Grape Solar 400-Watt Off-Grid Solar Panel Kit

[Mike90250]

Sunfrost fridge with danfoss compressor, draws the same wattage on 12V as 24V, but with 24V the amps are half of 12V amps

[palmsandpines]

Hi Mike, So about how many amps would that be for 12v or 24v? Just trying to get an idea if I have enough power for a fridge or not. I don't want a cooler, but a small fridge. Thanks much!

[Mike90250]

Thought I had the manual here, but I don't. The sunfrost manual has a couple pages on power requirements for the Danfoss DC compressor they use.

[Sunking]

Forget Amps, does not mean anything. Amps is just a end result and is what it is. Forget about Amps. You want to know Watt Hours and how many watt hours you need in a day. Once you know that then you find your panel wattage, controller, and battery. Amps will be whatever they need to be, so Forget Amps.

Did I mention Forget Amps? Once you know panel wattage, watt hours, and battery voltage then you worry about amps when selecting cable size. Other than that FORGET AMPS.

[Logan5]

Example: 10 amps @ 12v is only 5 amps on 24v. The higher voltage reduces heat in feed wire and connections. shorter compressor run time for thermal recovery. If you want 12v and USB power just purchase the necessary 24v step down converters. a chest type refrigeration unit will consume 1/2 the power of a front load. A DC native chest refrigeration unit running from 24v will consume 1/2 of that. Get your head out of the 12 volt box. 12 volt refrigeration comes at great cost due to loss.

[palmsandpines]

Logan 5, A neighbor thought that it would be simpler for me to just stay with 12V. I'm a true novice and don't know what I'm doing. I hear you say to pick a chest type cooler that is 24 V and I will do that. Would be nice to know if I will have enough power before I buy it. They do not make this easy by telling you the watt usage ( requirements) up front. That all said, I need to also figure out how many batteries I will need. So two in series just to get to 24V and I get that, but do I need four for the total storage I will need? Again, I have a 400 watt system, but I really only want to plan on getting 200 watts for 8 hours or 1600 watts a day (winter). On a nice summer day, I could get 3200 watts...or at least I think that will be close. Am I looking at all this right?

[Sunking]

I have a 400 watt system, but I really only want to plan on getting 200 watts for 8 hours or 1600 watts a day (winter). On a nice summer day, I could get 3200 watts...or at least I think that will be close. Am I looking at all this right?

Nope no place on earth gets 8 Sun Hours. 4 to 6 is about as good as it get in summer, and 2 or less in winter.

Anyway a 400 watt solar panel requires:

12 volts @ 300 AH battery
24 volts @ 150 AH battery
48 volt @ 75 AH

All three batteries are exactly the same size and can deliver up to 800 watt hours per day.

You are going about it all wrong. You first determine how many watt hours you need in a day. Let's say 1000 wh or 1 Kwh. Next find your shortest or worse case winter month Sun Hours which will likely be around 3 Sun Hours.

Panel; Wattage = [Daily Watt Hours x 1.5] / Sun Hours = [1000 wh x 1.5] / 3 Hours = 500 watts
Battery Capacity = Daily wh x 5 / Battery Voltage = 1000 wh x 5 / 12 volts = 416 AH.

3rd grade math and science in any country except the USA which would be Phd thesis.

[palmsandpines]

Sunking,
Thank you for your post. So , I'm thinking of going with the 24 volt system and getting two 12v batteries in series for weight. It looks as if I will need two - 150 AH, AGM, deep cycle batteries and that should meet my need. I'm kind understanding that you are saying that I can only afford to talk my batteries down by about 22% to have them suffencialty charge back up and be sustainable. In other words, about 800 watts a day max draw. I hope this is all correct. I had it in my head that I would draw down to 50% and will correct that to about 22%. Please correct me if I'm off base.

[Logan5]

The 24v chest refrigeration unit will use 1/4 the power of a front load inverter powered refrigeration unit. Your 400 watts will be more than enough, where as you would need several hundred watts more watts plus more batteries to run the inverter. The choice is yours. Order a 24 to 12 volt step down converter and a 24v to USB power adaptor when your order your refrigeration unit. You wiil not need to run an inverter for any of these loads, therefore increasing your overall efficiency. If you have a laptop and or a TV, you will need a 24v to 19v converter for them as well. You will also want a terminal fuse directly on your battery bank and distribution fuses for each circuit. Don't skimp. Buy quality fuse blocks. some are made of cheap plastic and with a lil heat can become unusable. do not use an in line car stereo fuse in place of a proper bolt on terminal fuse.

[palmsandpines]

Logan5, I will start looking for 24v chest style refrigerators. Thanks for the information.

[Logan5]

compare sizes, go a lil larger than you think you will need, Look for thick insulation/walls. separate freezer compartment. single or double door. Using a chest style take a lil getting used to. be creative. If you buy farm non refrigerated eggs, you can baste in olive or vegetable oil for counter ready eggs.

[Sunking]

Palm my point is and still is you put the cart in front of the horse. You first determine your daily watt-hour requirement. Everything is based on daily wh, location, time of year use, shade issues.

Batteries are easy AH = [Daily Watt Hours x 5] / Battery Voltage

So if you have a 24 volt 150 AH battery, means it is the right size for 24 volts x 150 AH / 5 = 720 watt hour per day. Is that enough? I don't know and neither do you. Is 400 watts enough? I do not know and neither do you.

Take a look at one of the 24 volt Danfrost and some others to get an idea. Remember their numbers are conservative. If they say 500 wh/day, make it 750 wh/day.

You start with Daily Watt Hours. Get a handle on that and we can help you. How much you need is not a question we can answer.