Clean energy
100% clean electricity is feasible almost everywhere, however there are significant challenges. This is vital for us to reach net-zero emissions of greenhouse gases.
Technical challenges and solutions
Variability
Many clean sources of energy such as wind and solar have high variability.
One solution is "demand response" (also called "demand flexibility" or "flexiwatts"). This involves using the smart grid to shift electricity demands to be more consistent with the availability of energy (for example on charging a car during day time when there is solar energy available).
Storage
Short-term storage (minutes/hours) is relatively easy to achieve, but longer term storage is harder and more expensive. However as with other clean-tech solutions the technology and economic viability are improving rapidly.
Transmission
With renewables there is a higher demand for transmission, and specifically long-distance, high-capacity transmission. This helps solve two issues. First is that it enables transmission over energy between places experiencing different weather conditions (e.g. sunny/windy area to non-sunny/non-windy area). The second is facilitating the push to "electrify everything".
The issues with transmission tend to be organisational and regulatory in addition to technological and economic. Legacy systems for how we manage and regulate the grid are ill-suited to the era of clean electricity. 1
Sources of renewable energy
Solar photovoltaics
Solar PV systems convert light photons directly into electricity. Most solar cells are made from silicon. According to the IEA, we need to triple our capacity additions of solar PV by 2030 to be on track to achieve net-zero emissions from energy by 2050.
While costs were intially high, they've plummeted over the past decade to the point where the IEA declared solar "the cheapest electricity in history".
Wind turbines
The largest wind turbines are capable of powering approximately 12,000 homes. Smaller turbines scaled for a community or even just an individual home are also available.
According to the Global Wind Energy Council, "Total global wind power capacity is now up to 837 GW, helping the world avoid over 1.2 billion tonnes of CO2 annually – equivalent to the annual carbon emissions of South America.” Globally, wind is the primary non-hydro renewable technology, generating almost as much electricity in 2020 as all other renewables combined.
Onshore wind was one of the cheapest new sources of electricity in 2020, and offshore wind power has seen price reductions exceeding 67 percent over the last decade, although, like solar, wind recently became a bit more expensive.
According to the IEA, we need to increase wind capacity additions fourfold by 2030 to be on track to achieve net-zero emissions from energy by 2050.
Geothermal
Advantages of geothermal energy are its constant generation and low maintenance cost. It can also provide both electricity and heating and cooling energy at the same time.
Its dependent on the underlying geology, though technology for deeper drilling is advancing and will expand the places where geothermal is viable. So far, geothermal technologies haven't managed to scale at a pace comparable with wind and solar, but that could change.
Geothermal technologies can also include ground-source heat pumps, which use steady shallow-earth temperatures to heat and cool buildings and sometimes provide hot water—and which are starting to take off globally.
Sources of clean energy
Biomass energy
This is energy derived from plant materials or animal waste. In theory it is carbon neutral, but a growing body of research has documented the devastating environmental effects of bioenergy crop cultivation at scale. The E.U. started backing away from biodiesel once it discovered that the fuel was derived from palm oil plantations created by cutting down tropical rainforest and critical biodiversity habitat in Southeast Asia.
About 10% of global primary energy comes from biomass, including usage of wood, charcoal, and other biomass for home cooking and heating.
One issue with biomass energy is "indirect land use", where biocrop cultivation simply displaces other types of cultivation, like food crops, and causes encroachment into former rainforests or other natural habitats, and result in a net increase in greenhouse gas emissions. A type of carbon removal approach called BECCS, or bioenergy with carbon capture and storage, featured in IPCC scenarios for 1.5°C, is also shown to be unsustainable from a land-use perspective.
Nuclear energy
Nuclear energy can be generated by either fission or fusion. All commercial nuclear power is produced through fission, which involves the splitting of atoms to release energy. Fusion is the process of combining or fusing atoms—it's how the energy in the sun is generated. No fusion reactor exists, though it remains the holy grail of nuclear research.
Nuclear energy is clean as far as carbon emissions go, as it does not emit greenhouse gases during operation. However nuclear waste management is still a large problem in some countries.
Nuclear is failing out of favour as alternatives such as wind and solar become more cost efficient.
Hydropower
While large dams have provided very cheap electricity and other vital development services (like irrigation water) to millions around the world, they are also the cause of significant deforestation, biodiversity loss, and forced human displacement. 1
In tropical regions, large dams can contribute more emissions than fossil fuel power plants for decades, as submerged forests decompose releasing potent methane.
Mini- and micro-hydro projects can power local mini-grids and provide other services (e.g. water reservoirs for the dry season). These systems typically make the most sense in hilly regions where perennial streams and waterfalls exist.
Wave power tends to be expensive and technologically complex. It can also affect delicate coastal ecosystems where some species depend on natural waves.
Storage solutions
Hydrogen
"Green" hydrogen storage works as follows:
You can use solar or wind energy for electrolysis, a process by which you split water into hydrogen and oxygen. You then liquefy and store the hydrogen. At times of low solar and wind resources, you can use it to power a fuel cell to generate electricity. 1
This is a good option for handling seasonal storage issues. It can also be used for handling excess energy generated by renewable sources.
There are also "blue" and "grey" variations of hydrogen, where "blue" is produced from carbon capture at fossil fuel plants, while grey is similar, but without any carbon capture. Both options can end up causing more methane and carbon emissions than just directly using fossil fuels.
While long-term energy storage and seasonal balancing of the grid may be its most promising application, hydrogen can also play a role in decarbonizing “hard-to-decarbonize” industries like ammonia and steel, shipping and aviation, and possibly long-distance freight transport. Hydrogen is not competitive or well-suited for heating buildings or most forms of ground transport. 1