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СКАЧАТЬ from this method needs very high temperature heat at 500–2000 °C which can be produced from CSP. This is a closed‐loop reaction in which only water is utilized and splits into hydrogen and oxygen and rest of the chemicals are recycled (Acar and Dincer 2014). It is a cost‐effective technology with high efficiency and apt for mass‐scale production (Wang et al. 2019). However, high cost of solar concentrators and heat transfer medium renders this technique to reach at commercial level, currently. With advances in the CSP, this process can be commercialized in future.

      2.4.1.4 Bio‐Hydrogen Production

      This is a biological way of producing hydrogen via microorganisms which are normally present in aqueous atmosphere at normal temperature and pressure conditions (Kotay and Das 2008). Last two decades have seen tremendous input at R&D level to advance various technologies needed in this process to make these methods economically viable. This process consumes bio‐wastes and offers an interesting path for their minimization along with energy generation. Energy from this process can be harnessed locally due to availability of primary resources on which microorganisms will act upon, thus making possible production of distributed hydrogen. Bio‐hydrogen generation processes have further categories, namely direct bio‐photolysis, indirect bio‐photolysis, photo fermentation, dark fermentation and bio‐catalysed electrolysis (Pareek et al. 2020). All these methods need further advances due to their poor hydrogen conversion efficiency and high cost, at present.

2.5 Challenges

      2.5.1 Efficiency

      Energy conversion efficiency of various technologies which utilize renewable energy sources is still small except hydropower (Sahli et al. 2018). Advances are taking place worldwide to increase the efficiency. Since, solar and wind sectors are expanding at much larger scale compared with other energy sources. These two are further discussed with respect to efficiency increment.

      In solar industry, scientific community is evaluating various new materials to produce electricity more efficiently. Thin‐film solar cells are cheaper in cost and flexible in nature; however, efficiency of these cells is still a matter of concern for researchers so experimental studies are carried out on the range of materials such as amorphous silicon, CdS/CdTe and CIS to overcome this barrier (El Chaar et al. 2011). To improve the efficiency of organic and polymer solar cells, use of a controlled layer of multi‐wall carbon nanotubes is also reported (Capasso et al. 2014) which improves the efficiency of these cells from 8 to 10%. DSSCs also fall in the same category of low efficiency which is again between 8 and 12%. To increase the efficiency of PV system, generated current is transferred to grid systems. This grid is either mounted on ground or built on the roof of a building so that PV system provides better efficiency as it mainly depends on the intensity of solar radiation. On an average, capacity of PV panel ranges from 10 to 60 MW. Lifetime of a well‐developed PV panel is approximately 10 years at 90% capacity, and it increases to 25 years with a 10% decrease in capacity (Devabhaktuni et al. 2013).

      A major challenge in CPV system is reduction in efficiency of PV due to increase in temperature while concentrating light as conversion efficiency of CPV is still small. Remaining solar radiation gets converted into thermal energy which raises the temperature of junction in the cell, thereby decreasing efficiency. Lifetime of PV also decreases due to increase in temperature. This leads to overall degradation in performance of PV system (Pandey et al. 2016). So, more studies are required to explore ways to decrease temperature of the CPV system.

In wind energy sector, replacement of components of wind turbine system with latest components having cost‐effective technology will increase the efficiency of the existing wind farm. In addition to this, repowering of onshore wind assets can enhance operating lifetime of the current wind project. Repowering can be either full or it can be partial.

      2.5.2 Large‐Scale Production

      Large‐scale production of solar PV systems is at infant stage due to low efficiency and high cost. Government is supporting these installations to promote renewable energy sources. Technically solar PV systems are viable but not economical. So, this area needs more R&D and innovative methods to increase the production at large scale.

      One of the major challenges in deployment of offshore wind energy at a large scale is its high cost of installations and maintenance. With the latest technology developments in the field of manufacturing, installations and operations, its cost has significantly decreased. By 2050, cost of offshore wind energy is expected to decrease by a large factor, and it can directly compete with electricity generation using fossil fuels (IRENA 2019d). So, this challenge could be tackled by the wind industry based on the advanced technologies developed by scientific research community.

      Other than solar and wind sector, all alternative sources of energy technologies are not economically viable compared with conventional sources of energy. Thus, large‐scale production in these sectors needs more advances in technology from cost and production viewpoint.

Figure 2.6 Worldwide, LCOE from the alternative energy sources for the period 2010–2017.

      Source: https://www.irena.org/Statistics © IRENA.

      Note2: Dashed line represents the global weighted average LCOE and band shows the fossil‐fuel‐fired electricity generation cost range.

      2.5.3 Cost‐Effective Production

Globally, levelized cost of electricity (LCOE) from solar and wind energy is decreased by a large factor from 2010 to 2017 as depicted in Figure 2.6. Electricity production from other energy sources has not realized any major change. In fact, global weighted average LCOE as represented by the dashed line in Figure 2.6 has increased for geothermal and hydropower while for biomass it remains the same for the period from 2010 to 2017.

      Onshore and offshore wind technologies are competitive to fossil fuels and in some regions, LCOE from wind energy is less than that from fossil fuels. Electricity production cost from PV is also approaching the cost from fossil fuels. Cost of crystalline PV has reduced by 99.5% in the last 30 years due to tremendous research in PV industry with the development of novel materials and techniques (www.economist.com). As reported by (IRENA 2019a), the global weighted average total installation cost for offshore wind projects will decline in the near future, and it will be USD 1700–3200/kW by 2030 and USD 1400–2800/kW by 2050.

      Electricity generation using hydro technology is the most cost‐effective and preferred over the other renewable energy sources method where available. Using gravity water wheel instead of Kaplan turbines in small‐scale hydro plants reduces the cost as the former cost is 33–60% of the latter (Quaranta and Revelli 2018). Further, usage of PATs also decreases the installation cost which leads to overall reduction in electricity generation cost from the small hydro plants as well.

      Cost of power generation using geothermal energy largely depends on the site. Normally, cost of geothermal plant lies between USD 1870 and 5050 per kW. Compared with direct dry steam and flash plants, the cost of binary plant is high. СКАЧАТЬ