While walking the four miles from the boat to the Providence airport last week, I thought a lot about the impact Maryanne mentions above.
Footprint gets electricity from four sources: Solar panel, wind turbine, main engine driven generator and shore power. She burns three types of petroleum in four different places: Propane for refrigeration and cooking, kerosene for heat and diesel for propulsion and electrical generation.
First, electricity. - Our primary ethic with regard to consumption is to keep it as low as possible in order to reduce the need for generation of any type. With Footprint not underway in the daytime, our electrical consumption is around 14 watts total. It is possible for us to reduce our load to less than that in the event of depleted batteries but this is essentially the boat's base load with everything operating normally. In a 24 hour day, this amounts to just over a third of a kilowatt hour. Underway at night in fog, with many of the systems up, this number can be as high as 100 watts for short periods, but more typically is about 40 watts continuous or about 3/4 kwh/day. Compare this to the average Maine resident(America's lowest electrical power user) who uses about 18kwh/day or Alabama (the highest) at 43kwh/day.
Our largest source of electricity is our 100 watt solar panel. Our solar panel produces (depending on battery need) between 1/5 kwh/day on a cloudy day up to about 1/2 kwh/day on a good, sunny day with zero carbon emissions (not including the energy used in the production of the panel itself).
Our wind generator produces a wildly variable amount of power. Our first two days out of Norfolk during the storm, the wind generator alone kept up with all of our needs, even with most systems on and the batteries stayed completely charged the whole time. A more typical daily contribution would probably amount to 0.15 kwh/day. Again, with zero carbon emmisions. Wind generator production tends to be better when sailing and on cloudy, stormy days so it compliments our solar panel nicely, even though its overall production is less.
Only under the combination of several days of high load and cloudy, low wind conditions have we found it necessary to resort to using the engine to provide our electricity. For several reasons, I will not use the engine solely to produce electricity but instead will serve the dual purpose of getting us somewhere while producing electricity. Generally, recharging our house battery bank from 50% (effectively dead) to fully charged takes between three and four hours running time while underway and running many of the systems as well. While underway under power, Footprint gets about 10 nautical miles per gallon at 6 knots.
While plugged into shore power in the Winter, we use about 3kwh/day, which decreases to 1/2 kwh/day in the summer. We use more electricity when plugged in because using a space heater becomes an option and because the propane refrigerator runs off of electricity when the boat is plugged in.
Now for the Carbon part. A U.S gallon of Diesel or Kerosene weighs about 6.7 pounds or 3 kilos and, when combined with oxygen in the combustion process, produces just over 22 pounds or 10 kilos of CO2. Gasoline has less energy and has about 90% of those numbers. Liquid propane weighs just over 4 pounds (1.8 kilos) per U.S. gallon and produces 12.67 pounds (5.75 kilos) CO2 per U.S. gallon. At its peak output our engine driven generator puts out about 500 watts of electricity. This is probably more realistically half that number averaged over the battery charging cycle. If we use the diesel engine as an electrical generation plant and disregard its use as a propulsion engine, we find that it would take about 3 hours of engine run time to produce 1 kilowatt hour of electricity. This would use about 2 gallons of diesel and put 44lbs or 20 kilos of CO2 into the atmosphere at a cost of about $9.00. Contrast this with Narragansett Electric Co. (to which our shore power is currently connected), which produces 61% of its electricity from petroleum. NECs CO2 emmisions are .909lbs or .41 kilos per kilowatt hour at a cost of $0.15. The U.S. average is 1.363lbs/kwh and .62kilos/kwh respectively. This means that keeping Footprint's battery charged using the engine puts almost 50 times as much carbon into the atmosphere at a cost of 60 times (although, we know of many marinas that charge $10.00 to plug in a 30 amp shore power cord for one day which effectively makes the cost 100 times higher).
Since purchasing Footprint last year, we have used 100 gallons of diesel, 20 gallons of kerosene (for heat), 40 gallons of propane and around 1 megawatt hour of shore power (mostly in Virginia). This has produced 2200lbs, 440lbs, 520lbs and 1146lbs (Virginia's CO2 emission rate is higher) of CO2 for a total of 4306lbs or just under 2metric tons, or 1 mt per capita. This contrasts with per capita amounts of 16.64 tons in the U.S., 9.15 in the U.K. and 1.05 in India. The world average is 4.44 tons per capita.
There are a few ways for us to offset our carbon production, the main two being carbon offsets and energy credits. Carbon offsets are basically a means of creating a means of absorbing and thus offsetting a given amount of CO2, like planting trees. Energy credits are involved in the process of converting a certain amount of energy production from carbon based to renewables, thus reducing emissions. The cost of purchasing carbon offsets or energy credits is generally in the neighborhood of $10.00 to about $35.00 per ton, with a good mix in the $20.00 range. This means that offsetting our carbon production for the last year will cost us around $50.00 (we've wasted more than that on one mediocre restaurant meal) The cost of our diesel and kerosene would go up 20 cents per U.S gallon (you know it's going to do that anyway, might as well get used to it), Propane would cost us another 10 cents per U.S gallon. At today's prices, that's about 5%. I also have the carbon cost of air travel as a passenger commuting and hotel rooms to consider at work. These should cost us less than I've been tipping hotel van drivers.
Our first priority is to reduce our carbon footprint through conservation, our next is to offset/credit the carbon that we do emit. All of this should give us a neutral carbon footprint. With all of this becoming a bigger issue globally, it is getting easier and more convenient to find ways for people to do this. As cruisers, we are naturally interested preserving the world we have gone to so much trouble to see as a way of life.
[Maryanne]Wow, Kyle, that was quite a bit of research! To put it in more human terms, I know we live an unusually low energy life, and don't expect many of our friends and family to have any thing as low as us! But we still made lots of little changes to reduce our energy consumption even more (LED lights, manual pump for water, etc). We also walk or cycle more (even when we have a car available). But, don't think we suffer at all, I turn the heating on when I'm cold and have a pretty comfortable life!
Here are some of the web sites Kyle found useful when researching his opus
- CarbonCounter.Org gives calculators to calculate your carbon emissions, tips how to reduce, and even allows you to purchase offsets.
- To see what energy sources each USA electric company is using : Renwables? Nuclear? Coal? see the USA EPA web site
- Finally, nearly all airlines now have links with some kind of company where you can understand and offset your travel carbon usage - you can even add the cost of the offsets at the time you pay for your flight! Cool! Here is one example (the one that Continental use)