Feb 22

Energy Accountability–The Currency

Tag: energy efficiencymattholmes @ 2:12 am

The Amp-hour, Ah for short, is the currency of energy on the boat.  Every electrical device on the boat has an amperage rating; multiply the amperage rating by the number of hours it runs, and you get the Amp-hours that it consumed.  The stereo, for example, consumes 0.5 amps.  If I listen to music for 3 hours, I have used 1.5 Ah of energy.  Our battery capacity is currently about 130Ah (we will replace and upgrade the batteries before we depart).  So I could listen to music for 260 hours straight without recharging our batteries.

The electrical panel on the boat has both an ammeter and an amp-hour counter.  We can use the ammeter to determine the precise amperage of any device on the boat, and the amp-hour counter tracks exactly how much energy we have stored in the batteries.  At any point in time we can immediately measure the effect of turning something off.  When we open the icebox to get a cold beer, half of the time it will cause the refrigeration compressor to kick on for cooling: the ammeter shows the spike in energy usage.  In this sense, the energy cost of even the simplest conveniences is noted on a digital readout.

Everyone loves to talk about lights, to compare the energy efficiency of various lights.    We have three different types of overhead light on the boat: incandescent, compact fluorescent, and LED.  These are the same choices that we have for home use.  On the boat, we have measured exactly how much energy each uses.  The incandescent uses 1.5A, the fluorescent .75A (on the brightest setting), and the LED .05A.  The incandescent uses 30 times more energy than the LED.  In our world, that means we could use the LED for 30 times longer than the incandescent before we use up our batteries. 

You can do some of these same calculations for your own home.  The currency of electricity in the domestic house is the kilowatt-hour (kWh), and every device has a wattage rating.  Our amp-hour is your kilowatt-hour.  To find the number of kWh consumed, multiply the wattage of the device by the hours it runs, and divide it by 1000.    A 100 watt lightbulb, left on for 5 hours, will consume 500 watt-hours; divide that by 1000 gives you 0.5 kWh.  The average cost of a kWh in california is 12 cents (US average is 11 cents), so it costs 6 cents to leave that lightbulb on for 5 hours.  Thus we come to the real reason why people aren’t doing more to save energy and to reduce carbon emissions: on land, POLLUTING IS CHEAP.  People can talk all they want, but realistically they aren’t going to change unless it directly affects them, and energy is just too cheap for people to notice the cost savings. 

Let’s compare home to boat.  With a single conversion factor we can convert home energy measured in kWh to sailboat energy measured in Ah. You may be surprised: 1kWh = 83Ah.  The moral of that story is that it takes a whole lot of amp-hours to make a single kilowatt-hour.  Our new batteries will hold about 500Ah, and a kWh costs 12 cents, so with a little calculation you can figure out that the value of the energy stored in our fully charged batteries is $0.72.  Yeah. 72 cents.

The purchase cost of those batteries is over $1100, but the value of the energy they store, fully charged, is less than a dollar–that’s the sailboat for you!  Remember those SAT analogies?  Here’s the sailing version:

land life :: sailboat life
73 cents :: 1,100 dollars

So, energy is not cheap on the boat.  Energy is cheap on land and there’s no incentive to reduce consumption–hence the polluting nature of our modern society.  But on the boat, we will spend $1200 on batteries for storage, $1100 on a wind generator, $1200 on solar panels, and we already own a $1000 tow generator.  And even with all this money spent on energy creation, and carefully counting every amp-hour made and used, we will probably still have to run our engine occasionally to make up an energy deficit–and that will cost us in the price of diesel fuel.  As a result, on the sailboat we are motivated to monitor energy usage in a realistic, practical way, and we are directly rewarded for saving energy.  And this is only one of many reasons why sailboat life motivates us to live SIMPLY and to live CLEANLY.

One Response to “Energy Accountability–The Currency”

  1. Gary says:

    Nice article. I appreciate the technical side of things.

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