Scream last plugged into grid power in El Salvador in May 2009. Since then we have lived on a tiny electricity budget and dealt with all kinds of adversity. We have a few insights to share.
Scream has 390 watts of solar panels, which works out to 1 KWh per day as an annual average. We run them through an MPPT charge controller, which adjusts the voltage to maximize the amps absorbed by the batteries. In mid 2010 we added a wind turbine, which is rated at 300 watts and averages about 1/10th of a KWh per day.
Our main load is a freezer. We also have lights, navigation equipment, radios, and a 2 KW inverter that we use mostly for our laptops.
Chronologically the first thing that went wrong for us, and the first thing you need to guard against, was the failure of our single source of electricity. In 2009 Scream was a solar powered boat. We have a diesel engine for propulsion, and it does have an alternator, but we existed almost entirely off our solar panels. Then in October 2009 our charge controller died. Xantrex replaced it free of charge, but we were without solar power for four months. We ran the engine for power a bit, but mostly we cut away at our already tiny energy budget. Don’t let this happen to you: if you’re going to live off grid you need at least two completely independent sources of electricity.
Controlling your consumption is usually more practical than increasing your electricity generation. LED lights are a must. We have fluorescent, compact fluorescent, and LED lights on board.
Batteries are a temporary power storage technology. They are most suited to getting your boat through the night, not through long periods of time. On Scream we had a 1260 Amp hour bank of AGM batteries that cost $5,000. Notice the past tense. They went entire seasons between being fully charged as we cycled them in their bottom half. Not surprisingly, they died in less than half of their design lifespan. Instead of buying lots of batteries with less ability to charge them, we should have bought fewer batteries with more generating ability. As an absolute rule, the cost of your power generation equipment should exceed the cost of your batteries. For a primarily solar powered boat, another measure would be for the amp hours of your battery bank to be roughly equal to the watt rating of your solar panels.
While we’re on batteries, if you’re in the tropics the heat damages batteries. When we were in El Salvador the overnight lows were 29 or 30 celsius. Your battery care instructions say that your batteries should never be allowed to get to that hot, and those were the ambient daily lows. If you are in the tropics you will regularly exceed the design specifications of your batteries. So don’t bring a lot of expensive batteries into the tropics, they won’t last.
Refrigeration is the big consumer of electricity. When we are flush with power the refrigerator is half of our daily use, when we are rationing that figure approaches 99%. I strongly recommend not having a freezer on a cruising boat in the tropics. If we didn’t have a freezer then our available power would have averaged ten times what it was. Or phrased differently, if we didn’t have a freezer we could have had half the generating capacity and still taken much better care of our batteries.
If you are going to have a freezer, make it efficient.
If you are going to stock your freezer, and rely upon that food in your provisioning, then you need a fossil-fuel generator. I sincerely wish that this wasn’t true and I tried to deny it for years. But after killing a battery bank and still repeatedly throwing out food that wasn’t properly frozen, and repeatedly eating “food” that was going bad because there wasn’t anything else, I have to insist that depending on a renewable-powered freezer in the tropics is wrong.
We recently acquired a 1 KW gasoline generator. It has helped. I wish that I didn’t need it, but it would have greatly improved the morale of the crew last season in the tropics. We’re running it less than an hour a week, mainly because the cold waters of New Zealand make the refrigeration efficient.
Before we acquired the generator we ran our 64 horse power diesel to charge the batteries. Truth be told, between running the engines at anchor and motoring when we could have sailed but needed the electricity, we burned something like a litre of diesel a day “for electricity”. That is a frightening long term average. It should sober anyone who makes it this far in the post and still thinks that a fossil fuel generator isn’t necessary for them. If we’d had that gasoline generator we’d have made twice the power for less than half of the fuel burned.
We’re going back on grid shortly. We’re so exicted. It’s like we’re addicts waiting for our fix or children finally getting the toy they’ve always wanted. We won’t use anywhere near the power we did when we lived on land, but being able to use our laptops whenever we want is going to be huge for us.
To summarize, living off grid is tough. You’ll enjoy it more if you have several means of power generation. Try to keep your power consumption down. Your refrigeration draws almost all of your non-discretionary load so focus on it. Batteries are for short term storage, not for powering your fridge during week-long rains. But with self control and careful planning, you can live off grid on your boat too.