Month: September 2018

Scalability is a hallmark of solar photovoltaic technology. It is not just a single advantage. It paves the way for a bunch of benefits. A benefit-generator!

In this article, we are going to discuss some key benefits of scalability embedded in the solar photovoltaic technology.  

Attracts small, medium and large investments

As we already know it, concentrating solar is still not a scalable technology. It is feasible at the utility-scale only. Simply, concentrating solar attracts utility-scale investments but is born with a stumbling block to retail and medium-sized investors. That’s why nobody is going to have a concentrating solar thermal system on his/ her rooftop. Anyway, tens of thousands of householders have already get installed solar panels on their rooftops!

Why?

Unlike concentrating solar power, solar photovoltaic is a fully scalable technology, as we discussed earlier. One can get installed a 1 kW, 3 kW or 5 kW system on his rooftop depending on his requirement. An investor having a sufficient amount of funding can even think of a utility-scale system having a capacity of 1 MW, 5 MW, 10 MW…

Simply, solar photovoltaics technology fits almost all residential, commercial, and utility-scale electricity generation projects whereas concentrating solar thermal is ill-suited to small, mini and micro-scale electricity generation.

Solar photovoltaic technology: How much scalable it is…

Let us study the following tables which compile randomly selected solar photovoltaic farms in different capacity ranges.  

Table 01: Solar photovoltaic farms with capacities of 1 GW or higher

Table 02: Solar photovoltaic farms with capacities in the range of 500 MW < 1 GW

Table 03: Solar photovoltaic farms with capacities in the range of 100 MW 500 MW

Table 04: Solar photovoltaic farms with capacities in the range of 50 MW < 100 MW

Table 05: Solar photovoltaic farms with capacities in the range of 10 MW< 50 MW

Table 06: Solar photovoltaic farms with capacities in the range of 1 MW≤ 10 MW

• Almost all the systems with capacities less than 1MW are now rooftop solar. It is almost impossible to enumerate the number of such systems due to the fact that an innumerable number of rooftop solar systems with capacities less than 1 MW has been installed worldwide. Further, solar street lighting systems that generate several Watts of power, are now more common in many countries.  To sum up, solar photovoltaic technology is fully scalable and feasible to generate a few µW or even several GW of power.

All these facts say a lot about the astonishing degree of scalability accompanied by solar photovoltaics!

Especially, millions of people have already invested in rooftop solar even though an average citizen cannot invest in a concentrating solar thermal project. This supports the simple rule: One may have enough money to have a boat but not a ship!

Distributed generation

Traditionally, electricity is generated by centralized, large-scale power plants. Most of such plants are located far away from the areas where electricity is needed and therefore, they require expensive/ massive transmission infrastructure. In addition, there is a huge energy lost in the electricity transmission in such centralized electricity generation. A distributed generation network, on the other hand, creates a golden opportunity to generate electricity where it is needed and thereby helps minimize the energy lost. Further, such network helps reduce the stress or load on the transmission lines and needs for expensive upgrades in the electricity transmission network. Norms have been changing so fast. Nowadays, instead of centralized large power plants, governments and policymakers are now enthusiastically encouraging the investors for distributed electricity generation systems. Scalability of solar photovoltaics makes it an ideal for distributed electricity generation (rooftop solar for residential and commercial buildings). So, solar photovoltaics has been in the spotlight. Various incentive mechanisms have been introduced by many countries inspiring their people to invest in distributed generation systems (especially, rooftop solar). This has been a win-win for both the country’s economy and individual electricity producers.

Power of incentives

Figure 01: Rooftop Solar Vs. utility solar in Europe (2016) [8]

Most of the European countries have introduced some overwhelmingly impressive incentives for distributed solar photovoltaic systems. The result is quite astonishing that cumulative solar photovoltaic capacity in Europe was 105 GW by 2016. Surprisingly, as much as 65% of it (68 GW) was rooftop-based solar [8]. This is an ideal example to demonstrate the role of incentives and their power in attracting public attention towards rooftop solar. And it has been an aggressive attraction, as shown in the pie chart above!

In the next article, we will see how photovoltaic technology has been competing against concentrating solar thermal technology.

References

[1] Šantić, A., & Aksamovic, A. (2018, May). Photovoltaic plants in Bosnia and Herzegovina—State and perspectives. In 2018 41st International Convention on Information and Communication Technology, Electronics and Microelectronics (MIPRO) (pp. 1501-1506). IEEE.

[2] Mendelsohn, M., Lowder, T., & Canavan, B. (2012). Utility-scale concentrating solar power and photovoltaics projects: A technology and market overview. Contract, 303, 275-3000.

[3] Najafi, G., Ghobadian, B., Mamat, R., Yusaf, T., & Azmi, W. H. (2015). Solar energy in Iran: Current state and outlook. Renewable and Sustainable Energy Reviews, 49, 931-942.

[4] Khare, V., Nema, S., & Baredar, P. (2013). Status of solar wind renewable energy in India. Renewable and Sustainable Energy Reviews, 27, 1-10.

[5]Trevisani, L., Fabbri, M., & Negrini, F. (2006). Long-term scenarios for energy and environment: Energy from the desert with very large solar plants using liquid hydrogen and superconducting technologies. Fuel processing technology, 87 (2), 157-161.

[6] Chimres, N., & Wongwises, S. (2016). Critical review of the current status of solar energy in Thailand. Renewable and Sustainable Energy Reviews, 58, 198-207.

[7] Alemán-Nava, G. S., Casiano-Flores, V. H., Cárdenas-Chávez, D. L., Díaz-Chavez, R., Scarlat, N., Mahlknecht, J., & Parra, R. (2014). Renewable energy research progress in Mexico: A review. Renewable and Sustainable Energy Reviews, 32, 140-153.

[8] Park, W. M. W. (2017). THE 44th IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE.

We need an extension to our previous discussion simply because a few pages is not enough to encapsulate the benefits of solar photovoltaics.

So…

Let’s expand our discussion to find out some other unparalleled benefits of solar photovoltaics.

Suits better for the dwindling land area availability: As we understood it in the previous discussion, solar photovoltaics are more space-efficient than concentrated solar power. That means solar photovoltaics generates a greater amount of electricity per unit area than concentrating solar systems. In this case, it is important to realize that the world’s available land area for solar energy harvesting is continuously shrinking due to the increasing demand for land that accelerated by global population growth. One day, space-efficiency would become one of the most critical factors in determining the most suitable solar energy technology pointing more and more attention to solar photovoltaics.

Multi-junction solar photovoltaics technology is the most space-efficient solar energy technology which would probably wipe out the concentrating solar systems in the future. Although this technology is still too expensive for commercial electricity generation, their cost has been falling while their efficiency is gradually being improved. Some believe that multi-junction solar cells with Fresnel lenses would become an economically viable technology in near future. This technology has already archived an incredible efficiency of 46% [1].

Flexibility: Solar photovoltaics can be installed on the ground with or without solar tracking systems. They can also be mounted on a rooftop of a house, factory, or public building where concentrating solar systems cannot be employed at all. Solar photovoltaics are also used as a power source for street lighting.

Building integrated photovoltaics (BIPV) is another new aspect in the renewable energy industry where photovoltaic modules are incorporated into building structures such as windows, facades, roofing tiles, etc. Solar car parking canopy is an ideal example for a successful BIPV application. The goal of BIPV is that they serve as a part of a building structure while generating electricity with no emission. Not only that, BIPV concept allows to access unconventional areas of a building for electricity generation. Some countries have been extensively encouraging their citizen to make use of the BIPV technology by offering additional incentives. For instance, France has introduced a feed-in tariff scheme where BIPV systems are paid up to €0.55/ kWh. Another example is Italy which pays BIPV systems €0.49/ kWh while ground-mounted systems are paid €0.34/ kWh only [2].

Scalability: Concentrating solar systems are based on thermodynamics and rely on a large amount of concentrated solar energy to archive high temperatures. Therefore, they need a large land area to collect a sufficient amount of solar radiation and concentrate. In other words, they are suitable if their capacity exceeds at least several MWs but are not at all feasible in small or residential-scales (to generate a few Kilowatts of power). Solar photovoltaics, on the other hand, fits anywhere concentrating solar does. But it is not the other way around!

Why?

It is due to the fact that solar photovoltaics technology is all scalable. They can be used to power a small calculator, a house (mW to kW) or even a large city (MW to GW).

Unlike concentrating solar, solar photovoltaic technology is a completely scalable and versatile technology!

Environmental impact: Unlike solar photovoltaics, concentrating solar technology uses hundreds of mirrors or reflectors to focus solar energy onto a small region. This creates an extremely hot region in and around the solar receiver making an injurious zone for birds flying across the area.

References

[1] Raza, A., and Ali, J. (2017). A review on carbon nanotubes based organic solar cells. Invertis Journal of Renewable Energy, 7 (4), 187-199.

[2] Celik, A. N., Muneer, T., and Clarke, P. (2009). A review of installed solar photovoltaic and thermal collector capacities in relation to solar potential for the EU-15. Renewable Energy, 34 (3), 849-856.

Advantages of solar photovoltaics over concentrating solar power  

In the previous article, we discussed advantages of concentrating solar power. This article mainly focuses on the advantages of solar photovoltaics.

Energy conversion efficiency: As we discussed in a previous article, the energy conversion efficiency in concentrated solar thermal power depends on the technology. Parabolic trough configuration is currently considered to be the most advantageous concentrating solar technology and thus is the most popular concentrating solar technology which, however, still cannot operate with an efficiency higher than 15%. The typical system efficiency is still in the range of 10-15%. When it comes to conversion efficiency, single crystalline silicon solar cells are now more efficient than ever before offering impressive conversion efficiencies ranging from 18-22%.

In particular, recent years have seen a boom in the crystalline silicon solar cell manufacturing industry which has fueled a huge competition among government and private research institutions to break the existing conversion efficiency. For example, LONGi Solar, a leading manufacturer of high-efficient crystalline solar cells/ modules has broken their own efficiency record to set a new efficiency record of 23.6% for nanocrystalline PERC (Passivated emitter rear cell) solar cells. [1]. Heterojunction back-contact (HBC) solar cells have achieved a striking efficiency of 26.6%.

High efficiency means high energy yield per unit area. So, solar photovoltaics are more space efficient than the parabolic trough systems which are the most realistic concentrating solar technology.

Space efficiency: Space efficiency is primarily determined by the energy conversion efficiency. The higher the energy conversion efficiency the greater the space efficiency of the system. It has been estimated that the parabolic trough systems require 91000 m² to generate 3855 MW h of electricity while solar photovoltaics (with single axis solar tracking) generates the same amount of electricity 62, 346 m² (during the first year) [2].

Initial investment needed per kW / Payback time:

Payback time, one of the most important aspects that attracts investors’ attention is largely determined by the overall system efficiency and the initial investment needed.

• The greater the energy conversion efficiency the shorter the payback time.
• Higher the initial investment the longer the payback time.

Following chart illustrates the capital investment needed per kW by different types of solar energy technologies. It can be seen that solar photovoltaics require less amount of capital investment compared to solar thermal tower technology (Note that the value of energy storage capacity offered by the solar thermal tower systems with energy storage is not taken into consideration in this discussion).

Thin film solar cells require the same amount of capital investment as crystalline solar cells but are less space-efficient than their crystalline counterpart (We will discuss later).

Figure: Capital cost per kW by technology (Lowest scenario) [3]

Unlike concentrating solar technology, cost of solar photovoltaics has been substantially falling in recent years while the efficiency has been steadily increasing. To illustrate, the cost of photovoltaic (per Wattage) decreased from $ 1.3 (2011) to $ 0.5 (2014) [4].

So, it is clear that solar photovoltaics offer the shortest payback time as they are more efficient than the concentrating solar power but require less amount of capital investment.

Solar photovoltaics are born with several other powerful benefits. We will discuss them in the next article.

References

[1] Rodriguez, J., Wang, E. C., Chen, N., Ho, J. W., Li, M., Buatis, J. K., and Wong, J. (2018). Towards 22% efficient screen-printed bifacial n-type silicon solar cells. Solar Energy Materials and Solar Cells, 187, 91-96.

[2] Desideri, U., Zepparelli, F., Morettini, V., and Garroni, E. (2013). Comparative analysis of concentrating solar power and photovoltaic technologies: technical and environmental evaluations. Applied energy, 102, 765-784.

[3] Lazard, N. (2017). Lazard’s Levelized Cost of Energy Analysis–Version 11.0.

[4] Kabir, E., Kumar, P., Kumar, S., Adelodun, A. A., and Kim, K. H. (2018). Solar energy: Potential and future prospects. Renewable and Sustainable Energy Reviews, 82, 894-900.

Why concentrating solar thermal power capacity has not been proliferating fast?

In the previous article, we noticed that the contribution of concentrating solar technology to the world’s energy supply was negligible though the concentrating solar was a well-matured technology.

What about solar photovoltaics technology…

Is it beating the concentrating solar technology or a loser?

First of all, let us take a look at the following table. It tells a lot about two compelling solar energy technologies.

Table 01: Cumulative capacity and growth rate of two solar energy technologies in 2014 and 2015 [1]

It is true that no commercial-scale concentrating solar power plants would have been constructed if they were not economically viable. So, the above table reveals that both technologies are economically feasible at least in certain regions. There is another important story embedded in the table. It is nothing but the huge gap between the cumulative capacities of two technologies. Further, the growth rate of concentrating solar power lags far behind the solar photovoltaic technology.

Why this?

This is largely due to the fact that solar photovoltaic technology is often more advantageous over the concentrating solar power technology and is down-to-earth.

But… How can we come to such conclusion?

Well…

There are so many technological, economic, climate, environmental, and geological factors that must be taken into consideration when we evaluate the advantages and disadvantages of concentrating solar and solar photovoltaic technologies.

Let us start our evaluation from the advantages offered by concentrating solar power.

Advantages of concentrating solar power over solar photovoltaics

Cheap energy storage: Solar photovoltaics are devices that directly convert solar energy into electricity with the help of photovoltaic effect without an intermediate state and thus essentially require an energy storage in order to supply electricity when they do not receive enough sunlight or during night time. Typically, lithium-ion or lead acid-battery systems have to be deployed as energy storage which considerably increases the investment required. Concentrating solar, on the other hand, convert solar energy into electricity with an intermediate state which is typically heat of a fluid. Heat is one of the best forms of energy to store energy in large-scale for later use. Since concentrating solar technologies always work with an intermediate state of the heat of a liquid, it is much easier to integrate them with a thermal storage system at a reasonable additional cost. Thermal storage is usually molten salt stored in tanks which retain heat efficiently to use when needed.  This ability is an added advantage often accompanied by the concentrating solar technology.

Flexibility to work with an auxiliary fossil fuel-fired heaters/ being dispatchable: A concentrating solar power plant equipped with a thermal storage can be easily connected to an auxiliary fossil fuel-powered heater. This enables the system to generate dispatchable electricity at utility-scale and guarantees its full electricity generation capacity even when the Sun is not in the sky or during the night. In particular, this type of power plants can be used either as a gas-powered peaking power plant or as a base-load power plant (just like a coal-powered or nuclear power plant).

Beneficial byproducts: Heat is an essential product created by any type of concentrating solar power plant. Therefore, thermodynamics of concentrating solar power technology relies on both heating from the Sun and a continuous cooling route. The residual heat produced in the process can be used for district heating, industrial processes (soldering, melting, etc.), even for ventilation and air conditioning.

Low CO₂ emission: It has been estimated that the amount of carbon dioxide released by concentrated solar plants (29.9 g/ kWh) is less than that of solar photovoltaics (47.9 g/ kWh). This estimation is based on the emission occurs during the entire life cycle and the complete disposal of the power plants [2].

Concentrating solar technology offers all the above-mentioned benefits. However, solar photovoltaics currently generates nearly 50 times the power produced by concentrating solar technology.

Why this?

Let us discuss in the next article.

References

[1] Kabir, E., Kumar, P., Kumar, S., Adelodun, A. A., and Kim, K. H. (2018). Solar energy: Potential and future prospects. Renewable and Sustainable Energy Reviews, 82, 894-900.

[2] Desideri, U., Zepparelli, F., Morettini, V., and Garroni, E. (2013). Comparative analysis of concentrating solar power and photovoltaic technologies: technical and environmental evaluations. Applied energy, 102, 765-784.

Today, concentrating solar and solar Photovoltaics are two proven solar energy technologies which have been successfully implemented in commercial scale to generate electricity.Both technologies are now economically and technically viable in certain regions but each technology has specific and intrinsic constraints. In this article, we are going to determine the technology which will most likely to help conquer the energy crisis in the near future. Then, we will answer the question “Which technology is the best?”

Well.

Concentrating solar or solar Photovoltaics? Which is the best?

Nowadays, this question is creating news bulletins in mainstream news sources. The answer is often controversial, biased and depends on the editor’s point of view. So, prior to drawing our conclusion, let us discuss both the pros and cons of having a concentrating solar thermal power plant and solar photovoltaics. Then we can draw an unbiased conclusion.

Several decades ago, concentrating solar power received much interest and was recognized as a potential renewable energy technology for generating clean electricity. Although it was not cost-competitive compared to conventional fossil fuels, concentrating solar power was a straightforward concept. Many believed that it could be developed to generate grid-scale electricity. And finally, it became a reality.

Several types of concentrating solar power technologies were developed as we discussed in a previous article. Their system efficiency has been continuously improving with the advancement of science and technology. In addition to the continuous improvement in the energy conversion efficiency, this technology has shown outstanding achievements and has now evolved into a commercially viable, technically feasible solar energy technology. Dozens of commercial-scale concentrating solar power plants are currently fully operational and the number of commercial plants keeps increasing with the increasing demand for electricity. The worldwide cumulative energy conversion capacity of concentrating solar thermal power was 3.4 GW, and 4.4 GW in 2013 and 2014, respectively which grew by nearly 9 % to 4.8 GW in 2015.

It is an investors’ rule of thumb that no investment is attracted by a small beer. Simply, the commercial-scale concentrating solar power plants which are currently operational clearly manifest the success of the technology.

If it was not an efficacious technology there would not be operational concentrating solar thermal power plants in the world.

How important they are…

As mentioned earlier, the cumulative capacity of concentrating solar thermal power was 4.8 GW in 2015. This is equivalent to about 10 coal-powered plants each with a capacity of 500 MW. However, this is just a derisory capacity when we compare it with the cumulative hydropower capacity which was 1064 GW in 2015 and current global power demand, 17.5 TW [1, 2].

Why concentrating solar thermal power capacity has not been proliferating fast? It is one of the most matured solar power technology, though.

What is wrong with it?

Let us discuss in the next article.

Reference

[1] Kabir, E., Kumar, P., Kumar, S., Adelodun, A. A., and Kim, K. H. (2018). Solar energy: Potential and future prospects. Renewable and Sustainable Energy Reviews, 82, 894-900.

[2] Hu, A., Levis, S., Meehl, G. A., Han, W., Washington, W. M., Oleson, K. W., and Strand, W. G. (2016). Impact of solar panels on global climate. Nature Climate Change, 6 (3), 290-294.

Image Source

[1]http://canberraaircon.com.au