Most electricity in the world is produced using steam to push turbines, which generate power by transforming kinetic energy into electricity within a generator. Electricity is thus inextricably linked to movement and to heat, and as we shall see below, there are many resources on our planet with which we can produce renewable energy beyond the near-ubiquitous solar, wind, and hydro.
The inside of the Earth is an amalgam of hyper-dense molten rock and metal that is constantly generating heat due to radioactive decay. We are mostly insulated from this heat by the earth’s crust, but there are places where it seeps outwards and where we can tap into it to generate renewable energy. Specifically, we can use the hot water and the steam that is trapped underground at certain locations to power generators on the surface and produce electricity. There are three types of geothermal generators in use today: dry steam, flash steam, and binary cycle.
Dry steam power plants draw steam directly from underground and pipe it into a turbine system. Flash steam power plants use extremely high temperature water to produce steam by channeling it into low pressure chambers. Deep underground, water can be packed into the rock at such high pressure that it can remain in liquid form well above its boiling point. When the rock is perforated and the water is given a channel to escape it rises because of the immense pressure, and when it reaches a space where that pressure diminishes it vaporizes instantly, providing the steam needed to push a turbine in a power plant. Lastly, binary cycle power plants also use hot water from underground but instead of powering generators directly it is used to heat a specially made working fluid with a much lower boiling point than water, some going even as low as 57ºC.
Although geothermal electricity can in theory be generated anywhere in the world by simply drilling downward to sufficient depth, the cost and technical difficulty of doing so means that not all locations are truly suitable. Currently the largest producers of geothermal electricity (as a percentage of their total electricity production) are Kenya, Iceland, the Philippines, El Salvador and New Zealand. In the UK geothermal electricity production is virtually non-extant, with the focus being on using geothermal energy for heating instead. However, according to a 2012 study, the UK could meet up to 20% of its power needs by exploiting deep geothermal resources, a total of 9.5GW or what is the same, the output of nearly 9 nuclear power plants.
Biomass and biogas:
In our piece on artificial photosynthesis, we described the photosynthetic process and the chain by which energy from the sun comes to power every life form on our planet. Beginning with plants, which use sunlight to ignite the chemical process in which carbon dioxide and water are transformed into glucose, and going all the way up the food chain, all the energy we use is essentially “borrowed” from the sun. This is true of the fossil fuels we burn today, which are derived from plant and animal matter that became trapped underground millions of years ago, and also true about biomass and biogas — what changes is the ‘when’, as with these two energy is extracted from biological matter once it has become waste.
Biomass is a catch-all for a variety of organic fuel substances that can be used to produce different types of energy. Wood scraps, solid municipal waste, plant matter and a host of others can be burned as is or broken down via chemical processes, rendering combustible fuel. These fuels can then be burned to power generators like we outlined above or simply to produce heat. Unlike other forms of renewable energy generation, biomass does not require large infrastructure investments, making it ideal for distributed and modular power solutions. It is especially popular on farms and in isolated rural areas with deficient or no grid connection because it allows people to transform waste materials such as animal slurry into energy. This can be done through anaerobic digestion, the process by which certain types of bacteria break down and consume organic matter, producing methane as a remnant, which can be used as fuel. This methane can then be used directly or even upgraded and injected into the regular gas grid. Burning is not a well looked upon term in green circles, but Biogas is actually carbon neutral because the carbon that it produces was initially drawn from the atmosphere by plants through photosynthesis at the beginning of the chain we described earlier.
Marine energy is an umbrella term for different renewable energy producing technologies whose common denominator is using the power of the seas and the oceans to produce electricity. Just like the Earth is a massive reservoir of heat, the oceans are a massive reservoir of kinetic energy. Due to the earth’s rotation, to winds, and to gravitational forces the large water masses of our planet are in constant movement, and this movement can be captured and harnessed to produce electricity. Of the three alternative forms of renewable energy discussed in this piece, marine energy is the least used and the most experimental.
Marine energy devices come in many shapes and sizes, and they make use of different aspects of the sea’s kinetic energy. The most widely known, despite still being a very experimental technology, is wave energy. Wave energy is the energy obtained from waves on the surface using machines that convert the water’s oscillations into power using hydraulic pumps. There are dozens of different types of machines that achieve this but so far implementation around the world has been limited. However, the global potential for wave power is estimated to be over 2 terawatts, and the UK’s northern coast happens to be one of the best locations on the planet. Currently, the European Marine Energy Center based in Orkney, Scotland, is one of the global hotspots for wave energy technology development.
Another way of extracting energy from the sea is tidal power, of which we will highlight two forms: tidal stream generators, which are essentially underwater turbines that draw on the movement of water to generate electricity in the same way that wind turbines do with wind, and tidal barrage power, which uses rising and falling water levels to reproduce the functioning of hydro-electric dams through the height difference between high and low tides. Both of these have seen limited implementation so far, like all marine energy technologies.