Thursday, June 23, 2011

Pure Energy

When you're living out here, power management is key!
Energy management is one aspect of life on a boat that very few boaters have mastered.  After living the cruising lifestyle for over nine months I think we might have met one boat who has their energy situation perfectly worked out.   After my post about our favorite systems on our boat, we got a few comments and several emails asking about our energy situation. One of the greatest challenges of living on a boat is living "off the grid".   Our power doesn't come from a company and it can and will run out if improperly managed.  Because of this, we strive to be energy efficient and we are hyper aware of our carbon footprint; we catch wind in our sails to propel us forward, we capture the sun's light to charge our batteries, all of our appliances are energy efficient, and so on.

We have two six volt deep cycle AGM marine batteries in series for our "house" battery bank (this is the 'bank' that runs all our systems; lights, electronics, fans..etc.) and one 12 volt deep cycle AGM for our dedicated starter battery (that way, in the very unlikely event that we run our house battery bank down to zero - we will always be able to start our engine, which, in turn, will charge those batteries back up).  This means we have about 220 amp hours to work with.  Before you go building your battery bank, however, you first need to know what your energy needs will be.  Without getting too technical, you must calculate how much power you consume and thus begin a balancing act with your batteries (we have a Victron battery monitor so we can always see what we are pulling out of our batteries, how much life is left in them, or what we are putting back in).  There is a good worksheet here if you are interested in doing some math.

When we are at anchor, we are usually "balanced"; meaning what we take out of our batteries, our 65 watt (4 amps) solar panel can usually put back in.  When we are sailing, however, we draw much more power than we can replenish (chartplotter and autopilot are the main drainers) and after 24 hours, we typically need to run the engine for a few hours to put some juice back in (we have an alternator that puts power back into our batteries, much like a car would do).

One thing we did NOT want to have aboard is a generator.  Not only are they messy and noisy - they take up a fair amount of space that we would rather use for other things.  In addition, we've found that we motorsail enough that we don't need one.  This is one (of the many) reasons we selected our Village Tec Little Wonder Watermaker.  It runs right off our batteries and draws 11 amps.  We don't need to start our engine, we don't need to fire up a clunky generator and, after one (quiet) hour - we have added our daily 4-5 gallons to top off our water tank and taken precious little out of our batteries.  Obviously, if we are motor sailing - we try to make water then so as not to drain out of our batteries - but knowing that we don't have to is nice.

What is also nice is the fact that we are a very low amperage boat.  If you, for example, have refrigeration/air conditioning/television/Sony Playstation (?!) - you will need significantly more amp hours than we have.  Despite the fact that our energy demands are low - we need more power to stay ahead of the game!  Solar power, while great, is not very efficient.  The sun doesn't always shine, night falls, and if there is a shadow on the panel the amperage drops considerably.  We think a wind/solar combination is ideal and are currently in the market for a wind generator and we'll be adding at least one more solar panel by the end of hurricane season.  We have also been looking into this gadget but the jury is still out on whether the pros outweigh the cons...

The battery balancing act is complicated and, to be quite honest, can make your head spin.  We are by no means experts - but, like everything when it comes to cruising, you live and you learn!

Brittany & Scott


Mid-Life Cruising! said...

Yet another great post for us to refer to in the future! My husband doesn't like to read and imagine me trying to learn this stuff and then try to repeat it to him... aint gonna happen! He does enjoy reading your short posts, so this should make it a lot easier!

J said...

Excellent post guys! I love reading about your experiences actually "doing it" and appreciate the time you take to share.

Brady said...

Hey Brittany,
When charging your Macbook on board are you guys using an inverter? Since the laptop itself is DC, its inefficient to go from DC->AC->DC when you use the normal Apple power block. I bought this kit for use on our boat to try to avoid this. I haven't been able to measure anything to see the gain, since we don't have an inverter, but it should have some impact.

So now we're running DC --> DC for onboard charging.

They're currently including the 12 volt cig adapter, everything you need to set it up, its pretty slick.


hans and laura said...

We don't have a generator either but unfortunately the problem with running engines solely for recharging batteries is carbon build up in the mixing elbow. A diesel mechanic told us about this and said he sees it all the time on charter boats. Apparently diesels are meant to be worked under a full load and don't like to idle (picky little things aren't they?). You probably already knew this but just in case you didn't...
Anyway we had it happen to us once and we're pretty sure it's happened again. When we move back on board in a few months we need to clean out both of ours.

Ford said...

Great post! Very informative for those of us not "out there" yet when thinking about what systems to add and what to leave behind.

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