new to solar

System

I have done a whole lot of reading here, but I just can't seem to find my situation. I recently purchased a Whynter Portable fridge/freezer (FM-85G). There aren't any really good power consumption numbers on it. I found a forum where a guy did some experimenting with a FM-45G, which is a smaller fridge, and found that under 70 degree ambient temp it pulled about 37 ah in a 24 hour period. I figure that doubling that would be a good starting point.

So here is what I have:

I received two of these today:

CHARACTERISTICS:

Power at STC ( pm ): 125 Watt

Maximum Power voltage ( Vpm ): 18.1 Volts

Maximum power cusrrent ( Ipm ): 7 Amp

Open circuit voltage ( Voc ): 21.9 Volts

Short circuit current ( Isc ): 7.29 Amp

Tolerance: +- 5%

Operating temperature : -40C to +85C

Maximum system voltage: 1000V DC



I also purchased two Exide GC 145s. I do understand that these will need to be wired in series to get the 12 volts that I need to run the fridge.

I have not purchased wire or controller yet. Although money is an issue, I would rather spend a little more now for the ability to expand in the future.

My question to you all:

Should I wire the panels in series or parallel? If in series, I will need an mppt controller. I like the looks of the rogue, but can't seem to find anyone selling them. The Blue Sky 3024 looks like another option. Am I trying to over do it?

I'm thinking that I will be building a unistrut frame that will require about 40ft of wire (40 ft of positive and 40 ft of negative). My understanding is that if wired in series, I will be able to use a smaller gauge wire, but I just can't seem to figure out which way would be better for my application.

My primary goal at this point is to make sure that this fridge does not lose power. Of course, with this being my first solar experience, I'm sure that I will be experimenting to see what it's capable of.



Thanks in advance for any advice or thoughts that you may have.

Tony

Cariboocoot

Re: new to solar

Welcome to the forum.

The reason you can't find any reliable info on refrigeration power consumption is because it varies greatly. It's affected by ambient temperature, humidity, how often the door is opened, how much is inside, et cetera. The more it has to cycle, the more power it uses. The numbers you see on "Energy Guides" in stores is for a fixed set of testing conditions and is only relative to other models.

That said, we can go at the numbers "sideways" and see what you can expect from your panels. A total of 250 Watts, right?
So 250 @ 77% efficiency = 192.5 / 14.2 Volts (charging for a "12 Volt" system) = 13.5 Amps. That should be sufficient for 135 to 270 Amp hour battery at most. Of that you could use 50% maximum, so you have 67.5 to 135 Amp hours to work with. This should be within your estimated usage range.
(Rough calculations to give you an approximate idea of what is possible.)

Don't bother wiring the panels in series if you can avoid it. Use the Voltage Drop Calculator to see what size wire you'd be looking at for your total 80' run: www.solar-guppy.com/forum/download/voltage_drop_calculator.zip
If you do need to, you'll need to use a MPPT type controller which is inevitably more money. One choice would be the Morningstar 15 MPPT: http://www.solar-electric.com/mosumpsochco.html
I think the BlueSky 3024 has an input limit of 35 Volts, which your two panels will exceed at their Voc of 21.9. The Morningstar is good up to 75 Volts.

The specs on the Exide GC 145 say it is 245 Amp hours. This could be marginal for the charging capacity of those panels.

niel

Re: new to solar

the 3024 is rated to take a voc up to 57v, but i wouldn't take it anywhere above 50v.

System2

Re: new to solar

Thanks so much for the input. If I went with the Morningstar 15a mppt, would that allow for future expansion? Maybe two more panels and another 2 or 4 batteries. Money is an issue, but there is nothing worse than that feeling you get when you realize another 100 bucks would have saved you 300 bucks.

I am so glad that I joined the forum and asked these questions. I was about to buy the Blue Sky model.

Thanks again!

Tony

Cariboocoot

Re: new to solar

There's more than one way to expand a system.
Unfortunately none of those ways are particularly economical.

It helps if you can define your needs for now and your wants for later. Then you can design both systems and see if there's any possibility of shared components.

Expansion can be increasing the loads on an existing system Voltage, upping to higher system Voltage for greater loads, or adding additional stand-alone systems for future needs.

The 15 Amp controller from Morningstar is about at its limit with 200 Watts on a 12 Volt system, but it can handle 400 Watts on a 24 Volt system.

System Voltage is very important to expansion, especially if you are using or plan to use an inverter. For instance a 12 Volt system is really only good for around 1000 to 2000 Watts at most. If you need higher Wattage then upping the system Voltage is recommended. Otherwise the DC current gets dangerous and unmanageable. (1200 Watts @ 12 Volts = 100 Amps, but that same 100 Amps will allow 2400 Watts @ 24 Volts or 4800 Watts @ 48 Volts - roughly speaking.)

You might also want to look at the Tristar 45 Amp MPPT http://www.solar-electric.com/motr45ampmps.html More capacity for the $, but also more $.

System2

Re: new to solar

Cariboocoot wrote: »

There's more than one way to expand a system.
Unfortunately none of those ways are particularly economical.

It helps if you can define your needs for now and your wants for later. Then you can design both systems and see if there's any possibility of shared components.

Expansion can be increasing the loads on an existing system Voltage, upping to higher system Voltage for greater loads, or adding additional stand-alone systems for future needs.

The 15 Amp controller from Morningstar is about at its limit with 200 Watts on a 12 Volt system, but it can handle 400 Watts on a 24 Volt system.

System Voltage is very important to expansion, especially if you are using or plan to use an inverter. For instance a 12 Volt system is really only good for around 1000 to 2000 Watts at most. If you need higher Wattage then upping the system Voltage is recommended. Otherwise the DC current gets dangerous and unmanageable. (1200 Watts @ 12 Volts = 100 Amps, but that same 100 Amps will allow 2400 Watts @ 24 Volts or 4800 Watts @ 48 Volts - roughly speaking.)

You might also want to look at the Tristar 45 Amp MPPT http://www.solar-electric.com/motr45ampmps.html More capacity for the $, but also more $.

Well, I have thought a lot about it. I think that the best expansion option for me in the future is probably going to be another stand alone system. The system that I am working on now will be located in my barn. I would like to be able to hook up some 12v lights and maybe charge drill batteries in addition to the fridge. Could I add another panel for a total of three in series to my 12 volt battery bank and still use the morning star 15a MPPT controller? I hate to ask so many questions, but wow this is a lot to take in.

Thanks so much for all of your help!

Tony

Cariboocoot

Re: new to solar

Yes, it is a lot to take in. So much that some of it ends up getting pushed back out of your brain!

I would not put three of the same panels on the MS 15. As you can see from the previous calculations two of the panels would be around 13-14 Amps output, so unless you have a very long down lead that will use up a lot of Voltage two is the limit. It's a shame that the next step up is a 45 Amp MPPT (because the 30 Amp Rogue or BlueSky have Voltage input limitations).

rollandelliott

Re: new to solar

Tony if you are still around, how it your system working. I'd love to have a portable fridge.