In the realm of alternative energy production, there are three main players: Solar, Wind, and Hydro.
Each of these systems has its advantages and disadvantages, making none of them a magic bullet on their own. When used in combination, they will overlap and cover for each others downfalls.
To be happy with any of these, you must understand what they can do and what they can't do. If you want it to do something that it can not, you will be very displeased. Learning how to work within the limitations will lead to a very pleasant cruising life.
Solar works by converting the suns radiant energy into electricity. It works completely silently without any moving parts! While this sounds incredible, it does have its limitations. Solar panels need direct sunlight to work their best. If a shadow is cast over a small portion of the panel, its energy production will drop drastically. They also do absolutely nothing during the night hours, as well as on cloudy days.
While cloudy days and darkness will limit your ability to keep your batteries topped off, solar generators can help alleviate this issue by helping to bridge the gap until the sun returns and you can resume producing power. A comprehensive evaluation of different solar generators, as well as a look into "what is a solar generator" can be found by following this link: http://www.allthingsboat.com/best-solar-generator-reviews/
Wind works by converting fast moving wind into electricity. These devices have many moving parts and are anything but silent. The quiet ones sound like a wispy whistle howling through the air while the loud ones sound like a helicopter. They do wonders for night cruisers, as they can produce loads of electricity on an overnight passage to keep the electronic autopilot energized. The problems with wind generators is they require fast moving apparent wind to operate; this means you will not generate any electricity in a protected anchorage or while sailing downwind. If you only have a wind generator and stay an extended period of time in a quiet creek, you can expect your batteries to run down after a few days. While sailing downwind on long crossings, you may find that the light apparent wind will not be enough to produce the necessary amounts of electricity your vessel demands.
Hydro is a relatively new player on the scene, it works via a similar concept to the wind generator, but the blades run through water instead of air. These units will produce massive amounts of power under the right circumstances. Hydrogenerators require a lot of boat speed to produce their power, so sailing downwind in the trades will produce plenty of power, even with the light apparent breeze; while ghosting along on a quiet day will not produce much power.
As you can see, none of them work perfectly all the time. If you have all three, you will always be able to rely on at least one of them to produce enough power to meet your needs.
The electric motor we installed from Electric Yachts also works as a hydrogenerator. As we sail quickly, the water rushing past the propeller causes the prop to spin, which in turn spins the motor. In these situations, the electric motor functions as a massive generator, cranking out the amps!
When we did our summer trip in 2015, we only had a Hydrogenerator (the electric motor) and it did supply us with our needs for electricity when sailing quickly. The problem was we were not always moving fast enough to generate enough to meet our needs. A few consecutive days of light airs would cause our batteries to run down. We are now in the process of installing solar panels to help fill in some of the gaps.
If you ever feel like charging your batteries through alternative methods, consider the pros and cons of each system. If you can accept each system for how it works and live happily with the energy produced within its constraints, you will be able to maintain your battery bank while supplying your electrical needs without the use of fossil fuels!