Newbie to the forum. I am trying to figure out what size solar panels and how many And what size batteries would be required for my off the grid cabin. My cabin is completely wired with all LED lights probably 20 total. I do have outlets that run a TV and mostly cell phone chargers. Very rarely are any appliances used. I have no refrigerator or freezer to worry about. Would like to have a system that I would be able to add small appliances if necessary but do not want too big of a system and have money wasted. Cabin is mostly used on weekends only and maybe two full weeks a year. Right now everything is ran off a generator. Thank you any help would be greatly appreciated.
What size system?
- Thread starter Radtech
- Start date
marbella
New Member
- Joined
- Feb 11, 2022
- Messages
- 93
Solar Panels are cheap now, but keep in mind that montage materials are expensive, the smaller the panels the more flexible but also more work!
to calculate your battery size and panels needed there is a nice excel spreadsheet to download in this forum!
diysolarforum.com
to calculate your battery size and panels needed there is a nice excel spreadsheet to download in this forum!
System Energy Audit and Sizing Spread Sheet
To get the spreadsheet, click on the orange button at the top of this page. This sheet is intended to help you plan your system. Fill it out down to the last decimal place, look at the results..... and then make your best guess;) Notes...
diysolarforum.com
Last edited:
MichaelK
Solar Wizard
I'll give you the guide I used.
loads ≤1000W = 12V system
loads ≥1000w ≤2000W = 24V system
loads ≥2000W = 48V system
With the very smallest systems, you might want to chose between having 12V DC only, or a 12V system that can produce 120V AC.
The advantage of DC only for a very small system is that there are no losses from leaving an inverter on that is doing nothing. The disadvantage of a 12VDC system is that there's a price premium for 12V appliances, so if you want a 12V refrigerator, you'll pay thousands for it.
Me, personally, would start with a 24V inverter based system, because that would allow me grow more over time as I felt my needs change. If you go the route where you finally chose to add a refrigerator, or microwave, or other big-ticket items, you will be glad to have 24V.
But, sticking with 12V, here's what you can do. Plan on charging your battery at 1/8th of C. So, let's say you buy a 200Ah battery. 200Ah/8 = 25A. Charging at 13V that would be 25A X 13V = 325W. Assuming you don't get more than 85% of output out of panels that's 325W/85% = 382W of panels.
loads ≤1000W = 12V system
loads ≥1000w ≤2000W = 24V system
loads ≥2000W = 48V system
With the very smallest systems, you might want to chose between having 12V DC only, or a 12V system that can produce 120V AC.
The advantage of DC only for a very small system is that there are no losses from leaving an inverter on that is doing nothing. The disadvantage of a 12VDC system is that there's a price premium for 12V appliances, so if you want a 12V refrigerator, you'll pay thousands for it.
Me, personally, would start with a 24V inverter based system, because that would allow me grow more over time as I felt my needs change. If you go the route where you finally chose to add a refrigerator, or microwave, or other big-ticket items, you will be glad to have 24V.
But, sticking with 12V, here's what you can do. Plan on charging your battery at 1/8th of C. So, let's say you buy a 200Ah battery. 200Ah/8 = 25A. Charging at 13V that would be 25A X 13V = 325W. Assuming you don't get more than 85% of output out of panels that's 325W/85% = 382W of panels.
12VoltInstalls
life passes by too quickly to not live in freedom
I run offgrid except for this winter - my first winter using solar- where I need to supplement due to cloudy days and short sun.
I have a 12V system that is more than sufficient in summer with only 400W of panels. I use a 1200W soon to be 1500W inverter 24/7 for a fridge, coffeemaker, vacuum, tool charging. Furnace, pump, lights, etc are all 12V. A 1500W inverter is around 130A at full tilt 2/0 cables handle that fine.
The plethora of excellent 12V lighting options make 12V attractive. In your case, with no fridge, an inverter only turned on when needed makes sense to me if you use 12V lights and phone chargers.
I have 800W of panels now and I’m not at a lack of power on sunny days. Even with the furnace fan my batteries will last well after sunset this winter. With the lengthening days and this coming summer I will have silly amounts of unharvested watts.
I’m never at our cabin in the winter. It’s sometime impossible to get there with a big snow. We usually stay the entire week of thanksgiving and maybe a weekend or to afterwards. But by mid December we never stay. Then we usually start going back up late March early April through the summer and fall staying maybe a weekend a month. So with what you have running on your system; I’m looking at either a 200 watt panel system or a 400 watt panel system with a mppt controller. $350 and $700 respectively. Would like to have the ability to add more appliances in future if needed. We do have a led tv we watch during thanksgiving week. Love our football. Lol. What are your thoughts. 200 big enough or 400 overkill. Looking at Renology kit. With a 1000w inverter.
Rednecktek
Solar Wizard
Well, I'll start the default answer to these questions and we can work from there. Here's you To-Do list:
1: Power audit! This will give you some important information on how big your inverter needs to be as well as how much battery capacity you'll need. There is a link in the FAQ section (I think, or someone here will post it shortly) so fill in the blanks and see what it comes up with. You'll probably need some sort of Kill-A-Watt to get accurate measurements. Are you going to be running a 12v system? 24v system? 48v system? What are the specs on your solar panels? VoC? Vmp? Being as this is a new build, throw together a wish list of what you want and estimate on the high side.
1a: Where do you live? Speccing out a system for Scotland is a LOT different numbers than Arizona due to the amount of light you actually get. Someone here can post the link to the PVwatts.com or JCR Solar Uber-Sun-Hours calculator sites to help figure out how much you'll have to work with. That will be a box in the Power Audit form.
2: Parts list: You don't need a make & model list, just a parts list to start from for reference. You'll need an inverter, a MPPT charge controller, fuses, shunt, buck converter, batteries, wire, etc. Once you have a basic list it can be fine tuned to make & models after that. If you're looking at the All-In-Ones check for correct voltage outputs (120v or 240v Split Phase for North America, 220v Single Phase for European type areas) and make sure it has enough capacity for a little bit of growth and fudge factor.
3: Budget!: Steak is great but doesn't mean anything if your wallet says hamburger.
Figure out what you're able to spend now vs what you'll have to cheap out on now and upgrade later.
4: Tape measure! Figure out where you're going to stick all the stuff you'll need. A dozen 3000AH batteries sounds great until you're sleeping on the floor because there's no room left for a bed. Is there a compartment that can house all this stuff? Will the server rack batteries fit? Are you going to have to make space? Physics can be pretty unforgiving.
5: Pencil out what you think you need and throw it at us so we can tell you what you've missed (because we ALL miss stuff the first go-round ) and help figure out which parts and pieces you're going to want to get.
1: Power audit! This will give you some important information on how big your inverter needs to be as well as how much battery capacity you'll need. There is a link in the FAQ section (I think, or someone here will post it shortly) so fill in the blanks and see what it comes up with. You'll probably need some sort of Kill-A-Watt to get accurate measurements. Are you going to be running a 12v system? 24v system? 48v system? What are the specs on your solar panels? VoC? Vmp? Being as this is a new build, throw together a wish list of what you want and estimate on the high side.
1a: Where do you live? Speccing out a system for Scotland is a LOT different numbers than Arizona due to the amount of light you actually get. Someone here can post the link to the PVwatts.com or JCR Solar Uber-Sun-Hours calculator sites to help figure out how much you'll have to work with. That will be a box in the Power Audit form.
2: Parts list: You don't need a make & model list, just a parts list to start from for reference. You'll need an inverter, a MPPT charge controller, fuses, shunt, buck converter, batteries, wire, etc. Once you have a basic list it can be fine tuned to make & models after that. If you're looking at the All-In-Ones check for correct voltage outputs (120v or 240v Split Phase for North America, 220v Single Phase for European type areas) and make sure it has enough capacity for a little bit of growth and fudge factor.
3: Budget!: Steak is great but doesn't mean anything if your wallet says hamburger.
Figure out what you're able to spend now vs what you'll have to cheap out on now and upgrade later.4: Tape measure! Figure out where you're going to stick all the stuff you'll need. A dozen 3000AH batteries sounds great until you're sleeping on the floor because there's no room left for a bed. Is there a compartment that can house all this stuff? Will the server rack batteries fit? Are you going to have to make space? Physics can be pretty unforgiving.
5: Pencil out what you think you need and throw it at us so we can tell you what you've missed (because we ALL miss stuff the first go-round
) and help figure out which parts and pieces you're going to want to get.
Bluedog225
Texas
- Joined
- Nov 18, 2019
- Messages
- 2,903
I get by fine with 12 volt stuff and no inverter. No ac. Lighting, radio, computer, cell phones, bluetooth speaker.
Cheap and easy.
Cheap and easy.
12VoltInstalls
life passes by too quickly to not live in freedom
400 is what I’d do. I squeaked by on 200W for a couple of years. Going to 400W snd then going to mppt were both big improvements. 200W just didn’t have the power to sufficiently charge enough batteries for a fridge over a cloudy day. It would work but not well too often. The tv will be a similar demand but for a longer time. You need enough watts to run the loads AND charge the batteries at the same time.
I personally wouldn’t do the renogy buy. I’d pick a different brand.
Rich solar or windynation for 100W polycrystalline panels are $90/each on Amazon. Or recently the WindyNation monocrystaline 100W panels were $165/pair on Amazon. Or another thread here recently showed some various 250-350W panels for that same price- and I would look into a 350W panel pair dollar for dollar! 700W is way more useful than 400W and your expansion is already done and didn’t cost more. US MPP Solar has a 12V 1000W all-in-one that would handle that for $425 and that makes a substantial system for you for ~$800
In case you don’t know, an All-in-one combines an inverter, solar charge controller, auxiliary charger for boosting with a generator if ever needed, and everything is neatly connected and self-contained in a single unit
After starting small 4 years ago (with 200W) and “growing” into my current 800W system there is absolutely no question that if I were you I’d be buying the MPP Solar 12V AIO and whatever 600-800W of panels I could find at a decent price.
Thank you so much. I’ll do a little research on Rich solar. Once I figure out what I find I’ll run it by you again if that’s ok.
12VoltInstalls
life passes by too quickly to not live in freedom
Yes
I have a 12V inverted 120V AC system at my hunting cabin with 400W of panels. I was using 2x-100A AGM batteries, and running a small fridge was my biggest power consumer. Those AGM batteries would just barely run the fridge overnight. I replaced them with one Lifepro4 200A battery when they died after 3 years of use, and the difference between the lead batteries compared to lithium is astronomical. My lithium battery has never been below 13V, so don't short yourself on battery power if you can afford lithium. I also went with one battery this time to cut down on the chance that if one battery went bad like my old AGM's, it won't ruin the other battery. They cost almost twice as much, but well worth it in the long run because you can use all of the power stored in lithium, when AGM's can only be depleted to 50%.
Ok. Next question. So I have a 30 amp plug on the porch of my cabin where my generator plugs in to supply the cabin. It was from and old camper a buddy gave us. So I used that plug and breaker box for the cabin. Anyway I’m assuming I could the then just hardwire that cord into the inverter AC output.
Thanks for the tip on the batteries. So you using 1 200Aph lithium?
12VoltInstalls
life passes by too quickly to not live in freedom
NO!
I’m not sure what you are meaning by that sentence but you can’t connect two sources of power by hardwiring
The shorepower should go to the input of AIO, the output then goes to your RV 30A breaker/fuse box. The aio will select the generator input if/when present.
The 30 amp plug on the outside of the porch feeds to the breaker panel. I was assuming I could come out of the inverter and plug into that outlet to feed the cabin.
12VoltInstalls
life passes by too quickly to not live in freedom
That is a way to do it, but if you feed the aio with generator and feed the breaker box with the aio the aio battery charging and pass-through features are utilized.
Rednecktek
Solar Wizard
Whew! Yes, you can do that. Basically you can think of your system as a really big "Solar Generator" and plug it in like you would a "Gas Generator. Just not both at the same time please!
Yeah I am using one 200ah Lifepro4 battery. Make sure if you buy one it has at least a 5 year warranty. My 400W of panels keeps the battery charged during the day when I have over 10 hours of daylight, even with the power on during the day. I'm located in zone six.
