Off-Grid Power: Build a Solar Generator from Scratch

I’m going to need a sustainable power source for my off-grid observatory, so I built my first solar generator from scratch.  Here’s how.

The Craziest Year Ever

I wouldn’t call myself a prepper, but 2020 got me closer to becoming one than probably any other year in my life. With the beginning of the COVID-19 pandemic coming in March, my home state of New Mexico saw a state-wide ban on gatherings of more than five people at a time. Everyone quickly became shut-ins. We’ve seen everything from lockdowns to travel quarantine rules to long lines at the grocery store and everything in between. Getting outside anywhere but home became almost impossible as all of our state parks were closed for camping for most of the year. My family maintained our sanity by making lots of camping trips to the land we bought last year. We invested in a popup to make trips easier, and ended up going 24 times!

Figure 1: Ruby, the truck, and Sue, our new popup, at our land in western New Mexico.

A huge bonus to having a popup is that it has a propane heater built-in, which would make winter stargazing possible (our land sees many sub-zero nights per year). However, after using it so many times over the summer, we quickly learned that the small battery on the trailer couldn’t power the heater blower for more than a few nights at a time. Powering much else (the fridge, electronic devices like laptops and cameras) was out of the question. Once, the trailer battery died and I had to rig up my telescope battery in the middle of the night to keep the heater blower going. We needed something bigger, and something we could charge in the field. We do have a gas generator, but it’s pretty loud, ruining much of why we like to go camping; peace and quiet.

So I decided to go solar.

There are plenty of options on the market. Why DIY?

Cameras and telescopes don’t require much power, but keeping a trailer “plugged in” all night does.  After plenty of online research, I found many of the store-bought solutions to be lacking in overall capacity and throughput. For instance, here are the specifications for one solar generator that turns up first in Google’s Shopping list at the time of this writing:

• 60Ah Lithium Battery
• 1800W Peak Inverter (900W continuous)
• 100W Solar Panel
• 2 120v Outlets
• 1 12v Socket
• 1 12v Anderson Outlet
• 4 USB ports
• Total cost: $2500

In my opinion, this price point is about right, but the system is far less capable than what you could build for the same amount. Not only that, but these store-bought systems are typically not user-upgradeable, and in many cases, not even user-serviceable. Once something breaks or wears out, you have to buy a whole new system. The engineer in me says we can do a whole lot better for the money, and we can learn a thing or two in the process.

So we’re gonna build it ourselves. What do we need?

To keep things as simple as possible, I decided to build a 12-volt system. Pretty much every auto store in the USA carries 12-volt parts, so we’re not far from having replacement parts if/when something wears out (fuses, inverters, wire, connectors, etc.). I’m not going to lie, this list of required parts and tools can be daunting if you’re a first-time builder like me. But none of them are hard to use, we just have to take things one step at a time.

Disclaimer: as with anything electrical, be careful when using/building with any of these materials; improper use can result in a fire or personal injury. While I’ve been personally satisfied with the items on this list, this list shouldn’t be taken as a guarantee that any of these items are inherently safe or that you won’t run into problems if you use them.

Parts

• 170AH LiFePO4 12v battery from BigBattery.com with Anderson terminal rings ($823)
• 6AWG Wire, Red and Black, 10 feet each ($26 for the pair)
• 10AWG Wire, Red and Black, 25 feet each ($38 for the pair)
• 18AWG Wire, Red and Black, 25 feet each ($11 for the pair)
• Ticonn 500pc heat shrink wire connector set, 10-22AWG ($37)
• 6AWG terminal rings, 10 pack ($15)
• Blue Sea Systems 12v fuse block with connectors for 12 fuses ($48)
• AIMS Power 12v 4000W Peak/2000W Continuous Pure Sine Inverter ($350)
• AIMS Power RemoteEHF Flush Mount remote on switch ($29)
• EPEVER Tracer 4210AN 40-amp solar charge controller ($139)
• EPEVER MT50 Remote Meter ($35)
• Anjoshi 50-amp Circuit Breaker ($14)
• Anjoshi 250-amp Circuit Breaker ($14)
• NOCO Genius10 10-amp Battery Charger ($100)
• 2x FIRMERST 1875W Flat Plug Extension Cord Black 2 feet, 15A 14 AWG, UL Listed ($7 ea.)
• 1x Waterproof Flanged 120v Inlet ($17)
• 2x Waterproof Flanged 120v Outlet ($22 ea.)
• 2x Renogy 200W Solar Panels ($231 ea.)
• 15ft MC4 10AWG Solar power cables ($28)
• 30ft MC4 10AWG Solar power cables ($39)
• Drok 200A Hall Cullen Watt Meter ($15)
• Solar Panel MC4 Weatherproof Cable Entry Housing ($31)
• 2x Yohann Quick Charge 2-port USB charger and Cigarette Lighter ($8 ea.)
• 50 ft Heavy-Duty 120v Outdoor Extension Cord ($46)
• Stanley 19in. 24-gallon Tool Box ($68)
• 3/8″ Plywood ($16)
• 7/8″ Particle Board ($20)
• 100pc 3M Adhesive Cable tie downs with zip ties and screw holes ($10)
• 100pc 3/4″ wood screws ($5)

Total Price: $2510

The copper wire lengths may be overkill; I definitely bought more than I needed, so some cost savings may be had there. You don’t need both 15ft and 30ft MC4 cables, I just bought both so I had more flexibility in total wire length (shorter wire means less resistance, and more charging power, but you may need longer runs if the sunny spots next to your camp site are further away). Some of these things like the plywood/particle board can be obtained for free if you know where to look (construction site dumpsters, hardware store scraps, etc.). Other things like the outdoor extension cord and the toolbox may be things you already have lying around the house. I decided to include them in the final price in case you end up buying them new.

You can also save quite a bit of money by downsizing the battery and/or the inverter. Lower-capacity is fine if you don’t need it, just be careful not to buy lower-quality batteries or inverters. Aside from the battery, the solar charge controller is probably the most important part of the system. Don’t cut corners on the charge controller, spend the money and you won’t regret it.

Tools

• Wire Cutter (both light and heavy-duty; 6AWG is thick and requires a fair amount of force to cut)
• Wire Stripper
• Wire Terminal Crimper
• A lighter for heat shrink connectors
• Electrical tape
• Wood glue
• E6000 glue (for wood on plastic)
• Handheld jigsaw
• Phillips Screw Drivers (various sizes)
• Cordless Drill and various sizes of drill bits
• Hole Saw Set (up to 3″ in diameter)
• Flat carpenter’s hand saw with many teeth
• Carpenter’s square, or at least a tape measure
• Multi-meter (for measuring voltages and continuity while wiring things up)
• Allen Wrenches

Building the Box Lid

Okay, let’s get started! The first thing to tackle is the lid, which is where we’ll be mounting our inverter, charge controller, fuse block, and circuit breakers.

Tools/Parts Needed

1. Stanley 19in. 24-gal. tool box
2. 7/8″ particle board
3. 3/8″ plywood
4. 3/4″ wood screws
5. Drill
6. Jig saw
7. Carpenter’s square
8. Carpenter’s hand saw

First, we’ll prepare the surface of the plastic grid in the toolbox lid. Use, your hand saw to cut off all the protruding bits of plastic that stick out above the surface of the grid in the tool box lid. Once the grid is flat, we’ll fill in a checkerboard pattern using our 7/8″ particle board. Depending on what box you buy, 7/8″ might be more than enough to clear the grid, or not enough. Use whatever will be just tall enough to rise above the surface of the grid.

Cut the particle board with your jigsaw into rectangles that fit within alternating squares of the grid. Using E6000, glue them against the bottom of the grid cells. Next, use your drill to pre-drill screw holes through the grid and into the sides of the particle board, then screw the particle board in. I ended up using at least three screws per piece of particle board on at least three separate sides, four sides wherever possible. Don’t screw the particle board in from the outside of the lid; this will keep the lid more or less weather-proof.

Figure 2: Left, using screws to secure the particle board to the grid. Right, the finished grid.

Now it’s time for the most difficult part, cutting out the plywood insert. This box lid has a ton of protrusions. Trace the outside of the lid onto your 3/8″ plywood and cut out the rough shape. Then, work around the sides of the lid with your jigsaw until your piece of plywood fits flat onto the particle board grid. It should fit entirely below the lip of the toolbox lid. Take care not to cover the plastic straps that hold the lid to the rest of the box. When you’re satisfied with the fit, pre-drill some small holes into the plywood and secure it to the lid using one screw for each grid square. The finished lid piece should look like the image below.

Figure 3: Finished generator box lid. The plywood in the lid resides entirely within the lid and does not protrude below it when closed.

Building the Box Floor

The bottom of the box floor is uneven. To level it out, we’ll put a plywood floor in.

Tools/Parts Needed

1. Hand Jigsaw
2. 7/8″ Particle board
3. 3/8″ Plywood
4. E6000 Glue
5. Wood Glue

The bottom of the toolbox has a raised middle with two deeper tracks that run along the front and back end of the box. First, cut two strips of particle board to fill the tracks. Then, cut a piece of 3/8″ plywood to fill the floor. Use E6000 glue to secure the particle board to the bottom of the tracks, then use wood glue to secure the plywood to the particle board. Set something really heavy on it (like your giant Lithium battery, or some weights) and let it cure overnight. The finished box floor should look something like this.

Figure 4: Completed generator box floor.

Installing the Lid Components

By now, we’ve finished creating all of the surfaces we’ll need to secure electrical components to. The lid of the box is where we will install our Solar Charge Controller, Power Inverter, DC Fuse Block, and DC Circuit Breakers.

Tools/Parts Needed

1. Drill with small bit for pre-drilling screw holes (this will keep the plywood from cracking).
2. Solar Charge Controller
3. Power Inverter
4. DC Fuse Block
5. DC Circuit Breakers (50-amp and 250-amp)

Depending on the make/model of your components, you may want to change the layout of your components. For me, the heaviest part of the lid setup was the inverter, so I decided to place it as low on the lid as possible so that it wouldn’t be as hard to lift or keep open. My particular inverter is enormous, which didn’t leave me a lot of space for the other components. I knew I wanted to keep the breakers and the charge controller close to the inverter, because I wouldn’t have room for bus bars and would end up using the inverter post terminals as the central wiring place for everything. Here’s something close to what I ended up with, although I would later move the fuse block and inverter a little further to the right.

Figure 5: This lid layout kept most wiring attachment points close and most of the weight as close to the bottom of the lid as possible.

I did not arrive at this arrangement on the first try. You may need to experiment with different placements so that your components don’t run into the moving lid straps or areas of the lid with little clearance from the box when closed. Thankfully, if you can stand having a few extra holes, plywood is very forgiving!

Installing the Front Panel and Left Side Components

Next up is to get all of our displays and external power connectors laid out.

Tools/Parts Needed

1. Drill and hole saw set
2. Small hand saw
3. Screwdrivers
4. Solar Charge Controller Remote
5. Power Inverter Remote
6. Drok wattage display
7. 120v inlet and outlets, 12v sockets, and USB charge outlets
8. MC4 inlet gland
9. E6000 for sealing things

First, figure out where you want everything to go. I decided to put my MC4 Solar inlet glad on the left side of the box a few inches below the handle, and then everything else as close to the top of the front panel. I did this because this box has a bit of a “roof” towards the top, and putting everything there would keep them better shielded against rain (even though I hope to never leave this generator out in bad weather, mistakes happen). My toolbox had some vertical spines running up the front panel for rigidity, so I made sure to cut between those without damaging them, in order to maintain as much strength as possible.

Figure 6: Use a big hole saw to cut the area for the Charge Controller’s display. I used smaller hole saws for the 120v AC ports and 12v sockets.

Figure 7: Finished front panel. My AC inlet is on the left side, with the charge controller display and power inverter remote in the center. USB, 12v, and 120v outlets continue to the right. I ended up adding a Drok battery wattage meter below the inverter remote later on.

Figure 8: MC4 solar panel inlet gland, just below the left handle. This is directly below the charge controller mounted in the lid.

Wire Up Everything

For me, this was the most challenging part. Plan on it taking up the most time out of everything in this build.

Tools/Parts Needed

1. Copper wire (6AWG, 10AWG, and 18AWG)
2. Heat Shrink Connector kit (we’ll be using ring terminals, fork terminals, and butt connectors)
3. Crimp ring terminal connectors for 6AWG wire
4. Lighter or heat gun
5. Wood Screws
6. Wire Cutter
7. Wire Crimper
8. Wire Stripper
9. Electrical Tape
10. NOCO Genius10 (or whatever battery charger you bought)

Breakers, Charge Controller, and Inverter

The breakers are for safety and prevent too much current from running through the inverter power lines or from flowing through the charge controller. These are the most important features of this entire build and are there to keep bad things from happening! The battery’s positive terminal will eventually connect to the input of the 250-amp breaker, and the battery negative will connect to the negative terminal on the inverter. We’ll do that at the very end. For now, let’s focus on the breakers, the inverter, and the charge controller.

1. Cut a piece of Red 6AWG wire to run between the output of the 250-amp breaker and the positive terminal of the inverter. Terminate with ring terminals and attach (we’ll be doing this a lot). If you’re using heat shrink connectors, use a heat gun or a lighter to carefully heat up the connection until sealed.
2. Cut a second piece of Red 6AWG wire to run between the output of the 250-amp breaker and the input of the 50-amp breaker, terminate, and attach.
3. Cut a piece of Red 6AWG wire to run between the output of the 50-amp breaker and the positive battery connector on the Solar Charge Controller. Terminate one side of the wire with a ring connector and attach it to the 50-amp breaker. Strip about half an inch off the other side and insert it into the charge controller’s positive battery port. Use a Phillips screwdriver to secure the connection.
4. Cut a piece of Black 6AWG wire to run between the charge controller’s negative battery connector and the negative terminal of the inverter. Strip half an inch from one side of the wire; this one goes into the charge controller. Use a ring terminal on the other side and attach it to the negative post of the inverter.
5. Using 10AWG red and black wire, connect the charge controller’s solar input connectors to the MC4 glad on the left side of the generator box (you’ll need butt connectors for this). Do NOT connect a solar panel yet; the battery needs to be connected first, which we’ll do at a later step.
6. Use a volt meter to check continuity between everything you just wired up.
7. Connect the charge controller display to the charge controller using the supplied RJ45 cable.
8. Connect the NOCO Genius10’s 120v supply to 120v AC inlet on the generator box. Remove the alligator clips from their respective ring terminals using an allen wrench. Then, connect the positive ring terminal to the input of the 250-amp breaker and the negative ring terminal to the inverter’s negative terminal post.

Word of caution: do NOT connect solar panels to your charge controller without having a battery connected to it first. Some charge controllers will fry if they have nowhere to send the power to.

Below is what my breaker/charge controller/inverter area looks like. I’ve taped up all exposed positive metal surfaces with electrical tape to prevent accidental short-circuits and used 3M tie downs to keep things tidy (don’t do either of these until everything is wired up, or you’ll end up doing it twice).

Figure 9: Breaker/Charge Controller/Inverter area all wired up and secured. The large black wire is the battery negative cable and connects to the inverter’s negative terminal. The large red wire connected to the bottom of the 250-amp breaker is the battery positive cable. Again, don’t wire these up until everything else is done.

Fuse Block and Front Panel Ports

This step is easier than the breaker area as the wire we’ll use is much smaller (and therefore more flexible), and we’ll have more space to work with. Be sure to leave a small bit of extra wire as we’ll be securing these wires to the inside of the box and the lid as needed.

1. Run Red 6AWG wire from the inverter’s positive post to the fuse block’s positive post using ring terminals for both ends of the connection.
2. Repeat step 1 but use black wire for negative.
3. Use 10AWG wire to wire the first two connections on the fuse block to the 12v Socket/USB combo panels. Use fork terminals for the fuse block side and butt connectors to splice into the panel wires.
4. Use 15 amp fuses for these two connections.
5. Use your multi-meter to test connectivity between the inverter and the panels.
6. Use 18AWG wire to run power from the fuse block to the Drok wattage panel (if you have one). Use a third piece of 18AWG to wire the Drok’s yellow line to the input of the 250-amp breaker. You’ll need both a ring terminal and a butt connector to do this. This yellow line is what the Drok display uses to measure battery voltage.
7. Connect inverter remote display to inverter using supplied RJ11 cable.

Your results may vary, but this is what my fuse block and front panel wiring look like now.

Figure 10: Left, the fuse block. Right, front panel wiring.

The Battery! And some cable management, too.

Now it’s time to connect up your battery with the Anderson connector and ring terminals it came with. After connecting the cable to the battery, run the positive cable through the white loop (hall effect sensor) on your Drok wattage display. Then, connect this positive ring terminal to the input of the 250-amp breaker. Finally, connect the negative ring terminal of the battery to the negative terminal on the inverter. Be VERY CAREFUL not to touch these ring terminals directly together. It will certainly trip the battery’s internal fuse (if it has one), and could potentially cause a fire.

Also, you WILL see a small spark upon completing the circuit. This isn’t bad, it just happens because initially, the capacitors in the inverter are not in a charged state and will draw a small amount of current upon connection to the battery. Now, test everything to make sure it all works. If you bought the same battery I did, you’ll need to turn it on first. The inverter should power on, the USB ports should charge your phone when plugged in, and you should see information displayed on both the charge controller display and the Drok wattage meter. Test the NOCO Genuis10 by plugging an extension cord into the wall and the AC inlet port we installed on the left side of the box.

When you’ve verified everything works, tidy things up with some more of those cable ties wherever necessary. I screwed mine into the plywood of the lid, and just used the adhesive on the plastic box. Here’s what my whole setup looks like.

Figure 11: Left, the lid and front panel. Right, the inside of the box, with the Noco charger to the left of the battery in the bottom of the box.

You will want to close the lid and make sure everything moves as it should as you go along securing cables with the cable ties and adhesive squares. Also, I noticed that the inverter just barely rests on the top of my battery, so I put a small piece of foam between the two to keep them from wearing each other down. This also keeps the battery fairly secure, although I will probably build a small footprint out of wood in the bottom of the box to keep it from sliding around.

You may notice the extra black box on my lid. That’s an old Wifi router I’m experimenting with; it uses 12v DC power, and I want to try to build a 4G/5G modem for it using a Raspberry Pi and a tethered Android phone … more to come on that experiment in a future post!

Connect Your Solar Panels

Finally, we can start generating our own power! If you bought the same two 200W Renogy panels that I did, you can wire them up in series. Unfortunately, I never took a photo of this. Simply connect one positive MC4 connector on the back of your panel to the negative MC4 on the other panel. Then, use your MC4 cables to connect the remaining positive and negative to the appropriate connectors on your generator box. I’ve only used mine in winter so far, but I saw solar input power levels stay steady at 360 Watts all day.

So, what can it do?

Well … I’ve not been able to do extensive testing quite yet, but so far initial results are very promising. I’ve been able to run an electric chainsaw with it for an afternoon and only see a small decrease in charge voltage (it went from 13.2v to 13.1v of charge after about 3 hours of use). It can no doubt run other power tools like my miter saw and table saw. It will easily run a microwave or coffee pot for as long as you need to make a cup of coffee or tea. It should be able to run my camper’s fridge 24/7, provided there’s sun at least every few days. And it can charge from 0-100% in about 5-6 hours. Granted, it can’t power my whole house indefinitely, but within reason, I’m having a hard time finding things that it can’t do, and I’m pleasantly surprised at what it’s capable of doing. And, unlike a gas generator, it’s completely silent and requires zero maintenance, save for replacing fuses every once in a blue moon.

Figure 12: Working with my brothers to clean up a huge fallen tree limb. The chainsaw was running off the inverter in my solar generator box.

How does this DIY generator compare to the store-bought solutions?

Well, as I said, we spent about the same amount of money on this generator as we would have on a similar store-bought unit. Here’s a side-by-side comparison of the features and capabilities.

Feature	Commercial Generator	DIY Generator
Battery Capacity	0.72 kW/h	2.04 kW/h
Peak Power Output	1800 W	4000 W
Cont. Power Output	900 W	2000 W
Solar Charging Power	100 W	400 W
USB Ports	4	4
12v Sockets	1	2
Anderson Connectors	1	0
Charge via A/C?	no	yes
Price	$2497	$2510

At $13 more expensive, the DIY generator is the clear winner on overall features and capabilities. However, there are some pros and cons that can’t be captured here. For one, the DIY generator took several days to build, and required a number of tools that would have been extremely expensive to acquire if I didn’t already own them or have people I could borrow them from. It’s also undoubtedly heavier and larger than the commercial solution presented here.

But, I believe the DIY generator makes up for this in sheer flexibility. Don’t have enough power ports or need new ones when new connectors come out? Amazon sells just about any kind of external DC connector you can think of, and for very cheap (think $10-$15). You can just wire some new ones in, and probably in less than 20-30 minutes. Need more battery capacity? There’s plenty of space to add a second one, just wire it in parallel to the first one and your capacity doubles. And if anything breaks, you can replace it individually; no need to buy a whole new setup.

What do YOU think?

I sure had a lot of fun building this generator, and I look forward to continue adding new features in the future (I’ve since built a 4G modem out of a Raspberry Pi and used it and an old Wifi router to turn the generator box into a portable Wifi network; read about that project here!). What do you think about it? Are there some improvements you can think of that would make this a better build? Let me know in the comments below.

And have a happy New Year!