text: Well let's see:\n\nOil Shale:\nPositives- Can extract a large amount of petroleum products from a source that is largely untapped.\nNegatives: The process is time consuming and requires the use of fossil fuels.\n\nEthanol:\nPositives: Burns more cleanly and isn't derived from a nonrenewable source.\nNegatives: There is not enough plant matter out there to satisfy all energy needs.\n\nCoal:\nPositives: With new clean coal technology, coal can satisfy much of the energy needs while polluting less.\nNegatives: Still dirty, still nonrenewable, and still dangerous to mine.\n\nNuclear:\nPositives: "Clean" since it does not technically produce ozone-depleting gases; fuel has the potential to provide nearly unlimited energy.\nNegatives: Nuclear waste is an environmental and political nightmare; most nuclear plants are not highly profitable given the cost of fuel, maintenance, safety and other considerations.\n\nSolar:\nPositives: Very clean, renewable and unlimited.\nNegatives: Equipment expense makes it cost-proibitive- for now. Solar plants generally do not generate sufficient power for large metropolitan areas.\n\nWind:\nPositives: Very clean and renewable.\nNegatives: Equipment, as with solar power, is expensive.\n\nHydroelectric:\nPositives: Clean and renewable. Can generate significant amount of power.\nNegatives: There aren't enough huge rivers, like the Colorado, Amazon, and Nile, to power a hydroelectric plant of large scale everywhere. Very costly.\n\nHydrogen fuel cells:\nPositives: Efficient and very clean- end product is water- and renewable. Has portability.\nNegatives: You must expend the same energy making the hydrogen (as from a hydrocarbon molecule) as you get out of it. Net: no energy gain. Usually fossil fuels are required to process hydrogen. Hydrogen is not readily available. Cost prohibitive for mass market as of now.\n\n\nTaken individually, neither one of these alternatives will replace our energy needs. One of the biggest problems which typical renewable energy sources have had (such as wind, solar, hydroelectric) is that they are not portable. That is, you can't simply strap on a huge solar panel to your car and start it up. While it is true that batteries can be recharged with energy from wind, solar, or hydroelectric, the conventional batteries we have today- the lead-acid types we see in cars- do not provide sufficient power (even if you add a bunch of them in series) for trips of long duration.\n\nHydrogen fuel cells solve the problem of portability and power: all you really need is a source of hydrogen. That hydrogen can be condensed so that there is a sufficient supply to last several hundred miles (researchers are working on improving this). But hydrogen itself is not readily available. In fact, we have very little of it on earth because it all tends to float up into outer space.(it being the lightest gas).\n\nOne way to solve this is to take a hydrocarbon molecule- such as methane- and remove the hydrogen. But removing the hydrogen requires energy. So even though hydrogen and oxygen combine in a fuel cell to yield energy, that energy is about the same as that required to displace the hydrogen from a hydrocarbon. So why would anyone want to have fuel cells if the net energy gain is zero?\n\nWell, because of that portability issue again. Say we have a solar, wind, hydroelectric, or even nuclear plant that produces electricity. While that electricity is not portable, we can use it to power up a hydrogen-generating power plant. We, in effect, transfer the energy from a renewable source into hydrogen, which we can then use at hydrogen "gas" stations. \n\nSome environmentalists claim that because hydrogen necessitates a hydrocarbon source, we're still using the nonrenewable hydrocarbons we were using with petrol. They further claim that this makes the whole process non-clean. These claims are valid only in the sense that today we are, indeed, using nonrenewable fuel 