Clean Energy Solutions

There is a huge abundance of clean renewable energy on the earth. In this first essay of the series I illustrate that it is possible to get all our energy from clean sources by discussing some of the more promising known systems. In subsequent essays I look at some serious evidence about how important it is to make a substantial and urgent investment in clean energy.

If people had a more optimistic outlook about the prospect for clean energy maybe they would more readily embrace the needed changes. Optimism is needed to help overcome the technical, social and political challenges.

The density of renewable energy is low and variable, so building systems to collect it looks daunting. However, most of that cost is in the early stages of development and having taken the trouble to establish clean energy collection machines the running costs are low; and the pollution is negligible. Once the volume of production reaches a critical level the total lifetime cost will result in renewable energy being cheaper than fossil fuel derived energy and everyone will benefit.

Solar energy

To have a meaningful discussion about any technical subject it is essential to look at the figures so let us start by looking at how much energy hits the earth from the sun. The answer is 174 000TW reaching the planet and of this 96 000TW gets through our atmosphere and hits the surface. These figures are not so meaningful on their own but can be divided by the population of the world to get a personalized figure. Assuming 6 734 million people at the time of writing we see that 14 256kW per person gets to ground level. That is like a million 14 watt light bulbs burning all the time for every person. Considering that humanity's total energy usage is about 15TW or 2.2kW per person we can see that we only need to use a tiny proportion of the Sun's energy to supply all our needs (1/6400^th).

Another way to analyse the figures is to consider that the average intensity of the sunlight we receive is about 300W/m² when the sky is clear (average for night and day). Assuming a conversion efficiency of 8% that means the average person would need 92m² of solar collector each. This suggests that if every roof was covered in photovoltaic (PV) panels we would get maybe a quarter of the energy we use today. That would be a good start:- provided we used the new thin film technologies being developed that pay back the energy used to manufacture them.

Large solar thermal generators are more efficient than any PV, but facilities built so far have to be situated in deserts to make economic and ecological sense. They use mirrors to concentrate the sun onto a heat engine, and track the sun so that the engine is always supplied with concentrated light. Regenesys have outlined a very promising system that has the potential to reach 60% efficiency and supply power night and day.

The desert location would often require the transmission of the power over great distances but that is possible using high voltage DC (HVDC). The construction of a global HVDC network is technically possible and economically viable even though it would require a large investment and cooperation between many countries.

Wind

A significant proportion of the Sun's energy is turned into wind. It is estimated that at the height of modern large turbines the total resource is up to 100TW (14kW per person). Wind gets much stronger at higher altitudes so a technology that could tap into this resource could produce many times more power. Going from the present typical hub height of 80m to 1000m would increase the available power by more than 20 fold. Kite based wind interceptors mounted on floating generators far out to sea could easily provide all the power we could ever want. This system would save us from having to cover our terrestrial environment with controversial turbines. Done on a sufficiently large scale it would also bring down the price of energy.

Large wind turbines have already reached the stage where they pay back the cash investment in their construction before they fall apart. If the price of oil shoots up again investors will make a fat profit from them. Typically they recover the carbon used to make and install them within 3 months. Because of this demonstrated success the industry is growing at about 30% p.a.

Small wind turbines are more economical in their use of materials. The difficulty is that their price is dominated by the labour costs of their construction and installation. If someone with enough money to start mass-producing them was brave enough to go ahead their price would come way down. The lower specific mass and economy of scale could make them a bigger success than big turbines.

Wave

Wind blowing over thousands of miles of ocean creates the most concentrated of the renewable energy sources; waves. In the roughest oceans the power averages about 100kW per metre. That means that a 10km long collector could, in principal, generate the same power as a typical fossil fuel power station which is approaching 1GW. A large initial investment would be required but with a sufficiently large effort we could, again, bring the energy cost down below what we pay today.

Tidal and ocean current

Turbines, or water-kites, in the sea can generate power from the motion of the water caused by tides or currents. The main problem I foresee with tidal energy is getting consensus that the disruption caused to the local environment is worth the value of the energy generated.

A very interesting extension of the basic idea is to build what have been called energy islands. Essentially a long dam wall is built to enclose a significant area of ocean. A set of turbines that act as either generators or pumps are installed in the wall. When there is a surplus of energy the turbines pump water out of the dam. When there is a shortage the turbines allow water back in and generate power from the level drop. Using a more complex system of staged dams and prediction of energy use and supply the scheme can work with the tides so that tidal movement adds to the total energy generated.

Geothermal

The uranium and other radioactive elements in the granite, and similar rocks, deep in the earth creates a valuable heat resource. Their depth in the earth means they are well insulated and over time have become very hot. Deep boreholes down to these rocks can be used to create super-heated steam. This steam can be used for heating or to generate power. Geothermal is limited both by the areas in the world with a viable resource and by its total capacity. It is therefore best exploited in combination with the resources listed above. When the sun, the wind and the waves are not producing enough power the geothermal can be turned on. When it is not needed it is turned off and the heat is allowed to build up again.

The word Geothermal is sometimes incorrectly used to describe ground source heat pumps (GSHP). Both involve pipes in the ground but with GSHP they are much nearer the surface. GSHP uses a heat pump that requires an external energy source. That energy input is amplified by taking advantage of the high thermal mass of the earth. Geothermal systems output energy and because of the depth of the boreholes they only make sense for systems that can supply a whole town, or more. GSHP is suitable for single homes and together with air source heat pumps they are growing rapidly in popularity because of their ability to save energy.

OTEC

OTEC stands for ocean temperature energy conversion. In deep oceans in the tropics the water gets rapidly colder the deeper it is. By pumping large quantities of water from the deep ocean to the surface we can create a significant temperature gradient. Temperature gradients can be used to do useful work, such as produce electricity. To be viable the process would have to be done on a very large scale. Developing the process is therefore risky. As with geothermal energy the resource is limited. If it has a place in our future it is likely to be as a topping-up supply as with geothermal. It has interesting implications for the fertilisation of the surface ocean and the boosting of fish stocks.

Biomass

For a while into the future we are likely to need hydrocarbon fuels to power aircraft. No one to my knowledge has demonstrated a viable alternative. Hydrocarbons will also be needed to some extent for surface transport. Attempts so far to supply this hydrocarbon fuel from biomass have not had good publicity. The biofuels produced so far have been blamed for increasing deforestation and pushing up the price of food. We should try to step back, rethink our approach, and do some more research.

Looking at the fundamental science it is clear that biomass could be used to make clean renewable fuel, the sort of hydrocarbon fuel needed by aircraft. A complete technical solution has not yet come to my attention, but some interesting work is being done with algae. Algae grows very fast in the right conditions and can be made to produce oils that need little processing to turn them into fuels. There is more than enough space in our deserts to grow all the algae we would need. There is also no reason why the production could not be done out to sea on floating islands. The detailed technical answers about how to do this are likely to come from multiple sources so a multi-pronged development effort needs to be funded.

Energy efficiency

A huge proportion of the energy we use is for directly, or indirectly, keeping our indoor environment at a comfortable temperature. When it is cold outside we turn on the heaters and when it is hot we turn on the air conditioners. We also use many energy consuming gadgets indoors and these contribute to the heating when cold and add to the load on the air conditioners when hot. In the UK nearly 50% of the total energy used is a contribution to this process. It is therefore by far the most important single category of our carbon footprint.

The ridiculous thing is that it does not have to be this way. Addressing the issue would save us a lot of money with pay-back times sometimes being as short as a few months. That is before considering the huge ecological benefits. The fact that we have done so little for so long is a damning reflection on our culture.

The technology for building passive houses that require no extra energy for heating or cooling has been demonstrated in many climates. The only thing that is required is a sufficient shock to make us change the way we build houses.

Considering how slowly existing houses are replaced with new ones it is clear that most effort needs to go into fixing existing houses to make them better insulated. This can be expensive and inconvenient but more could be done if the motivation was high enough. Loft and cavity wall insulation is widely promoted and it helps. Ideas like insulating wall plaster and cheap external cladding need more support.

Besides indoor temperature control there are other big energy users that need attention. I have touched on this subject elsewhere. There is also already a lot of talk and a bit of action on these matters so I will not say more for now.

Fresh water

Fresh water is in increasingly short supply in many places. Renewable energy resources are fickle and sometimes do not produce. Considering these 2 problems together reveals a solution that solves both problems. Desalinating sea water requires a large amount of energy but having produced the fresh water it can be stored for long periods until needed. Therefore, if the capacity of our renewable energy sources was increased beyond our average energy needs we could use the periods of excess energy to desalinate saline water resources that are otherwise useless to us. This, in combination with the extensive HVDC network discussed above, would ensure that we always have power when we need it.

Nuclear

I am not a fan of nuclear power for several reasons.

Fuel for nuclear fission is not truly renewable. Whether we use uranium or thorium or anything else there is a finite supply.
Fission produces some incredibly nasty waste products and I have not yet heard of a satisfactory method for dealing with them.
In the early days nuclear power was over-hyped because of its military importance. This has created a legacy of mistrust and there is still a big doubt that it makes economic sense to build new fission reactors. Besides, we would not need them if we embrace the solar and other clean energy sources mentioned above.
Nuclear fusion is a long way from being practical. The sun does that for us anyway so why not just use the energy it sends us every day without fail?

I am not saying fusion research should stop because we are learning valuable information from the effort but it should be kept in perspective so that sufficient money can be spent on renewable energy systems that will produce quicker results. The same applies to fission because a certain number of fission reactors are a very valuable resource. One example is that they supply a range of radioactive isotopes crucial for many branches of science. However, it needs to be kept in balance because nuclear presently does not make a lot of sense for pure energy supply and sustainability reasons.

The Nuclear Illusion by Amory Lovins and Imran Sheikh make an extremely well supported case against the nuclear industry. They say our money should be spent on energy efficient measures first and then wind power which is what I also believe.

Fuel cells

Having spent many years doing fuel cell research I have become very familiar with their advantages and problems. When I first started hardly anyone knew what they were. Interest in them has since exploded because in principle there is no more efficient way to turn fuel into electricity. Some major problems include

Efficiency drops rapidly as power output increases (in most types, but in types where this is not true efficiency is always low).
The cost of construction has been incredibly difficult to decrease to a level where they compete with existing technology.
Very pure fuel is required for low temperature types.
It is difficult to find an efficient way to make fuel for them without using fossil fuels.

Some FC types still offer advantages that other technologies struggle to match so there will definitely be a place for them in the future energy mix. However, I no longer believe that they will be the major contributor to the future of clean energy.

To take best advantage of them we need to take advantage of the fact that most types are far more efficient when they are delivering a small proportion of their maximum power. These types should therefore be built into applications where full power is only occasionally needed but trickle power is needed for long periods. I write more about this in Ideal hybrid car

Sequestration

Numerous schemes for pulling CO₂ out of the air are being investigated. The gas is being pumped into oil wells to help extract the last dregs of oil out of the ground. There is talk of making it react with silicate rocks and so on. Looking at the bigger picture I see no advantage to these schemes except for the balance sheet of companies already making money from pumping CO₂ into the atmosphere. Nearly all the CO₂ we make is because of our demand for energy; yet collecting the CO₂ to sequester it uses extra energy! Pumping it into the storage system takes energy. The gas reacts with silicate rocks anyway but to make it happen fast enough to absorb all we make a huge volume of rock would have to be mined and crushed. That takes extra energy. Would it not be far better to just stop making CO₂ in the first place? It is possible.

An important twist on this story is the sequestration of charcoal. Every year plants absorb CO₂ from the atmosphere at a rate that is equivalent to about 95TW (14kW per person). Because there is more land in the northern hemisphere than the south there is a dip in the atmosphere's CO₂ concentration every northern spring and summer. It then rises again every Northern autumn and winter. The plants grow in summer and capture carbon from the air and then after the fall (autumn) much of it is released again as the leaves rot and the animals continue to eat. We can capture that carbon by charring biomass before it rots. On a scale that does not damage soil fertility this has at least 3 advantages.

The charring process can supply us with energy.
Once charred the fungi, bacteria etc. responsible for the rotting process cannot oxidise the charcoal.
Charcoal ploughed into the ground is an excellent soil enhancer. It stays there for many centuries benefiting both the soil and the atmosphere.

The economics of this process are difficult to balance but if I had the development money I have an idea that would make a big difference. That is one of the reasons why I am asking for donations.

In my next essay I start explaining why it is so important to invest in clean energy; Global warming