A: What are the advantages and disadvantages of nuclear fusion compared to renewable sources?

This will be the second entry in the Guide to Thermonuclear fusion. You can see the Table of Contents here where you can navigate to the subject you wish.

This part of the Guide will be focused on the advantages and disadvantages of fusion compared to other renewable or "clean" energies especially through the light of climate change, our biggest motivator for change.

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Lets first look at the renewable energy types, highlighting their advantages and weaknesses.

I will not be talking about hydro energy, because of the lack of its viability in the long term. Hydro energy is especially hindered by the fact that hydro power plants are quite expensive to build while still having a massive impact on the local ecosystem. These facts make them extremely unlikely to be successful in the distant future.

The second energy type I want to talk about is wind energy. The much smaller scales on which it can be built make it much less invasive concerning the local ecosystem and they are less expensive per W of power generated. Lets compare its cost efficiency to that of hydro power. The largest dam producing energy in the world is the Three gorges dam in China, which produces about 22.5 GW of power. It cost about 22.5 billion dollars to build. This means its efficiency is about 1 W/$. For comparison, a standard wind turbine generating about 3-4 MW of power costs about 2 million dollars, making the efficiency about 0.5 $/W. It comes with an added benefit that it can be built on much smaller scales making it more versatile. Hydro-power dames are always very large. But wind turbines have a quite bad property. If there is no wind there is no power. Power output intermittency make it unlikely that they will be used as a reliable power source.

The third and last power source I want to talk about in this first section is solar power. In the figure to the left one can see that because of advancements in materials science the cost of solar panels per W had been steadily falling. It now comes just at bellow 0.4 $/W making it even cheaper than wind turbines. This trend of cheaper and cheaper solar panels has not slown down in recent years, making the technology possibly even cheaper in the future. In the blue line one can see that adoption of the technology has skyrocketed with the ever cheaper technology.

But solar power has its own issues. Again power intermittency is an issue. With no sun, there is no energy. Also energy storage is difficult for energy consumption during the night, with battery storage being still quite ineffective.

The next on the list of possible energy sources is energy gathered from the process of splitting massive nuclei - fission.

The energy source needs no introduction really. After the invention of the atomic bomb during the second world war civil research on the possibility of harnessing its power has boomed. The first generation 0 fission reactor was built only years after and additional reactors of various generations followed suite.

The advantages of fission are many. It emits no CO2 or other greenhouse gasses and is therefore considered clean when it comes to the climate change debate. Compared to other fossil fuel sources it requires a relatively small amount of fuel. The power output is of course very stable and reliable with breakdowns of reactors occurring extremely rarely.

But the downsides are also massive. The final output of the standard uranium reactor is plutonium which has an extremely long half life. This means that once it is produced it will stay on Earth for about 40 thousand years. Also it is extremely radioactive. Also mining of uranium ore is extremely expensive, its refinement even more difficult. This means only a handful of countries on Earth are able to mine and refine U which means they have a monopoly over it. Despite accidents occurring very rarely, when they do they are catastrophic. This was elucidated on the examples of Fukushima and Chernobyl. Also the cost is pretty expensive, with the latest generation being predicted to be from 2-5 $/W. Source

All pros and cons combined together make fission energy a viable alternative as an energy source while we try to shake our addiction to fossil fuels and while we try to develop other sources of energy and while we make existing ones cheaper and cleaner. But in the long term fission energy as it is now is not viable.

Well we have to get one thing out of the way first. The cost of fusion power is not known as of yet, as no reactors are running currently. If we take the construction of ITER into account we can compute a nice upper bound for the cost. The construction will cost around 20 billion dollars while the power output will be around 500 MW. This means that the cost is around 40 $/W. As one can see it is very expensive currently. But with future innovation and taking into account that all that is needed for power generation is a little bit of water and lithium the cost will be much lower in the future. Another downside is that neutrons produced in the fusion reaction will impact the wall and cause transmutations of the wall material. This can cause radioactivity on a small scale. It is also possible that lithium could become the next gold because of its uses in the energy sector like in Fusion and batteries.

There are no real other downsides to nuclear fusion. The heat used for wall cooling will be circulated in a closed circuit and used in turbines for electricity generation. The amount of fuel needed is very low. Only about half a kilogram of sea water and about 2 kg of lithium will suffice to power a average family through the year. Compared to coal, several tons of coal is needed. In the first generations of reactors D and T will be used. In the D + T reaction only He and neutrons are generated. Neutrons will deposit all of their energy in the wall so they will be harmless. He is already in the air so we know it is also completely benign to humans and to the environment. It is also important that even in the most catastrophic scenario of a reactor malfunction, the instability of the fusion reaction will just cause it to stop. No severe accidents that could impact the environment can possibly occur.

So how do I predict the future energy production will look like. I personally think that most of the energy will be produced by renewable energies like wind and solar because of their versatility, ease of construction and cost effectiveness. But to combat their intermittency we can expect that several fusion reactors will be used instead of the current fission reactors, which will be slowly decommissioned.

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