Renewable Energy Overview
Renewable energy is a central component of sustainability. Generating electricity from resources that are indefintely renewable such as solar, wind, tidal, hydro, and geothermal among others are simply the way of the future if mankind is to have a future on this planet. Off-grid power generation provides further energy security and stability as well as removing the costly infrastructure and limited range of the modern power grid system.
In order to become energy independant the problem must be approached from two different spectrums. It's common to think of solar panels and wind generators when thinking of off-grid power, but the other equally important part to this equation is lowering energy consumption both with energy efficient appliances as well as being conscientious in using those appliances.
The benefits of living "off-grid" are two fold. By generating one's own power from renewable resources you are participating in a lifestyle that could continue indefinitely and eliminates large amounts of pollution from our environment. At the same time you no longer are reliant on a system in which you have essentially no control over how and where the power is being generated and are not placed at it's mercy when the entire grid goes down or prices soar. Power outages become a thing of the past unless of course you are living beyond your production means and the sun and wind won't cooperate.
Heating and cooling account for almost half of the annual power consumption of a typical American home. We can slash that energy consumption by using passive heating and cooling design practices. Other areas that homes typically use large amounts of power in are for refrigeration. Root cellars can be dug which can be more than adequate for a large number of foods, and an efficient refrigerator inside a root cellar will use less energy as it will need to run less often. Lighting can be minimized with sky lights and CFLs, and there are now amazingly energy efficient laptops. The StepNote NC1500 runs on only 12 watts compared to an average small laptops energy consumption of 65 watts.
These reductions in power need reduce the amount generation capability, and if you've ever looked into the prices of solar panels and wind generators then you will realize that reducing your power needs is often much cheaper than buying more panels. This is true even with the ever-falling price of solar panels and generators, but it may become quite a bit less true in the near future. Several companies are working on thin film solar panels which can essentially be rolled out onto roofs or other surfaces to generate electricity. These films are expected to sell for extremely cheap and produce energy even cheaper than burning coal! Currently it costs about 17 cents to generate a watt from a solar panel, while it only costs 4.4 cents to generate one from coal. The new films are expected to cost only 4.3 cents per watt, just undercutting coal and hopefulling sending the coal burning practice to rest with the other fossil fuels.
A simple solar power system works like this. The solar panels generate a DC current that varies depending on how directly the sun is hitting the panels, weather conditions, etc. The solar panels are often connected to a charge controller which stops the batteries from being overcharged and some more advanced controllers can charge batteries more optimally. The charge controller is then connected to a bank of deep cell batteries which are designed to be slowly discharged as compared to car batteries which are used for quick discharges such as when a car is started. The batteries are then connected to an inverter which changes the DC batter power to 120V AC which can be used by common household appliances. There are different kinds of inverters which are more or less efficient and have higher and lower maximum power ratings.
Wind generators work in a similar manner, but can complement solar panels by generating power when the sun isn't shining at night and during bad weather. They are often mounted on towers, typically the taller the tower the more wind power available, but towers get exponentially larger, more expensive, and more complicated with increased height.
Solar and wind are the most commonly, because sunlight and wind are typically available in every location to some degree, hydro power is relatively common but needs a significant amount of running water and a good difference in altitude such as a waterfall or quick flowing stream.