Lesser-known renewables: tapping into the power of Nature

— Anh NGUYEN

We have examined the pros and cons of the seven most popular sources of energy in our previous article, ranging from fossil fuels (coal, oil, natural gas), nuclear energy & renewables (hydro, wind & solar power).

And we are not yet exhausted of renewable options. There exist other energy sources, but much less popular or discussed, such as biomass, biomethane, geothermal and solar thermal. 

But before getting into the examination, we must discuss an important notion – grades of energy. There exist two grades of energy: low-grade energy & high-grade energy. I admit, nothing fancy about their names, but it is crucial to note the difference between the two. 

Low-grade energy such as heat is available in nature and can be used to do work (boiling water, heating places) but it can dissipate rapidly. High-grade energy such as electricity, the burning of coal, on the other hand, is highly organised and compact (concentrated in a small space). 

Illustration on the difference between Heat and Work, Low grade energy vs high grade energy
Low grade energy vs high grade energy: “Heat is the energy associated with the random motion of molecules, while work ordered motion in one direction. Thus heat is low-quality energy and work is high-quality energy.” Thank you, fellow Internet user. Source.

A small amount of electricity can do a great amount of work, such as fueling our searches on the Internet. Yet it takes a lot of energy and resources to produce and yield the power of high grade energy, while low grade energy is either quite available and abundant (i.e. the Sun).

We have probably been told this at school. What we haven’t been told is the absurd but common practice of yielding high grade energy to do work that only requires low grade energy. We use an enormous amount of energy & resources with a sophisticated production process to produce electricity to heat our water and our home, and to cook, while heat is low grade energy that can be yielded directly from the heating of the Sun or other low-level transformations such as biomass. 

The missing element in our sustainable energy strategy is a renewable source of heat energy

Kris de Decker – Low-Tech Magazine

With this in mind, let’s examine these lesser-known renewable sources of energy.

Biomass – it is made from organic matters, it is, therefore, “green”?

Biomass is used to produce electricity or heat and the materials can be wood, energy crops (plants that are grown solely for energy production), or wastes from forests, yards, or farms. Biofuel is “transportation fuels such as ethanol and biodiesel that are made from biomass materials.”

Biomass is a renewable source of energy (because even though a single plant or animal can not resurrect, we can, instead, farm lots of them). 

Biomass from plants is carbon-neutral, meaning that plants capture almost the same amount of CO2 through photosynthesis while growing as is released when it is burned. But it burning wood releases other greenhouse gas, such as nitrogen oxide and micro-particles, into the atmosphere.

Biomass is a very important energy source in Sweden, accounting for 23% of the national energy supply, thanks to its large forested areas. Finland, on the other hand, uses more biomass for energy purposes per capita. 

Biomass used per capita per country for different sectors
Biomass used per capita per country for different sectors. Source.

In the documentary “Planet of the Humans”, Michael Moore lists out many limitations of biomass. (I know, I know, it’s Michael Moore, he does not always have his facts straight in this documentary, but he was not criticized on his opinions on biomass either). 

A massive biomass plant, a scene in the documentary “Planet of Humans” by Michael Moore
The equivalent of a horror movie scene: a massive biomass plant, shown in the documentary “Planet of Humans” by Michael Moore. Source.

Biomass, when being ill-managed and used on a massive scale, will lead to the destruction of forests & their ecosystem, loss of habitat for animals, damages to water systems, while not being the most efficient energy source in comparison to other alternatives. 

Imagine the absurdity of burning organic matter and woods to produce high grade energy such as electricity to heat water and to cook – which can be done right in the first place, the same way the first men did back in prehistoric times. 

The control of fire by early humans
The control of fire by early humans. Photo source.

Biomass can make a lot of sense when it comes to heating and cooking – work that requires only low grade energy (though it is not possible to fuel our computers or internet search). The practice also depends largely on the availability of woods & plants in the region or community and should be coupled with techniques that allow the optimization of the burnt biomass materials such as rocket stoves or tile stoves. 

We have examined these practices here in this article “Less waste, less energy: better ways to heat places in a temperate climate” if you want to delve more into this. 

Biogas, syngas, biomethane, methanation, pyro-gasification: different things, but not quite

Biogas is a term used for the process and products after the breakdown (or “fermentation”, roughly speaking) of organic matters in the absence of oxygen (the process is called methanation). 

How biogas is produced: waste is stored and fermented in tanks without oxygen, this will produce methane and other gases
How biogas is produced: waste is stored and fermented in tanks without oxygen, this will produce methane and other gases. Photo source.

The same principle is applied to other types of man-made gas, with different materials and configurations. Biomethane is one type of biogas with a methane concentration of 90% or greater. Pyro-gasification is a term to describe pretty much the same process of methanation but with organic and non-organic matters (i.g household waste), to produce synthetic gas or syngas

Illustration of a Pyro-gasification process, according to GRDF, a French gas provider.
Pyro comes from the Greek word πῦρ (pyr), meaning fire or heat. Pyro-gasification process, according to GRDF, a French gas provider. Photo source

These renewable natural gases are marketed massively in the past few years in Europe, as a “greener” alternative to natural gas – fossil energy as it valorises waste from industries, household as well as residues from agricultural activities, and it is renewable (presumedly that we will perpetually produce waste). What is often overlooked, however, is that they still emit greenhouse gas (GHG) during their production & usage. 

In the rest of the world, the practice was encouraged by governments in regions where it is too expensive to build electricity grids and where agricultural waste is abundant. Below is an example of biogas in the rural areas of Vietnam to fuel their cooking. 

A biogas structure in the countryside of Vietnam
The dung produced by the animals flows into a brick-built fermenter set in the ground”. Small-scale farmers “with two cows or six pigs have enough manure to run a digester that meets their own energy monthly cooking needs”. Source

Beyond heating & cooking, gas is high grade energy that can be monitored to fuel complex work and machines. It can also be compressed and stored in tanks, as described here in this paper

The produced biogas is stored in the black plastic balloon on the left. We then can use a foot compressor to compress produced gas into a cylinder for later use.
The produced biogas is stored in the black plastic balloon on the left. We then can use a foot compressor to compress produced gas into a cylinder for later use. Photo source.

Geothermal – journey to the crust of the Earth 

Geothermal energy is the thermal energy generated and stored in the Earth. It is a renewable source of energy because our heat extraction is considered small compared with the Earth’s internal heat budget which is 47±2 terawatts, or 47±2 x 1012 watts, which probably means A LOT, but I don’t know how much.

Another good news is that geothermal is not intermittent and not dependent on a third-party supplier such as waste or residues or plants etc.

The earliest exploitation of this energy that we all know about is natural hot springs or hot public baths.

Monkeys chilling out in a hot spring in Japan in a snowy weather
Chilling out in a hot spring – enjoying that lovely heat of the Earth. Photo source.

Geothermal energy can be used for electricity and heating, based on different energy grades. At a very low-energy level of less than 30°C, a geothermal heat pump can draw heat or coolness from the surface layers of the Earth (which does not vary much through seasons of the year) to heat or cool a house, and to produce hot water. The system can be installed vertical, horizontal, or connected to a pond.

Three types of installation for geothermal heat pump: vertical, horizontal or connected to a pond
Three types of installation for geothermal heat pumps: vertical, horizontal or connected to a pond. Photo source
A horizontal geothermal heat pump setup with plastic tubing placed in loop
A horizontal geothermal heat pump setup with plastic tubing placed in loops. Photo source.

On a low-energy level between 30°C and 90°C, geothermal energy is used to heat or cool agricultural greenhouse, or to desalinate seawater to produce fresh water, or to prevent the build-up of snow and ice in countries with frequent snow cover. 

How farmers in Iceland harnesses hot springs to power year-round farming
How farmers in Iceland harnesses hot springs to power year-round farming. Probably an interesting alternative to importing tomatoes produced in hotter countries such as Spain or Italy?

On a high-energy level (over 150°C), which is only possible in certain areas with specific geological characteristics (sedimentary basins or volcanic regions), geothermal energy can be used for industrial uses – even though this is still a very costly installation at the moment. On a positive note, geothermal power plants have low emission levels – hence they emit 97% less acid rain-causing sulfur compounds and about 99% less carbon dioxide than fossil fuel power plants of similar size.

Structure of an enhanced geothermal system for industrial use
Structure of an enhanced geothermal system for industrial use – with number 10 being the Crystalline bedrock down at 600 meters deep. Source

Solar thermal – enjoy it the way we enjoy a hot Sunday afternoon

Solar thermal energy is a renewable energy source that harnesses heat from the sun to directly generate thermal energy for heating in industries and households. The same way you heat yourself by lying on the beach on a nice spring day. 

Solar thermal aims at creating heat – low grade energy. The production process is much less of a nuisance – you’ll need large black surfaces or large mirrors to harness the heat from the sun. (Meanwhile, solar panels so far require a very polluting production process & rare metals to produce high grade energy as electricity, yet with low energy density in comparison to other popular energy sources, as explained in our previous article here)

Low-tech solar heater for water heating, using used grills found at the back a broken fridge
Low-tech solar heater for water heating, using used grills found at the back of a broken fridge. Here’s a complete guide on how to build this for your house.
The solar furnace at Odeillo, Pyrénées-Orientales, south of France - a structure used concentrated solar power to produce high temperatures for industrial uses, which can reach temperatures up to 3,500°C.
On an industrial level: the solar furnace at Odeillo, Pyrénées-Orientales, south of France – a structure that used concentrated solar power to produce high temperatures for industrial uses, which can reach temperatures up to 3,500°C. So far the structure is used for research purposes. Photo source.

The biggest downside of this energy source, however, lies in its intermittent nature and geographical dependence (one would probably yield more solar heat in Italy than in Ireland). Yet all is not lost, because heat can be stored quite easily (while electricity can only be stored with batteries, which still require a complex production process).

Construction of the Salt Tanks in Solana Generating Station, Arizona, U.S to store heat
Construction of the Salt Tanks in Solana Generating Station, Arizona, the U.S, which provide efficient thermal energy storage so that output can be provided after the sun goes down, and output can be scheduled to meet demand requirements. Source.

Solar heaters have been popular in the milieu of low-tech practitioners at a household level, but their industrial capacity is still being tested. Low-tech Magazine did a wonderful job in explaining the bright future of solar thermal energy for industrial uses in this article, which I wholeheartedly invite you to read. Spoiler alert: it is very possible. 

Fossil fuels have been the major fuel of our societies since the Industrial Revolution in the late 18th century. Wonders and damages have been done during its 300-year reign. We are now presented with more renewable energy sources – some require so much more energy and resources to produce, some will leave bigger impacts to their local ecosystems but not on a global scale, some will be applicable only on a community level and should not be cloned on a massive scale…More choices mean more headaches, but this time it seems like a welcome one to shift away from our addiction to fossil fuels. 


If you want to read further on this topic:

Different sources of energy: which one is less “bad”?

Our growing addiction to energy: what could be the remedy?

Less waste, less energy: better ways to heat places in a temperate climate

 

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