Carbon-free energy

Globally, 87% of our energy comes from fossil fuels. These are dense sources of energy (see previous post on why oil tastes so good) & oil transports and stores well...but what about greenhouse gas emissions? Reams of evidence have demonstrated that greenhouse gases, such as CO2 (carbon dioxide), in excess, contribute to the overall warming of our planet. And fossil fuels produce A LOT of CO2. Another problem with fossil fuels is that they are a finite resource. Some estimates say that only ~100 years of oil resources remain (Source: World Energy Assessment 2000 & 2004/UNDP ). http://www.undp.org/energy/activities/wea/drafts-frame.html

Renewable energy sources (such as solar, wind, biomass, and geothermal), on the other hand, have very low CO2 output per kilowatt-hour of energy produced (See figure at http://www.sciencemag.org/cgi/reprint/329/5993/786.pdf). But given the amount of energy we currently use, is there enough renewable energy to meet this demand? The single largest potential comes from solar energy, where the total amount of solar energy available on earth's surface is several orders of magnitude greater than what we currently use, as a planet. And there is a good chance we could capture enough of that to generate the amount of power the world now consumes. One of the current challenges with solar, however, is energy storage. Sunlight does not shine in one solar panel 24/7, and we need more inexpensive, more efficient ways to store this energy when it is not being generated. There are many great leads to building better batteries out there..but I am not an engineer and will pass on further comment for now.

Biomass can be thought of as another source of solar energy, as plants convert sunlight into energy that is stored in the plant as sugar (via photosynthesis). Even though plant growth is seasonal, with an abundance of plant material (feedstock) at the end of the summer growing season, the leaves can be harvested and stored until energy is needed. A disadvantage of biomass, however, is that is requires resources such as water and land.

While there is much promise in renewables replacing fossil fuels, most experts agree that the best future outcome will include a number of different renewable energy sources and technologies.