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Storing solar energy cheaply and efficiently is a key component for the future of renewable
energy. Even though lithium batteries are great, they can still be costly and, depending on the
chemistry, there can be safety concerns. There are ways we can store solar energy more directly
though … and one of those is heat. For instance, concentrated solar energy plants can use that
heat for producing electricity, cement, steel, green hydrogen, or anything else that needs high
temperatures. A recent breakthrough could allow us to store solar energy directly into a liquid for
up to 18 years. How’s it work? And could this be a viable path forward for solar energy storage?
Let’s see if we can come to a decision on this. Solar panels are great! I’ve got solar panels
on my home, which are converting sunlight into electrons that end up getting used in my
home or shared out onto the grid. However, energy storage is key for renewables due to their
intermittency. In order for me to supply my own energy at night, I need to store my excess
solar production into my Tesla Powerwall. Photons are converted into electrons,
which get shuttled into a chemical battery and back out again … and then the conversion
from DC into AC electricity for my house and the grid … there’s a lot of conversions happening
throughout this process, each losing a little more energy. That’s just for my home. Scale that up to
utility scale and it gets a lot more complicated. Many of the battery technologies available today
are still quite expensive and large, and when it comes to lithium, there are also safety
concerns. Harnessing solar energy with solar panels and storing it in traditional
lithium batteries isn’t the only way to go. Between some tried and true methods, as well as
recent R&D projects, there are interesting ways to directly store the sun’s photons as heat or
in a chemical form, like that liquid I mentioned earlier that can store it for up to 18 years.
Before getting to that one, let’s start with some of the tried and true methods to see how
they compare and where this could potentially go. The first approach is concentrated solar
power (CSP). It uses mirrors to reflect and concentrate sunlight onto a specific point to
produce heat…and a lot of it! This incredible amount of heat can be used to drive a steam
turbine or engine to produce electricity, but they can also store thermal energy to provide
power when the sunlight reaches low levels. However, it's not limited to just that. The
heat can be used for water desalination, enhanced oil recovery, cement production, steel
production, and even to create green hydrogen. CSP is primarily used for grid-scale power generation
and is classified into three general types. In parabolic trough systems parabolic reflectors
angled toward the sun focus sunlight onto a central receiver pipe --- usually called an
absorber tube. The parabolic, curved shape focuses the parallel light rays onto a central
point, which boosts their reflection capacity 30 - 60 times. That makes the tube, which usually
contains thermal oil, heat up to 750°F (about 390ºC) and that heat can be used to boil water to
power traditional steam turbines and generators. Solar parabolic trough systems are the most
advanced and widely used CSP technology. The Genesis parabolic trough power plant, which
is located in Riverside County, California, is one of the largest CSP plants in the U.S.
with a generation capacity of 250MW and has been operating since 2011. This system, like many power
plants, takes advantage of the Rankine cycle, where a fluid flows from a heat source to a
heat sink, performing mechanical work along the way. In the case of the CSP, this fluid is
steam that’s generated at the boiler and flows through a turbine, just like many other power
plants. The CSP and other parabolic trough power plants can also be used to create hybrid systems
with thermal-fired power plants that use fuels like coal, natural gas and biofuel. However,
of all the CSP technologies, trough systems have the lowest efficiency (about 15%) since the
fluid doesn't achieve as high of a temperature as the other systems. That’s right … 750°F isn’t
considered that hot. I guess it’s a dry heat. Then there are dish systems, which kind of
look like a satellite dish ... except you won't be watching the big game on this one. They’re
composed of parabolic disk mirrors that use sun tracking to focus and concentrate sunlight onto
a power conversion unit that’s located along an extended arm from the disk's center. Inside the
power conversion unit are thermal receivers, which can be a bank of tubes with a cooling fluid.
That absorbs the heat reflected from the mirror and transfers it to the heat engine, which is
usually a Stirling engine. That’s an interesting topic on its own and I actually have a video
on Stirling engines if you’d like to watch it, but it’s that engine that drives an
electric generator to produce power. Dish systems can usually produce between
10-25kW per dish and have a conversion efficiency of about 30%. However,
the combination of the reflector with a Stirling engine doesn't make the
technology a great fit for storing energy. And finally the towering giants of CSP are
the power tower systems, which use flat, sun-tracking mirrors known as heliostats
to focus and concentrate sunlight onto a receiver on the top of a tower … kind
of obvious with “tower” in their name. It’s there that a fluid moves to transfer
heat to a boiler to produce steam, which is then utilized to generate electricity
in a turbine. While some power tower systems use water as the heat-transfer fluid, other advanced
designs have been using molten salts due to their superior heat transfer and energy-storage
capabilities. Because molten salt can effectively retain heat, it can be kept for days before being
used to generate power. Even on overcast days, or several hours after sunset, electricity
can be generated during times of high demand. The largest concentrated solar thermal plant
in the United States is the Ivanpah Solar Electric Generating System. The project, which
is situated in the Mojave Desert of California, can generate 392MW with its 173,500 heliostats. It started commercial
operations in 2013 and it’s still running. The Norwegian company Yara has been working on
a new ternary mixture of molten salts based on Calcium-Potassium-Sodium-Nitrate that reduces the
risk of molten salt freezing and solidification. Molten salts are intended to be used at high
temperatures as a liquid - usually from 270ºC to 565ºC - so if its temperature gets lower
than that minimum it can freeze and solidify. The frozen salt can clog pipes, cause
damage and stop the power plant operation, which increases risks and maintenance
costs in current molten salt technologies. The mixture has a low melting point of 131°C
and a wide temperature variation (438ºC), which increases the energy yield/efficiency,
requires less of the molten salt blend, and the composition of the salt reduces
corrosion. These features increase the lifecycle of the plant and lower costs due
to the lower amount of material needed, the competitive price of potassium calcium
nitrate, and reduced corrosion maintenance costs. But molten salt isn't the only way to
go with solar energy storage in CSP. But before getting to that, I’d like to thank
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to Policygenius and to all of you for supporting the channel. Now back to the
interesting alternatives for storing solar. Heliogen, a California-based company, is
developing a concentrated solar solution that stores energy in rocks and uses advanced computer
vision/AI to precisely align an array of mirrors. The position of the mirror edges and the angles of reflection are evaluated and
adjusted 30 times per second. While most power tower systems usually
produce heat anywhere from 400 to 500ºC, this system is capable of reaching 1500ºC
due to AI and machine learning. The heat is directed down an insulated,
steel tube to a bed of rocks, which can stay hot for days or even up to a
week in a properly insulated storage unit. Heliogen's technology provides higher efficiency
and reduced water usage compared to traditional steam turbines. In addition, when it comes
down to costs, the company's founder, Bill Gross, mentioned that its technology
is targeting delivering heat at $0.01/kWh. In March 2022, the company signed
a project agreement with Woodside Energy to develop a concentrated solar energy
project at a site in Mojave, California, with a capacity of 5MW. A couple months
later, the company announced that the project had moved from design into
the testing and implementation stage. Innovations in storing solar energy
as heat aren't limited to CSP. This is on a very different scale than what CSP
provides for utility scale energy generation, but it’s a sign of where research is heading
for storing that solar energy in even more areas of our lives. Scientists from Chalmers
University of Technology in Sweden have been developing a fluid that’s potentially
able to store solar energy for up to 18 years. The fluid contains a molecule that's
composed of carbon, hydrogen and nitrogen. You might have flashbacks to high school science
classes here, but just bear with me for a second. Two or more atoms make up molecules and,
through the bonds that hold them together, the atoms share electrons. Different kinds of
molecules have unique three-dimensional forms. Methane, for example, is shaped
like a tetrahedron. When energy is added to the molecule, it
can change its structure/shape, and its atoms can join together in new bonds
that could store varying amounts of energy. In the case of the Chalmer University's molecule,
it was modified by the researchers to absorb more of sunlight's different wavelengths. It can
harness energy from UV and the blue and green light spectrum. When hit by sunlight the molecule
undergoes a transformation into an isomer with high energy, which is a molecule made up of the
same atoms but bonded together into a new shape. In order to manage the storage and release
of energy from the molecule, the research team created a catalyst to act as a filter
for the liquid, which puts the molecule back into its original state. This change in shape
raises the temperature of the fluid by 63ºC. Once it’s back into its original state
it’s ready to capture more solar energy. This new technology is called Molecular Solar
Thermal (or just MOST) Energy Storage System. That's the most interesting
acronym I've seen in a while. I had the chance to talk to Kasper
Moth-Poulsen, who’s leading the research, and he provided me with a full
high-level explanation of the cycle: “We have a liquid system flowing through a
panel. It's basically two glass plates with a liquid in between, and the molecules are
flowing through and being exposed to light and then converted. Then, they're going
into a small tank, and that small tank is where the molecules with the high energy form are
stored. Later, they can flow over a catalyst that is sitting in a little device that is then
triggering the heat release and sending out the stored energy. Finally, the molecules can go back
into the panel and go and capture energy again. So, it's a close cycle where the input is solar
energy, and we store it as chemical energy and we release it later as heat on demand and recover
the original molecule. So, in this way, it's like a cycle that can operate several times, hundreds
of thousands of times..." -Kasper Moth-Poulsen They sent the molecules with energy absorbed
from Swedish sunlight to China, where researchers from Shanghai Jiao Tong University released
and converted the energy into electricity using a generator developed by them. I’d say this
sounds MOSTly promising. The fact that Swedish sunshine was sent to the other side of the world
and converted into electricity is kind of crazy. Zhihang Wang, a researcher from
Chalmers University of Technology said: “...The generator is an ultra-thin chip that could
be integrated into electronics such as headphones, smart watches and telephones. So far, we have
only generated small amounts of electricity, but the new results show that the concept really
works. It looks very promising...” -Zhihang Wang When it comes to efficiency, Kasper said: "...The best systems operate between
30 to 50% efficiency at the wavelength that they receive. But then we have the full
solar spectrum. It's many wavelengths. So, in reality, our best system captures about 3%
of the incoming solar energy right now...The theoretical max is between 12 to 16% of the
incoming energy. It'll not be as much as a photovoltaic, and that is because you
have to pay something for the storage in the molecules and therefore it cannot be
as efficient as that... -Kasper Moth-Poulsen He also mentioned that the molecule
has been the hardest part to optimize. "...The heat recovery is going fairly
well. We extract the heat that we are storing. There are quite some losses in the
storage process, and we would like to expand to a bigger part of the solar spectrum and at
the same time maintain the high inner density and so on. There are like three or four parameters
we are trying to optimize at the same time and they're pointing a little bit in
different directions. The difficulty is to create systems that are good in all
aspects..." -Kasper Moth-Poulsen This is still ongoing research and they've been
testing new molecules and improving them along the way. The next step, according to Kasper,
is to scale up the system from just a few watts to possibly a thousand watts. Although the
molecule may not achieve efficiencies similar to photovoltaics or CSP, it could be layered into
other existing things to make them even better. Imagine layering this with a
photovoltaic system on your home. Not only would you be converting photons into
electricity for your home, but you’d also be storing it as heat for use later … like helping
to produce hot water in the middle of the night. In my chat with Kasper he mentioned some
possible applications for their system, including heating your hot water without needing electricity
or burning gas, heating a car’s cabin, and more. As we move forward towards a greener future,
storing solar energy for later use is essential. Harnessing sunlight,
converting it into electricity, and then converting it again to store
it into batteries isn't the only path. While storing heat in CSP power plants using
molten salts has been around for a while, newer approaches like storing solar energy
directly into molecular bonding is still at the early stage. Scaling it up and finding the
best applications for it will still take time, but the benefits that it can offer, like storing
solar energy for 18 years, are very promising. So are you still undecided? Do you think molecular
bonding sounds like a promising direction? Jump into the comments and let me know
and be sure to check out my follow up podcast Still TBD where we’ll be
discussing some of your feedback. If you liked this video, be sure to check out
one of these videos over here. And thanks to all of my patrons for your continued support and
welcome to new supporter+ member Robert Reichner. And thanks to all of you for watching.
I’ll see you in the next one.
