Energy is defined as renewable if it comes from natural sources or processes that can’t run out. For example, while levels may vary due to time and weather, the sun always keeps shining and the wind keeps blowing (it’s worth noting, however, that the word renewable doesn’t apply to the resources needed to build infrastructure for renewables such as turbines or batteries).
The power of nature has been used for centuries for things like heating, lighting and transport. However human reliance on fossil fuels has increased exponentially in the last 500 years. Non-renewable sources of energy are only available in limited amounts and rely on extractive methods that come with vast arrays of ecocidal dangers including habitat destruction, pipeline spills, earthquakes and pollution from fracking, violation of Indigenous land rights, and greenhouse gas emissions which lead to climate breakdown.
They’re also typically found concentrated in specific areas of the world, whereas things like wind and sun are accessible globally. Shifting towards renewables reduces a country’s reliance on exports from fossil fuel-rich nations, as well as potentially reducing conflict over these insufficient resources.
Renewables are increasingly displacing fossil fuels in the power sector. At least 29 U.S. states have set renewable portfolio standards—policies that mandate a certain percentage of energy from renewable sources, More than 100 cities worldwide now boast at least 90-100% renewable energy, and at least 230 others are making commitments to reach 100%.
However, no place on earth can run on one renewable energy source alone. So what are the options for full decarbonisation?
A variety of solar energy technologies are used to convert the sun’s energy and light into heat: for example illumination, hot water, electricity and cooling systems for businesses. Homes can also be built with a passive solar home design. Passive solar homes are designed to receive sun through south-facing windows and retain warmth through materials that store heat.
The most well known solar technology is Solar (PV) panels. Solar panels, made up of multiple solar cells, use something called the photovoltaic effect to create direct current (DC) electricity. This then goes through an inverter to become alternating current (AC), to be used on the grid or fed directly into a building. As well as immediate use, solar plants can store energy in water, salt, fluids and other battery systems to generate electricity later, so solar power can be used when it’s dark.
We mainly see solar panels in large fields, or on top of individual buildings, however floating solar farms are also an option that can be an efficient use of wastewater facilities and bodies of water that aren’t ecologically sensitive.
When individuals install solar in their homes, this can take two forms. Solar thermal panels use the sun’s energy to heat water, which can then be used for things like heating, showers, and washing machines. PV solar panels, meanwhile, create electricity homeowners can use in real-time. Additionally, they can also earn money if more electricity is generated than needed, as they can sell excess power back to the grid.
The main benefits of solar is that the sun is available every day, excess power can now be stored, and more storage is being developed. The downsides are that solar is less efficient on bad weather days, while large scale solar plants can take up a lot of space.
Wind is caused by differing air pressure in the atmosphere. The greater the difference in pressure, the faster the air flows. Wind can be used to generate mechanical power (for example pumping water or grinding grain) or electricity by using a generator to convert this mechanical power. The wind turns propellers around a rotor, which spins a shaft, which connects to the generator to create electricity.
If a wind turbine is positioned well, it can produce electricity approximately 70-85% of the time, though the output varies depending on wind speed. Throughout a year, a wind turbine typically generates 30% of its theoretical maximum output. While this may not sound like much, conventional power stations typically generate around 50%.
Plus, wind is a free resource that produces no air or water pollution. Once a wind turbine is erected its operational costs are almost zero, and advances in mass production make it increasingly cheap and safe.
It’s not surprising, therefore, that wind has become increasingly popular. The UK relies heavily on wind power, especially offshore wind farms. We have a large coastline with shallow water, which makes installation easy to install. From 2000 to 2015, cumulative wind capacity around the world increased from 17,000 megawatts to more than 430,000 megawatts, with experts predicting that if the pace of growth continued, by 2050, 1/3 of the global electricity needs will be met by wind power.
Wind is also an inconsistent source of power, as speed changes all the time, however the power it generates can be stored for later use through batteries.
Biomass represents approximately 10% of global energy supply. It involves the use of organic matter, such as wood pellets, grass clippings, and dung, to generate energy. The main forms of biomass include:
- Wood and agricultural products: things like logs and wood chips make up the largest proportion of biomass energy, mainly used to generate electricity.
- Solid waste: 1 ton of rubbish has as much heat energy as 500 pounds of coal.
- Landfill gas and biogas: sewage and agricultural waste is put into high-temperature digesters, so it rots more quickly. The gas is then captured and used as fuel.
There are multiple ways to generate electricity from biomass, for example capturing and using methane produced by the natural decomposition of organic material. The most common, however, is burning the materials to heat water, producing steam which spins turbines. In some biomass plants, any excess steam can also be used in on-site manufacturing processes, or for heating, which raises the energy efficiency of biomass electricity generation to approximately 80%. Although bioenergy generates a similar amount of CO2 to fossil fuels, crops grown for biomass remove an equal amount of CO2 from the atmosphere, keeping impact somewhat neutral.
Crops like sugarcane and corn can also be used to create biofuels, with the first biofuel engine powered by vegetable oil invented in the late 1800s. Nowadays, biofuels are playing a growing role in the transport industry. While biofuel can replace diesel in vehicles, it’s usually blended to reduce overall pollution from diesel engines.
Positives of biomass include that organic matter (especially waste) is always available, using waste for energy reduces the amount in landfill, and it releases less nitrogen than coal while not producing sulphur or mercury. Some positive examples include The Blackburn Meadows Cogeneration Plant, which uses excess heat from combustion to provide heating to nearby businesses and The Templeborough Biomass Plant, which provides energy for 78,000 homes and saves up to 150,000 tonnes of CO2 each year.
However, biomass also produces a lot of debate. Energy crops take up land that could be used for growing food, plus monitoring is key to avoid deforestation. It still produces CO2, as well as methane, and it often isn’t as efficient as fossil fuels.
While countries like Brazil gradually free themselves from oil by increasingly blending biofuels for transportation, biomass is still not as clean or renewable as other options unless the context is right.
Still, some forms of biomass energy could serve as a low-carbon option under the right circumstances. For example, sawdust and chips from sawmills that would otherwise quickly decompose and release carbon can be a low-carbon energy source
Hydroelectric power is created by water, which is usually fast moving in a river or descending from a high point. The force of that movement is converted into electricity as water spins a generator’s turbine blades.
Many hydroelectric plants were created by building manmade mega-dams. Because these huge dams divert rivers, impact biodiversity and restrict access for animals and humans, they are often seen as nonrenewable energy. Small hydroelectric plants that are carefully managed cause less damage, as they only divert a fraction of flow.
Today, the most common system is pumped storage hydropower, where dams are built to store water which is cycled between lower and upper reservoirs. When electricity demand is high, water is released from the higher reservoirs, flowing downward through turbines to produce electricity. There is also “run-of-river hydropower,” which channels a portion of a river and doesn’t require a dam to be built, as well as the waterotor, which is designed for slow moving water.
While hydroelectric potential varies, many areas could utilise the energy of local waterways with small/medium hydroelectric systems. This wouldn’t cause too much impact and would allow more decentralised energy to be used by local communities.
The earth’s core is extremely hot due to radioactive decay. Drilling deep wells can bring hot water underground to the surface, which can be used in a few ways. Hot water can be directly pumped into buildings to heat them, and power plants can pump water/steam through a turbine to create electricity. If geothermal plants pump the steam and water they use back into the reservoir, they usually have low emissions.
Geothermal plants can also be created without underground reservoirs, but they may increase the risk of an earthquake in areas already considered geological hot spots.
Geothermal or geoexchange pumps can also be popular in domestic settings; using the constant temperature of the earth (a few feet below the surface) to cool homes in summer, warm them in winter, and to heat water. While these systems can be expensive to install, they typically pay off within 10 years while also being quiet, requiring less maintenance, and lasting longer than air conditioning units.
Tidal and wave energy is generated by the power of seas and oceans. This can produce two types of energy: thermal, from the sun’s heat, and mechanical, where the movements of tides and waves pushes a turbine to generate electricity. This relies on the moon’s gravity, so has no chance of running out, and releases no greenhouse gases. Plus, with the tide going in and out twice a day, that’s four chances per day to create power. Right now tidal is around 80% efficient, reliable as we know tide times in advance, and storage is under development.
However, tidal infrastructure can be expensive and there are few places that have ideal conditions for a tidal power plant. Plus some approaches, such as tidal barrages (which work like dams located in an ocean bay) can harm wildlife.
Hydrogen is comprised of one proton and one electron, making it the simplest and most abundant element in the universe. However, it doesn’t occur naturally as a gas on earth, instead being found in organic compounds (hydrocarbons like gasoline) and water. Hydrogen is also high in energy but produces little to no pollution when burned.
While hydrogen has a lot of potential, its wider adoption will be limited until it becomes cheaper and more durable. There are currently some vehicles and trains that run on hydrogen, which will likely increase as the cost of fuel cell production drops and the number of refuelling stations increases.
hydrogen and hydrogen-based fuels like synthetic methane are my favorites, the ones I believe warrant the most intense research, development, and deployment. For the most part, that’s based on expert research and current developments in the field
Currently, most hydrogen is produced through steam reforming of natural gas, which is energy- and carbon-intensive. But it can also be produced through electrolysis, which uses electricity (ideally generated by wind and solar) and a catalyst to free hydrogen directly from water. About 4% of current hydrogen is made through electrolysis. Nuclear power plants can also be used to make hydrogen, it’s one avenue of discussion to give nuclear plants stable markets and enable them to stay running.
Can renewable energy meet demand?
The main sources of renewable energy, wind and solar, vary in reliability. They can’t be turned off and on when needed by grid operators, meaning they aren’t dispatchable. When there’s not enough renewable energy available, grids often have to turn to fossil fuel energy sources to top up supply. However, with the right infrastructure and energy storage in place, experts say renewables could power the world by 2050.
We know that deep decarbonization is going to involve an enormous amount of electrification. As we push carbon out of the electricity sector, we pull other energy services like transportation and heating into it. (My slogan for this: electrify everything.) This means lots more demand for electricity, even as electricity decarbonizes…
Deep decarbonization of the electricity sector, then, is a dual challenge: rapidly ramping up the amount of variable renewable energy (VRE) on the system, while also ramping up carbon-free dispatchable resources that can balance out that VRE and ensure reliability.
So, what could this look like?
Multiple current models that look at deep decarbonisation generally find that it’s cheaper to get to zero carbon electricity while including nuclear and CCS (carbon capture and storage). The cost of renewables-only options increase sharply above 80% decarbonisation, and it’s suggested that utilising nuclear and CCS keeps these costs down.
To summarize: Most of today’s models place high value on large dispatchable power sources for deep decarbonization, and it’s difficult to muster enough large dispatchable power sources without nuclear and CCS.
Fortunately, there’s likely already enough nuclear capacity in many countries to provide this dispatchable generation. There’s no need to build new nuclear or CCS plants, it just requires not shutting down existing nuclear (apart from any that are unsafe). Nuclear is, understandably, a controversial sector. However many experts argue that, from a decarbonisation perspective, no nuclear plant should be closed before a coal one. It makes decarbonisation harder and, ultimately, serves as a source of carbon-free power that can be dispatched during this transition period.
And ultimately dispatchable, carbon-free resources will be key to balancing out variable renewables. Whether it be nuclear, hydropower, biomass or improved renewable storage, all will likely have a part to plan in full decarbonisation. Although CSS, perhaps not so much.
I personally think fossil fuel with CCS will never pass any reasonable cost-benefit analysis. It’s an environmental nightmare in every way other than carbon emissions, to say nothing of its wretched economics and dodgy politics.
Regardless of how exactly we get there, the 2017 Renewables Global Futures Report interviewed energy experts around the globe and found that 71% agreed that 100% renewables is ‘reasonable and realistic’. While actual models may vary in their optimism, there are several reasons for this. Models are based on current technologies without taking into account new concepts that are still in development, outdated costs as studies take years to come to fruition, and current markets, which are changing and will continue to. Once constructed, renewable energy incurs minimal costs, essentially undercutting all competition, while production and storage constantly become cheaper.
After all, energy models have often underestimated renewables. In the past wind and solar weren’t taken seriously because of their unreliability but, alongside battery technology, they have consistently outpaced forecasts and exceeded expectations.
Plus, models focused on cost often leave out environmental impacts and social benefits. When we consider the full range of benefits from decarbonisation including improved air and water and energy security, we get different cost-benefit analysis.
Why we need to ditch natural gas
One thing that is vital to decarbonisation, however, is not to rely on natural gas to lower emissions or balance VRE. A majority-renewables grid needs a backup source of energy that can be stored for long periods and in large quantities, but be immediately available when renewable supplies lag.
Natural gas, aka methane, fills this role well. It’s a stable form of stored energy and can be stored indefinitely, unlike chemical energy in lithium batteries which leaks over time. Many places with a lot of renewable capacity use natural gas as a back up, but it is still a fossil fuel. If its emissions aren’t captured and stored, it can never be part of a decarbonised system.
Focusing on natural gas will create a lot of fossil fuel capacity that will end up shut down or left idle before the end of its useful life, which is a bad decision economically and politically. However, there is a relatively new technology that may provide some answers. It’s known as power-to-gas, or PtG.
Fossil fuels are hydrocarbons, meaning they’re made up of hydrogen and carbon. If you can gather hydrogen and CO2 separately they can be combined to produce synthetic natural gas, through a process known as methanation.
How carbon intensive this process is varies on how one sources these elements. If the hydrogen is produced through electrolysis powered by renewable energy or nuclear, and CO2 is captured directly from the air, then this can be carbon neutral. Carbon is taken from the air and returned when the methane is burned; no extra emissions are added in the process and it’s ultimately driven by renewables.
It is a way for renewables to create their own long-term energy storage and dispatchable generation, their own backup, which they can leverage to ratchet up and grow further.
A recent white paper was released about the cost effectiveness of PtG. It found that utilising a small number of natural gas plants using PtG technology could reduce the land needed for solar by a third, potentially freeing up a lot more land to be regenerated or rewilded. Plus, they can increase efficiency.
One other benefit of keeping a few gas plants around is that they reduce the amount of wind and solar power that must be “curtailed,” i.e., wasted. First, they reduce the need for overbuilding. Second, PtG can serve as a load for all that excess renewable energy. When wind and solar are producing more power than the state can consume — a more and more common occurrence as they expand — all the surplus power can be channeled into making synthetic methane
On the other hand, there’s an argument that the extra step of converting hydrogen to methane is useless, and instead hydrogen should be stored and combusted in power plants directly. There are already many hydrogen pipelines across the world, current natural gas pipelines can be converted to carry hydrogen, and companies are already investing in gas turbines that can run on either methane or hydrogen. Plus, not converting hydrogen could reduce the need for flaring. Only a small amount of plants would be needed to stabilise renewables, so directly burning the hydrogen rather than adding an extra step, is a good solution too.
Ultimately, we don’t know what will happen. It’s likely a mix of these technologies, plus things we haven’t even developed yet, will all play a part. What ultimately matters is keeping fossil fuels where they belong: in the ground.