Solar Power – Problems of Plenty?
Solar panels are getting cheaper year after year, mainly due to Chinese manufacturers flooding the market. 
 
This leads people to think: Why not build more and more solar power plants and produce cheap electricity in abundance? 
 
For example, the Prime Minister (PM) Surya Ghar Muft Bijli Yojana encourages people to install solar panels on their rooftops and get free electricity.
 
Gigantic solar power plants are coming up, too. Adani Green Energy is building a 30GW (gigawatt) solar and a wind plant at Khavda in Gujarat, of which 1GW is on stream already. When completed in about five years, this plant will cover an area of 726sqkm (square kilometre), almost the size of Bengaluru. 
 
All this is great news – cheap power, no emissions, save the environment and all of that.
 
But, a little bit of cloud is appearing on the horizon. Experts are asking: Can we really use so much solar power?
 
To understand this conundrum, we need to consider the ‘duck curve’.
 
 
See the two lines – the blue (upper) line plots the total demand for electricity during a 24-hour cycle, and the lower (black) line shows the net demand after deducting the power received from renewable sources, principally solar power.
 
The two curves together roughly form the shape of a duck – hence, the name ‘duck curve’.
 
Solar power generation peaks between 12 noon and 4pm. Before and after this period, the demand for power has to be met largely by conventional power plants, i.e., fossil fuel burners.
 
California has been adding more and more renewable capacity every year, resulting in the duck curve for California becoming increasingly more pronounced over the years, as this diagram shows.
 
 
As the years passed, the net demand curve dropped more and more during the daylight hours. Today renewables, plus a nuclear power plant, provide all the power California needs during the 12 noon to 4pm period. Fossil fuel power plants (FFPPs) are not needed. 
 
But, as evening sets in, solar power fades out and the net power demand shoots up very sharply. Now the FFPPs are needed to meet the demand.
 
This pattern, repeated day after day, has two consequences:
- A natural limit sets in on the amount of solar power that can be used.
- The demand on FFPPs fluctuates a lot – low during the day, and very high in the evening.
 
No matter how much solar power is generated, we cannot get rid of FFPPs because we need them after dark, and on rainy days, when solar power is unavailable. Using large amounts of solar power means that FFPPs will run at very low capacity during the day, and at full blast in the evening. This is a very inefficient, and expensive, way to operate an FFPP.
 
There is a solution: 
- Run the FFPPs at an optimum load round the clock which results in maximum efficiency.
- Build a lot of renewables, and store the surplus electricity during daytime.
- Release the stored electricity in the evening to augment the output of the FFPPs.
 
This will create a better balance between the supply and demand of power, thereby increasing efficiency, reducing cost and cutting carbon emissions.
 
Ah, but how to store the electricity?
 
Various (somewhat unsatisfactory) methods are available:
- Storage battery – expensive, environmentally unsound, limited capacity.
- Green hydrogen – expensive, needs infrastructure for storage and transport, explosion risk.
- Pumped hydro – good solution, but expensive to build.
 
Now a new method has arrived – thermal energy storage.
 
This is how it works:
- Place a big block of graphite in a sealed and insulated container, filled with nitrogen to eliminate fire risk.
- Send surplus electricity (from renewables) through induction heaters embedded in the graphite, to heat it up to 700 degrees centigrade.  Thus, electrical energy is converted into thermal energy and stored in the graphite.
- To retrieve the stored energy, send water through pipes running within the graphite, producing high-pressure steam, similar to how a coal-fired boiler operates.
- Use the steam to run turbines and generate electricity.
 
This diagram (courtesy: E2S website) shows how the system is configured.
 
 
The system has many positive features:
- Graphite is easily available, non-corrosive, and long-lasting.
- It can be heated very quickly. 
- It can store thermal energy for many hours, even days.  
- It can supply the energy back into the system when needed. 
- The system has a very high efficiency (above 90%) in converting electricity into thermal energy and then into steam power.
- The entire system is non-polluting, and the energy stays ‘clean’ throughout.
 
An important side benefit is that the steam can be used to run the standard turbines and generators in a FFPP which means that existing infrastructure can be used with few modifications.
 
Furthermore, existing FFPPs need not be scrapped. They can be linked to a solar or wind power plant, whose surplus electricity can be stored in graphite blocks, and later used to produce steam to feed the FFPP’s turbines when demand rises. The FFPP continues to be available to generate power (by burning fossil fuels) when the output from renewables decreases, such as on rainy or low-wind days, 
Believe me, this is not an idle dream.
 
The first such system is up and running, and in India!
 
A pilot plant has been set up in an existing coal power plant in Asansol (West Bengal). After reviewing the trial runs of this plant, NTPC has floated a tender for installing a thermal power storage system in its 1,820MW (megawatt) coal/ gas-based thermal power plant at Dadri (Uttar Pradesh). 
 
The bottom line...
 
Thermal energy storage could be a way for India to:
- ramp up renewable power generation and store any surplus ‘green’ power for use at peak times, without having to invest massively in new equipment.
- Reduce reliance on FFPPs, run them more efficiently and have them at hand to maintain power supply when renewable power runs low.
- Overall, achieve lower energy costs and reduction in carbon emissions.
 
Desirable goals, don’t you think?
 
(Deserting engineering after a year in a factory, Amitabha Banerjee did an MBA in the US and returned to India. Choosing work-to-live over live-to-work, he joined banking and worked for various banks in India and the Middle East. Post-retirement, he returned to his hometown Kolkata and is now spending his golden years travelling the world, playing bridge, befriending Netflix & Prime Video and writing in his wife’s travel blog.)
Comments
blsomani
2 weeks ago
I think idea is good and novel, but economics will need to be worked out. However , presently the best system would be hydrostorage by lifting water. It will just need another water storage down stream and lifting pumps etc but would not need any other system so geographically where it is feasible should be constructed and used.
pmbhate
2 weeks ago
The system perhaps very efficiently converts electricity into thermal energy (first law of thermodynamics), but it cannot over-rule the second law of thermodynamics while converting thermal energy back into electricity via a steam turbine. The most modern thermal power plants operating at super-high steam pressures have not yet crossed and will probably never will, an efficiency of 50%. This is all because of the 2nd law of thermodynamics which says that only a part of heat can be converted into work (in this case, electricity), the rest is given away to the environment as generally unusable heat. Very unfair, this 2nd law; but what to do? We have to lump it.
kvasoftpllc
2 weeks ago
What is missing in the article is space requirement. This is a good offset to reduce use of fossil fuels, and extend their use until a silver bullet is found (could that be SMR, jury is still out on that). In meantime community solar is decentralized option to pursue and this graphite solution on smaller scale could service multiple community solar setups.
pgodbole
3 weeks ago
Interesting article and innovative idea. But a question remains. This mean first we generate power, then store it as thermal energy, then release thermal energy to generate steam and use that steam to run turbines and (re) generate power! This virtually means that power is being generated, used (only to heat graphite to store) and regenerated for end use. The resulting power is bound to be quite expensive (twice as much?). Article has not discussed economy aspect of storing and using power in this way.
Amitabha Banerjee
Replied to pgodbole comment 3 weeks ago
Solar energy is cheap and plentiful, but available for a limited time - hence the need for storage. The process of storage and retrieval of electricity involves losses, e.g. batteries require conversion from DC to AC, voltage change etc, all of which create losses. Existing methods of storage have inbuilt losses of 30% or so. Thermal energy storage is much more efficient, - losses of less than 10%. Hence the effective net cost will be only slightly higher than the cost of the solar energy which will be stored. Exact numbers will be known only after large scale implementation. However, two facts are relevant : 1. NTPC seems to think that it is worthwhile. 2. If it works, we can use much more solar energy than presently possible, which will reduce cost and carbon at the same time. THAT is why this system has generated interest.
iaminprabhu
3 weeks ago
Nuclear Power is the BEST (with least pollution) when SAFETY is taken care off. Now decades of Safety experiences make it most suitable across the World ????

SOLAR cells & related usage life with its POLLUTING DISPOSAL (like eWaste) will be a humongous issue in environment in next few Decades.
Amitabha Banerjee
Replied to iaminprabhu comment 3 weeks ago
I agree with you. Nuclear is an excellent solution, provided it is used with extreme safeguards. India is trying to build Thorium reactors which may get around the problems associated with using other nuclear fuels. However, this is still some time away, because at present nuclear accounts for only about 2% of power generated in India.
yerramr
3 weeks ago
The article is very informative and futuristic. We should continue to focus on Thermal power despite its ramifications to the Carbon reduction goals we have set. Developed nations enjoyed the luxury of fossil fuels. Every home and every commercial establishment, all the office spaces work with ACs and they emit carbon and heat. This has been going on for decades. At a time the developing nations like India get into new forays and ride on competition, the developed economies are trying to bind us through bilateral and multilateral arrangments in the name of climate change. While we are conscious of the same, the forests, flora and fauna India has can generate carbon credits of a higher order if the price of greenery generation and retention are suitably revised that can be traded.
adityag
3 weeks ago
I would say we need to focus on nuclear. Not only is it the most cost-effective over the long run, it is also the "cleanest". Unfortunately, India isn't part of the NSG (and thus acquiring rich uranium remains a pipe dream) -- all this despite the landmark nuke deal with US several years back. It's sad.

I'm not sure the current crop of renewables, however it is defined, is viable for mass consumption. It might make sense for micro consumption i.e. village heating systems, etc. Renewables are notoriously inefficient when it comes to scale. Coal is the only viable source. If India somehow gets through the NSG gridlock, for nuclear power, there's no stopping us. IMHO, nuclear is the future (and its downsides i.e. nuclear waste, nuclear sabotage, etc are all hyped up and made it look like big problems when it isn't)

Good article.
kvasoftpllc
Replied to adityag comment 2 weeks ago
With NVDA bursting on the scene , and power hunger in hyperscale data centers, opportunity for SMR to shine. Jury is still out, but in a decade there would be clear picture. EV sales are stagnated in US, but Hybrid are now getting the attention.
gbrhyd
3 weeks ago
Good concept, should be tried.
prasanna
3 weeks ago
Excellent system if it is actually working satisfactorily. I wish we could have smaller capacity power turbines for our home electricity also!
kvasoftpllc
Replied to prasanna comment 2 weeks ago
Single home is too small. But serving community solar plants is an option down the road.
gbrhyd
Replied to prasanna comment 3 weeks ago
It’s expensive and difficult to maintain in domestic and small scale , however it is advisable for industrial scale .
narayansa
3 weeks ago
Excellent!
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