Month: March 2019

Every day, our Sun reports for its duty conscientiously. It rises in the East and wake us up from the bed. It works for about 12 hours a day and then sets in the West reminding us to find the bed and sleep in the night. This has been its daily routine for billions of years.

What if the Sun did not rise?

Hmmm!

It is a thought-provoking question. Isn’t it?

We would not have an extraordinary experience on the very first night even if the Sun didn’t rise. But how would we feel the daytime on the following day? It would be the very first daytime buried in the dark. Owls will be so busy with the order of the day, shouting all day long.

Hereafter…

There would be no luminous daytime. Only dark nights and dark days.

We would witness no evaporation, no winds, no waves, no cyclones, no rains …

What else would happen?

Yes. A lot of things…

Plants will stop producing food and they will no longer bear fruits. This will lead to a famine and mass extinction. No doubt. The final result will be a dead planet with no living beings.

We all are indebted to our Sun for what it has been doing. The chronicle about life on the Earth totally relies on the unrivaled service of the Sun. It illuminates our planet and helps our eyes view the world around us. Not only that our Sun is what keeps our planet worm making it an inhabitable place. Feeding numerous energy-consuming processes like photosynthesis, it plays a vital role on the Earth. Maybe that’s what our ancestors motivated to worship the sun god or solar deity. Today, our Sun has been assigned an additional but important job: To generate electricity with the help of solar PVs.

Nothing to explain. We have no access to the free service of Sun during the night. Just like you, solar PVs stop working and go to sleep in the night.

Dark side of solar PV technology

The glorious side of solar PVs is well known and not needed to magnify. To illustrate, the contribution of solar electricity to the German electricity supply was 0.3% and 6.6% in 2007 and 2017, respectively [1]. In other words, German cumulative solar PV capacity was 42 GW in 2017 [2]. It is enough to shut down as many as 84 coal-fired power plants each with 500 MW of capacity. This mind-blowing development manifests the power of solar PVs and encouraging other nations to replace coal, oil and gas with solar.

Today, almost all the nations are engaging in a constructive dialogue to solve the energy crisis, and detrimental consequences of climate change, and environmental pollution. Governments are belligerently encouraging the utility customers and private companies introducing various incentives and rebates, to invest in solar PVs. We have never seen such keenness before. Unfortunately, solar PV technology is still discriminated by some opponents. They highlight some technical challenges in solar PV technology and speak well of fossil fuels.

Nothing to argue. Like in any other technology, solar PV technology is confronted with some technical difficulties. The biggest challenge is that solar PVs cannot generate enough power under cloudy skies. And they cannot generate electricity during the night at all. This is the saddest side of solar PVs.

These challenges pose a serious question…

How do we meet the electricity demand with solar PVs after the sunset?

Well…

Today, we are heading straight for a 100% renewable energy or at least vow to replace fossil fuels with renewables. And solar PV is the best way to exploit energy from sunlight. In order to achieve our solar goals, we want our solar PVs to supply electricity even in the night and also under cloudy skies. This requires our Sun to reverse its old-fashioned journey and emerge in the West shinning in the night sky. But this will never happen!

What if we could mount a shining star in the sky to turn the darkness in the night away from us?

Yes. Pumped hydro is such an amazing idea which is not a star but still can act as a virtual Sun in the night sky!

The idea is straightforward. Following are some basic facts that highlight the need for energy storage in achieving our renewable energy targets.

• Current global power demand is approximately 17.5 TW [3].
• The amount of technically/ economically viable solar power is estimated at about 580 TW [4]. This is nearly 33 times the global power demand.
• Solar PVs can play a vital role in achieving our sustainable goals. They are truly capable of generating more electricity than the current electricity demand during the daytime.
• When the generation exceeds the demand, the excess amount must be stored so that it could be released to meet the demand during the night.

Grid energy storage

Grid energy storage becomes an essential component when we are extensively dealing with solar electricity as solar PVs are unable to power your home in the night. Various energy storage technologies have been developed such as batteries (Li-ion, NaS, lead acid,), flywheel, superconducting magnetic energy storage (SMES), compressed air, and pumped hydro. However, neither flywheel nor SMES has shown to be appropriate for large-scale energy storage. Batteries are already being used even in MW-scale but are expensive.

While both compressed air and pumped hydro are being used in grid energy storage, pumped hydro has shown to be the best grid energy storage technology. It is a cost-effective, technology and can come online very quickly to respond to the variation in supply-demand. Once built, pumped hydro plants can serve for decades. Therefore, pumped hydro has become the most popular grid energy storage technology.

How do pumped hydro plants work? Let us explore more about this topic in the next article.

Reference

[1] Smolen, J., & Dudic, B. (2018). Electricity Price and Demand Pattern Changes Due to Increases in Solar Generation in German Electricity Markets. International Journal of Energy Economics and Policy, 9 (1), 168-173.

[2] Feldman, D. J., Margolis, R. M., & Hoskins, J. (2018). Q4 2017/Q1 2018 Solar Industry Update (No. NREL/PR-6A20-71493). National Renewable Energy Lab. (NREL), Golden, CO (United States).

[3] 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.

[4] Jacobson, M. Z., and Delucchi, M. A. (2009). A path to sustainable energy by 2030. Scientific American, 301 (5), 58-65.

Ctd

In the previous article, we discussed two decisive factors that should be taken into consideration when we are buying a solar PV system. Let’s continue our discussion. Which is the best PV technology?

We may have to evaluate dozens of factors prior to making a decision, but having said that, capital cost is of paramount importance as no significant difference in the performance or lifespan between two PV technologies could be observed.

What does it mean?

Ten to one the cheapest product may be the most preferred in a typical case where all other factors have been shown to have a minor impact on the final decision you are going to make!

So, what is the cheapest panel type?

Initial cost needed: pc-Si PVs are cheaper than s-Si PVs

The Czochralski process which is used to produce s-Si results in a huge amount of waste silicon. Further, the manufacturing process of s-Si solar PVs involves a number of complicated, energy-intensive steps. Unlike the s-Si PV manufacturing process, the process used to fabricate pc-Si PV is relatively straightforward and less energy intensive. And it generates less amount of waste silicon. So, pc-Si PVs are involuntarily cheaper than s-Si PVs even though we want s-Si PVs to be the cheapest as they are the most efficient.

Appearance: pc-Si solar PVs are less aesthetically pleasing than s-Si PVs

pc-Si solar PVs have a speckled blue color  and an irregular look. As such, they are less aesthetically pleasing than mono crystalline silicon and thin film solar PVs. Some people, indeed, hate their miserable look whilst some others do not concern on it at all. s-Si solar PVs, on the other hand, appear black in color and have a regular, aesthetically pleasing look.

Which technology fits my solar energy plan?

This explanation is just to have a simple idea about how to choose the best panel type. First, let’s take a look at the following table. It summarizes what we discussed above.

Table 01: Key upsides and downsides of s-Si and pc-Si solar PV technologies

Relatively speaking, s-Si solar panels tend to be more efficient at converting solar energy into electricity and as such, they require less amount of space. Not only that s-Si solar panels do not annoy your eyes or mind though pc-Si solar panels are quite aesthetically unpleasant. However, the dark side of s-Si solar panels is that they are expensive than the pc-Si rivals. This is what is hindering the growth of s-Si solar PV market share and what is behind the large market share of pc-Si solar PVs. The cheaper pc-Si PV technology allows us to install more panels than s-Si panels for the same investment. This nicely outweighs the main drawback of pc-Si solar panels: Being less efficient than s-Si solar panels.

Making the final decision

Now we have a rough idea of how to choose the best solar panel type. Taking all above-discussed facts into consideration, we can make followings general recommendations.

• Monocrystalline solar panels are expensive but more efficient and require less amount of space. Therefore, they are suitable for a location where available space is limited.
• If you have a large rooftop it would be wise to adopt the cheapest solution: pc-Si solar technology. It is, of course, less efficient and takes up more space. But it seems to be the most favorable PV technology for a location where space availability is not a serious challenge.
• If you are investing in a utility-scale solar PV project, your key concerns would be achieving a higher return on your investment and shorter payback time. Appearance of the solar panels is not a big issue since the ultimate goal of such investment has nothing to do with what your solar panels look like. Simply, the cheaper pc-Si solar panels would be the best choice.
• In a case where you have a large rooftop (Fits for pc-Si solar panels) but still worry about the visual look of the rooftop, then s-Si solar panels would automatically be your handpicked choice. But you should be able to afford them.
• If unpleasant look is the only concern, it would not be wise to choose expensive single crystalline solar panels. Think thrice and move forward with your plan. Anyway, it depends on your personal taste.

Keep in mind!

Before we come to the final decision, we need to weigh the impact of each key factor and some features pertaining to two PV technologies. In addition, your specific requirements must be given a hearing and the site needs to be inspected by an expert in the field. But these facts should not keep you up in the night. Ask your installer for technical assistance and site-inspection. They are always ready to help you find the best choice for you.

Are you thinking of buying a solar PV system? If so, you may have several factors that need to be taken into account. Needless to say, we would be in a dilemma whenever we have two or more options. So, you might also be in a dilemma over how to decide the right tech as we have two commercially viable crystalline PV technologies: s-Si and pc-Si. It is not prudent to make an immediate decision and go forward. All your personal requirements must be evaluated and your site needs to be inspected by an expert. Further, any prerequisite pertaining to your site has to be identified by a PV expert. This article is to help you evaluate some crucial variables you would find when choosing the best crystalline PV technology for your particular requirement.

Let’s start this discussion with the upsides and downsides of both technologies and then we will see how to make a wise decision.

Efficiency: s-Si solar PVs are more efficient than pc-Si PVs

Take a look at the table below. You can see that s-Si PV is the oldest version of commercial PV technology.

Table 01: Technological maturity of different PV technologies [1]

s-Si PV technology is almost three decades elder than pc-Si PV technology. As the most matured PV technology, s-Si solar PV technology has reached a technological zenith approaching its maximum obtainable efficiency limit [2]. And we know, people have enjoyed long-lasting, superior performance of s-Si PVs during the past. Besides the technological maturity, single crystalline silicon appears to be an is an intrinsically ideal material for making efficient solar PVs.

Why?

In s-Si solar cells, electrons feel less resistance to move within the cell as each s-Si solar cell is made of single crystals. Less resistance means more efficient!

Electrons in pc-Si solar cells, on the other hand, experience less freedom to move since each pc-Si solar cell consists of many crystals. Less freedom for electrons means high resistance and thus less-efficient! So, pc-Si solar cells are less efficient than their single crystalline counterparts as we can observe in table 2.

Table 2: Performance of commercial solar PV technologies [3]

To illustrate above point, a study carried out by LONGi Green Energy Technology (formerly Xi’an LONGi Silicon Materials Corporation) has shown that monocrystalline solar power plants yield 5%-7% more power output than their polycrystalline silicon counterparts under the same conditions [4].

Space-efficiency: s-Si solar PVs are more space-efficient than pc-Si PVs

s-Si solar cells require less space than the space required by pc-Si solar PVs to generate the same electrical power since s-Si solar PVs are more efficient at converting sunlight into electricity. Take a look at table 2. You can realize how space-efficient s-Si solar PVs are. As shown in the table, s-Si solar panels require merely 7 m2 of area per kW whereas 8 m2 of area is needed for pc-Si solar panels per kW.

If you have limited space, it would probably be wise to come down in favor of s-Si solar PVs.

Reference

[1] Lacerda, J. S., & van den Bergh, J. C. (2016). Diversity in solar photovoltaic energy: Implications for innovation and policy. Renewable and Sustainable Energy Reviews, 54, 331-340.

[2] Geisthardt, R. M., Topič, M., & Sites, J. R. (2015). Status and potential of CdTe solar-cell efficiency. IEEE Journal of photovoltaics, 5(4), 1217-1221.

[3] Islam MR, Rahman F, Xu W (2016) Introduction, advances in solar photovoltaic power plant. Springer-Verlag, Berlin Heidelberg, pp 1–6

[4] Deng, H., Fu, N., Liu, P., Wu, G., Wang, F., Luo, C., & Deng, L. (2015, March). High-performance monocrystalline silicon could lead the photovoltaic power generation in the future. In Semiconductor Technology International Conference (CSTIC), 2015 China (pp. 1-3). IEEE.

Ctd

Solar PV is an ever-evolving, ever-changing technology where researchers keep improving the light-harvesting efficiency. Researchers have also been developing new species of solar PV with the intention of making more cost-effective, environmental benign solar PVs. Hundreds of different solar PV technologies have already been developed. However, only crystalline silicon (single crystalline and polycrystalline) and thin-film solar PV (CdTe, CIGS, a-Si) technologies meet the requirements needed for cost-effective, terrestrial-based electricity generation.

Crystalline silicon solar cells are incredibly long-lasting, cost-effective, environmentally friendly and reasonably efficient. So, crystalline silicon solar PV has become the most-demanding, highly remunerative PV technology with a market share of more than 90% [1]. While both s-Si and pc-Si solar panels are increasingly being manufactured, shipped and installed, they are competing with each other to protect and defend their place from the others in the fast-expanding PV market. Following pie charts clearly illustrates how these two technologies performed in the PV market in 2014 and 2007.

Figure 01: Market share by different PV technologies in 2007 [2]

Figure 02: Market share by different PV technologies in 2014 [3]

The cumulative contribution of solar PV to global electricity generation increased to 0.9% in 2014 [3]. As can be seen in the above pie charts, both s-Si and pc-Si silicon PV technologies have been able to keep their market share nearly unchanged. However, the market share of a-Si solar PVs has shrunk from 4% to 2% whilst the market share of CIGS solar PVs has doubled from 1% to 2%. Further, the market share of CdTe solar PVs has narrowed down from 6% to 5% as a result of improving efficiency and the falling price of crystalline silicon PVs which led to an extensive demand for crystalline silicon PVs in the market.

Now let’s take a look at figure 03. It illustrates trends in the market share by PV technology in detail, observed from 1990 to 2013. Interestingly, ribbon-Si PV technology has been experiencing the worst trend. Its market share has been fluctuating and has almost vanished by 2012. Market share of s-Si PVs reached a low in 1997 and then gradually increased until 2000 to reach a peak. After 2000, the market share of pc-Si solar PVs has been expanding and outperforming all of its rivals.

Figure 03: Market share by different PV technologies from 1990 to 2013 [4]

s-Si solar PVs are more efficient than their pc-Si counterparts. But efficiency is just one factor one should give thought to before choosing a solar PV system. Capital cost, return on investment (ROI) and payback time, etc. are also crucial factors that we must take into account. Price of pc-Si solar PVs has declined sharply during the recent past, especially as a result of the immense Chinese contribution to the solar PV industry. Meanwhile, the efficiency of pc-Si solar PVs has been brought into an acceptable level making pc-Si solar PVs the most cost-effective, most dominant technology in the solar PV industry.

Reference

[1] Lunardi, M. M., Alvarez-Gaitan, J. P., Bilbao, J. I., & Corkish, R. (2018). A Review of Recycling Processes for Photovoltaic Modules. In Solar Panels and Photovoltaic Materials. IntechOpen.

[2] Tao, M. (2008). Inorganic photovoltaic solar cells: silicon and beyond. The Electrochemical Society Interface, 17(4), 30-35.

[3] Ramanujam, J., Verma, A., González-Díaz, B., Guerrero-Lemus, R., del Canizo, C., Garcia-Tabares, E. & Rath, J. (2016). Inorganic photovoltaics–planar and nanostructured devices. Progress in Materials Science, 82, 294-404.

[4] By Own work. – Fraunhofer ISE, Report, current editiondata from archived edition, July 28, 2014, page 18, Public Domain, https://commons.wikimedia.org/w/index.php?curid=35756530