SCIENCE16 - The Quest for Clean Renewable Energy

With all the concern today about global warming and climate change due to the use of fossil fuels, I thought it would be timely to do a blog on alternative clean renewable energy sources that could mitigate the climate crisis.

 

After a short introduction to define some terms and to establish the need for clean renewable energy, I will discuss clean renewable energy sources in use and/or in development today, then look at global energy source consumption history: 2000 - 2021, energy source projections to 2030, potential future longer-term clean renewable energy sources, and finish with any conclusions I can draw.

I will list my primary sources at the end.

 

Introduction

One of the world’s ongoing critical requirements is to produce energy for electricity, heating and cooling, and transportation.

Fossil fuels - coal, oil, and natural gas - have been used for decades, and are still widely used today, to supply that energy.

Note:  Fossil fuels were formed from the fossilized remains of dead plants by exposure to heat and pressure in the Earth's crust over millions of years. 

Humans first started using fossil fuels thousands of years ago.  The use of coal started 5,000 years ago in ancient China, while the use of crude oil and natural gas began around 4,000 years ago in areas that are now present-day Iran. These early uses were primarily for heating and lighting.

The Industrial Revolution (1760 - 1840), the transition from creating goods by hand to using machines, and the general availability of electricity later in the 19^th century, sparked a rapid increase in the consumption of fossil fuels for energy that continues today.

The growth of fossil fuel energy production from the mid 19^thcentury.

But fossil fuels exist only in finite quantities, and are rapidly being depleted. 

Note:  Estimates of when we will run out of fossil fuels vary widely (from 2060 to well into the 2300s) depending on future usage rates, that in turn depend on future population and economic growth, and finding additional reserves.

Moreover, as we have learned in the last few decades, fossil fuels, when burned to produce energy, contribute to pollution of the ocean and atmosphere, and produce harmful greenhouse gas emissions, such as carbon dioxide and methane that take many years to be fully absorbed, and that contribute to global warming and climate change.  Carbon dioxide is causing about three quarters of global warning.

In 2015, the international Paris Agreement was negotiated by 196 countries to mitigate the effects of climate change by establishing a long-term goal to limit global temperatures, reduce greenhouse gas emissions as soon as possible, and reach net zero emissions by the year 2050.  Net zero emissions means removing an equal amount of carbon dioxide from the atmosphere as we release into it.

Today, the methods used to pull carbon dioxide out of the air are slow and expensive.  Carbon dioxide can be removed from the atmosphere as air passes through a big air filter and then stored deep underground.  This technology already exists, but is being used only on a small scale.  More research is needed to help carbon removal methods work fast enough to make a dent in the rapid rise of greenhouse gasses. Additionally, some methods of pulling carbon dioxide out of the air pose risks to the environment.  For example, iron fertilization involves adding iron to the ocean to increase the amount of phytoplankton - tiny ocean life that use carbon dioxide during photosynthesis.  However, increasing creating phytoplankton could disrupt ocean ecology, posing risks to marine life.  A report by the National Academies noted that iron fertilization might pose risks that would be greater than the benefits of removing carbon dioxide from the air.

The Paris Agreement therefore established an urgent need to develop alternative clean energy sources that are renewable, i.e., that are derived from natural sources that are replenished at a higher rate than they are consumed, and that do not harm the natural environment.  

Clean Renewable Energy Sources in Use and/or in Development Today

Clean renewable energy sources in use and under continued development today include hydropower, wind, solar, and geothermal energy.  Ocean energy sources are in early development.

Hydropower.  Humans have been harnessing water to perform work for thousands of years.  The Greeks used water wheels for grinding wheat into flour more than 2,000 years ago, while in the third century B.C., the Egyptians used a machine to lift water from a low-lying body of water into irrigation ditches (Archimedes water screw).  The evolution of the modern hydropower turbine began in the mid-1700s.

In the 1920s, the U.S. started building dams on rivers all over the country to produce reservoirs to provide drinking water, water for irrigation, flood and drought control, navigation services, as well to provide electricity.

Reservoir hydropower (or hydroelectric) plants rely on stored water behind a dam.  When that water flows through an intake to a lower level in front of the dam, the force of the moving water is converted into electricity by spinning a generator’s turbine blades that then rotate a generator to produce electricity that is sent to power homes and businesses. 

Run-of-river hydropower plants harness energy in the same way from the available flow of the river. 

Today, hydropower comes from both large dams and reservoirs, and smaller dams on small rivers that require only low-impact development.  The largest of the hydroelectric plants are the Three Gorges Dam (2003) in China and the Itaipu Dam (1984) built by Brazil and Paraguay.  China is the largest producer of hydroelectricity in the world and has more than 45,000 small hydro installations. 

The Three Gorges hydropower plant in China is the largest in the world.

 

Hydropower currently is the largest source of clean renewable energy, and is produced in 150 countries.  Of the top 50 countries by percentage of electricity generated from renewables, 46 are primarily hydroelectric.  About 7% of all power in the United States, and 19% of power in the world, comes from hydroelectric plants. China is the world’s largest producer of hydroelectric power.

Hydropower relies on generally stable rainfall patterns, but can be negatively impacted by climate-induced droughts, or changes to ecosystems which impact rainfall patterns.

Hydropower does have some negative effects on the environment.  Dams and hydroelectric plants change the flow and temperature of rivers.  These changes to the ecosystem can harm fish and other wildlife that live in or near the river.  And although hydroelectric plants do not release greenhouse gases, rotting vegetation trapped in the dams’ reservoirs can produce them.  Dams also have an effect on people living near the rivers.  For example, more than 1.3 million people had to move from their homes to make way for China’s Three Gorges Dam and its reservoir.  In addition, dams can affect fish populations and the fertility of flood plains. Fish may not be able to migrate and spawn. Farmers that depended on the fertile flooding may be cut off from the river by a dam. This can harm the livelihood of fishermen and farmers who live along the river, as well as consumers who must pay higher prices for food.

High cost and lead times from permission processes, including environmental and risk assessments, with lack of environmental and social acceptance, are therefore the primary challenges for new hydropower developments.

Wind.  Wind energy has been used for millennia, and is one of the cleanest and most accessible sources of energy. 

Today, wind energy harnesses the kinetic energy of moving air by using large wind turbines located on land or offshore in the ocean.

Wind energy technologies have evolved over the last few years to maximize the electricity produced - with taller turbines and larger rotor diameters.  Thus, wind power generation has tripled over the past 10 years in the United States, making wind energy the number one largest renewable energy source in the nation after hydropower.  Wind power is one of the alternative energy sources that serves both individuals and entire communities.  It’s versatile, and can be produced from small-scale windmills or wind turbines on residential properties to large-scale land- and ocean-based wind farms. 

Windfarm in southern California.

 

Wind-generated electricity met 7.33% of the global electricity demand in 2022.  Wind energy was the leading source of new capacity in Europe, the U.S., and Canada, and the second largest in China.  In Denmark, wind energy met more than 40% of its electricity demand, while Ireland, Portugal, and Spain each met nearly 20%.

Globally, the long-term technical potential of wind energy is believed to be five times the total current global energy production, or 40 times current electricity demand, assuming all practical barriers needed were overcome.  This would require wind turbines to be installed over large areas, and likely also industrial use of new types of turbines.  As offshore wind speeds average ~90% greater than that of land, offshore resources can contribute substantially more energy than land-stationed turbines.

Solar.  Humans have been harnessing solar energy for thousands of years - to grow crops, stay warm, and dry foods.  According to the National Renewable Energy Laboratory, “more energy from the Sun falls on the Earth in one hour than is used by everyone in the world in one year.”  Today, we use the Sun’s rays in many ways - to heat homes and businesses, to warm water, and to power devices.

Solar energy is the most abundant of all energy resources and can even be harnessed in cloudy weather.  The rate at which solar energy is intercepted by the Earth is about 10,000 times greater than the rate at which humankind consumes energy.

Solar technologies convert sunlight into electrical energy either through photovoltaic panels (solar PV) or through mirrors that concentrate solar power.  Concentrated solar power growth has been slow due to technical difficulties and high prices, thus hindering market growth.

Solar power today most commonly refers to the use of photovoltaic cells (or solar cells) to create energy.  On a small scale, you may see a few solar panels on a house or building roof, or over an outdoor parking lot, used to produce energy for just that one site.  On a larger scale, you may see a solar farm used as a power plant to produce electricity for many consumers. 

This solar farm in central California is the largest in the U.S.

 

Photovoltaic cells are made from silicon or other materials that transform sunlight directly into electricity.  Solar farms on land can generate enough power for thousands of homes.  Floating solar farms can be an effective use of wastewater facilities and bodies of water that aren’t ecologically sensitive.

Solar PV energy systems don’t produce air pollutants or greenhouse gases, and as long as they are responsibly sited, most solar panels have few environmental impacts beyond the manufacturing process.

The cost of manufacturing solar panels has plummeted dramatically in the last decade, making them not only affordable, but often the cheapest form of electricity.  Solar panels have a lifespan of roughly 30 years.

Solar PV energy can be harnessed anywhere that receives sunlight; however, the amount of solar energy that can be harnessed for electricity generation is influenced by weather conditions, geographic location, and time of day.

Solar PV has turned into a multi-billion, fast-growing industry, continues to improve its cost-effectiveness, and has the most potential of any near term renewable technology.

In 2022, solar PV supplied 4.5% of U.S. electricity generation. 46% of all new generating capacity came from solar PV in 2021.  Australia has the largest proportion of solar PV electricity in the world, supplying 9.9% of the country's electrical demand in 2020.  More than 30% of Australian households now have rooftop solar PV.

In 2011, the International Energy Agency said that the development of affordable, inexhaustible, and clean solar energy technologies will have huge longer-term benefits.  It will reduce pollution,

and lower the costs of mitigating climate change.  The global potential of direct solar energy far exceeds that of any other renewable energy resource.

There are, however, environmental implications of scaling up solar PV energy.  In particular, the demand for raw materials such as aluminum poses concerns over the carbon footprint that will result from harvesting raw materials needed to implement solar energy.

Geothermal Energy. The Earth’s core is about as hot as the Sun’s surface, due to the slow decay of radioactive particles in rocks at the center of the planet.  Drilling deep wells brings very hot underground water to the surface as a hydrothermal resource, which is then pumped through a turbine to create electricity, and finally pumped back into the Earth.

The technology for electricity generation from hydrothermal reservoirs is mature and reliable, and has been operating for more than 100 years, but today supplies less than 1% of global electricity.  The largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California.  The Philippines follows the U.S. as the second highest producer of geothermal power in the world.

Geothermal wells release greenhouse gases trapped deep within the Earth, but these emissions are usually much lower per energy unit than those of fossil fuels. 

Ocean Energy.  Ocean energy derives from technologies that use the kinetic and thermal energy of seawater - waves, or currents - to produce electricity or heat.  Tidal and wave energy are still in the early developmental phase, with several prototype wave and tidal current devices being explored.  The ocean will always be ruled by the Moon’s gravity, which makes harnessing its power an attractive option.  The theoretical potential for ocean energy easily exceeds present human energy requirements.  Some tidal energy approaches may harm wildlife, such as tidal barges, which work much like dams and are located in an ocean bay or lagoon.  Like tidal power, wave power relies on dam-like structures or ocean floor-anchored devices, on or just below the water’s surface.

Global Energy Sources:  2000 - 2021

So, with these clean renewable energy sources in mind, let’s look at the last couple of decades and see where we are today.

The “layer cake” graph below shows global energy sources from 2000 to 2021. 

Global energy sources from 2000 to 2021:  Clean renewable electricity is growing, but so is coal and gas.

 

From 2011 to 2021, clean renewable energy grew from 20% to 28% of global electricity supply. Use of fossil energy (though still growing) shrank from 68% to 62%, and nuclear from 12% to 10%.  The share of hydropower decreased from 16% to 15%, while power from the Sun and wind increased from 2% to 10%. 

Note:  Nuclear energy, though used extensively since the late 1950s, isn’t classified as a renewable energy source today because it is produced by a fission process using elements like uranium and thorium, which cannot be replenished and have a finite amount in existence.  Moreover, nuclear fission produces hazardous radioactive waste material that must be managed.

The chart below is another way of looking at global energy consumption over the same period - with more detail for the period 2016 - 2021.

Coal, oil, and natural gas remain the primary global energy sources even as renewables have begun rapidly increasing.

 

The use of renewables in 2021 varied considerably over the world, as the bar chart below shows.

Note:  The following chart is somewhat tricky to navigate.  First go to the lower left-hand corner to see that the numbers to the left of the countries shown correspond to the ranking of overall fossil fuel usage.  The countries are listed in the order of fossil fuel usage.  For example, the USA is the number 2 overall user of fossil fuels, but down the list, towards the middle of percentage of fossil fuels used compared to total energy sources.

 

The countries most reliant on fossil fuels for electricity vary widely on how great a portion of that electricity is generated from renewables, leaving wide variation in renewables' growth potential.

 

Projections to 2030 

From 2010 - 2019, worldwide investment in clean renewable energy capacity (excluding large hydropower) amounted to US$2.7 trillion, of which the top contributors were China US$818 billion, the United States US$392.3 billion, Japan US$210.9 billion, Germany US$183.4 billion, and the United Kingdom US$126.5 billion.  This was an increase of over three and possibly four times the equivalent amount invested in the decade of 2000 - 2009.

In 2023, an estimated US$1.75 trillion was invested globally.

Global energy investment 2015 - 2023.

 

In 2023, electricity generation from wind and solar sources was projected to exceed 30% of global electricity generation by 2030.

Wind and solar energy sources are forecast to equal fossil fuels in the early 2030s.

 

Potential Future Clean Renewable Energy Sources:  2050 -

Today, we have no long-term way of getting to net-zero carbon emissions, especially because the global energy demand is projected to triple between 2050 and 2100.   Clean renewables such as wind and solar PV energy have a role to play, but they aren't likely to be enough.

As our technology advances and populations grow, so does our need for reliable, sustainable, and clean sources of power.  And solving the problem of climate change is not a one-time affair.  If we can navigate the bottleneck of the next few decades without transforming the climate too radically, the road beyond may be smoother.

Two energy sources offer significant potential for satisfying long-term energy needs, as reliable, sustainable, and clean sources of power:  nuclear fusion and space-based solar power.

Nuclear Fusion.  Nuclear fusion - the merging of light atomic nuclei - has the potential to produce energy with near-zero carbon emissions, without creating the dangerous radioactive waste associated with today's nuclear fission reactors, which split the very heavy nuclei of radioactive elements.

Nuclear fusion was recognized as a potential source of energy almost as soon as fission was.  In a debriefing meeting of the Manhattan Project for atomic bomb development in late 1945, Italian physicist Enrico Fermi, who led the project to build the first fission reactor in Chicago during World War II, envisioned fusion reactors for power generation.  Scientists figured out how to release fusion energy a few years later, but only in the uncontrolled Armageddon-like explosions of hydrogen bombs. 

Physicists have been studying fusion power since the 1950s, but turning it into a practical energy source has remained frustratingly elusive.  The fusion of two hydrogen atoms to make helium is the main process that powers the sun and other stars. 

Fusion in stars happens under extreme conditions: high temperatures and pressures that overcome the natural repulsion between the positively charged atomic nuclei, allowing them to merge.  On Earth, these conditions are challenging to replicate.  Conventional fusion experiments use massive, energy-hungry machines to generate the required heat and pressure, making it currently inefficient as a power source.

 

Over the long term, nuclear fusion may be the best option to satisfy our energy needs without destroying the planet.

 

Forecasting when efficient, affordable fusion energy will arrive has always been a risky business, but experts now mostly agree on the approximate timescales.

Fusion plants might be feeding power into the electricity grid by around 2050, and then could become steadily more important to the energy economy in the second half of the century, especially post-2060.  Over the long term it may be the best option to satisfy our energy needs without destroying the planet.

In the quest for the ultimate energy solution, one controversial yet promising field is cold fusion.  Dubbed by many as the “holy grail” of energy production, cold fusion promises limitless, clean energy generated at room temperature.

Researchers have proposed several theories to explain how cold fusion might occur, involving quantum mechanical effects or exotic states of matter.  Today. several research groups and private companies claim promising experimental results.  However, these claims are often met with skepticism due to the lack of peer-reviewed publication or independently replicated results.

If cold fusion could be reliably achieved and harnessed, it could revolutionize energy production.  The fuel for cold fusion - deuterium - is abundant and readily available in seawater.  The process, unlike nuclear fission, wouldn't produce long-lived radioactive waste, and it could theoretically provide a limitless, clean energy source.

Space-Based Solar Power.  Space-based solar power (SBSP) also offers tantalizing possibilities for reliable, sustainable, and clean sources of power energy.  In the future, orbital collection systems could harvest energy in space, and beam it wirelessly back to Earth. These systems could provide energy anywhere in Earth.

Many proponents of SBSP believe the technology has greater potential than nuclear fusion to help the world meet its net zero target.  With sufficient investment, space solar power could be available sooner than fusion.

“Space-Based Solar Power,” a new report from the NASA’s Office of Technology, Policy, and Strategy considered the potential of a space-based solar power system that could begin operating in 2050.  Based on that timeline, the report found that space-based solar power would be more expensive than terrestrial sustainable alternatives, although those costs could fall if current capability gaps can be addressed.  

Once dismissed as technically impossible, and far too expensive even if the technology existed, SBSP is again being assessed as a potential source of limitless clean energy, as public and private sectors in space-faring nations are now seriously considering developing their own SBSP systems.

NASA, the European Space Agency, and the British government are dusting off a decades old idea to beam space-based solar energy to Earth from an array of orbiting satellites beaming power by laser or microwave to help reach net-zero carbon emissions by 2050, and other nations including China, Japan, and South Korea are doing the same.

There have been some recent promising developments.  The costs of commercial space launches have dropped dramatically as private companies entered the market.  New highly modular solid-state solar-power satellite designs have been conceived for high-volume commercial manufacture. This also lowers costs.  Technologies required to make SBSP a reality have matured.  These include high-concentration solar photovoltaic panels, wireless power transmission, and space robotics.

In one SBSP concept, multiple solar radiation collectors (e.g., solar cell arrays) are placed in geo-synchronous orbits over the Earth’s equator (high enough above the Earth to remain above a particular spot on the Earth’s surface, i.e., synchronized with the Earth’s rotation) - with their positions arranged so that the entire Earth is covered by line of sight from at least one solar collector.   The solar energy collectors would convert solar radiation energy into microwaves that are beamed to the appropriate Earth-based antennas that feed into a local power grid.  The microwave beams can be directed to multiple locations - anywhere with the appropriate receiving antenna.

Many proponents of SBSP believe that the technology has greater potential than nuclear fusion to help the world meet its net zero target.

 

SBSP advantages include a higher collection of energy due to the lack of reflection and absorption by the atmosphere, fewer and shorter periods of night, and a better ability to orient to face the Sun.  The space-based system would need no protection from terrestrial wind or weather, but would have to cope with space hazards such as micrometeors and solar flares.

Conclusions

No matter what we believe about the near-term danger of climate change caused by burning fossil fuels and adding carbon dioxide to the Earth’s atmosphere, we certainly need to develop alternative renewable energy sources to supplement and eventually replace our finitely-limited supply of coal, oil, and natural gas.

The goal of net-zero emissions by the year 2050, set by the 2015 Paris Agreement, seems somewhat arbitrary to me (and probably impossible to achieve), but that goal has indeed spurred development of alternative clean renewable sources of energy such as wind and solar PV, which in the near term can supplement fossil fuels and help mitigate global warming.

For the longer term, working hard now to harness the energy from nuclear fusion and space-based solar power seems like the way to go.  I’m happy to see so much international government and private company participation.

 

Sources

My primary sources include: “Can We Pull Carbon Dioxide Out of the Atmosphere?” scied.ucar.edu; “The Complete History of Fossil Fuels,” oilprice.com; “Renewable Energy” and “Space-based solar power,” en.wikipedia.org; “What is Alternative Energy: Types of Alternative Energy Sources,” inspirecleanenergy.com; “What is renewable energy?” un.org; “Renewable Energy: The Clean Facts,” nrdc.org; “Why Alternative Energy Sources Are The Future,” justenergy.com; “Technology Reboot Would Beam Space-Based Solar Power to Earth,” jpt.spe.org; “What is the Future of Fusion Energy?” scientificamerican.com; “Cold Fusion: The Holy Grail of Energy Production?” miragenews.com; plus numerous other online sources.