Renewing renewables (part 2 of 2): The path for change

The need to shift from the current fossil fuel economy to a low-carbon economy based on alternative energies is at a tipping point. However, despite the numerous solutions available today; our focus is limited to a few renewable energy technologies. Others remain highly unexploited despite the fact that they could provide a significant contribution. We must continue developing the current primary renewables (solar and wind), but we should also start exploiting other alternatives on a much larger scale than they are used today. No single currently available technology can provide a global solution to the energy crisis.

As highlighted in the first article of the series (Renewing Renewable: The case for change), unless major changes are made, it is likely that the world will adopt coal and nuclear as the two main energy sources in the decades to come. Both of these are unwanted outcomes.

A better and highly necessary alternative

A better alternative would be a complete shift from fossil fuels to renewables. And although it may seem unrealistic to many, it is possible based on today’s technologies. Here is an overview of the pros and cons of the available options:

The common

Solar photovoltaic: Solar photovoltaic (PV) has greatly improved in efficiency and cost-effectiveness thanks to extensive research and development in recent years. Even so, efficiency remains relatively low (the conversion factor efficiency of commercial photovoltaic panels based on crystalline silicium cells is approaching 20 per cent) and the cost relatively high. Furthermore, in order to produce significant energy supply from PV, very large surface areas would be required. However, keep in mind the following attractive fact: if we were to convert even a fraction of the world’s deserts into solar photovoltaic farms (e.g. the Sahara desert) we could power the entire planet on solar energy alone. Indeed, the average solar radiation power falling per year on a square meter in the Sahara is higher than 200W. Based on this fact alone, solar photovoltaic is and will remain a major area of focus and hope. New technologies such as concentrated solar and solar films will significantly change the current usage of solar cells. Solar energy could also be harvested directly from space and brought back to Earth in the form of microwaves (such technology is possible and countries such as Japan are considering the option). As Thomas Edison once said: “I’d put my money on the sun and solar energy. What a source of power! I hope we don’t have to wait till oil and coal run out before we tackle that”.

Wind energy: Wind energy has been the most rapidly expanding renewable energy source in recent years and offers great potential. However, we must not forget (and it is often forgotten) that modern wind turbines are complex machines which are resource- intensive to make and maintain. For example, one single turbine contains kilometres of copper wires for which mining and production is a highly polluting and energy-intensive process. From a life cycle point of view, wind turbines actually emit significant amounts of greenhouse gases (GHGs). However, wind turbines do pay off over time from an energy perspective and the potential to exploit wind patterns (especially offshore where they do not compete for space) is promising. The main advantage of wind is that it is widely available. Modern wind turbines can generate about 100 megawatts (MW) per square kilometre, which is on par with solar thermal. A major disadvantage of wind power is that it requires storage capabilities (the grid can only absorb variable energy output if wind power is limited to a small percentage of total installed power). It is quite realistic to assume that wind power will contribute no more than about five per cent of total power production as a larger implementation would require significant changes to existing electrical networks.

Hydropower dams: Hydropower dams are well used in countries that have access to large amounts of fresh water. Hydropower works well from an energy efficiency point of view but the construction of dams, especially in biodiversity-rich areas, are sometimes truly devastating. Furthermore, the construction of large scale dams (such as the Three Gorges Dam in China) can be responsible for the disappearance of entire villages, cultural heritage sites and cause major disruptions to natural river flows. For these reasons alone, hydropower dams are in many cases far from a sustainable alternative. In addition, the large amount of cement required, as well as the destruction of forests, are responsible for the release of significant amounts of GHGs. Hydroelectric project should be evaluated carefully for their impacts on both the surrounding environment and the communities. Smaller scale hydroelectric projects sometimes make more sense as the destruction to the surrounding areas is minimal. On a smaller scale, there is significant potential for micro hydroelectric turbines. These systems, which make use of the pressurised flow in transportation pipes and other installations such as buildings, remain virtually unexploited.

The less common

Passive solar (largely unexploited): New solar passive technologies which use the sun’s heat to generate steam to spin turbines are on the rise and very promising. Several long term trials of solar towers (concentrating mirrors on a central heat exchanger) have been held in locations such as Seville, Spain or in the United States. Meanwhile, Australia is constructing another type of passive solar technology on a massive scale: tower funnels that will produce energy in the range of 200 MW. Modern solar thermal power plants have a conversion efficiency of about 30 per cent, about the same as nuclear plants. Furthermore, the energy payback time for solar thermal is highly favourable at about 5 months. We are only beginning to realise the potential of this relatively simple technology, which is reliable and requires little maintenance. One drawback is that it requires large surface areas with high solar exposure. However, as with photovoltaic, desert regions exist where such technology could be implemented on a large scale.

Ocean thermal energy (largely unexploited): Ocean thermal energy has great potential and is one of the least exploited renewables. There is a significant thermal gradient, or temperature difference, between the deep ocean and the water surface. Commercial exploitation of this energy would require significant investment for relatively little output, but it can be accessed almost anywhere on an ocean and is a constant source. Furthermore, new technologies suggest that the process efficiency could be significantly improved by using passive solar to increase the temperature gradient between the deep sea and the surface.

Tidal energy: Tidal energy which is constant and very powerful is also largely unexploited to date. Many locations on the planet have particularly strong tidal currents. A range of new turbine technologies have been tested in recent years and proved that the biggest barrier to the energy source – corrosion – can be reduced. Furthermore tidal energy is predictable (as opposed to wind) and therefore reliable.

Geothermal (largely unexploited): If we put the technology difficulties to the side and focus on the problem as a whole, we come up with the following observation: we are on a planet which contains mostly melted rock at very high temperatures and we are only on a small crust which sits on this magma. We can therefore see our planet as a giant “cooker” with an unlimited supply of energy just below our feet! Of course the situation is a bit more complicated when it comes to drilling and accessing this heat. However, the situation has changed dramatically in recent years as advances in drilling technologies (quite ironically mostly developed by oil and gas companies) now allows drilling at much greater depths and makes the exploitation of geothermal energy possible in many parts of the world that were before non-exploitable. Furthermore, an advantage of geothermal is that it does not require the use of much land area, giving it an advantage over more land-intensive renewables that are increasingly competing with agriculture and forests for space. Much more research should be allocated to the development of geothermal.

Bioenergy: Bioenergy has big potential; despite serious mistakes made in the early development of biofuels. Decisions to replace large swathes of agricultural fields with biofuel crops have led to global food price rises and security issues. Furthermore, biofuel crops have been a major driver of deforestation. However, new developments such as algae biofuels, which would cultivate supplies from oceans rather than on land, are promising although still experimental. Bioenergy’s main advantage is its emissions reduction potential - recently grown biomass does not contribute to climate change as fossil fuels do. Furthermore, there is enormous opportunity to convert the tremendous amounts of waste generated by society to biofuel (waste to energy).

Others: Several less conventional potential renewable sources have barely reached the level of experimental research. One example would be deriving energy from bacterial activity on a large scale (many bacterial processes are exothermic and the free heat generated could be used to derive energy).

The forgotten energies:

Clearly the emphasis is increasingly on photovoltaic and wind energies when it comes to renewables. We should continue and even accelerate those efforts. But at the same time, other renewables need much greater attention and research if we are to avoid the unwanted outcome of a major shift from petroleum to a coal-based energy.

Geothermal, passive solar, ocean thermal and tidal energies in particular should become predominant focus points. We need to “renew renewables” in the sense that in addition to current photovoltaic and wind, other renewable energy sources deserve their chances of large scale deployment. They may actually prove more successful at providing sustainable alternatives to the energy crisis.

Sylvain Richer de Forges is head of sustainability at Siloso Beach Resort.

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