In a recent podcast I did with Ken from the Prepper Podcast we talked about grid down scenarios and what we can do about them. Right after that podcast I decided to build my own DIY portable solar generator.
My plans are to build a solar generator that will run my well pump in a grid down event, and while this generator does not have the power to continually run it, I have set it up to be able to scale up fairly easily.
Keep in mind as you read this I am no expert, as a matter of fact I had very little knowledge other than solar panels collect energy, send it to the battery and you can turn on a light. Now that I have done this I have a better idea about watts, amps, volts and what makes it all work together.
There are quite a few article about how electricity works, and sometimes it’s too much information for my brain to absorb (repercussions of a misspent youth I guess), so I am going to keep this article a simple as possible and hopefully it all makes sense to you at the end.
Don’t forget to download the power needs cheat sheet at the end, it will help you figure out how much stored energy you need and use on a daily basis.
If you want more information on this you can listen to the Podcast Ken and I did, or you can check out a few of the podcasts ken has done in the past about battery banks.
A quick side note before we get into this: Ken will also be on the next SPTV episode talking about alternative energy. Sign up here to get updates about the show.
Here is the video explaining my DIY Solar Charger.
Parts is Parts
Minn Kota Trolling Motor Power Center: The reason I purchased this box is because it had a couple 12 volt ports already wired in and ready to go. I’ve seen a few videos where people add accessories, but this seemed easier…and I’m all about easy [Find One On Amazon Here]
30Amp/400Watt Solar Panel Regulator Charge Controller: A charge controller keeps the battery from over charging and there are many shapes and sizes. Like I state in the video you don’t want your solar panels to push more power than the charge controller can take. [Find One On Amazon Here]
My 13 watt solar panel only puts out about .5 Amps/13 Watts, meaning I can (and will) add a couple of 100 watt solar panels. That would bring me to 4.5 Amps and 13 Watts, well below the rating of the solar charger.
Thunderbolt Magnum Solar 13 Watt Briefcase Solar: Like Ken said in the Podcast start small, learn the process and then build bigger, so that’s what I did. Everything I purchased for this solar generator was purchased with price in mind, I wanted to get this done for around $300. I also wanted the ability to scale up when the time came, so everything else I purchased was a little bigger. [Find One On Amazon Here]
These solar panels run about $80 on harbor freight, but I got these on eBay for $45. At .5 amps per hour in full sun these would take about 20 days to charge my 100 Ah battery. I wanted to make sure it worked before I spent a lot of money on solar panels.
Cobra 800 Watt Power Inverter: Like I said, I wanted the ability to add solar panels to this generator so I purchased an 800 watt inverter. This was a little more expensive than a smaller one but it will run most of my small appliances and most of my power tools. [Find One On Amazon Here]
Here is a chart that shows how many watts a typical appliance uses.
Milwaukee 150 lb. Capacity Folding Hand Truck: This was about $25 at Home Depot and I got this to make it a little easier to move around. I don’t know if I will be using this to go up and down stairs or drag across the dirt because batteries should remain upright, but it does help moving it around the house because the battery weighs around 75 pounds.
100 Ah (Amp Hour) Deep Cycle Marine Battery: A 100 Amp Hour battery is pretty big when it comes to batteries, but you would be surprised at how quickly the energy in the battery can get used up depending on the appliance or tool being used.
Example: The average laptop uses 50 watts per hour, that’s almost 4 amp hours it takes from the battery, after 20 hours it would completely drain the battery if it wasn’t being charged. That might seem like a lot, but that’s only 50 watts. Also keep in mind that you never want to completely drain your battery, it will decrease its life span. I’ll explain this in more detail below.
How Solar Charging Works
Like I said I am going to keep this as simple as possible, so if you need more information follow the links above, or leave a comment below and I will answer to the best of my ability.
The Solar Panels
A solar panel collects energy from the sun, the wattage of your solar panels is how much energy you can collect from the sun…duh right? The reason this is important is because everything else you buy need to be able to handle the energy the solar panel collects.
You will need to decide what you want to use the solar generator for and figure out how many amp hours you will need (download the cheat sheet) to get an idea about what solar panels you need. But remember, you can always add more solar panels if your charge controller and inverter are large enough.
The Charge Controller
I kind of explained this above, but think about your future needs when you get the charge controller. My charge controller can handle 400 watts, if I plan on going over 400 watts I will need to get another charge controller.
The charge controller has positive and negative leads that come from the solar panel, and positive and negative leads that go out to the battery.
There are many different shapes and sizes of batteries, but I’m not going to go into detail about which one to choose, I’ll leave that to the experts. The main thing to keep in mind with batteries is the Amp hours. My 100 Amp hour battery will last 100 hours at 1 Amp, or 5 hours at 20 Amps etc.
There is quite a bit more that goes into this but you never want to discharge your battery %100. My rule of thumb is 50%, I have a 100 Ah battery, so I have 50 Ah.
The Power Inverter
A power converter takes the DC current from your battery and changes it to alternating current that household appliances use. In an emergency situation if all you had was a power inverter you could hook it up to your car battery to plug in a lamp…not very practical, but it works.
There are pure sinewave and modified sinewave converters, this is less important than the wattage of the inverter. The wattage is what you will be able to run off that inverter. If the grid goes down and you plan on running 2 lights, a heater and a small refrigerator you need to have an inverter that will handle that wattage all at once.
Confusing Power Conversions
Now let’s get into how this all works, I’m going to try and make this as simple as possible so bear with me. This can all get a little confusing but that’s why I started small, to get an idea about the process before I spent a lot of money.
Important: None of these calculations factor in efficiency and loss. These are just simple equations to give you an idea how it works. The actual figures will be different…always err on the side of caution.
I created the cheat sheet below to make it a little easier to make these calculations because my memory is not what it used to be, and there are a few calculations you need to know. All you need to remember are these 3 calculations…
- Amps = watts / volts
- Volts = watts / amps
- Watts = volts X amps
Let me give you a few examples and explain how to use the cheat sheet.
Example: A 20 Watt bulb running for 5 hours would be 20 (watts) x 5 (hours) = 100 Watts. To figure out amp hours you take 100 (watts) / 12 (volts from battery) = 8.33 amp hours. My 100 amp hour battery will be drained to 92% (100 – 8.33) if I run this 20 watt light for 5 hours.
What if your appliance doesn’t tell you watts?
My air compressor doesn’t tell me how many watts it uses, but it does say how many amps it uses. To figure out how many watts it uses just remember Amps X Volts = Watts
Example: My small air compressor is 2 amps x 110 volts (AC wall outlet) = 220 watts.
How many watt hours is that? Watt Hours are the number of watts X number of hours.
Example: Air compressor is 220 watts X 3 hours = 660. Then divide the watts (660) / 12 (Volts DC) = 55 ah (amp hours.) My hundred amp hour battery will be drained to 45% if I run this Air compressor for 3 continuous hours.
Laptop Example: With items that have a power supply you need to look at the output on the adapter. My Laptop power supply is 2.3 Amps and 19.5 Volts. That would be: 2.3 Amps X 19.5 Volts = 44.85 Watts. My laptop for 2 hours would use 90 (Watts) / 12 (Volts DC) = 7.5 ah (Amp Hours) My 100 Amp hour battery will be drained to 92.5% if I have my laptop on (sitting idle) for 2 continuous hours.
A little confusing? That’s why I created the cheat sheet.
1. Enter the item name of everything you plan on running with the solar generator.
2. Enter the watts used by that appliance. If your appliance doesn’t tell you watts remember: Watts = Volts (AC) X Amps. I included these formulas in the cheat sheet.
3. Enter the Amps that item uses. In the U.S. we use 110 – 120 AC. Remember: Amps = Watts / Volts
4. AC Amps will convert to DC Amps by itself, just remember that DC Amps are AC amps X 10.
5. Enter how many hours per day you plan on using the item.
6. The worksheet will calculate the Amp Hours all by itself, at the bottom of the worksheet it will show you a total of Amp Hours needed.
Download the Watt Hours Calculator
How Much Power Will My Solar Panel Produce?
This one is fairly simple, my 13 watt solar panels will put out 13 watts of power an hour with maximum sun light. I can get 7 hours of direct sun light on a good day so I could collect 13 (Watts) X 7 (Hours) = 91 Watts.
To get the Amp Hours going back into the battery take the 91 Watts / 12 (Volts) = 7.58 Amp Hours
On a perfect day I can only get about 7 Amp Hours out of my 13 Watt solar panel, that means if I use anything over 8 Amp Hours per day I will be draining the battery. Like I said…I need more solar panels!
To some of you this might still seem a little confusing, some of you might think it’s fairly simple. If you have any questions leave a comment below and I will answer if I can. If I can’t I’ll point you in the right direction.
Ryan Chamberlin says
A remarkable post! Even I could follow the instructions.
Is there a way to clean the solar panels and /or protect them from blowing sand an other stuff that might scratch the outer covering and diffract light-energy? Or is this not a big consideration? (I live in a high wind / desert environment, and have always been concerned that small amounts of “sand blasting” over time, would derail my long term efforts).
I looked into something like this, even purchasing a standalone Goal Zero Yeti type device. I too wanted to run my well pump and other less essential items if my generator(s) were out of fuel. The math just stinks though in that solar at that level is just not practical for running those items. Roughly, I figured I could run my well pump for an hour or two at most and then it would take a day or two of perfect weather to charge the battery back up. Just not worth it.
Patty Hahne says
I LOVE that you showed the math about what a person might be able to realistically expect out of a solar panel. To many people overestimate the ability of a particular PV panel to actually recharge a deep cycle battery.
The other thing that you mentioned is the importance of a charge controller. When we bought our off the grid cabin, it had some solar panels, batteries, and an inverter but the battery bank was toast because the previous owner neglected to put a charge controller between the panels and the bank of batteries.
I think that portable solar charging systems like this have their place in prepping but people need to understand their limitations.
Thanks Patty, I just read your article and it’s great information for people who read this. http://preppersillustrated.com/1803/5-reasons-your-plans-to-use-a-solar-generator-will-fail/
Patty Hahne says
It was your article that inspired me to write mine. Don’t you just love how we can share ideas and gain inspiration from other preppers?
Thank YOU for the inspiration!
Great build! I love seeing people get out there and get their hands dirty. I always highly recommend building a small system to learn about off grid solar.
As another point on the charge controller, make sure you also look at the amperage capacity as well. Every charge controller can only intake and export a specified amount of amperage. This can really affect expanding your array in the future.
Keep up the good work!
Mickle Clarck says
Great creation! I must try it. It was more clear by your tutorial. But I am worry to find out the raw materials. Even then I get inspire by your article so I’ll must try to build one Thanks for the article.
David Bell says
I really appreciated lesson the solar generator . I would like to build a system around the 2500 to 3000 watts. Can you advise on the proper compenents.
Eric Ankudavicius says
I like your design. Do you have a pdf of the wiring. I am sure it should not be hard to figure out. It helps to have references.
I don’t, but I plan on doing a more detailed video in the near future…I’ll do a PDF as well. Thanks.
I want to create a solar generator to power a mini refrigerator. The specs are:
120 Watt, 1.5 amp
I have a 125 watt solar panel the generates about 19 volts, 6.5 amps.
I have a 100 amh 12 volt marine battery
I have 1500 watt inverter
Can you recommend the size of charge controller I need?
A standard “starter” controller is 20A. That should be fine for your set up!
Ken Riley says
I’m looking to build a system that I can grow into. First, just 60watt light bulb in my goat house and an accessory outlet that I could get DC power from. Then I want to add another system to light up a couple of chicken coups and eventually add a submersible pump for my new well and an in line irrigation pump.
I know it sounds like a lot but the principles seem to fall in line. More power from the panel, bigger inverters and more storage capcity.
I guess I’m looking for suggestions as to where I need to consider my starting point.
Side note. Is there a suggestion for adding a wind turbine for a hybrid system.
Bottom line. Once it’s all set up, what kind of dollar figure can I plan on?
I would add this thought regarding the issue of pure sine wave and modified sine wave inverters. If you plan to charge electronic devices with the system, you are much better off spending a few extra dollars on a pure sine wave unit. The modified ones can mean an early death on electronic devices, just when you need them most (and when you might not be able to replace them, for a long while).
ozark prepper says
To run a well pump, you will need to understand it will be 220 volts needed to turn the pump on not 110…….to set it up correctly.
4 100 watt panels
4000 watt inverter
40 amp charge controller
4 125 ah deep cycle batteries
Felix Sarabia says
Excellent work sir, and I am now more confident I can make one also, and to think of the money to be saved every month, this video breaks it down simple, thanks again!!!!
Lol that’s Minn Kota, not Minny Tonka.
With this setup, would one be able to use AC current (household current) to recharge the battery? If so, how would this be done? Thanks.
I work for a cattle rancher who had a well pump go out on him, so he got a generator to power it. The problem is that this has happened before, and immediately I thought of somehow building a portable solar unit mounted on a trailer so that he can move it around to various wells when needed.
I’m pretty handy since I worked in construction for many years, and working on misc. projects, such as electrical, around the house, but I don’t have a clue on creating a system I’m thinking of.
I don’t know what type, size, output, etc. of panel we would need, type(s) and quantity of batteries, and so on and so on. Plus money is an issue.
Any thoughts of where I should look to get started with this? Any direction would help.
Thanks for your time.
Good article – thanks for posting. My requirements are similar to yours perhaps except for some 12vdc led lights I want to run also. I have the system working on a bench, yet to package it up. I don’t understand a problem I’m getting with my panel and controller. The panel is putting out 18vdc, but when I connect to the charge controller this drops to 13vdc. The charge controller specs say it will except up to 23v on a 12v battery. Any ideas?
I wanted to thank you for putting together a video on how to make your own solar generator as they are extremely expensive.
These generators seem to be anecessary for someone like myself who lives in Florida, we have hurricanes, tornados, power outages.
anyway ,I appreciate your taking time also in putting this together with prices.
I have not attempted it yet but over the next few months I plan on doing so.
is this where I would come to ask questions? Thanks in advance for your help,