How I Went Off Grid At My Hawaii Tiny House

Solar energy has been a passion of mine for well over a decade now, but I finally got to go solar when I bought some land in early 2014 on the Big Island of Hawaii that included a run-down cabin. I decided to invest some money to retrofit the cabin (Figure 1) and convert it into a liveable tiny home that could double as a writer’s cabin and vacation rental. And I decided to go entirely off-grid, including for power.

Going off-grid for water was pretty easy. Water falls from the sky and is stored in a catchment tank. With filters and a water pump, this is a sustainable and healthy solution for water that doesn’t involve the authorities at all. There’s also a very cute little outhouse that has its own rainwater catchment tank and a flushable toilet. Going offgrid for power was a bit harder but I was able to get it done without great expense and mostly by myself. And if I can do it anyone can do it.

Figure 1. My tiny home near Hilo, Hawaii.
Figure 1. My tiny home near Hilo, Hawaii.

Hawaii has been making news due to its high saturation of solar power on the grid. Oahu, the most populous island, and the Big Island, the biggest island, have well over 10% of homes opting for solar. But these figures include only grid-tied homes. Hawaii’s utilities have dramatically slowed interconnection of new solar facilities due to increasing concerns about the stability of the grid. Going entirely off-grid is one solution to this growing problem, which has many other benefits, but also some downsides that I’ll discuss here.

My little cabin is up a fairly long driveway and it would have cost many thousands of dollars to have my local utility company, Hawaii Electric Light Co. (HELCO), install power at my place. This made going off-grid an easy decision. Since my cabin is small and the climate is warm all year around, it doesn’t need a very big solar system. As preparation, I read Michael Boxwell’s Solar Electricity Handbook, 2014 Edition, and with some help from a local solar installer who specializes in off-grid systems I figured out the appropriate size and type of equipment I’d need.

I wanted to do as much of the design and installation myself because I’ve been wanting to learn more about the nitty gritty of solar for some time. This was a perfect opportunity to get my lawyer hands dirty and take my eyes away from staring at my computer screen for a while.

Boxwell’s book is a great resource, and even though he’s a Brit the advice applied just fine to the US. I decided to build a 24 volt system. Combining four batteries serially got me to 24 volts. Ditto with two solar panels, which are 12 volts each.

Figure 2. The homely little solar system.
Figure 2. The homely little solar system.

In looking at my power needs, I calculated that I could probably get by with just two 250 watt panels, for a total of half a kilowatt. My equipment list included, accordingly: the two panels (Schott Solar, bought from Provision Solar, a Hilo-based company owned by Marco Mangelsdorf, costing about $800 including racks to install them on my roof), a ProStar charge controller (bought from Off-Grid Solar Specialists for $350), a Schneider Electric inverter (from the same store, $1,200), four Interstate batteries ($130 each, bought from Pahoa Propane and Batteries), and a bunch of wire and battery connectors.

I did most of the installation myself, painstakingly and with much trial and error. I ended up needing an hour of a professional installer’s time to wrap it up, so the total cost of my system was about $3,500, or $7 per watt installed.

The batteries are 232 amp-hours each, but because they’re connected in serial fashion, they supply a total of 232 amp-hours at 24 volts. They are charged directly from the charge controller at 24-30 volts. The inverter connects to the batteries and the home’s central power panel connects to the inverter. When I leave for extended periods I turn off the inverter but leave the charge controller running. This allows the panels to keep the batteries fully charged and healthy, while avoiding the risk of something going awry with the home power that could leave my batteries dead again.

The ProStar charge controller is addictive to watch, since it shows how much power is coming in from the panels and how full the batteries are. I think of this as “watching TV.” I’ve seen as high as 38 volts coming in during very sunny times at mid-day. I was also pretty happy to see how much power comes in even when it’s cloudy or rainy — from 1/10th to 1/4th of full power. Power production starts as soon as it gets light but doesn’t really get going until a few hours after sunrise.

My pre-installation calculations showed that my little system could power a small fridge, lights, and a TV and DVR player, as well as chargers for computer and cell phone. I was happy to find that my calculations were accurate, but I did get worried a few times when I woke up in the morning and found my batteries very low, as evidenced by the blinking red light on the charge controller. But invariably by noon or mid-afternoon my batteries go back to green. My new lava rock wall shower, fed by rainwater and powered by the sun, was in business.

Figure 3. Off-grid lava rock shower heaven.
Figure 3. Off-grid lava rock shower heaven.

It can be challenging at times being off-grid, particularly when you’re working out the kinks. I initially installed the system in April last year and I returned to Santa Barbara for a few months. When I went back to Hawaii in July I found my solar system down and my batteries dead dead dead. I couldn’t figure out what happened so I called the same local installer who had helped me wrap up installation in April. He diagnosed loose battery connections as my problem. I had to take the batteries back to the store to charge the batteries back up. That took three days, for various reasons, so I was living without solar power for a week.

I didn’t mind it too much since I have plenty of candles and also bought a kerosene lantern. I kind of liked the primitive living conditions and I have a backup generator for when I needed to charge my computer and phone. I’m also rarely at home at night so it wasn’t a big deal. The fridge was the only thing that I really missed. But since I was only in Hawaii for three weeks on that trip I wanted to get the system back up and running so that I could rent out my place while I was gone.

I was able to get the batteries re-installed and wired in snugly, but still my system refused to come back to life. I double checked everything and called the installer again. No help. I went back to the store where I bought the charge controller and he agreed to give me a new one since it seemed that the problem must have been the charge controller. I re-installed it. Still nothing. Long story short, we finally figured out that I had been given the wrong configuration to install my panels and the panels were in fact supplying twice the voltage that the charge controller could handle, so it had burned out. I re-wired the panels and finally the whole system snapped back to life. It’s now been running fine since then and it should keep running fine for a long time (fingers crossed).

Here’s where it gets interesting. Another major benefit of being off-grid was highlighted with the  hurricanes that threatened Hawaii in 2014. After Iselle hit the Big Island in August, downgraded to tropical storm status by the time it hit, well over 20,000 utility customers went without power for many days and sometimes longer.

My tiny house, on the other hand, was sitting pretty with solar power and batteries going steady.

tambookIn sum, going off-grid in Hawaii can be very liberating and can save money too. Power bills are high in Hawaii since most power is generated by imported diesel. My power bill would probably be about $100 a month if I was on-grid, but I’d also have to pay the large fee for building a line to connect to the grid. With my off-grid system all of my costs are up-front and there are no ongoing costs except when/if things break down or go awry (again, fingers crossed).

I can’t calculate the payback time accurately since I don’t have a power bill to compare. Based on my estimated $100 monthly bill I would, if I had been on-grid previously, pay off my system in about three years; but that again leaves out the cost of connecting to the grid in the first place.

Going solar also allows me to be secure when the grid is down due to storms or falling trees, and to avoid things like dirty diesel emissions, spikes in electricity rates, and dealing with the utility on interconnection or net metering.

I’m still very new to off-grid solar and I may find new issues cropping up. I’ll report back if anything newsworthy happens. My tiny home in Hawaii is available for vacation rentals most of the year, so you too can witness the benefits and challenges of off-grid solar firsthand.


Tam Hunt is a writer and lawyer who splits his time between Santa Barbara, California, and Hilo, Hawaii.

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  1. Loved your article Thank you for sharing ~ Would love to see inside that cute itty bity house 🙂

  2. If you click on the link at the end of my article you can see a lot more pictures 🙂

  3. Wow Thanks Tam. Really good information! I love the every little detail you added in there. It’s great man. l wanna do something like that some day 🙂 Power to the people!

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