Most of the developments on the alternative energy front are, at most, “possibilities” and not practical realities. Just focusing on automobiles for the moment, many of the promising articles you have read are little more than promotional pieces by people looking for investors:

Electric Cars: You hear a lot about $100,000 roadsters that will get 250 miles on a charge, but the reality is something entirely different. What makes a car useful is the combination of range and speed, a function of the power available. Electric car promoters use a sleight of hand to fool you into thinking that their technology is almost equivalent to the internal combustion engine you know and loath. They create a false impression by citing maximum range and top speed, without telling you the whole story.

There is no electric car that will take you 90 miles at 70 MPH freeway speeds. Sorry folks, it doesn’t exist. You think it does because the websites tell you the car has a range of “up to 250 miles” and a top speed of “85 MPH”. But they don’t tell you what range to expect at that top speed. That “250 miles” could be 10 miles. The basic problem is that today’s batteries, even the new lithium ion batteries that are not in production yet, just don’t have the energy density that gasoline has. And the laws of physics apply.

Electric car manufacturers should produce a chart with “Speed” along the X-axis, and “Distance” along the y-axis, so you could see that your electric neighborhood car has a usable top speed of 18 MPH if you want to go more than 14 miles. But they don’t do that.

Why can’t they just add more batteries? Because there’s a weight penalty, even with the new lightweight alternative batteries. And more weight requires more energy to move. And the weight of the batteries is there for the entire ride, forcing you to experience a real world example of “diminishing returns” ... you get to a point where adding more batteries results in less range. Rod Adams notes at Clean Technica that gasoline stores 20 times the energy per pound than the most efficient batteries.

Biodiesel: Proponents of biodiesel will tell you that you can run used french fry oil in your diesel car, and you can. But you take a great risk in doing so, as any damage the automaker deems might be caused by the fuel would not be covered under warranty. Anyone who has fought with an automaker over a valid warranty claim will recognize this as a major detriment to the biodiesel movement. But what about ASTM certified biodiesel blends? Auto manufacturers have not yet adopted the blends; some, like VW, approve only up to 5% blends. As far as I know, the highest recommended blend is B20, 20% biodiesel, approved by Peugeot and Citroen in Europe (there could be others as well, but no one has approved blends over 20% as far as I’ve been able to tell.)

ASTM D-6751 biodiesel blends are, for the most part, made from food crops like soybeans, adding to the concerns about rising food prices due to the shifting of crops from food production to energy production. What about all those cool projects like biodiesel from algae you’ve heard about? Well, there are a lot of pilot projects and test setups, but no one is actually producing biodiesel from algae yet. Judging from the press releases I’ve been following for over two years, it appears that the test projects are capable of squeezing money from investors, but perhaps not biodiesel from algae.

Hybrids work: Hybrid car technology is here now, and it helps squeeze more mileage out of the energy-dense gasoline we use. Because the on-board batteries are not tasked with supplying the entire energy load, they can be smaller and lighter. And you won’t be stranded because the battery output is affected by cold weather, as you have your gasoline engine to get you home safely.

So what’s an environmentally aware consumer to do? Look at your needs and determine what is best for your family. Trading in a 17 MPG fuel hog for a 28 MPG daily commuter makes sense, but do the math on your actual fuel cost and calculate the payback. That change can be done fairly economically with an econo car. From an environmental standpoint, it might make more sense to keep the old car rather than impacting the environment with the cost of creating a new car.

The jump to higher mileage technologies might not make sense economically, and that generally means it doesn’t make sense environmentally either. The Market builds in the relative efficiencies of these options. Go green, but only if it saves you money in the long run.