Interesting Questions

What is the best energy source?

Since our worldwide energy consumption continues to grow each year1, it is not a mystery that energy sources are a constant topic of debate. I regularly find myself discussing the subject with people on both sides of the political divide. Yet, I have only recently realized that I have been discussing the subject without really having any knowledge in the area. Like you, I have heard different things from different sources – often contradicting each other – leaving me confused about what is true. Who are we supposed to believe?

Finally, I decided that it was time to consult the scientific literature, as I should have done a long time ago. With a topic this complex, however, it took me a few days of initial research to figure out what energy sources to compare and which dimensions to compare them across. It quickly became obvious that the scope needed to be limited to the most important pieces, lest I get lost in the realm of scientific research and never come to any conclusions that can be used in daily life. What is presented below is the synthesis of my findings from this journey. I hope it is as illuminating to you as it has been to me.

Sources and Dimensions

As stated above, I have narrowed the scope to focus on our main energy sources to avoid making this synthesis too complex. This narrowing has the added benefit of only including sources that might be considered legitimate alternatives for the future and have substantial amounts of research data tied to them on which to base conclusions. As such, I have chosen to focus on the following sources of energy:

  • Nuclear
  • Wind
  • Solar
  • Hydro
  • Natural gas
  • Oil
  • Coal

These sources have been compared on a global scale (ignoring local peculiarities – such as more or less sun or wind) across seven dimensions to form a clearer picture of how they match up against each other on a macro level. Where relevant, all metrics are measured on a per-unit basis to control for differences in total energy production. The dimensions that have been focused on are:

  • Danger to Humans
  • Danger to Animals
  • Emissions
  • Power Density
  • Cost of Energy
  • Energy Return on Investment (EROI)
  • Reliability

Danger to Humans

Let us first look at how many human lives are lost in the production of energy. It should be noted that these numbers include deaths from clearly traceable accidents and, to a large extent for coal and oil, estimates based on the known mortality rates from air pollution. The lack of anti-pollution regulations in places like China accounts for a substantial portion of the estimates2, 3.

Considering the air pollution resulting from the combustion of coal and the dangerous nature of its mining and transportation, it may not be a surprise to most that it performs poorly on this dimension. What might come as a shock, however, is the low number of deaths resulting from nuclear power. Despite the prominent accidents of Chernobyl, Three Mile Island, and Fukushima, nuclear power is surprisingly safe. In fact, though these numbers are from before the Fukushima meltdown, the per-output-unit death rate will be lower now; a lot more power has been generated since then and the number radiation-related deaths from the event were in the low single-digit range4, 5, 6. The vast majority of deaths were caused by the earthquake/tsunami and the ensuing evacuation6.

Danger to Animals

Unfortunately, there are no concrete numbers for all animals killed by the production of energy. Numbers for avian deaths are the most commonly researched and thus the most generalizable across the different energy sources. No such number was found for hydropower, as the technology has minimal impact on birds, but it is clear from the research that hydro plants disturb river systems and thus the wellbeing of the inhabiting species. Examples of such species include salmon and river dolphins. The use of dams necessitates the flooding of areas that would otherwise have been habitat for other species. From this, we can conclude that though some sources of energy have a larger impact on animals, the very act of energy production cannot be carried on without wildlife incurring negative externalities.

This is not to say that we should not try to minimize the extent of said negative impact; quite the contrary. In instances like these, we are obligated to look to the research so we might properly consider wildlife welfare as part of the complex problem of determining the future of energy production. Once again, fossil fuels come out unfavorably on this dimension. Though it may be easy to disregard these technologies at this point, there are confounding factors to consider. Fossil fuels continue to lessen their negative impact through stricter safety standards for waste and emissions. At the same time, increasing efficiency for wind (through larger turbines) and solar (through concentrating the sunlight) seems to increase the number of animals killed by these technologies7, 8 – muddying the already murky waters further.


On to the hot topic of emissions. At this point, it is clear that humans are having a heating effect on the environment12. The implications, however, are far from certain – though it is reasonable to assume it will be detrimental for some species and beneficial for others, just like past environmental changes. Our worry regarding this environmental change, at its most fundamental, is that the world will be less beneficial to us, as our species has thrived under the current conditions*. It is natural then, to examine the energy sources based on emissions, which is related to this heating process.

Several gases contribute to this process. To make the comparison easier to follow, the overall emissions have been expressed in grams of CO2 equivalent per kilowatt-hour (g CO2e/kWh). The numbers reported are the total life-cycle emissions of the various power sources, including building and operating the plants, and transportation of necessary supplies/raw materials. As can be seen below, wind and nuclear power come out best on this dimension, while coal and oil are the worst.

Power Density

Here, unlike in the prior graphics, more is better. This metric shows how much power capacity you get out of 1 km2 of land – the power density. As our consumption of electricity keeps climbing, power density is important to consider. Denser energy sources leave more land available to other uses – such as farming or natural preservation – lessening the worry of overpopulation of the planet and increasing our ability to let natural environments remain untouched. By sparing natural landscapes from human intervention, wildlife is preserved together with the plants that pull CO2 out of the atmosphere. Since all sources of energy need to be connected to the power grid to be useful, consolidating the power supply to a smaller area also means less wiring. Thus, power density has a plethora of implications for the sustainability and environmental impact of electricity generation.

Cost of Energy

The cost of electricity impacts the entire economy, as few (if any) businesses or individuals conduct their daily business without it. It may be easy to overlook the importance of this fact, but as our peaceful global society is predicated on constant economic growth – growth largely fueled by cheap electricity – the stakes are enormous. People cannot be expected to take a long-term view of environmental health when they are busy worrying about feeding their families. This may seem hyperbolic, but to many people around the world, this is an everyday worry. As such, any viable alternative must at least be close to the lowest price in the market.

Energy Return on Investment

In addition to the monetary cost of energy, we must also consider the energy cost. Energy Return on Investment (EROI; also known as Energy Returned on Energy Invested, EROEI) captures the relative cost of producing energy. For example, an EROI of 2 means that every kWh of energy invested results in 2 kWh of output. That might seem like a good rate of return, but it means that only half of the energy output can be used consumed as the other half has to out back into the process of energy production. As such, every metric we have looked at so far will be affected by EROI.

Here, a quick demonstration is due. Consider the following: you need 2 MW of electricity for a factory and this is being supplied by an energy source with a power density of 1 MW/km2. If the EROI of that plant is 3, your factory will need 3 km2 worth of energy. The reason you do not need 2 km2 is that a third of the energy is going back into the production process. If the EROI was 2, half the energy would be used for the production of energy and you would need 4 km2 for energy production. The same phenomenon will apply to emissions, deaths, etc., as the total amount of energy that needs to be produced to supply the grid will vary greatly depending on the EROI.


Finally, the critical factor of reliability, measured through the capacity factor**. Here, the actual output is compared to the theoretical maximal output, indicating the ability of an energy source to meet the demand from the grid. This is where the intermittency of solar power, for example, poses a problem. A temporary lack of sunshine (e.g. night time) can lead to a decrease in energy production, leading hospitals, businesses, and the government to rely on back-up generators or batteries to avoid shutting down.

The implications of such uncertainty surrounding energy production are wide-ranging. Let us consider a few: The need to include batteries in the calculation would lessen the environmental benefits of renewable energies, not to mention the fact that batteries run out – a fact that anyone living in our technological world can relate to. Backup generators will likely rely on fossil fuels and are not as efficient as larger power generators, leading to higher emissions than current fossil fuel powerplants. To meet the demand most of the time, the overall capacity would have to far exceed the energy demand of the grid***.

So what energy source is the best?

Throughout the process of doing this research, I found myself changing my mind several times, depending on the dimension I was currently focused on. Looking at emissions, wind looks like the clear choice, but what about when you have to consider land use or reliability? Suddenly, other options look far superior. And we have only considered a few of the most prominent factors; there are yet more to consider if you dig into the research. If anything has become clear, it is that if an option looks clearly superior to its alternatives, you are probably not considering all factors.

That being said, a decision needs to be made. We cannot delay decisions forever and must, therefore, accept some level of informational incompleteness. From this standpoint, the best option seems to be nuclear power, which has consistently been among the best alternatives across all the examined dimensions. The major detriment of nuclear technology is the public fear of nuclear disasters. Yet, when the data is examined, we find that nuclear powerplants are incredibly safe. The low number of casualties at the Fukushima meltdown – caused by a natural disaster that will not be a threat to most powerplants (a tsunami will not be a threat inland) – should serve as a testament to the safety of newer nuclear plants. And the Fukushima plant was commissioned in 197121. Newer plants have gone on to improve safety even further.


If we are to improve the conditions under which we and our descendants will live, it is necessary to face our fears and question the common knowledge we think we have. Surprisingly often, our fears are not founded on reality and our “knowledge” is simply regurgitated rumor. In the case of energy production, the best solution is being sidetracked by the battle between ideologues so deeply entrenched for either renewables or fossil fuels they forget why they are fighting. Taking a step back from the battle affords a view of the big picture, allowing us to reorient ourselves and get back to the main problem we were initially trying to solve. Thus, instead of putting our heads down and marching forth toward the perceived enemy, we must fight the urge so we might together find the real enemy: the stagnation of progress.


* This topic brings to mind George Carlin’s brilliant bit about saving the planet. It is certainly worth 8 minutes of your life.
** Capacity Factor = actual energy output / maximum possible output
*** A cushion of additional supply beyond the demand would allow even sub-optimal performance of energy production to satiate the demand. However, the construction of the additional capacity would impact the costs – monetary, environmental, and in terms of energy investment – per unit of output.


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Sources (continued):

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