Building a solar generator

Guest Post by Bill Brooks

As many of you know, I recently completed my tiny house on a trailer. I plan to travel to a few locations beginning this winter. I built my tiny house to be self contained, since most of my time will be spent in places without services (electricity, water, etc.). Since batteries will supply the house’s electrical power, I will need to recharge them often. While I will have a propane generator, I plan to use solar power for most of my needs. This should allow me to get power, and keep the costs down by not buying propane as often as if I was using the generator.

Completed Solar Cart

Often, trailers have the solar panels mounted on the roofs. This allows the panels to charge the batteries as long as there is sunlight available. The problem with this set up is you need to park your trailer in the sunlight. While this might work well in some locations, others will have trees and other obstacles that can block the sunlight. Also, certain locations might result in parking the trailer facing away from the sun, hence lowering the output of the solar panels.

Originally, I decided to place the solar panels on a cart. This would allow me to move the panels into the sun, reposition them as needed, and provide storage for the panels. As a further enhancement, I added a solar controller, battery, and inverter to the cart and turned it into a solar generator. That way I could have power available in almost any location I plan to go. With this set up, I can use both AC and DC items, such as a microwave, and even a refrigerator all powered by the sun.

The Solar Generator Parts

First, the technical details for those who are interested. The solar generator (which I call the SolGen 160) has a four major components. The 2 solar panels are rated at 80 watts each, for a total 160 watts. The solar charge controller is rated at 30 amps. The battery is a marine deep cycle model, and is rated at 210 amp hours. The inverter is provides a steady output up to 1100 watts of AC power, with a peak output of 2200 watts.

Ok, so what does all that mean. Based on the manufacture’s solar panel ratings under ideal conditions, the SolGen 160 should provide approximately 460 amps of power each week to charge a 12 volt battery. While you never want to discharge a battery completely, the output is enough to fully recharge the battery in 3 to 4 days. If you use only 25% of the battery each day, the solar generator should be able to fully charge it up during the next day. With this set up, it can power a number of appliances, such as a small microwave, TV, laptop, or even some power tools. All the comforts of home can be available wherever the cart is located, in a campground, a forest, or even the desert.

How was the cart assembled

I used 2×3 lumber as the framing for the cart, and enclosed it with the T-1 siding. The overall size of the cart is approximately 4 feet wide by 4 feet long by 4.5 feet tall. I began by building a wooden frame that fit around each panel. I then built two L-shaped pieces for each panel to hold the panels at a 45 degree angel. The L-frames were cross braced to provide a solid base for each panel. Then the two panels were attached together by screwing the frames together. Next I added the T-1 siding to enclose the cart, and a piece of plywood to form the cart floor. After that, I built doors on the back to allow access to the battery and components inside the cart. Finally, the cart was painted and caulked to prevent leaks, and wheels added to make it mobile.

Here is a video slideshow of the building process…(video created by Steven at Tiny House Listings)

Cost of Materials

The SolGen 160 cost approximately $1500 to build. The cost breakdown is as follows:

Solar Panels – $ 850
Battery+box – $ 180
Solar controller – $ 100
Power Inverter – $ 70
———-
Subtotal – $ 1200

Cart – $ 300
————
Total – $ 1500
========

The major portion of the cart expense was for the T-1 siding and the 2×3 lumber. The wheels, hardware and paint were a small additional cost, and purchased locally. While they lumber was purchased locally, the solar panels, controller, and inverter were all purchased from Amazon.com. While this configuration was designed to fit my needs, buying fewer or less expensive solar panels and components would reduce the cost of the cart.

Several people have expressed interest in the SolGen 160 since I posted it on Twitter and Facebook. I am considering selling a set of plans so people can build their own solar generators. If there is any interest in this, please let me know by responding to the poll below. Thank you!

Would you be interested in plans for a Solar Generator Cart?

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35 Comments Building a solar generator

  1. Harvey Pwca

    Now you have to lug that cart around AND find some place on/in the trailer to store it. Worse yet, now that it’s mobile and some distance from your trailer… those wheels sure make it far easier for someone to walk off with it or do malicious damage to it.

    An easier solution would have been to create a swivel mechanism that tracked the sun and mounted this on your trailers roof.

    If there are obstacles then move the stupid trailer to where there aren’t any. Please, don’t insist that in “some” places this is not possible. Seriously, how often will that be an issue??? My money is on it being statistically insignificant.

    Reply
    1. V

      Good Morning Harvey… and how was your sleep last night? sounds like you didnt GET any!!!
      Damage, theft and shade are all valid issues… I could see making this as a hat on the cab of the tow vehicle… which doesnt necessarily have to be IN THE SHADE and which makes it easier to move… along with a mechanism to lock/unlock auto turning to find the sun…(swiveling wouldnt work while on the move) might need a shield to protect the solars from road pebbles wherever you put it…. I wonder about the weight, wouldnt really WANT to tow it, might consider some collapsable version on rigid poles rather than the permanend WOOD tentike….. then could be stored in tow vehicle on the move, along with the bikes. also could extend the poles to UPPPPP like an antenna if it weres permanently fixed in a ‘box’… Harvey, have ya had your coffee yet? checked your sugars?

      Reply
      1. V

        dont think, as shown would be towable… could see that the panels could be made to be clamshells and mountable on a pole for ON THE MOVE. and, this unit is heavy. COuld see it with piano hinges to be collapsed upon itself to a center point and could be fixed permanently to a 2 wheeler for maneuverablility. Battery does not HAVE to be adjacent to it, in fact, would be better attached to the unit that will be USING the power with disconnects….

        Reply
  2. Canoez

    I have to agree with Harvey’s comment on the ability for people to walk off with it.

    I think that overlooking that point, it is an interesting idea – what would make it nicer would have been to hinge the base (where the bottom of the panels meets the cart) to allow for storing the cart in a smaller size and adjusting for seasonal changes in the height of the sun versus the horizon.

    Also, a simple solar tracking system can be made from a pair of small solar panels with a septum between them driving a reversible DC gearmotor to turn the assembly. When light falls more on one panel then the other (shadowed by the septum), it drives the motor in the direction of the sun. It will even re-set itself in the morning.

    Reply
  3. Beth

    Geez, Harvey, chill out. No need to be a jerk. You spend your money your way, and let Bill do the same.

    The storage question for something bulky like this cart, and the possibility of theft, are valid concerns.

    But what Harvey fails to note is that in hot weather, it’ll make sense, if possible, to park a tiny house or trailer in a shady spot. Yet hot sunny weather is best for generating solar power.

    I wonder if a collapsible version is an option? You’d probably have to detach the battery and such and stow them separately for transit.

    Reply
    1. Steve

      For the record–I didn’t see your reply ’til I’d posted mine. Please take my similar thoughts as a vote of confidence.

      Reply
  4. 2kids2cats

    My goodness Harvey–did you forget your morning coffee??

    I have been looking at the cost savings of building a solar generator vs. buying one. At $1200-$1500 that seems to be a good $1000 less than purchasing a comparable manufactured unit, and well worth it. I am looking at purchasing some forest property where sunlight would be an issue (and moving my stupid trailer isn’t an option) but I could place the generator a bit from the house.

    Thank you for your ideas and keep up the innovations!

    Reply
  5. Steve

    I wondered if someone else would have the idea for a collapsable trailer–and the prospect of a too-mobile version ‘disappearing’. Great minds think alike, eh?

    BUT–I like the quality of the construction; lost of nice details.

    Here’s a thought–could the battery be in a fixed location on your trailer (under the porch?) and then connect via cords to the panel/assembly? If so, are the panels light wt. or heavy? If light, you could have a series of locations on the exterior of the Tiny House where you position/hang them, then connect the cord to the battery(ies). Or if heavy and if you want more remote positioning avail. , they could have wheels at the base so you roll them to wherever you’re going to set them up (with sturdy legs that swing down to prop them up), then run a wire back to the batteries. They’d still be relatively flat and compact, and maybe could be secured flat on the side of the Tiny House for transport.

    But–maybe they’re too fragile? Maybe running a (long) cord to the batteries means losing power? Maybe other problems?
    I only know enough about all of this to know that I don’t know very much about all of this. Glad to hear what others have to say.

    Reply
  6. Al Mollitor

    At $70, I imagine your inverter is a modified-sine-wave one. Have you been able to power everything you want with that, or have you wished for a pure-sine-wave inverter?

    Reply
  7. kenny

    I don’t think I’ve heard of solar alot on this site si it never occurred to me to help everyone save money on it. You best bang for the buck is buying from Sun Electric out of Miami. I have been dealing with them for years and you can not beat their prices. I bring them up because you paid way to much for your panels (like $500 to much for the pair).
    I am in no way affiliated with the above mentioned company, I just don’t like paying too much for anything.

    Kenny

    Reply
  8. kenny

    Forgot to mention, nice job. If everyone has you worried about it being lifted add a vibration sensor and a loud siren to it. Minimum might be to have retractable wheels that go up into the inside. That might help keep it from rolling around while underway also. Let us know how it works.

    Kenny

    Reply
  9. www.kevinsmicrohomestead.com

    Bill this is awesome I have been pondering this for some time. I have a four pannel 60w set on a pvc frame but an enclosed unit on wheels is just what the Dr. ordered . Thanks for taking the time to do a video and post this to share with others .

    Reply
  10. Nerida

    I also like this idea, and have for a while. You are going to need a beefy tow vehicle anyway so I figure it could travel in the tow vehicle and collect some rays along the way.

    I have also battled with the issue of shade, I live in a hot climate so we design for and tend to seek out summer shade, which isnt so compatible with solar. Now my main aim is to be relatively stationary and I figure the first thing my 4 legged companion will do is cock his leg and make his mark. :) But I will not trade him in. However, I could easily raise this above dog-leg height and this unit is going to be easy to clean, maintain and service.

    I love to see clever/handy people solving my problems for me and even more those same people willing to share.

    Nice little slide show too.

    Harvery brings a funny picture to my mind, some shifty character in a hoody pushing a mobile solar cart down some back street in the middle of the night. Around here – that would get noticed. I wonder if you can trade solar carts for outlawed stimulants?

    Thanks Bill you got a’yes’ vote from me.

    Reply
  11. Shalin

    I live in an apartment that faces North – this probably won’t be soo useful…

    However, I would LOVE to figure out a windshield/sunroof shade for my car that charges a battery that I can then take into my apartment and run various items (computer, lamps mostly).
    I understand the new Prius vehicles have a PV-array/sunroof (or something like that) to help run the AC and other items…

    –S

    Reply
  12. alice

    Might not be consumer ready at reasonable prices or very powerful quite yet but there are some interesting advances in flexible solar technology. Hopefully in the near future there will be some kind of solar tarp available to set over vehicles or portable folding frames. In the meantime, if this setup fits your needs, seems like a reasonable approach. An internet search for “flexible solar” shows several sites of interest. The solar fabrics are really intriguing – I’d love a sun poncho with integral cooling and plug for an e-reader for an enjoyable day at the beach in the not too distant over-heated future.

    Reply
  13. Benjamin

    Re: “…460 amps of power each week to charge a 12 volt battery.” Amps is a measure of current, not power (watts). Adding in “each week” is even more confusing (watt-hours). You may want to look into this and clarify the information.

    It looks really heavy! Have you weighed it? How do you transport it?

    Are the two independent mounts, one for each panel, for modularity? The framing could have been lighter if you had put both panels on one set of 2×3′s.

    If you are worried about theft, as a few of the posters seem to be, you could make the wheels removable. Actually, you could probably get by fine with just 2 wheels and lift the other hand, like a wheelbarrow.

    I agree that the battery would be better to be placed in or on your trailer. Just extra weight to lug around. Although I can see how you might want the unit to be a self-contained power source, in which case you might want to add a weatherproof AC outlet to the outside surface.

    Nice work!

    Reply
  14. Moontreeranch

    Its a good sound design…and for those with portable homes a great option. My small cabin is run with a system about half this size in Northern NM. I have 1 80 watt panel and 110 ah storage…my inverter however is 2500 watt to allow me to run a few bigger power tools.

    I got my 80 watt panel from solar blvd. for under 300…they have come down some since I got mine.

    In the portable dept. I built this smaller laptop charging station.

    http://kmswoodworks.wordpress.com/2010/04/05/solar-laptop-station-update/

    Reply
    1. Ralph Sly

      Great laptop charging station! Now that is compact. I had one built into a backpack to use with my laptop and run a video camera. Never once ran out of power and ran the camera for hours on a small 400 watt inverter.

      Reply
  15. Bill Kastrinos

    Nice job Bill. Anyone who has lived in a tiny house, knows it really lowers energy bills to park in the shade (summer), and in the sun, (winter). It actually would be easier to steal the house than the solar unit :) (or the truck with unit attached as someone said). And your design would lend itself to larger wattage panels, a larger inverter, additional batteries, or an a/c panel mounted mini inverter with no batteries, whatever one needed. We have been working on several designs for a mobile generator, but I like yours. Nicely done.

    Reply
  16. Vaidotas

    Sorry for bad comment but since it has no automatic sun tracking it has low efficiency. Solar cells are very high in price so there is need for sun tracking may be reflectors also for good efficiency, or your 1kwh will cost thousands…

    Reply
  17. Bill Brooks

    Thank you for all of your comments regarding my solar generator cart. There are a lot of good points raised in the comments. Rather than address each one individually, I will try to answer them here.

    I purchased the solar panels about 2 years ago when I first began building my trailer. The panels were purchased through Amazon.com. Since then, prices decreased and panel availability has increased. This alone could reduce the cost of the cart substantially.

    The inverter is a modified sine wave model. I have tried it on several different things, but I have not tested everything yet. I hope to do that once I start traveling.

    The solar generator was designed to be a mobile power station so that I could use it for more than just the trailer. I can put it in the back of my truck, haul it where I need to, and then use it there. I will be adding a cable and lock to the cart so I can attach it to the trailer or truck when I am not around.

    Because of my needs and time constraints, I went with the fixed panel angle. I had thought of various designs, but ended up with this for simplicity sake. If I need to change the panel angel, I can put a few blocks of wood underneath the cart to raise one end or the other. If I had a fixed location to place this, I would design it differently to allow for ease of changing the angle, or even some solar tracking as well.

    The cart frame itself is 2×3 lumber, but could be made with smaller lumber to reduce the weight. The heaviest part of the cart is actually the battery and panels. The cart is light for its size, but could be changed to reduce it further.

    Again, thanks to everyone for your comments and interest. If you have any questions, please let me know.

    Reply
  18. Donald B. Beams

    I just want to thank and acknowledge you for posting this, Bill. You created a great conversation and thus generated something really cool for all of us to think about, expand upon, and personalize for our particular situation. I am in the process of finishing up an all-climate 192 sq.ft. mobile cottage, that I want to be completely off-grid capable.

    A friend of mine suggested creating a lightweight towable 2 wheel “POWER TRAILER” that one person could move around, incorporating PV, batteries, inverter, etc. plus a propane generator in a sound insulated box with intake/exhaust ports, and a solar water heater, all in one package. I think its a fabulous idea offering the ultimate in flexibility, AND a possible product line, perfect for retrofitting existing RV’s, tiny cabins, etc.

    Also, thanks to Kenny and JC for resource recommendations.

    Reply
  19. Ralph Sly

    Love your innovation Bill, I seen one built on a two large wheeled cart (box type) He had 4, 6v batteries wired to 12v, and 4 panels that folded out with a 3000 w inverter. A motor on the cart (from a handicap scooter) made moving it up and down hill on rough terrain a breeze for the older than me guy and he had a winch lift bracket built onto the back of his RV to haul it with him anytime. This whole set up was far less than half the size of yours and worked pretty slick. Most of the purchases were made at swap meets and places like Craiglist and he got away pretty cheap. To each our own, build it and someone will build it better, smaller and cheaper. Good Job but I couldn’t use that in my application. I would hate to tell anyone the ridiculous prices I paid for my first solar experience. I suppose our best bet is to put the idea out there with some ideas as to what we want to build, have it critiqued first and request the best locations to purchase items. But what fun would that be.

    Reply
  20. Jeremy Womack

    Bill,
    Great build and problem solving.

    I use a portable plug and play 80w solar system with integrated charge controller. I bought one to test whether I like it to sell. Well I love it! Cranks out enough power to run my 50L fridge and charge my batteries on a good day. Rated to 4.6amps but you’ll never see that in the real world, realistically 3.8amps. I’ve learned that panel ratings are lab settings, perfect angle, perfect light source, etc.

    I do a lot of backcountry vehicle dependant travel, think safari style. The PV system I use is pretty tough, lots of un-maintained trails with these panels bouncing around in the truck.

    Getting the most out of any solar setup means moving the panels to maximize the light, for the non motorized, that means moving the panels every hour or so, not a big deal if you’re around.

    Check out power film for the flexible panels, friends are using them and love em!

    To see the panels I use and sell(I’m not try to sell y’all, just sharing my compact solar experiences) http://www.expeditionops.com thanks. Ps all the pics on the product page are from my truck in hideout canyon, UT. Enjoy.

    Jeremy

    Reply
  21. Dustin

    Bill,
    I love your creativity and adaptability! Your solar generator is well designed. For others, who might lack the skills or time to build their own, I wanted to present a second option: A portable solar generator manufactured in the USA! Its small size is a perfect match for a tiny house. http://www.suburbsolar.com

    Keep up the good work!

    Reply
  22. anne

    I found this trailer to be intriguing. I live in California in the middle of the hot central valley and often wondered if I could use such a set up to power an electric or hybrid car. Please Mitt, and Obama if you are listening, solar is the sustainable way to go cuz it frees up money to be spent elsewhere. I would like the plans, thank u very much…

    Reply
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