Power System

Power System

Power System

I just finished installing most of the electrical outlets and switches this past weekend, and thought it would be a good time to discuss the power system.  It’s an off-grid system, mostly out of necessity, as I’m about 2/3 of a mile away from the nearest power line.  As convenient as it would be to have grid power, for me at least it’s not worth the considerable cost of running a line that distance.

The main source of power for the system will be several solar panels, which will be installed this summer, in addition to a generator for backup and power tools.  Running just from the battery, the system can output a continuous 300 watts of 115 VAC.  While that’s not a lot of power, it’s more than adequate for my needs.  I figure I’ll be running maybe three to four 9 watt CFL lights at any one time, and maybe recharging a laptop or cellphone now and then.  Some planned future loads, such as the water pump and Coleman Stirling power cooler, will run directly off 12VDC to avoid the inverter losses.  If I need more power, or have to top off the battery bank, I’ll use my portable Honda eu2000i generator I usually bring along.

Aside from designing the cabin itself, I probably spent more time designing the power system than anything else.  Having little to no electrical experience, designing a properly sized solar system was difficult.  I’m not sure I would have been able to do it correctly without the Solar Electric Power Discussion Forum and Northern Arizona Wind & Sun who hosts it.  The members of the forum, and the people at NAWS, were extremely helpful to a solar newbie like me.  NAWS also carries most everything needed for an off-grid solar setup like mine, and offers excellent technical support to boot.

The specific components I used are as follows:

Uni-Solar US64 solar panels.  These are 64 watt flexible thin-film photovoltaics mounted on a steel backing plate.  There’s no glass on these and it’s beneficial in that if a single cell is damaged, say from hail or vandalism, the rest of the cells in the panel will continue to function.  Unfortunately these are now discontinued and are still relatively expensive, on a dollar per watt basis, if you can find them.  I only have two of these, which is probably not enough, so I will have to find some old stock somewhere or buy another brand.

Morningstar SS-10-L solar charge controllers with low voltage disconnect.  While these are very good units, I would not necessarily have chosen them except for the fact that I got a great deal on two new units in an eBay auction. I do recommend the low voltage disconnect feature though if you plan to have any 12VDC loads hooked up to them.

Morningstar SureSine 300 watt sine wave inverter.  This is the best small sine wave inverter you can get in my opinion.  It has the lowest stand-by power usage, at 55mA, of any inverter I’m aware of. A similar 300 watt unit from Samlex, at half the cost, uses 700mA – that’s a lot of wasted power for standby mode.  Don’t be tempted by the cheap modified sine wave inverters as they can damage certain electronic devices.

Concorde SunXtender 104 Amp-Hour AGM (absorbed glass mat) deep cycle battery.  Since I really can’t do justice to a battery discussion here, I strongly recommend reading the excellent Battery FAQ at NAWS.  What I will discuss though is the use of AGM batteries.  The main advantage to AGM batteries, for my purposes at least, is that they are resistant to freezing.  Since my cabin is in northern Wisconsin, and unheated most of the winter, I wanted the peace of mind that my batteries would not freeze. Another benefit is that they do not release hydrogen in the amounts that flooded batteries do and can be kept indoors without a vented battery box in small numbers.

Iota DLS-30M battery charger.  While a battery charger is not a necessity, it is useful if you have a generator tied into your system.  If you’re going to be running your generator anyways, you might as well be charging your batteries at the same time.  It’s also useful in winter for those short or sunless days.  Make sure to choose the proper amperage charger based on the size and type of your battery bank.  The IQ4  Smart Charger, either integrated or as an add-on, is also nice to have for a more complete charging process.

Iota ITS-30R transfer switch.  This device automatically switches power between the inverter and the generator, and is only necessary if you have a generator hooked up to your system.  You’ll notice that I included a couple of switches between the generator and the power system.  The right switch allows me to control when the transfer switch receives or loses power from the generator.  This is most useful when turning off the generator to prevent questionable power from being fed into the system before it switches to the inverter.  The left switch allows me to disable the battery charger in case the generator needs to run and the battery doesn’t need to be charged.

All of my 12VDC fuses, breakers, and switches are made by Blue Sea Systems for the marine industry.  Unfortunately, the online company I purchased these from does not carry Blue Sea anymore, but I will provide the links to the products I used on the Blue Sea site.

m-Series Battery Switch
ST Glass Fuse Block with Negative Bus
PowerBar Common BusBar
187 Series Thermal Circuit Breaker
MAXI Fuse Block
Terminal Fuse Block
DC Analog Voltmeter

Most everything else, such as the wire, AC breaker box, outlets, and switches, I was able to pick up at my local hardware store.

13 thoughts on “Power System

  1. KL

    Very impressed with your melding of containers, living space and security in a remote location. I’ve been following this movement for a number of years and it’s great to see such commitment, research and information on construction issues. A real eye opener into the potential tricky aspects of committing to this type of construction and giving real answers re: floors and joining containers.

    1. Steve Post author

      KL & Jesse:

      Glad I can help. When I started this project there was a dearth of practical information on how to build with containers. There were a lot of pretty drawings and pictures on the net, but nothing that showed the nuts and bolts of what to do. I’m hoping that others don’t have to go through the level of effort to get started that I did.


  2. Dale Sale

    I believe that the Coleman Stirling cooler is no longer available. I purchased a similar cooling system from Global Cooling Products for my boat and it works well. It can be a little difficult to get a unit, but I was able to get a cooling unit that could be fitted into my existing icebox. They do sell complete portable units similar to the Coleman (which they provided the actual cooling assembly for). I plan to take my cooling unit with me later and install it into a larger upright 12V refrigerator I construct; similar to the old “monitor” units of the 40’s. Kudos to your work and I am sure you and your family will enjoy it for many years.

  3. Dale Sale

    I was able to pull up the Global Cooling site. http://www.globalcooling.com/products/collapsibles/scjs05.php I purchased the SC-JS05 unit. As you can see it is a self contained device that can be fitted into a DIY installation refrigerator. The only drawback is that the 12v cooling fan runs constantly and can be a little annoying in the middle of the night (even though it draws little power). You could just switch it off at bedtime with a well insulated box and it should be fine until you turn it on in the morning.

    1. Steve Post author

      Hi Dale:

      Thanks for the info Dale, although I was fortunate enough to pick up a new old stock Coleman Stirling last summer for about $350. When I was researching small 12V refrigerators and coolers, I found a lot of good reviews on the Coleman, and Global Cooling, on several boating sites. It would be tempting to build a custom fridge with one of their cooling units, but I have way too many projects right now to try that.

      There’s one thing I don’t like about the Coleman, and that’s the subtle noise it makes. I don’t notice it during the day, but at night it makes a very faint pumping sound that keeps me awake. I’m hoping now that the walls are up I won’t be able to hear it from the storage room. I could always just shut it off at night like you mentioned.


  4. Nerida

    Thanks for all the detail. The off-grid electrics are my next challenge. I havent started to build, I’m one of those that wants all my ducks lined up before I start. And I plan on building from scratch.

    I had heard of flexible solar panels before but at last they have a name. So thank you for that pointer. Hopefully they will be still available when I have my electrics worked out and start building, or an improved version of the same concept will come onto the market. Uni-Solar Australia still have them listed on their website if you get desperate. Dont snaffle them all please – leave some for me 🙂 I will be building very small and with a curved roof, hence the much greater preference for flexible panels.

    Curved roofs are quite popular here in Australia.

    So on coolers, there are some that operate using alcohol and I cant for the life of me remember what the technology is called. No power needed but frightfully expensive I believe and not so good in humid climates. Do you or any of your followers know what I am talking about.

    I am finally learning to keep tidy notes on small discoveries. Pity I didnt do that at the beginning of my research.

    Looking forward to seeing your finished project.

    1. Steve Post author


      I found a good deal on a new US64 panel a few months ago, so now I have a total of three. I’m still looking for a deal on one more, but I’m not in any hurry right now. Depending on the type of roof you plan on building you might be able to use Uni-Solar’s flexible adhesive panels. Their 68 watt panels are 68″x112″ and are designed to be applied directly to metal roofs. These save the cost of a mounting system and are much more resistant to theft.

      I’ve never heard of an alcohol refrigerator, though I do know that Dometic makes a Kerosene refrigerator. Lehmans sells them in the US, but they are pricey at about $1,900. http://www.lehmans.com

      Good luck on your project and please keep me informed.


  5. Omar

    Thank you for great work….I wounder if the rating of the fuses and all other breakers is too big and for that won’t do what they are designed to do.Can you explain how did you choose the rating for them?

    Good luck and keep on the good work.


    1. Steve Post author


      Most of the equipment I bought specified what size fuse or breaker to use in the manual, so that was easy. In most cases the type of fuse, or breaker, was up to me and depended on how I was going to use it. For example, I used a breaker instead of a fuse for the inverter so I could disconnect it from the battery easily – I do this every time I leave the cabin.

      For general fusing of the wiring throughout the system, there are a lot of resources on the net that can help you with that. My favorite is from Blue Sea Systems and can be seen here:


      Hope this helps.


      1. Chris

        Circuit breakers aren’t designed to be used as switches. They can easily be worn out and then won’t trip when you need them to. Please consider installing a proper disconnect switch. One that small shouldn’t be too expensive at all.

  6. Tim Schuy

    Not so sure it is a good idea to have the battery inside your cabin, unless it is in a sealed box with ventilation going outside. During charge the battery will gas which is not so healthy for you in an enclosed space. In fact it is a bit dangerous…

    1. Steve Post author


      As I mentioned in the article above, I am using an Absorbed Glass Mat (AGM) battery. These are unique among deep cycle batteries in that they can be safely used and stored indoors. They do not emit any toxic or flammable gasses during charging operations. I recommend you read the deep cycle battery FAQ at Northern Arizona Wind & Sun for more info on these.




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