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 eBay 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 eBay 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 eBay 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 eBay 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.