Will renewable energy sources be enough?

Humans consume energy. We want heat, light, we want to get to other places, we like to transmit information electronically. We like to make things, and ship them across the world. Much of the energy that we use is in the form of electricity but we also directly burn coal, and petrol, diesel and other oil products to propel vehicles and heat buildings. In some areas people burn wood for heat, light and cooking. Despite predicted problems, our consumption of energy is not going to change quickly, if at all. We are attached to our comfortable lifestyles and it doesn’t matter if the forecast is doom and burnout, humans will keep consuming until it is too late for our climate or for our energy-guzzling lifestyle. All this energy must come from somewhere. We use about 17 terrawatts (TW) from fossil fuel.[1] Fossil fuels release carbon into the atmosphere when burnt, which the balance of evidence tells us causes climate change. Fossil fuels are also a limited resource, with oil set to run out within my lifetime. Given that we are unlikely to reduce our energy usage, can we replace our fossil fuel dependency with something more sustainable and less harmful?

Carbon Capture

The immediate solution to carbon release causing climate change is Carbon Capture technology. The principle sounds simple – just remove the carbon from the exhaust gasses of your fossil-fuelled power station before releasing the rest into the atmosphere as before. Then bury the carbon, or pump it back down the oil well, or even recycle it back into some form of synthetic hydrocarbon to burn again. Unfortunately it isn’t simple. Carbon Capture is only really possible on a large scale, and so it can’t be used on vehicles or at home. It adds expense to power generation. Carbon Capture does not solve the issue of fossil fuels running out either. It may be a solution to keeping existing power stations running, but it is not the way forward.

Renewable Energy

Renewable energy is seen by most as the best solution. Renewable energy generally refers to using energy from our environment which will be continuously renewed by the sun, such as wind or solar, rather than extracting stored energy by burning fossil fuels. Some renewables are used directly, such as burning wood (biomass) for heat, using biofuels in internal combustion engines, or using a water wheel to turn machinery. Most renewables are converted to electricity for consumption. Wind, Wave and Tidal power all involve converting the motion of wind or water into electricity through the use of turbines or pistons that spin a generator. Solar energy can be converted with the use of expensive solar cells, or by collecting the light with mirrors and using it to generate steam to turn a generator. In the UK, solar power is more often used to heat water for homes. Geothermal power involves drilling down to find hot parts of the earth and then extracting the heat by pumping water through it, and using the steam to heat homes or generate electricity.

Problems with renewable energy sources

Most of the alternative energy sources have drawbacks. They depend on local climate as some places have more sunlight than others, some places have more wind, or rivers, big tides, or geothermal activity. In addition, wind, wave, tidal and solar power all vary in intensity at different times of day and in different seasons as well as varying by geographical location. Our energy needs vary continuously depending on the time of day, the weather, and what is on TV! This presents two problems. That of storing energy for when we need it, and that of getting the energy from where it is abundant to where it will be consumed. In addition, solar cells and the best battery technologies rely heavily on rare earth elements. China has a near 100% monopoly on these at the moment, although mines are being re-opened in the USA. China has reduced exports of these materials in order to keep in China the manufacturing processes that use them.

Energy Storage

While battery technology is great for small devices, and getting there for vehicles, storing electricity on the scale needed for the national grid is a different story. We store our energy in the form of coal, oil, gas and uranium, and we burn fuel to make electricity as and when we need it. We have teams of people dedicated to making sure that we produce the electricity at exactly the right time it will be needed for heat, light, air conditioning, or even just millions of kettles being used at the end of a popular TV programme. Once the fuel has been burnt and electricity produced, we have only one way of storing it – hydro-electric power stations. We use the electricity to pump water into reservoirs, and we can let that water out through turbines to get electricity back again. Unfortunately we have hardly any places where we can do this, so basically we can’t store electricity for later use by the grid. One promising technology is Molten Metal Batteries. Some Sodium Sulphur (NaS) batteries are already in use, but batteries using magnesium and antimony at 700 degrees look even more promising. A molten metal battery the size of a shipping container could provide about a megawatt of power.

Micro Generation

In recent years small wind turbines and solar panels on roof tops have become popular. Since April 2010 there has been a scheme for homes to sell electricity back to the grid through Feed In Tariffs which means that surplus electricity can be sold to offset the cost of installing equipment. The Green party have been pushing Micro Generation and small local projects as a solution, citing the inefficiency of the national grid as one reason. I believe that small power generation like this is not a particularly good idea. Generating electricity on this scale is inefficient and expensive, and in densely populated areas there can only be so many wind turbines before there is not enough wind left to turn any more. Solar water heating and ground source heat pumps can be good for providing hot water and heating homes, but are best installed at the time a home is built.

International Cooperation

To make the best use of renewable energy we will need many countries to work together. In the UK we have abundant wind and wave energy, but little usable solar energy. It is the other way around in the Sahara desert! Iceland and Norway have lots of geothermal energy. Some of these sources produce varying levels of electricity at different times. Ideally, we would all join an “International Grid” so that when our own energy sources are not up to it we can use surplus energy from other countries, and vice-versa. We already have a distribution system in the National Grid. This even extends internationally with links between countries, for example the UK is linked to France and at peak times we top up our own supplies with French nuclear power. Power distribution in this way is not particularly efficient though. Our power grid uses AC electricity for various reasons, some historical. To transmit power over international distances we could use High Voltage DC (HVDC) power lines[2] which will lose far less energy than the normal AC system. With an international HVDC power grid we could share British wind energy with other countries, and make use of Nordic geothermal energy and North African solar energy. I strongly suspect that the political will to do this does not exist though.

Renewable does not mean infinite

Worryingly, a paper by Axel Kleidon[1] found that there isn’t actually all that much energy available to extract from renewable energy sources. Extracting energy from the wind to make electricity means (of course) that the energy is no longer in the wind. Kleidon found that when we take into account the effects of removing energy from the wind, we will be able to take far less than was thought. He calculates that it may be possible to extract up to 70TW from wind but that it would cause serious changes affecting rainfall and the amount of solar radiation reaching us. There are also serious concerns about the environmental impact of wind farms and tidal barrages.

Where does that leave us?

Renewable energy sources are our future. I believe we must switch to these sources as much as possible. We will need a mixture of many power sources to overcome variation in power usage and supply, dependence on rare materials, and damage to the environment. To link up this variety of sources we will need an international “Supergrid” using HVDC, and we will need new forms of energy storage such as Molten Metal batteries. All of this will require huge investment and political willpower as well as international cooperation.

My personal opinion is that we just won’t get this done in time to prevent damage to the environment or avoid running out of oil, even if we can find the money. I also don’t believe that renewables will be enough to replace fossil fuel. I think that we will have to turn to nuclear power to fill the gap. Nuclear power has massive drawbacks, and yet there are a lot of things we can do to make it safer and less problematic. I will address the issue of nuclear power in a future article. (In about a month if my last promise is anything to go by!)


[1] Information is from a paper by Axel Kleidon due to be published in Philosophical Transactions of the Royal Society via New Scientist 2nd April 2011.

[2] While writing the above article I went off track a bit and wrote about AC and DC power lines. I’ve left it in here by request so you can read it if you want.

AC/DC

Electricity can be made in two forms. Direct Current (DC) and Alternating Current. (AC) With DC the electrons simply flow from one side of the battery / generator to the other. With AC, the electrons switch directions rapidly. When generating electricity it is easiest to create AC, and it is easy to change AC to a higher or lower voltage using a transformer. Batteries usually create DC. Electricity also has current, which describes the quantity of power flowing, and voltage, which describes the force with which it is flowing. (Forgive the bad descriptions, please, I’m tired!) Current and voltage are tied together, so that if you have a higher voltage, you can use less current to transmit the same amount of energy. When we transmit electricity through the national grid, we want a high voltage so that we can have a lower current. This has two benefits, it allows us to use a thinner wire with less metal in it, and it slightly reduces the amount of energy lots along the way. When the electricity reaches our homes, we need a lower voltage as high voltages are not safe or easy to work with. We use transformers in substations to convert the electricity from thousands of volts down to 230 volts.

HVDC distribution

When transmitting electricity over a large distance, some of the energy is lost as heat. Using a higher voltage, and therefore a lower current, reduces this loss. We usually put AC electricity on the national grid because our generators produce AC, and because AC is easily converted to a different voltage by using a transformer. Unfortunately when transmitting AC, some of the energy is lost as a magnetic field. The solution is High-Voltage Direct Current. (HVDC) In the past we didn’t have the ability to convert AC to DC and convert low voltage DC to high voltage DC on the scale that we needed for transmitting between cities and countries, but things have moved on. We now have to ability to create a HVDC SuperGrid covering whole continents. More on HVDC (Wikipedia)

In defence of nuclear power

Schematic of a Boiling Water Reactor
A Boiling Water Reactor. Image from Wikipedia.

When I was ten I remember being given some sort of exercise at school that required me to draw my answer. I drew a nuclear reactor. I drew it in some detail, including fuel rods and control rods and cooling system. This wasn’t actually unusual for me; I frequently drew machinery of many kinds, huge cogs and mechanisms and bizarre perpetual motion machines. Imagine my astonishment when the first thing my teacher said on seeing my drawing was “So you’re in favour of nuclear power then?”

I was astounded. It hadn’t occurred to me that anyone could be against nuclear power. It was a machine! It was THE ultimate machine! How could anyone not love it?

Twenty two years later I am still in favour of nuclear power, although this time for much more considered reasons.

Perception of danger

Nuclear power is much safer than you might think. Think of the safety of nuclear power as something like an aircraft. Cars have frequent accidents, killing quite a lot, injuring more often. Aircraft few accidents, but when they go wrong, they really go wrong and generally kill everyone on board. A car accident might make the local news if there’s something odd about it. An aircraft accident will probably make the international news. Despite the differing attention given between these two, road accidents kill and maim many more people than air accidents do. The safety record of electricity generation is much the same. Fossil fuelled power stations might have accidents, but generally they are of little consequence. Even so, fossil fuel waste causes a lot of damage to the surrounding area and people living nearby. Nuclear power stations have very few accidents, but when they do, they have really serious ones.

People imagine an accident in a nuclear reactor as something like a bomb. Say “nuclear accident” and they see mushroom clouds and flattened cities but it isn’t like that. A nuclear bomb makes use of a runaway chain reaction which requires the uranium to be dense enough and large enough to reach “critical mass.” Nuclear reactors have their fuel split up into smaller parts encased in fuel rods which are held too far apart for a nuclear explosion to occur. What can actually happen is a meltdown, where the fuel rods melt, run together into a pool at the bottom of the reactor, then burn down through the floor and leak radiation. This can happen when the fuel is not kept cool enough. In most reactor designs there are three levels of containment around the core, and molten fuel will be contained by a very thick concrete basin under the reactor and prevented from leaking.

Apart from meltdown, a reactor that uses water as coolant can also produce hydrogen when things go wrong, and evaporating coolant can cause a build up of pressure inside the reactor. If the coolant stops circulating, the heat of the reactor can crack the water into hydrogen and oxygen and fill the containment up with this explosive mixture. In old (or Russian) reactors it could explode inside the containment and break it open. In more recent designs, the hydrogen is vented from the core before it can explode and expose the fuel to the outside world. The vented gasses are themselves radioactive, but usually not very much and not for very long since the radioactive particles have a half-life measured in minutes. (That is, they break down very quickly.) A big flaw with old reactor designs such as those at Fukushima and all Russian reactors is that the coolant will stop circulating if the pumps lose power. Modern reactors are designed in such a way that if the power stops, the coolant will keep circulating through convection.

In summary, modern nuclear reactors are much safer than those from the 1970s. They have multiple level of containment to catch molten fuel. Coolant can keep circulating even without power. High pressure and explosive gasses are removed from the core before they can explode and destroy it. Instead of setting a reaction going and then restraining it, modern designs require human intervention to keep them going. If the people aren’t there, the reactor shuts down. The rules on dealing with accidents are incredibly strict, almost paranoid. Finally, there are many more advanced designs of reactor to choose from than just pressurised water reactors or boiling water reactors. Pebble Bed Reactors, in particular, are designed so that they produce less power as the temperature rises, and so are self-limiting and cannot overheat.

Dealing with waste

Radiation Warning SymbolI will admit, dealing with nuclear waste is a problem. I would like to make some points about this. First of all, fossil fuels also produce waste. That waste in the form of ash, CO2, sulfur dioxide, nitrous oxide and other gasses has traditionally been pumped into the atmosphere where it causes acid rain, smog and climate change. Pollution from fossil fuels affects the workers at the power station and the residents in towns nearby. Recent attempts to scrub pollutants out of smoke before releasing it have reduced this a little, but not enough. Carbon capture will improve things but is very difficult and hugely expensive. Secondly, fly ash from coal is actually radioactive! Not just radioactive, but during day-to-day operation a coal power station releases 100 times more radiation than a nuclear power station producing the same amount of electricity. People living near coal-fired power stations actually have more radioactivity in their bodies than people living near nuclear power stations.

Nuclear waste is usually buried deep underground. It will remain dangerous for millions of years. I think though, that I would much rather have waste that can be buried than pump smoke and ash into the atmosphere and destroy the planet.

We could actually produce far less nuclear waste than we do at the moment. Used nuclear fuel can be re-processed, and can be re-used to fuel Breeder Reactors. These reactors produce more fuel as they use traditional fuel and so they produce a lot more energy from the same fuel, and the waste is more effectively used up. They can also run on thorium, which is more readily available than uranium. Unfortunately Breeder Reactors are generally not used because they create plutonium and governments are terrified that it would be used to create nuclear weapons.

Thank you for reading this far. In my next post I will explain why I believe that nuclear power is neccessary and why renewable sources are not adequate. Please also note that I am not a nuclear physicist, I am a computer scientist that happens to be fascinated by nuclear power. If I am wrong and you can provide evidence, feel free to say so in the comments.

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