Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Best Replacement Energy to Fossil Fuels
Name: Laurel
Status: student
Age: 17
Location: N/A
Country: N/A
Date: 1999-2001

If at some point in the future our fossil fuel resources were to become completely depleted what would be the best replacement energy source both for cars as well as for supplying electricity to homes? I have searched the archives and couldn't find anything that answered my question, thank you so much for any information you are able to provide.

First, a simple point, you start with the condition: "If at some point in the future our fossil fuel resources were to become completely depleted..."

The situation is, that at some point in the future, our fossil fuel reserves will be depleted. When that will happen is greatly debated, but, we do have enough fossil fuel, particurlarly coal to last for many years before it all runs out. According to the department of energy, ( the United States has enough coal to last for more than 250 years at our current rate of consumption, and enough natural gas to last between 60 and 100 years. Oil, is our least plentiful. However, we use more and more energy each day, and no one is really sure how long it will really last.

The real problem is not necessarily how much we are using, it is how it is distributed. Fossil fuels account for 85% of all the energy used in the United states. Oil, our least plentiful resource, accounts for 40% of all our energy. The United States doesn't have enough oil production to meet our needs, and United States alone has more coal than the rest of the world has oil. So, we could possibly be out of oil, or the political situation in the Middle East could become such that we face an oil crisis, relatively soon. Politically it could happen any time. We will could use up all the oil reserves sometime in the 21st century.

Next, Natural Gas accounts for 25% of our energy, and is between oil and coal in availability, and it is projected to be depleted in the 21st or 22nd century.

Coal, our most plentiful resource, accounts for 20% of our energy needs, mostly producing electricity. In fact most electricity in the United States is in producting coal.

All other energy sources account for 15% of the total energy used. This includes Atomic, Hydroelectric, Geothermal, Solar, Wind, and any other type of energy.

Currently there really are no viable alternatives. Atomic power can produce electricy quite well, but already the hazardous waste it produces is quite a problem. If we suddenly tripled the amount of energy produced by it, waste would become an enormous problem.

We don't have enough hydroelectric power in the United States, even if we dammed every river, and we have more sources of hydroelectic power than most countries.

A lot of research is being done in this area, especially in finding new fuels for cars. This is because cars use most of the energy, and produce the most pollutants, so finding a clean, abundant source of energy for cars would greatly change how much fossil fuels we need.

If all the fossil fuels ran out next year, we could come up with an alternative. Fuel cells, solar power, or something, and we would. Right now, however, the greatest obstacles are social obstacles. People don't want to spend $75,000 on a car, and some of these alternatives are very expensive. It is much more convenient to go buy a cheap car and worry about solving the polution and energy problems some other time.

I hope this helps a bit.

--Eric Tolman

Hi Laurel,

It would probably be some combination of things depending on how far into the future you're trying to project. Hydroelectric, wind, solar, tidal, and biomass energy are renewable energy sources and could go on until the sun burns out, but whether this could supply enough for 10-20 billion people at the current (American) consumption rate is questionable. Improvements in energy efficiency can and will likely be made. Nuclear fission will probably play a role as well, but there's the problem of waste disposal and accidental releases, and there's a possible problem of running out of raw material for that as well. Nuclear fusion might supply enough power for humans as long as we are on earth, but current technology is not very close to achieving extended controlled fusion (uncontrolled fusion, i.e. the hydrogen bomb, does exist).


There is no "best", in absolute terms. This is a problem involving engineering, scientific research, and economics, in which the source, transmission, and application of energy will all figure in.

The answers will depend on what technologies are available, and at what cost, at the time we run out, and in the places where the energy is needed. The answers will also depend on the rate at which we run out, because this will influence funding for research and development of replacements, and determine how directed those efforts are.

Direct conversion of solar energy to electricity is attractive, though currently expensive. Indirect use of solar energy (e.g., hydroelectric and wind power, agriculture directed at producing fuel) is attractive, and the states of the technologies that convert energy produced in these ways into the actual work that needs to be done will determine which are most economical. Geothermal energy is certainly great if you live in Iceland, and we may find economical ways to use it in less obvious places. The use of nuclear energy is inevitable -- though many oppose it for some good reasons and some zany ones -- because of the huge amount of energy that would have to be replaced if fossil fuels were absent. Energy from tides, lightning, storm surges, etc. may figure in as well.

One "source" of energy that should not be ignored is conservation -- improvements in the efficiency with which we transmit and apply energy.

Tim Mooney

We will reach a point where we run out of fossil fuels. That is a known. When? It depends on how foolishly we squander the fuels. What might have potential? Wind, waves, sun, fuel cells, methane, corn alcohol might be an alternative. Much has been written concerning each type's pros and cons. Have you used your web search engines to look at any of these items?


The only resource that I know about is solar power. When fossil fuel resourses are gone, solar energy will be a main source of usable 'fuel'. Try searching your local library under solar cars, solar panels, and the like and see if they lead you to your answer.

Katie Page


You are correct that the supply of cheap, easily accessible, and environmentally suitable fossil fuels will diminish in the future; some sources sooner than others. For example, at the present rate of consumption, coal supplies -if I remember it correctly- can last for at least several hundred years while petroleum for perhaps less than a hundred years. The key issues throughout are the cost of exploration and exploitation (technical), and the cost of usage (in terms of environmental impact). These can make a fuel source viable or unacceptable in the future. So, complete depletion is not an issue, cost is.

There are some attractive alternatives to fossil fuels, including renewable resources (solar, wind, hydroelectric) and nuclear. Increasing "cost" of fossil fuels will make these alternative sources increasingly attractive. In the long run, unless we find other sources of energy, nuclear energy and conservation (in terms of more energy efficient products and life-style) seem to be our more reliable choices.


Ali Khounsary, Ph.D.
Advanced Photon Source
Argonne National Laboratory

Click here to return to the General Topics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory