Mono vs Poly – An introspective simulation study! – Part 2

25th Jul 19  

The first part of the article "Mono vs Poly – An introspective simulation study!” introduced the types of crystalline technology, the need for this study, the methodology we followed and detailed discussion of 4 climatic zones. This part would educate its readers on the results of the remaining two climactic zones. Further, it would also present a financial analysis of both the plants and the conclusions from the study.


Figure 1 : Division of climatic zones in India (Source: IIT Bombay)

Cold & cloudy climatic zone

Power plant based on fixed area

The climatic zones discussed in our previous article i.e. hot & dry, warm & humid, composite & moderate were relatively warmer with moderate to heavy rains. Few zones had extreme weather conditions which resulted in higher generation during winters and lower generation in summers. The remaining two climatic zones which are discussed in this article are relatively cooler (throughout the year). Found mostly in Northern and few North-Eastern (refer Figure 1) regions of India, cold & cloudy climatic zone could be significantly identified by cool summers and extreme winters with a cloud cover throughout the year. Despite such cool climate close to the ambient operating temperatures of solar module, mono crystalline technology is found to perform better under both fixed area and fixed power conditions. Considering the case of fixed area first, poly crystalline module loses 6.25% higher energy than the mono crystalline technology based power plants.Overall an energy boost of around 17.25% in summer can be realized while utilizing mono technology.Performance Ratio (PR) of a mono based power plant is found to 87.10%, which is 3.07% more than that of poly based plants.Energy injected into the grid by mono based plant is deemed to be 17.34% or 41.3 MWh higher (refer Figure 2) which directly enhances the plant’s financial returns.


Figure 2 : Energy generation in cold & cloudy climatic zone – power plant based on fixed area

Power plant based on fixed capacity

Considering the case of a power plant under fixed area, a power plant in cold & cloudy zone is expected to perform best during winters owing to reduced temperatures. Both the power plant on an average generate from 14.59 to 14.70% more in winters compared to summers. However when comparing both the plants, it was found that mono based power plant annually generates 8.8 MWh more. Further an annual boost of 0.50% is realized while utilizing mono crystalline technology over poly crystalline technology. The difference in temperature losses follows a similar pattern to the generation curve i.e. the difference is lower during and around monsoon season (average of 519 units) and higher during other months (average of 628 units). A total savings in temperature losses of 7 MWh was realized in power plants utilizing mono crystalline modules (refer Figure 3).


Figure 3 :  Energy generation in cold & cloudy climatic zone – power plant based on fixed capacity

Cold & Sunny climatic zone

Power plant based on fixed area

Deemed to be the ideal region for installing a solar power plant, cold and sunny zone are found at specific location in Northern India (around Leh) & the Aravalli range in Western India. They are identified with pleasant summers and extreme winters with fairly clear sky throughout the year. While plants at other location performed better during winters, the plant installed at cold & sunny location was found to be maximum in summers and monsoons due to its clear weather. In winters however, the reduced irradiance coupled with the cloud in the region results in the drastic reduction in the energy output (as high as 32%). Comparing the results for fixed area, we find that the overall generation utilizing mono crystalline module is 48 MWh more than poly crystalline module. Further the temperature loss in a mono crystalline plant stays at 13.85 kWh/kWp, which is 0.79 kWh/kWp less compared to that in a poly crystalline based plant. The PR gain by utilizing mono crystalline module is 3.10% more than that of poly crystalline module.


Figure 4: Energy generation in cold & sunny zone– power plant based on fixed area

Power plant based on fixed capacity

Comparing the results of fixed power plant, the difference in the energy pushed to the grid by a mono based power plant is 0.57% or 9.8 MWh more than the poly crystalline plant. Further, an approximate of 8.32% in winters and an overall average of 5.86% of energy could be saved from temperature losses if mono crystalline modules are utilized. The power plant during summers experiences a boost in PR up to 0.52% while an overall boost of 0.45% is expected. Overall, a boost in specific energy yield of 0.03 kWp/kWh could be obtained by utilizing mono crystalline module.


Figure 5: Energy generation in cold & sunny climatic zone – power plant based on fixed capacity

Financial analysis

With the energy sources around the world constantly increasing, it is important for a source to be commercially viable and give back good returns to ensure its widespread uptake. In such situations, only proving a source’s technical superiority may just not be enough. An in-depth financial analysis and its gains need to be identified in detail. The initial cost break up of a solar power plant is well known and is well represented by various bodies. In such break up, the solar modules constitute more than 50% of the cost, whereas the BoS accounts for around 35% of the cost. The civil works and other costs constitute merely 13% of the cost. While the number stands true, the comparison between mono and poly crystalline technology paints a different picture.

The study presented two different scenarios; the financial analysis however is calculated on per MW basis to fairly evaluate the technology. Firstly, the fact that the initial cost of mono crystalline technology is more cannot be argued upon. This leads to a sharp increase in the module’s initial price i.e. ~21% higher than poly crystalline technology. However, now with the changing dynamics in the PV market of the world and with the world demanding higher energy from the same module size, the prices of mono crystalline PV modules are deemed to fall down drastically. It is an already known fact that mono crystalline module (of similar sizes) are usually at 1~2% higher efficient than the poly crystalline modules. This efficiency advantage leads to a direct 12% reduction in number of solar modules required per MW of power plant when utilizing mono crystalline technology. Further, considering a standard double racking design in a power plant, the cost savings in module mounting structure installed in a mono crystalline modules is 0.25% (when compared to a poly crystalline module based plant). Considering the land requirement, significant savings could be clearly realized in a mono crystalline based power plant. Considering central inverter in both the cases, we find that a mono based power plant could use 31% less land (and hence 31% less cost) compared to poly crystalline module based plant.

While designing a power plant, adequate care needs to be taken to ensure that the electrical losses are minimal and/or within the tolerance limits. One of the easiest yet important parameter to optimize is the DC voltage drop in cables. The drop depends primarily on the internal resistance of the cable which is further governed by the length and the cross sectional area of the cable. With an increase in number of modules to be utilized in a poly crystalline technology based power plant, the length of the cable increases which directly increases the internal resistance of the wire. In order to mitigate such losses, the cross sectional area of the cable needs to be increases. Both increase in length and area acts as a double whammy increasing the cabling cost of module by around 10.50% when compared to mono crystalline based power plant. Operation & maintenance (O&M) plays a significant role in any power plant if it is to run smoothly and perform as expected. Considering the case of a solar power plant, as a rule of thumb O&M cost is considered only to be around 1% annually of the plant’s total cost. However with the need to clean & maintain more modules, AJB’s and other DC spares in a poly crystalline based power plant its cost raises significantly. It was found that in a mono crystalline based power plant, a savings in O&M cost to the tune of 38% could be realized (refer Figure 6).


Figure 6 : Difference in investments incurred per MW during the life time of the power plant
With both the incurred cost and energy generated in the favour of mono crystalline technology, it should be clear by now that mono crystalline technology which looks expensive, is actually profitable in the longer run. For the purpose of study, savings across each and every climatic zone was calculated. Hot & dry zone which is expected to have enhanced savings due to temperature loss is expected to realize 9.54% of savings by utilizing mono crystalline technology. Followed to this is the moderate climatic zone at 9.49% which due to lower ambient temperatures (around the year) are expected to generate adequate energy. This is followed by composite zone at 9.37% and warm & humid zone at 9.12% which due to higher ambient temperatures experience modest savingsin the northern and few north eastern parts of India, the savings for both cold & sunny and cold & cloudy are around 9%, which could again be attributed to lower ambient temperatures.


Figure 7: Savings realized while utilizing mono crystalline technology over the plant lifetime

Conclusion

Mono crystalline versus poly crystalline has been one of the hot topics of discussion amongst various stakeholders at different platforms. While there has been lot of information available on the matter, a complete guide seems always missing. Further with the clear trends of the PV market tilting towards mono crystalline technology, the adoptability of PV modules in the Indian market is still primarily based on cost. It was hence necessary to evaluate the technology fully till its end of life and further carry out both technical and commercial analysis for a clear understanding. The following were the results obtained from the study (refer Table 1&Table 2  for details):

  • Utilizing mono crystalline module enable efficient utilization of land by generating 41 MWh to 52 MWh more per fixed area (1000m2). This further converts to 8 MWh/MWp to 14 MWh/MWp more energy injected into the grid annually.
  • A boost in performance ratio (PR) of 3.0% (average) is found when utilizing mono crystalline technology in power plant with limited area availability. Utilizing the power plant with fixed capacity, mono crystalline technology was able to deliver a PR boost from 0.40 to 0.80%
  • Mono crystalline technology hasa better performance at location with enhanced ambient temperatures and hence acts as a perfect match for countries like India which lie between the tropics.
  • Utilizing mono crystalline modules would enable savings in total investment over the plant’s life time to the tune of 8.94% to 9.54% annually.
  • Implementing mono crystalline module to have ROI reduced between 0.5~2 years considering economies of scale

Table 1 : Advantages realized when utilizing mono crystalline technology - Power plant based on fixed area

Table 2 : Advantages realized when utilizing mono crystalline technology - Power plant based on fixed capacity

Let us all pledge to make solar energy the primary source of energy in the near future.
RAHE ROSHAN HAMARA NATION