Our Climate is Changing. Why Aren’t We?
Climate Reality activist Campbell Scott talks to DesiCollective about why Energy Storage is important for a sustainable economy.
When Texas lost power after two devastating winter storms mid-February 2021, over 4 million homes and businesses lost power for several days. In Austin, people were burning their furniture to cook food and to keep warm.
Campbell Scott says this disaster was preventable. The Texas electrical grid failed to keep up with the demand, and Texas repeatedly failed to protect its power grid against extreme weather.
What is the science behind energy storage?
Can California halt the frequency of its rolling blackouts?
How do you store green energy when the wind doesn’t always blow, and the sun doesn’t always shine? Are there energy storage solutions?
And what can communities do to advocate for a greener future?
We asked Campbell for answers.
A Primer on Green Energy Storage by Campbell Scott
Energy Storage is Key to Green Energy
Renewable, carbon-free electric power, generated by solar panels and wind turbines, is now cheaper than from any other source. However, sunshine and wind are intermittent sources: the sun sets every night or may be clouded over; the wind does not always blow. In addition, demand does not always match supply: peak demand usually occurs in the evening as people get home from work, cook dinner and turn on other electric appliances. Therefore, as electric utilities transition to renewable energy sources, it is necessary to provide a backup power supply.
Currently, there are many generating stations providing on-demand power. These are typically natural gas powered “peaker plants” that can be started up as needed. However, natural gas is a fossil fuel, and so these must also be phased out if we are to reach zero carbon-dioxide emission. The solution is to store electrical energy when supply exceeds demand and to use that stored energy as demand increases. It is just like “saving for a rainy day.”
Energy comes in many forms, each of which provides several way to store it. Familiar fuels, such as wood, coal, oil and gas, store chemical energy that is released when the fuel burns and combines with oxygen to form, mostly, carbon dioxide and water. Burning converts the chemical energy into heat, i.e., thermal energy, that we use to heat our homes, cook our food, provide hot water, power our vehicles, generate electricity and run our factories. These fuels have the great advantage of being easy to store in bunkers, railcars or tanks, and the fluids, oil and gas, can be distrusted in pipes.
Batteries are in many ways the most convenient way to store energy. They do so in electrochemical form. Just as combustion of conventional fuels requires two chemical reagents so too do batteries. The difference is that the two chemicals (or two different electrically charged states of the same chemical) are stored in the two terminals, the anode and the cathode, which are separated by a conductive salt solution – the electrolyte. During the charging process, an atom or molecule in the anode is positively charged by removal of a negatively charged electron. For example, in a lithium-ion battery, a neutral atom of metallic Li is ionized to Li+. The lithium ion moves through the electrolyte to the cathode where it is stored in a lithium salt. This process results in an electrical voltage between the anode and cathode, so that when the battery is connected to an external circuit (a motor, a cellphone etc.), current flows, and the energy used in charging is delivered back into that circuit. The discharged battery resumes its initial state and can be recharged.
From the end of the nineteenth century for about 100 years, the most common battery was lead-acid. When discharged, most of the lead is in the metallic anode and the electrolyte is sulphuric acid. During discharge, lead cations (Pb++) are generated at the anode and lead sulphate is deposited on the cathode. Lead-acid batteries can deliver high electric current during discharge and so are still in use today to start cars and trucks with internal combustion engines. They were also used in the mid-20th century to power vehicles for local delivery, such as milk-trucks, that travelled relatively short distances with heavy loads. However, lead is one of the heaviest metals, making lead acid batteries unsuitable for long-range transport, especially in vehicles where total weight limits the range. Gasoline, on the other hand, stores a great deal of energy in a relatively small mass which made it very difficult to replace until the recent development of affordable lithium-ion batteries.
Thermal energy is readily stored by heating up any suitable material. This method has been used for centuries, starting with the habit of “banking the fire” at night: the blazing evening fire would be partially smothered with ashes at bedtime to keep the embers hot, while slowing down combustion overnight. In the electrical era, we have storage space-heaters and water-heaters that heat, respectively bricks or water, overnight when electricity is (or was) less expensive. The stored heat could then be used during the day to heat the house or provide hot water.
Thermal storage is now also being developed by German and Danish companies for utility scale storage: rocks, bricks, or concrete block are heated electrically to well above 1,000 deg. C during the day when solar energy is plentiful. At night, high pressure steam is generated to drive turbines.
A commonly used storage mechanism uses gravitational energy – pumped hydroelectricity. When excess energy is available water is pumped uphill from a lower reservoir to an upper reservoir. When electrical demand increases, the water is allowed to flow back downhill through turbines to generate electricity. There are not enough places suitable for building a dam to create the upper reservoir, and in many cases the lower reservoir, such as the O’Neil Forebay at the bottom of the San Luis Dam near Los Banos) is also used to distribute water for other needs such as irrigation. Hence electrical generation may be limited by availability of water. These factors have led to installations that invert of the roles of upper and lower reservoirs, with the lower reservoir being deep underground, for example in old mines, while the upper reservoir is on the surface creating a large gravitational “head” while requiring considerably less water dedicated to storage.
A Swiss-based start-up company, Energy Vault, has developed a method to store gravitational energy, not with water, but with concrete (or other massive) blocks. Their demonstration unit uses a six-armed crane to raise and lower the blocks, stacking them to the height of a tall building. As they are lowered, their energy is recaptured to turn a generator. The installation cost is considerably less than a hydro-plant, power can be ramped up in just a few seconds, and the round-trip efficiency is 90%, which is better than pumped hydro. Moreover, the levelized cost of energy is about half that of current lithium-ion batteries.
Next, we turn to methods to convert electricity into fuel that, like oil and gas, can be put in a container for storage or distributed through pipes running from the production plant to the customer.
The most promising of these fuels is hydrogen, the lightest of all gases, which burns in air/oxygen to produce only water. Hydrogen is an odorless, colorless gas, but it has acquired several colorful labels depending on how it was produced. In the past, hydrogen was generated by chemical processes using water and coal as feedstock. Unfortunately, the byproduct is carbon-dioxide. This is known as black or brown hydrogen, depending on the type of coal, and has been used in industrial processes for two hundred years. More common nowadays is to use natural gas and water as the input materials. This produces so-called grey hydrogen, but still carbon dioxide is a byproduct, albeit in lesser amounts. If the carbon dioxide is captured and stored underground without (much) dispersal in the atmosphere, we get blue hydrogen. Now, the abundant supply of cheap renewable energy makes it economically feasible to produce hydrogen directly from water by electrolysis. This is green hydrogen – the byproduct is oxygen which can be captured for industrial and medical use or just released to the atmophere. Many companies are making major investments in electrolyzers with the intent to capture and store abundant, clean, renewable energy.
Hydrogen can be stored in several forms. The simplest is as a compressed gas, but this does not provide optimum energy per unit volume so other schemes are used. Cooling the gas increases the energy density but requires additional energy that is difficult to recover.
Many metals form stable solid compounds with hydrogen, known collectively as metal hydrides. One promising example is magnesium hydride. Finely powered MgH2 is made into a pumpable slurry with mineral oil. Hydrogen is released when the slurry is mixed with water, leaving magnesium hydroxide which can be recycled to the hydride.
Ammonia is made by reacting hydrogen and nitrogen in a catalytic converter. New catalysts are being developed to make this an increasingly efficient, low temperature process. Ammonia is easily liquified and stored under modest pressure, very similar to propane. Ammonia is used in many industrial processes such as fertilizer production, but it is also a fuel in its own right, burning under appropriate conditions in air to yield water and nitrogen. Also, hydrogen can be recovered from ammonia, again by catalysis.
Both hydrogen and ammonia are used in fuel cells to generate electricity and thus to provide backup power for the grid, or to run motors in electric vehicles. It seems increasingly likely that hydrogen, in some form, will play a major role in long-haul, heavy duty transportation: trucks, trains and shipping. Marine freighters are once again being built with sails for primary motive power, backed up by either batteries, or hydrogen fuel cells.
The final storage medium that we discuss here is biofuel. This does not involve the intermediate generation of electricity but rather directly harnesses sunlight via photosynthesis. Everything that grows under the sun is a potential fuel, from algae and seaweed to crops and trees. Even waste foliage from vegetables can be dried and burned. In order to avoid soot pollution and returning CO2 to the atmosphere many schemes are have been developed to process crops to yield more pure fuels, such as fermenting corn sugar to produce ethanol, or extracting oils from canola or soy. Microbes and synthetic catalysts are being evaluated to “digest” various types of biomass to better fuels, with jet-fuel at the pinnacle of ambition. Ideally, these fuels will be used in facilities that capture the carbon dioxide emissions and either store it deep underground or use it an industrial process that fixes it in a solid such as concrete.
The future of our energy supply looks increasingly clean and bright, but we must deploy these new technologies with great urgency in order to meet the carbon drawdown goals set for the coming decades.