Note October 2020: Do not let the original date of this post and model dissuade you for using it and instead going with salesman BS and pretengineering that will destroy large chunks of your wealth. The basic physics have not changed since 2014 and you can change things like the price of batteries and efficiencies of solar cells to reflect changes since then, using the instructions Eric provides.I have always believed that one of the most important things you can do in sailing, as well as life, is do some basic arithmetic before you make a decision. That would seem to be self evident, but it's amazing how many of us (I have made this mistake too) rush into things just because they are cool and/or the latest fashion without subjecting them to a bit of arithmetic rigour. I guess the classic error in this regard is whipping out a credit card and buying something without doing the simple arithmetic to figure out how long it will take to pay down the card or how much interest we will incur while doing so. In the same vein, investing large amounts of money in electric or diesel-electric drive options without doing the maths first can be expensive, as well as extremely time consuming and disheartening.