If you want to be free from the umbilical power cord of the marina, you will probably find that you need an alternative power source. There are people who cruise with no electrical power at all, but if you want little luxuries such as navigation lights, a vhf radio and gps, you will need some way of making electricity.
There are several options, of which the main ones are;
water powered generators
When we were researching these options, we ruled out water powered generators because they need to be towed to make power, and like most gunkholers, we want electricity when we are anchored for a week. Bicycle power we decided against on the principle that we would rather not pedal and talk on the vhf at the same time. That left solar panels and wind generators, and after doing quite a lot of research we plumped for a 60 watt Solarex solar panel and a Rutland 913 wind generator. We were looking for reliability and sturdyness, and although we often look for the cheapest options, here we went all out quality, because these items should work for many years, and are manufactured by companies which stand behind their products with a proper guarantee.
There are a few important things to know when choosing a wind generator. Firstly, listen to it working. Some are very noisy, and will bother your neighbors or you in a quiet anchorage.( The home made ones are usually worst in this respect.) The other thing to know is that no wind generator will produce power in less than about 10 knots of wind, even if the blades turn. And the most important thing to know is that no wind generator should be allowed to produce more than 10 amp hours of electricity for more than a few minutes, because this will almost certainly heat it to the point that it will destroy itself. Having said that, the Rutland on our boat has survived 84 knots of wind, and 50 knots for 8 hours, which is why I recommend it quite strongly.
Solar panels are pretty good nowadays, and ours produce about 3 amps in good sunlight. They require little maintenance, just turning to the right angle a few times during the day. However, it is important to look after your batteries when you connect solar panels. They can produce higher voltage than is good for your batteries, and can suck power out at night, so you need a good regulator that can handle both problems.
We can produce about 60 to 80 amp hours on a good day, which is enough to allow us to anchor without using the engine to charge the batteries for a week or so. It can be less if its really hot, because then the fridge uses a lot more power, but its something like that.This means that we can do without a marina fix for as long as we have water, and longer if we can find a tap! When calculating the cost of alternative power, this makes it economical, even though the per watt cost of generating energy is more than the cost of buying electricity.