Dear Oscar:

for the time being there are two technologies that dominate the solar power industry: the Concentrated Solar Power (CSP) and Photovoltaic (PV). These two may be similar in that they both use the sun in order to generate power. But beyond that, they are as different as can be.

At first, CSP makes use of the sun’s radiation to heat a liquid substance that will then be used to drive a heat engine and drive an electric generator. Meanwhile, PV uses light through the “photovoltaic effect” — the absorbing of light which then leads to the breaking of the electrons — to generate an electric current.

Both CSP and PV have their own pros and cons. In terms of energy storage and efficiency, CSP is superior since it can store energy with the help of TES technologies. PV, on the other hand, is incapable of producing or storing thermal energy since they directly generate electricity. Aside from that, it’s also difficult to store electricity.

Although CSP is obviously the more efficient one in terms of energy saving, that doesn’t mean it’s the best option. Between the two, PV is cheaper, so energy investors are more inclined to use it than CSP. In other words, despite its advantages, CSP isn’t the favoured one.

However, all these debates — of which is better the option — are pointless because they don’t have to compete against each other. In fact, the world will be a better place if they actually work together. Hopefully, one of these days, a new technology for solar power will arise, and it will be a hybrid of the two.

Whatever the case, both CSP and PV are helpful in promoting the solar industry. They both made solar power possible, and they will be the reason why solar power will be here to stay.

The rise in the popularity of solar power energy comes with the expansion of the technologies associated with it. After all, once people realized that the sun can be used to generate electricity, they would understandably find ways on how to do it. And so far, there are two technologies that are used nowadays to generate solar power. These are the Concentrated Solar Power (CSP) and Photovoltaic (PV).

Concentrated Solar Power (CSP) vs. Photovoltaic (PV) Technologies

To begin with, Concentrated Solar Thermal systems (CSP) produce electric power by converting the sun’s energy into high-temperature heat using various mirror configurations. The way these particular technology works is that the sun’s energy is concentrated by various reflectors, and this concentrated energy is then used to drive a heat engine and drive an electric generator. The plants that utilize this system consists of two parts: one that collects solar energy and converts it to heat, and the other that converts the heat energy to electricity.

CSP is an indirect method that generates alternating current (AC), which will then be easy to distribute on the power network.

Photovoltaic (PV) solar panels, on the other hand, are completely different from CSP. Unlike CSP which uses the sun’s energy, PV solar panels make use of the sun’s light instead. In other words, photovoltaics is the direct conversion of light into electricity. The way this works is that the solar PV cells absorb light, which will then knock electrons loose. Then once the loose electrons flow, a current is created, and this current is then captured and transferred into wires, thus generating a direct electric current (DC). After the direct electric current is generated, it is then converted into AC, usually using inverters, so that it will be distributed on the power network.

-- Energy Storage and Efficiency:

CSP systems are capable of storing energy through the use of Thermal Energy Storage technologies (TES). As a result, they can use it at times when there is little to no sunlight, like during cloudy days or during night time, to generate electric power. Because of the CSP’s ability to store energy, the penetration of solar thermal technology in the power generation industry is increased since it helps overcome irregularity issues.

Meanwhile, PV systems aren’t capable of producing or storing thermal energy since they use direct sunlight instead of the sun’s heat. And in addition to that, storing electricity (for example, in batteries) is also not easily done, especially at large power levels.

Because of this, it is then clear that in terms of energy storage and efficiency, thermal energy storage technologies are better, thus making CSP systems the far more attractive option for large scale power generation. Furthermore, since CSP systems are able to produce excess energy and store it for future use, they can help improve the financial performance and also the sharing ability of solar power and flexibility in the power network.

-- Market Update: Investor’s Perspective:

There are three main factors that energy markets consider when deciding on power sources: cost of energy, ancillary services, and power dispatch-ability on demand. Obviously, for energy investors, the competitive cost of energy is the most important issue. And since PV is a lot cheaper than CSP, more and more energy investors choose it. This trend of investors choosing PV over CSP will continue so long as PV remains cheaper. And it seems like that’s going to continue to happen because PV panels have recently demonstrated a large price drop — about 30% to 40% in just a couple of years — and some expect that these prices will keep on dropping.

As for CSP, if these systems want to be attractive to investors, then they have to find a way to be able to demonstrate high performance in all three attributes. Because they may be more efficient and able to store a lot of energy for future use, but if they also cost a fortune, no one would want to invest in them.

Aside from the cost, energy market players have also reported that PV systems are a lot easier to build. Building them doesn’t cost much, and it also doesn’t take too much time. This is not like CSP because CSP plants need more space for large-scale applications, and they also have greater risks. Some of these risks include higher investment, challenges with thermal shortage, and cooling.

Also you can benefit from this valuable article:

"Top Solar Statistics You Need to Know in 2019"

@ https://mag.solarfeeds.com/statistics/.

Indeed this article:

"A typical solar-coal hybrid power plant in China"

H. Honga, S. Penga,b, Y. Zhaoa, Q. Liua

, H. Jina.

Pdf attached ..

I hope it will be helpful...

With my best wishes...

Microgrid power system using coal power plant as the main power supply and PV as secondary power supply has been considered by many researchers

Hassan Nasser Thank you for the information! Until now, CSP is very expensive unless it is large scale. It is however, the technology of choice if paired with coal for a hybrid setup as per the pdf you provided. On the other hand, solar PV modules are commoditized and prices have fallen dramatically, so it is the cheaper option. I just want to understand how a solar PV + coal pairing would work, since as per literature, they would be dispatched independently of each other so this is not a true hybrid.

Ashraf Mohamed Typical coal power plants are large-scale, from hundreds of MW to gigawatt levels, so I'm not sure if solar PV + coal hybrid at the microgrid level would work. However, my team has designed and sized solar PV + diesel + BESS hybrid microgrids and saw the true cost of generation go down dramatically while ensuring 24/7 power. Thank you for this idea.

Dear Oscar,

As mentioned by colleagues CSP plants remain expansive to date in comparison to PV plants. Yet today's CSP plants always come with thermal energy storage (TES) which help to reduce the system price and highlighting the econmical interest of this technology. Without neglecting the high dispatchability CSP+TES offer compared to PV plants.

When it comes to your question PV is the lowest LCOE without electrochemical batteries, the idea of combining PV with coal is both economically and environmentally viable. Low-cost PV plants will be added to existent coal plants and optimization would be conducted on operation scheduling between the two technologies. And other novel systems consist of combining PV with unused coal plants parts (i.e. use the power block engines, heat exchangers,...) with TES. This way the price of the plant will be highly optimized since the expensive parts of the plants are already in there.

Dear Dounia Ziyati

This is quite an interesting update on CSP! I have always thought that CSP is the more expensive solar, since it requires a huge land area, expensive capex, and high-temperature requirements. Are there economic incentives that contributed to CSP+TES' reduction in system price or it is the economic dispatch attributed to energy storage that made CSP viable?

Perhaps the immediate solution would be to modify the dispatch of coal with solar, as you said, to schedule coal to satisfy the residual load while solar is the primary supply--assuming the transmission infrastructure is robust enough to handle variable RE :)

I would also like to understand further the combination of PV with unused coal plant parts with TES. Does this mean PV will supply coal's own power requirements?

Dear Oscar Lopez Alvarez Jr. ,

I hope you got extensive answers from colleagues. Yes, CSP + TES are now economical as well as load flexible. They are one of the best bets to answer the problem of the duck curve (additional reading: https://www.sciencedirect.com/science/article/pii/S1755008418300309).

In response to your query, I have the following suggestions to integrate electricity produced by PV in a coal power plant for hybridizations are:

Model 1: Use electricity produce by PV panels to cater to the need of auxiliaries’ load (like the pump, compressors, etc.) in a coal power plant. Excess electricity from PV systems can be injected into the external grid. There are few techno-economic benefits using this model which will not only reduce the LCOE of the coal power plant but also generate additional income for the plant operators. Probably, I will recommend this model for retrofitting in the existing coal-based plants as you don’t need any major change in the plant.

Additional reading:

A) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7726338/

B) https://www.pv-magazine.com/2020/12/23/new-model-to-deploy-cheaper-pv-at-coal-power-plants/

Model 2: Use excess electricity production from PV systems and windmills to change Thermal energy storage and then integrate this thermal energy storage to produce power from coal-fired plants. These types of plants are flexible in generating electricity according to load. I will recommend this model for upcoming plants as these plants need an additional power cycle.

Additional reading:

A) https://www.sciencedirect.com/science/article/pii/S0306261918318142

B) https://www.sciencedirect.com/science/article/pii/S1359431119354456

Exactly it's the high dispatchability the CSP with TES offers that makes this technology viable in the market. And you are right the price of the installations is quite high in comparison to PV but if you take a look at PV with Battery Energy Storage Systems (BESS) you will clearly see that the prices become close.

For PV with TES, the idea is to use PV to supply the main energy demand during the day and when there is extra power it will be converted to heat using an electrical heater to be stored using TES techniques namely molten salt and at night the TES will be used to supply the demand. Now for the coal part since one of the expensive elements in a TES unit is the turbine. The idea is to use the turbines of the original coal plant since it will not be used anymore and put it in the PV+TES configuration.

Dear, Dr Oscar Lopez Alvarez Jr.

I consider that these hybrid energy generation technologies are a step towards the necessary transition to renewable energy sources. Renewable energy sources such as solar and wind are becoming more profitable and widespread.

Thank you Dounia Ziyati and Vivek Tiwari especially for the very informative literature you provided. I've researched further on the LCOE's of solar + storage and was surprised that CSP+TES is cheaper than PV+TES. Obviously, ground mount PV is way lower but does not have the flexibility advantage. Solar on coal rooftops, having the lowest LCOE can be used as the short-term approach while CSP+TES can be explored as the long-term decarbonization solution when coal plants will be decommissioned and the turbines will be reused for TES.

Debrayan Bravo Hidalgo Thanks for the kind words. While I do energy economics research work I haven't earned a doctorate degree yet. I hope though that you will be right soon!

Maybe the following articles and the references therein are of interest:

Article Solar Photovoltaic Electricity Generation: A Lifeline for th...

Oscar Lopez Alvarez Jr.

At the macro level renewable energy technologies such as solar PV and wind have a very limited future role in the global energy supply equation. Renewable solutions will remain suitable for miniscule scale applications in boutique and niche circumstances only. Renewables lack the necessary attributes to qualify as enduring future mainstream energy generation solutions.

I understand that global climate change is largely fuelled by greenhouse gas emissions from fossil fuel energy generation, and gasoline powered engines. I also understand that well over half of the world’s population are energy starved; and as such are denied opportunities to aspire to reach the modern standard of living enjoyed by those of us fortunate enough to exist in an energy abundant society.

It is axiomatic without any doubt, that the energy deprived must do whatever and by any means possible, to redress this imbalance. The math around this premise is astonishing.

The current world’s total power generation output by all forms will need to increase by a factor of between 50 to 100 times (at least) and be steadily rolled out systematically and globally over the next 50 years, to begin to definitively redress this energy imbalance and moving societies forward rapidly into the next century!

Moving the world forward technologically; is not only about (1) stabilising GHG at insignificant levels permanently, but also and simultaneously (2) “powering up” the entire world’s population to enable the pursuit of a modern era of prosperity and standard of living by and for all peoples.

The key point here is that GHG mitigation concepts and technologies, are intrinsically linked with “global societies equalising power generation technologies”.

Let us not forget: the current global population of 7 billion will increase to over 10 billion by 2050, irrespective of whatever scientific and technological advances brings forth in the near foreseeable future; or worse, does not bring forth. It will still be around 10 billion with or without the right technological solutions put in train about now.

Energy commentators and readers might benefit from pondering a bit on the simple term “the new age global energy generation imperative”; it has a books worth of meaning in its few words. The “new age global energy generation imperative” demands a massive and enduring energy science technological solution that:-

1. Must be an energy dense power generation technology able to deliver massive, safe, clean, and low-cost power; and be one occupying the apex of the energy science technology pyramid;

2. Reduce power generation global greenhouse gas emissions GHG [from combined sources] to insignificant and ongoing manageable levels permanently;

3. Be of scalable and modular design, and easily deployed systematically and cost effectively; to power ‘’new age energy intensive industries and businesses’’ throughout the world;

4. Cost effectively enables all individuals, families, communities, states, and nations, throughout the world, the opportunities to aspire to achieve (1) prosperity through industrialisation and modernisation, and (2) a modern standard of living; and particularly post 2200.

The key takeaway phrase is: “massive, safe, clean and low-cost power”; and nothing less than this technological pursuit and outcome will cut it moving forward globally.

The technology that gets that right – will precipitate a falling into line of all other critical technological imperatives including: stabilising the worlds peoples and societies, and most certainly be regarded as “global in-perpetuity energy science technology” enabling all things that follow.

Finally: I recommend that global thinking scientists, researchers, and commentators, focus on my comments above and switch ideas from a narrow focussed “here and now” argument, to a more expansive global energy perspective moving forward; and one that is a more quantitative and purposeful viewpoint in which modern science takes precedence over misguided rear view ideology.

Lawrence Coomber