Energy storage
Energy Storage.
Energy consumption.
Storage of energy.
Store, large scale.
Thermal storage.
CSP.
Flow batteries.
Metal-air batteries.
Hybrid.
Lithium sulphur batteries.
Hydrogen.
Bio-engineering.
Artificial photosynthesis.
Photosynthesising particles.
Algae.
Rate of photosynthesis.
Methanol.
Methanol and storage medium.
Cryogenic storage.
Liquid nitrogen.
Micro grid.
Desirable scenario.
In 2004, the total electrical energy consumption, from all sources, fossil fuels, nuclear, solar
and renewables, was 15500 Terawatt hour.
This would be the amount of energy in 1200 million tonnes of oil equivalent.
MTOE stands for Million tonnes of oil equivalent.
This represents only electrical energy.
If we add heating, transport and agriculture,
the energy would increase to 9400 million ton oil equivalent.
The average energy consumption in Europe is 2000 Kilowatt hour, per person, per year.
In the U.S. the average consumption is 4400 Kilowatt hour, per person, per year.
A 1000 Megawatt power plant working at 80% capacity will provide enough energy,
for 640000 U.S. homes, or 1.3 million European homes.
The demand for energy varies at different times of the day.
Typically the day time load is double that required during night time.
In addition to this there are seasonal variations.
This varies depending on the region, in winter months for heating and summer months for cooling.
Electricity suppliers rely on a combination of experience, local knowledge, and hard data,
to make accurate predictions about demand
Fossil fuels can be transported and stockpiled.
It can be ramped up and down.
Matching load to demand, across the grid, with fossil fuel power, is very challenging - but possible.
With renewable forms of energy, this would be close to impossible.
Renewables are essentially intermittent sources of energy.
For example, the sun does not shine in the night.
The storage of energy generated from renewables, is vital, to make it viable.
The big question is, how to store the energy generated by renewable sources.
If electricity from solar has to be supplied outside the hours of insolation,
then it needs to be stored.
As of now, this means using batteries.
In the case of non-portable applications, like a building, lead acid batteries can be used.
Lead acid batteries are cheap, and robust enough to withstand the constant charging/discharging cycle.
However lead batteries are inefficient.
They are not suitable for use at a local, regional or national scale.
As of now, almost all the energy we store, is in the form of chemical bonds.
We are adept at converting heat, kinetic energy, and electro magnetic energy, into electricity.
We are yet to learn to convert these forms of energy into stored potential energy, on a large scale.
We get most of our energy by breaking chemical bonds in fuels such as oil and coal.
We lack the knowledge to store solar energy on a large scale.
Gemasolar located in Spain, is the world’s first solar power plant to provide energy 24/7,
on a commercial scale.
At the heart of this power plant, there is a 115 meter high tower,
surrounded by about 2600 adjustable mirrors called heliostats.
Each heliostat focuses sunshine on a solar receiver, and steam turbine at the top of the tower.
The solar receiver produces super heated steam at 275 degree centigrade.
This drives the turbine to produce electricity via a generator.
The energy conversion rate of solar to electricity is 17%.
Gemasolar can produce electricity even in the night.
A large proposition of the solar energy, it receives, is used to heat up molten salts,
to a temperature of 500 degree centigrade.
This heat could be converted to electricity for upto 15 hours.
This technology is called concentrated solar power, or CSP.
The electricity that it produces, is expensive compared to fossil fuels.
However the costs is expected to come down.
There are a number of competing systems that can supply solar power,
on demand via thermal storage.
They all use mirrors to concentrate sunlight on to receivers,
that converts the energy to heat.
This thermal energy can be stored and used to produce electricity via a turbine,
during the night.
Electrical battery storage have been employed for long,
to stabilise power across distribution networks.
CSP provides an alternative to electrical battery storage.
Batteries are expensive to produce and maintain.
It has limited life cycles.
The pure crystals that form in batteries cannot be dissolved back into the electrolyte.
Research into energy storage is key to overcoming the intermittency issues involved,
all forms of renewable energy.
Energy storage requires two commercial targets.
One is storage price and longevity for large scale stationary devices.
Another is energy density at a competitive price for automative and portable devices.
Energy storage at $100 per kilowatt hour would make it economically viable.
For automative applications 0.4 kilowatt hour per kg, at a price of $200 per kilowatt hour,
would make it economically viable.
At that level there will only be a small premium for electric cars with a range of 800 km.
There is ongoing research to produce what is called as ‘flow’ batteries.
These flow batteries have a number of advantages.
Power and energy components are separated.
There is no solid-state phase transitions.
The result is a flexible layout, a long life cycle, rapid response times, no harmful emissions,
and no need to ensure that all cells have an equal charge by overcharging.
Maintenance is low.
They have a high tolerance to overcharging and over discharging.
More important, is the revolutionary molten salt batteries, that are now being developed.
The magnesium and antimony electrodes in the battery, are separated by molten salt.
This could provide a very low cost stationary energy storage system.
Flow batteries are very complicated in comparison with standard batteries.
They require pumps, sensors, control units, and secondary containment vessels.
There energy density is lower than comparable lithium ion batteries.
The world’s largest flow battery in 2014 is in China.
It costs around $1000 per kilowatt hour.
They use vanadium, which is very expensive.
Some scientists are researching the use of cheaper organic chemicals called quinones.
They hope to get the cost below $100 per kilowatt hour.
Another highly promising technology is the metal-air batteries.
Lithium-air batteries use a chemical process, that involves the oxidation of lithium at the anode,
and the reduction of oxygen at the cathode.
This creates a flowing current.
The theoretical maximum energy for these batteries, is 1.1 kilowatt hour per kilo.
Though it is above the discussed target, the energy density is less than 10%,
of the energy density of gasoline.
For a battery however, this is very high energy density.
The oxygen is drawn in from the air, instead of storing it in a oxidiser.
This gives it an energy per volume equivalent to that of a petrol engine.
There are many challenges to this technology.
Scientists are researching on overcoming these challenges.
Using batteries in combination with liquid fuels,
is one of the developments in recent years.
These are the hybrid cars.
Hybrid cars have an electric drive system, that is powered by a battery.
It has a petrol engine that runs a generator to charge the battery.
Petrol engines run more efficiently at constant rotational speed.
Petrol is simply a high density fuel for charging the battery.
The generator recycles the kinetic energy from both braking and travelling downhill,
and stores it in the battery.
The battery can be charged from the mains supply overnight.
All these savings almost double the mileage that it gives, compared to conventional cars.
Another battery technology showing promise is the lithium-sulphur batteries.
They are very inexpensive.
They pack 5 times more energy by weight than lithium-ion batteries.
In a lithium-ion battery, a good deal of space is taken by the layered graphite electrodes.
In a lithium sulphur battery, the graphite is replaced by a silver or pure lithium metal.
This performs a double duty as both the electrode, and supplier of lithium-ions.
Scientists believe that a commercial size battery can achieve an energy density of 500 watt per kg.
Despite these promising developments batteries are unlikely to provide effective energy storage,
on a large scale.
A mobile phone and AA battery can store 0.2 kilowatt hour per kg.
They are much better than lead acid car batteries.
By comparison a chocolate cookie, has an energy of 7 kilowatt hours per kg.
This is 30 times more energy dense.
This illustrates that batteries has still a long way to go in terms of energy density.
Storing energy as electrochemical potential is not very mass efficient.
Storing it as oxidisable chemical bonds is more efficient.
We need to find a means to capture, convert and store the electricity that solar produces.
We could use the electricity to run electrolysis, splitting water into hydrogen and oxygen.
Another option is to make hydrogen from water, using a two-axis parabolic dish.
Our need is to scale up to 10 to 20 terawatt of energy.
To build this capacity to store this energy we will exhaust the world’s supply of steel and aluminium.
This is not to mention other scarce elements like platinum which will get exhausted much earlier.
The problem with hydrogen is that it is a gas at atmospheric pressure.
It can be stored as a gas, but it has a very low density, and requires a lot of space.
It can be compressed and stored as a liquid.
That requires high pressure or very low temperatures.
By combining hydrogen with carbon dioxide, we can produce methanol.
Methanol is much easier to store, transport and distribute.
Methanol can be used directly as a liquid fuel, or can be converted to other fuels.
Hydrogen comes from a renewable resource of water,
and atmospheric carbon dioxide is fixed to generate the fuel.
This makes methanol effectively a carbon neutral fuel.
To scale up the use of solar power, we need to develop technology,
to cost effectively produce chemically usable fuels.
Photovoltaic cells are essentially artificial photosynthesis systems.
They use light to separate charge.
They operate on the same principal as plants.
Plants use leaves and branches, where as they use silicon wafers and wires.
If we could bioengineer plants to produce fuels,
it will be the greatest achievement of the 21st century.
It will provide a clean alternative to oil.
Photosynthesis has existed on Earth for 3.4 billion years.
The big advantage that plants have over our photovoltaic systems,
is that they can store energy derived from sunlight and use it whenever they like.
Trees do not suffer from intermittence.
If we could store solar energy in a similar way,
it would make sense to have vast solar farms in the Sahara desert.
Photosynthesis took plants millions of years to evolve .
It uses the sun’s energy to separate water into hydrogen and oxygen,
and combining them with atmospheric carbon dioxide to produce energy storage molecules,
such as sugars and starch.
The process is not very efficient.
Vegetation has a green colour.
This means only a limited amount of the solar spectrum can be absorbed.
Ideally leaves should be black.
If the sun shines too intensely, the plant’s system gets overwhelmed.
They shutdown in just 30 minutes.
The energy they capture is stored as solid carbohydrates.
This has a relatively low energy density.
Bio-engineering photosynthesis, does not mean replicating the process.
It requires to be completely redesigned.
Gaining a better understanding of the fundamentals of photosynthesis,
and nitrogen fixation would have a profound implication for crop yield,
and energy conversion efficiency.
Currently plants and algae absorb only 35% of the spectrum.
Scientists are researching ways to increase the range of solar absorption.
Expanding the range of usable light into a longer wave near the infrared end of the spectrum,
could produce significant improvements.
Some bacteria already get their energy from these wavelengths.
It might be possible to bioengineer, plants and algae to do the same.
The technology required for solar energy and synthetic photosynthesis is quite straightforward.
We need a version of a photovoltaic cell to absorb light energy to liberate electrons.
Then these electrons must be guided by catalyst towards the right molecules,
so that they can react to produce the kind of fuel we need.
In practice guiding the electrons and producing the right fuel is a complicated business.
Commercial viability requires a system that is efficient, durable and cost effective.
We have a long way to go to achieve this.
Some scientists at MIT created a wireless artificial leaf.
The leaf can make hydrogen from ordinary water using catalysts, that are relatively cheap and efficient.
The cost was working out to $7 per kilogram of hydrogen.
In comparison making hydrogen from reforming methane costs just $2.50 per kilogram.
Many other scientists are also working on similar projects.
If they can reach a conversion efficiency of 10%,
only 0.16% of the world’s surface would be required to provide the 20 terawatt energy we require.
Artificial leaves can be located in arid land.
This will save valuable land needed for agriculture.
Scientist can produce hydrogen by splitting water into hydrogen and oxygen.
They use materials and processes which are very expensive.
Critical challenge is in developing catalysts from cheap and widely available materials.
Any new system to be viable, has to be efficient, cheap and robust.
Achieving all three objectives is a challenge.
Plants already do photosynthesis.
Scientists are motivated by this fact.
We need to learn to do artificial photosynthesis, in an efficient, cheap and robust manner.
We need to be able to produce photosynthesising particles,
like nano-scale semi-conductors.
We should be able to immerse this in water, and place it in sunlight to produce low cost fuel.
Scientists are working on suitable catalysts to make this possible.
Efficient water splitting technology is likely to prove the best way to store solar energy.
During the day, artificial leaves will use sunlight energy to split water.
During the night, hydrogen can be burnt to generate electricity, at the point of production.
This will avoid issues of storage and distribution.
Hydrogen is best when used in the place of production.
The energy density of hydrogen makes it many times more efficient as a storage medium,
than even the most advanced batteries.
With a little more complex chemistry, we could potentially be pulling carbon dioxide,
from the atmosphere to produce liquid methanol and dimethyl ether.
This fuel would be much easier than hydrogen to transport.
Liquid solar fuel can be produced by using photosynthesising micro-algae.
Algae produces a lipid or fat that has properties very similar to diesel.
The lipid content varies.
The strains with lower content grow 30 times faster than the lipid rich strains.
The challenge is finding a strain with a combination of good yield and growth rate.
Algae can produce 300 times more bio fuel than conventional biodiesel staples,
like rapeseed, palms, soya or sugarcane.
Using the fuel produced releases carbon dioxide into the atmosphere.
But since carbon dioxide was taken out of the atmosphere, for growing the algae,
it can be considered as carbon neutral.
Algae fuel does not require fresh water.
It can grow in sea water or waste water.
It can also grow in arid land, or saline land.
It is also biodegradable.
The U.S. department of energy estimates that domestic replacement of petroleum,
with algae biofuel would require 15000 square miles of land.
This would be 0.42% of the nation’s land mass.
It would be 14% of the area currently used to grow corn.
Algae grow 20 to 30 times faster than food crops.
They have a rapid harvesting cycle of 1 to 10 days.
With all its advantages, there are still several hurdles to overcome,
before it can become a genuine contender.
The concerns are regarding the amount of energy, water and nutrients.
The concerns can be overcome with more research.
Algae was originally cultivated in large open ponds.
Open ponds are prone to contamination.
The hardiest strains of algae do not yield the best amount of lipids.
Open pond systems are now being given up.
Today a most common system involves a photo bioreactor or PBR.
Nutrient rich water is pumped through bio-reactors, like tubes of plastic or borosilicate glass.
They are exposed to sunlight.
The process is expensive, but provides a high level of control and productivity.
PBR’s can operate in deserts, saline soil or even offshore.
PBR do not have contamination problems.
They can be cultured in well controlled environmental conditions.
Another system is the closed loop system.
Closed loop systems are not exposed to open air.
Carbon dioxide from a cheap source is required to feed the algae.
Carbon dioxide from industrial chimneys could be one such source.
Micro biologists are identifying algal species, for different locations and purpose.
Molecular geneticists are tailoring the metabolism for each need.
Organic chemists are identifying novel products of algal metabolism.
Engineers are developing infrastructure of the algal farm.
We may soon see coastal farms, drawing sea water for the culture of algae,
to produce biofuel.
They will concentrate mineral fertiliser from sea water, and remove pollutants,
including carbon dioxide from nearby power plants.
The whole activity could be powered by solar energy.
Cultivation of algae is half the problem.
There is the challenge of separating the useful lipids from the algae.
One method being researched by scientists, is producing micro bubbles that can float algae particles,
to the surface of the water.
This makes harvesting easier and cheaper.
For the mass cultivation of algae, sunlight is essential.
All the spectrum of sunlight are not absorbed by algae.
The rest of it goes for waste.
Scientists are researching using fluorescent dyes that absorb wave lengths of light,
currently under used by algal cells.
They can emit longer wave lengths of light, tailored to absorption peaks of light harvesting pigments.
This would enhance the rate of photosynthesis.
If successful storing the light energy emitted from the dyes during the day,
and reemitting it at night could allow photosynthetic productivity to continue during night.
Methanol has the chemical formula CH3OH.
Ethanol has the chemical formula C2H3OH.
Chemically both are alcohol, but with different properties.
Methanol is poisonous, and is generally derived through synthetic chemical processes.
Ethanol is created by fermentation of food crops.
This is the alcohol found in beer, wines and spirts.
Both substances can be used as stores of energy.
The many advantages of liquid fuels, provide the salient reason,
for it to be used as a fuel.
The proposed hydrogen economy would use the gas to store renewable energy.
This would then power fuel cells, internal combustion engines, and even electronic devices.
The challenges involved are production of hydrogen, and the necessary transport and distribution of it.
Some scientists believe that methanol would be a more practical fuel.
The easiest way to produce methanol is by steam reforming methane.
This is produced when a mixture of carbon monoxide and hydrogen, called syngas,
is turned into liquid hydrocarbons through a collection of well understood chemical reactions.
The chemistry is quite simple.
CO+2H2 gives CH3OH.
The process is not simple.
It is also energy intensive.
Like petroleum, electricity and hydrogen, methanol is a vector for energy storage.
Methanol can be produced from coal.
For it to be a renewable source, the syngas has to come from a carbon neutral source.
Scientist are researching a process which involves combining,
equal parts of hydrogen and carbon dioxide, with 2 parts of water to produce syngas.
Converting the syngas into methanol requires a constant supply of water vapour and carbon dioxide.
Both gases are released when methanol is burnt.
The released gases can be reused.
The energy carried by methanol produced in this way is less than the energy, needed to create it.
The advantage is the opportunity to use methanol, for storing energy from renewable sources.
This will be much more efficient than any battery.
There are many potential sources for syngas.
It will not require staple crops.
This means it will not compete with food production.
The amount of methanol can be produced from biomass, through gasification,
is much more than the ethanol that comes from biomass fermentation.
Methanol could be ancillary to other forms of power production,
and employed as a form of carbon capture.
Nuclear power could be used to split water and provide hydrogen.
Carbon dioxide could be captured from coal burning power plants, in the same site.
By burning coal the carbon in it is used twice.
The first time is to generate heat and produce electricity.
The second time the carbon dioxide is captured and converted to methanol.
This reduces the carbon intensity by a factor of four.
The same can be used for fracked natural gas.
Using fossil fuels more efficiently can be a stop gap arrangement.
Later we would be able to replace them with biomass.
This would provide a carbon neutral source of carbon dioxide.
Hydrogen would come from water split by sunshine, or electrolysis driven by solar PV cells.
China has established a domestic industry of coal based methanol and dimethyl ether.
The price is competitive with petroleum based fuels.
Methanol based fuels have a high octane rating, and cleaner burning properties.
Another technology works by using carbon dioxide from the atmosphere.
Air is blown through a mist of sodium hydroxide.
This converts the carbon dioxide to sodium carbonate.
The carbon dioxide is then removed from sodium carbonate using electrolysis.
It is then converted to carbon monoxide.
Finally carbon monoxide is combined with hydrogen gas to produce petroleum.
Hydrogen gas is produced by splitting water.
The science is entirely plausible.
The problem is with the economics.
In this process electricity-a high grade energy, is converted into low grade heat energy.
There is significant losses of energy, taking place in every step.
In motor vehicles 15% of petroleum’s heat energy is converted into kinetic mechanical energy.
In an electric car it is about 80%.
To synthesis enough petroleum to meet the global demand of 90 million barrels,
would require half of that energy in any form.
The bottom line with all carbon dioxide based technologies,
is that we need a cheap and readily available source of energy,
to turn carbon dioxide into liquid fuel.
Only 1/3rd% of atmospheric air is carbon dioxide.
It needs to react with hydrogen before it can become a fuel.
The technology we have for liberating hydrogen from its chemical bonds,
is energy intensive and expensive.
Plants get around this problem by using sunlight to split water to get hydrogen and oxygen.
The hydrogen is stored by combining with carbon dioxide to make carbohydrates.
Synthesising hydro carbons makes sense only if we have vast amounts of cheap energy,
to generate hydrogen.
Methanol should be thought of as a storage medium,
with an added convenience of a liquid fuel.
It is also possible that we could have methanol fuel cells,
where methanol is oxidised to produce electricity.
This way would allow us to store solar power for later conversion to electrical energy.
There are many cases, where storage liquid fuel is not required.
One example, is domestic heating.
One technology to do it is cryogenic storage.
It works on a similar principle to hydro electricity.
At night, it can be used to cool air from the atmosphere, to minus 195 degree centigrade.
At this temperature it liquifies and occupies a thousandth of the volume.
During peak demand the liquid air is pumped at high pressure into a heat exchanger.
This acts like a boiler with air, rather than water.
Ambient temperature or hot water is used to turn the air back into a gas.
The massive increase in volume, is used to drive a turbine.
Once the technology matures, it may become cost effective at $1000 per kilowatt hour.
The technology is suited for locations remote from mountains and lakes,
required for hydro electric schemes.
Another technology evaporates liquid nitrogen,
using waste heat from an adjacent biomass power plant.
The process can also use ambient heat.
Cold energy is then captured using a specially designed cold buffer.
This cold energy can be used to re- liquify nitrogen, when its needed to store more energy.
This doubles the efficiency of electricity generation.
The system can be applied to harness waste heat.
Low grade waste heat produced by IT equipment in data centres can be captured.
Cryogenic storage is similar to efficiency of much less energy dense compressed air plants.
The efficiency is comparable to the 70 to 85% efficiency of batteries,
and 65 to 75% efficiency of pumped hydro.
There is potential in this technology to scale up, to saving 100s of megawatts of surplus energy.
There is research taking place into energy storage by other means.
Flywheels are used to store energy generated by wind turbines, during off-peak periods.
Capacitors discharge their energy very quickly.
They are used to supply energy to robots.
End users can also become energy producers.
One example is a building, with its own turbine and PV system on the roof,
with a battery setup in the cellar.
Most countries generate electricity in large centralised facilities.
These plants have very good economies of scale.
The long distance over which the energy has to be transmitted, results in lost energy.
Local small scale generation offers greater efficiency,
because the energy is generated near the point of use.
These small scale systems can generate upto 10000 KW.
In principle the energy produced can be integrated to central grid.
A micro grid is a localised collection of energy generation and storage.
It can operate independently, and also connect to a central grid.
Considering the technical aspects of energy supply,
its entirely reasonable to conclude, that we are well equipped to solve the energy crisis.
A desirable scenario is that we ramp up, solar photosynthesis, nuclear capacity, solar PV,
wind, wave, and other sustainable technologies.