volt? Or will the light output terminals match the battery bank?

The battery voltage from a 24V bank can vary from 23-32V, depending on where the battery is in the charge cycle. Most good inverters operate reliably in this range, because they are expected to keep running under all charging conditions.
So, any 12V appliances, would need to have a special 24-12V convertor / DC-DC supply to run them, Some LED lights have a internal driver chip and can operate over a wide voltage range, you have to carefully read all the paperwork

[BLOWN93LX]

The battery voltage from a 24V bank can vary from 23-32V, depending on where the battery is in the charge cycle. Most good inverters operate reliably in this range, because they are expected to keep running under all charging conditions.
So, any 12V appliances, would need to have a special 24-12V convertor / DC-DC supply to run them, Some LED lights have a internal driver chip and can operate over a wide voltage range, you have to carefully read all the paperwork

Thank you for that explanation. Let me try to explain again, on an MPPT charge controller, normally the far two right side terminals are DC output to operate low voltage lights. My question is, will that match the battery bank or will it be 12v? Or maybe it depends on the manufacturer. I am curious only for planning my lay out.

Thank you for your patience
Nick

[BLOWN93LX]

The reviews seem good for this EPSolar 4215BN 40 amp MPPT Charge Controller. Does it appear to be within my specs? They appear to run around $239.

Specifications:

Model	Tracer1215BN	Tracer2215BN	Tracer3215BN	Tracer4215BN
Nominal system voltage	12/24V auto work
Rated battery current	10A	20A	30A	40A
Rated load current	10A	20A	20A	20A
Max. PV open circuit voltage	150V
Max. battery voltage	32V
Max. PV input power	130W (12V)	260W (12V)	390W (12V)	520W (12V)
260W (24V)	520W (24V)	780W (24V)	1040W (24V)
Equalize charging voltage	Sealed: 14.6V, Flooded: 14.8V, USER: 9~17V
Boost charging voltage	Gel: 14.2V, Sealed: 14.4V, Flooded: 14.6V, USER: 9~17V
Float charging voltage	Gel /Sealed /Flooded: 13.8V, USER: 9~17V
Low voltage reconnect voltage	Gel /Sealed /Flooded: 12.6V, USER: 9~17V
Low voltage disconnect voltage	Gel /Sealed /Flooded: 11.1V, USER: 9~17V
Self-consumption	≤50mA(12V) ≤27mA(24V)
Grounding	Common negative
Temp. compensation	-3mV/℃/2V
Communication Port	RS485 / RJ45 interface
Working temperature	-35℃～+55℃
Storage temperature	-35℃～+80℃
Humidity	≤95% N.C.
Enclosure	IP30
Overall dimension	196x118x36mm	217x143x56mm	281x160x60mm	303x183x64mm
Terminal	4mm2	10mm2	16mm2	25mm2
Net weight	0.9kg	1.5kg	2.3kg	2.9kg

[SunEagle]

Quick question: On an MPPT controller, if the battery bank is 24v, what will the DC light output be? Will it still be 12 volt? Or will the light output terminals match the battery bank?

Usually the output voltage of the CC "load" terminals would be the same as the battery voltage. Also some CC have load terminals may only have very small "loads" and can easily be burned out.

While that tracer CC is ok you really need something that is rated a little more then 40Amps with 1200 watts of panels you will be exceeding the max wattage of 1040w for a 24voltage battery system.

Note. edited my post due to math error pointed out by little harbor.

[littleharbor]

4 in series =160 Voc., or 3?

[SunEagle]

4 in series =160 Voc., or 3?

Yeah. My mistake 4 in series would be 160VDC and exceed most MPPT CC. Sorry about my math mistake. I will make the change in my post.

[BLOWN93LX]

Can anyone help me to understand whether there is value in placing a combiner box between the solar panels and the charge controller? Ideally I would place it as close to the panels as possible? Or is it over kill and some simple breakers which are much less expensive will accomplish the same thing?

[SunEagle]

You only need a combiner box if you need to wire you panel in parallel strings to you CC. I have a combiner box that can parallel 5 panels to my PWM CC. If you purchase an MPPT CC that is rated 50 amps or more you do not need a combiner box because you can wire the 4 panels in series to that CC.