Solar Panel Voltage Rating

Topic: Solar Panel Voltage Rating (Read 1059 times) previous topic - next topic

Solar Panel Voltage Rating

October 25, 2018, 02:07:19 pm

Lots of interesting chatter about solar lately. Got a general knowledge question for the solar gurus.

Our panels on our coach are 12 volt (nominal) 36-cell modules rated at 160 watts. I see the exact same size/shape panels being sold now that are rated at 180 and even 200 watts. The difference in the specs is the max voltage and amperage numbers. What is physically different in the higher watt panels that allows them produce higher voltage/amperage with the same number of cells?

Re: Solar Panel Voltage Rating

Reply #1 – October 25, 2018, 02:37:03 pm

Not a guru even but the new ones are 72 cell

Re: Solar Panel Voltage Rating

Reply #2 – October 25, 2018, 02:55:06 pm

Bout .5 volts a cell, higher watt panels have more cells.
Basic Tutorials: Solar Panels for Solar Energy Systems

Re: Solar Panel Voltage Rating

Reply #3 – October 25, 2018, 02:55:54 pm

2- 200 Watt 12 Volt Battery Charger Solar Panel Off Grid RV Boat 400 watt...

Yes, I bought these from the same seller on eBay last year, same size panel rated at 165 Watts now 200 watts. Great panels in my opinion.

Re: Solar Panel Voltage Rating

Reply #4 – October 25, 2018, 02:59:57 pm

Most panels of the same physical size have the same number of cells. The difference between a 295 watt panel and the 365 watt panels are the cells. Higher efficiency, slightly denser, more watts per sq cm. Price is not linear with watts. Many panels have a higher long term output life. After 20 years most panels will degarde by 10-10% output. More expensive panes usually have less long term loss. Most have a nominal voltage somewhere near 36 volts when operating in the sun. Voltage goes down when the sun goes down. Most solar controllers shut off when incoming voltage decreases to battery voltage. The charge controllers conver whatever is coming in to the voltage they need to be putti g out according the the charge profile, amps vary with panel power output.

For your coach, if you want to maintain some roof acdess for maintenance then four full sized panels is about what you can get up there. So a 300 watt panel vs a 365 watt panel may be easier to find and cheaper. A power use survey, battery capacity, charge controller cost all help choose the best balance of watts and cost. 4 panels gets you 1200 or 1460 watts total. Both are good.

Lots of variables here, lots to learn about, lots of experience and opinions here on the Forum too. I hope I got the techno-babble right.

Re: Solar Panel Voltage Rating

Reply #5 – October 25, 2018, 03:46:13 pm

Quote from: Roger & Susan in Home2 – October 25, 2018, 02:59:57 pm

Most panels of the same physical size have the same number of cells. The difference...are the cells. Higher efficiency, slightly denser, more watts per sq cm.

I understand more cells in a module produces higher voltage. That is not what I am asking. The link Doug W. provided is what I am talking about. It refers to a 36-cell module that is 58 x 26 inch - exactly the same physical size, and same number of cells, as the panels on our coach. But the panels in his link are rated 200 watts, and ours are rated 160 watts. The difference is in the voltage and amperage numbers - both are higher on his panels. So I'm just wondering what they do to get the higher numbers out of the same number of cells.

https://www.grapesolar.com/docs/GS-S-160-Fab8.pdf

My 160 watt panels: Vmpp = 18.5V Impp = 8.65A Voc = 22.2V Isc = 9.46A Efficiency = 16.4%
The 200 watt panels: Vmpp = 21.1V Impp = 9.50A Voc = 24.3V Isc = 9.87A Efficiency = 17.3%

1- 200 Watt 12 Volt Battery Charger Solar Panel Off Grid RV Boat 200 watt...

Perhaps Roger's answer is closest to what I'm asking. Just natural evolution of the technology? They are slowly getting better at building more efficient modules? Not that I would want to, but if I did replace my 160 watt modules with 200 watt modules, then (theoretical) total watts on our roof would jump from 960 to 1200 without adding additional panels. That's a nice 25% increase in watts per Sq.Ft. in the 3 years since we had our solar system installed. That's pretty impressive!

Re: Solar Panel Voltage Rating

Reply #6 – October 25, 2018, 04:02:01 pm

All panel ratings are not the same. The quality of the silicon used may be improved or it may be an exaggeration by the company/seller. So, perhaps the new cells are more efficient but unless tested, it could be just a sales gimmick.

Since All Solar Panels Are Not The Same, It's Important To Test Them

Commercial panels used in solar farms usually have an excellent reputation and the long term voltage drop is minimal.

Quite a few reviews online for each brand and model.

Pierce

Re: Solar Panel Voltage Rating

Reply #7 – October 25, 2018, 04:04:46 pm

One physical difference jumps out at me between my panels and the 200 watt panels. In the description of the 200 watt panels, I see reference to "5 buss bar" as a feature. I think this refers to the "lines" that you can see going through each individual cell. There are 5 lines in the 200 watt cells, while my 160 watt cells only have 3 lines. Could this have something to do with the higher efficiency rating (and watts) of the newer panels?

Re: Solar Panel Voltage Rating

Reply #8 – October 25, 2018, 04:34:13 pm

I installed my first solar panel (160 watts) on my first Foretravel in 2004, then quickly added a 75 watt panel. I lived in that coach for 11 years before selling it in 2015. I then bought another Foretravel and installed 500 watts of solar on that one. The biggest differences at that point seemed to be lower panel prices, higher panel output voltage and the MPPT charge controllers that converted the higher panel output voltage to 12 volts. The higher voltage from the panels allowed for use of smaller wire size from the panels to the controller.
I was very happy with the price and efficiency of the systems I installed in 2004 and in 2015 and I see now that prices have continued to drop. With today's prices, making the investment in solar power makes more sense than ever. PLUS, there are a lot more qualified people selling and installing solar equipment today than there was 10 or 15 years ago.
I had to laugh the other day. Someone I met commented that their 1995 coach -- which had no solar equipment -- had been "wired for solar". I don't know whether he meant that it was wired when it was built or sometime later and I wasn't about to ask.

Re: Solar Panel Voltage Rating

Reply #9 – October 25, 2018, 06:15:23 pm

Panel performance has been improving at an accelerating pace. Certainly in two years they will be more capable than today. So figure out what your needs are today and add some in for "needs creap", solve the roof placement puzzle, make sure you have enough battery capacity for a 16 hr overnight in the middle of the winter and size accordingly. Buy the best panels you can get that fill the need and do it now. Or wait.

Some of the best deals are left overs from a big solar project. Mine came from one in Nevada along with a full warranty and they shipped them.

Re: Solar Panel Voltage Rating

Reply #10 – October 25, 2018, 10:59:22 pm

Thanks for the post. Provided me with the opportunity to re-evaluate our needs/plans.

Re: Solar Panel Voltage Rating

Reply #11 – October 26, 2018, 10:06:42 am

If you convert your fluorescent lights to LED and the same for the TV, you just don't need that much wattage up top and a big bank of batteries. We only have 408Ah of battery storage and use the OEM inverter for the microwave, 50 inch TV, etc. We shut the inverter down at night and use the micro and latte maker in the morning. We have never come close to flattening the batteries. Our batteries are on float before noon. Generator last started for an oil change.

So, unless you have a residential fridge, you don't need any improvements in technology to start enjoying generator free dry camping. AC requires the generator but unless you have a dozen big panels, solar is not going to do it and you will still need the generator.

Pierce

Re: Solar Panel Voltage Rating

Reply #12 – October 26, 2018, 10:40:19 am

Bruce,

A high efficiency smaller inverter is in the works for the TV. We would also like to have a sine wave inverter to speed up the slow microwave but not really complaining. The big OEM inverter uses a lot just at idle. The efficiency must be really low powering low wattage appliances.

P

Re: Solar Panel Voltage Rating

Reply #13 – October 26, 2018, 12:13:38 pm

As usual, this thread has gone off the rails...but that's OK with me! I enjoy the comments and idle chatter. My original question was asking "How do recent technological advances allow more watts to be generated by the individual cells in any given size solar module?". I guess I'll have to Google the subject to get a more "scientific" answer.

We are perfectly happy with our "current" (ha, ha) solar setup, and have no desire to make any changes. But thanks, anyway......

Re: Solar Panel Voltage Rating

Reply #14 – October 26, 2018, 03:59:45 pm

Chuck, in identical cells, higher quality silicone. Read about advancements at: The Latest in Solar Technology, What are The Latest Solar Panels and Solar...
P

Re: Solar Panel Voltage Rating

Reply #15 – October 26, 2018, 04:21:43 pm

Not sure what if any advantage there is to a small inverter.

The difference in efficiency between any two current inverters is tiny.

And the difference in efficiency is basically on the exact load.

Running longer 12 volt wires unless giant sized probably loses as much power versus send the power through 110 volt wires like Foretravel did.

A 500 watt load difference in efficiency from a 90% inverter versus a 93% inverter is 15 watts. 1 amp.

The twelve volt wires heat up and probably consume more than 1 amp i would venture.

If the smaller inverter heats up to the touch it's consuming energy.

Never seen a post other than here where multiple smaller inverters were installed versus a central unit and 110v wiring?

Short giant battery cables from the battery bank to the inverter/ charger is how every unicoach was made as far as I know.

Now if the main unit is not full wave and the smaller inverter is that would be a good reason for a small one at the use.

Unfortunately few of the non full wave inverters have a BTMS so they are either over or undercharging the batteries always.

Unless the batteries are at 75 degrees always even during charging which heats them up?

Better to put a full wave unit in with a BTMS?

Re: Solar Panel Voltage Rating

Reply #16 – October 26, 2018, 04:37:44 pm

Need to have an invertor topic, but Xantrex 1000 watt pure sine invertor uses less than .6 amps at idle and my Xantrex sw3012 uses 3 amps at idle. Big difference there.

Re: Solar Panel Voltage Rating

Reply #17 – October 26, 2018, 05:02:21 pm

How often is an inverter at idle? If the tv is plugged in even if off I would think it is still turning the inverter on..

My magnum has a very low current draw between times it looks for a load.

My thought was the current drop from the long 12 volt wires. Bet a temp gun or touch if under a small load will show heating.

I am sure there is a technical number in power loss per foot for various size 12 volt wires.

Most 12 volt would not the multi strand flexible lower loss wires like welding cable and I am sure they have a loss also.

Probably why Foretravel only made batteries and inverters a short distance apart? Required moving the floor plan maybe to balance their coaches so closely.

How did you get big enough 12 volt wiring to the smaller inverter? That's a lot of amps through the wiring at 12volt.

Bigger fire hazard I would think if it shorts or heats a lot.

Would take 2 gauge multi strand marine wire to lessen the wires induction heating I would think. And would still have a drop per foot I am sure.

Re: Solar Panel Voltage Rating

Reply #18 – October 26, 2018, 06:25:09 pm

You are using 4/0 sgt cabling if memory serves me?

Re: Solar Panel Voltage Rating

Reply #19 – October 26, 2018, 06:50:20 pm

What did you end up using from your batteries in your coach to your inverter?. Sorry

Re: Solar Panel Voltage Rating

Reply #20 – October 26, 2018, 07:39:39 pm

Quote from: Chuck & Jeannie – October 25, 2018, 04:04:46 pm

One physical difference jumps out at me between my panels and the 200 watt panels. There are 5 lines in the 200 watt cells, while my 160 watt cells only have 3 lines. Could this have something to do with the higher efficiency rating (and watts) of the newer panels?

Quoting myself here, cuz I found several online discussions explaining the difference I noted in cell design. As I guessed, more "lines" in the cell may make the cell more efficient, thus contributing to higher output. So the next time you're out shopping for panels, count the lines!

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Re: Solar Panel Voltage Rating

Reply #21 – October 26, 2018, 09:45:56 pm

Marine cabling uses pvc outside as it's inherently fire retardant. Ul 1427. EPDM is not. No halogen in its make up.

Every 12 volt wire in a country coach and beaver was ul marine cable for the fire retardation built in.

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