By Khushboo Goyal
The wind and solar power markets are growing at unprecedented rates in the wake of competitive bidding. The growing customer demand for cheaper and more efficient products has led to several advancements and innovations in this industry. Most of the research and development (R&D) activities have been focused on improving the manufacturing process and reducing production costs to drive down costs. Significant efforts are also on to improve efficiencies and enhance performance, and hence achieve lower life cycle costs.
Renewable Watch highlights the key solar and wind power technology trends in the past year…
The increasingly low tariffs discovered in recent mega solar power auctions have led to a demand for not only cheaper solar modules but also balance of system (BoS) components such as inverters and cables. An equal focus on efficiency enhancement has created a need for new technologies that could ensure a lower levellised cost of energy.
Monocrystalline technology gains ground: The primary reason for the preference for polycrystalline modules had been their cheaper cost as compared with monocrystalline modules, despite the latter’s higher efficiency. However, the continuous decrease in the wafer thickness of monocrystalline modules has led to lower material costs, without compromising on module efficiency. According to European research organisation Fraunhofer-Gesellschaft, monocrystalline modules have reported efficiencies of about 24.4 per cent, against 19.9 per cent in case of polycrystalline modules. With manufacturing processes becoming more efficient and the technology becoming more competitive, the preference for monocrystalline technology has increased significantly.
Adoption of bifacial technology: Bifacial solar modules that capture sunlight from both sides of the panel have emerged as a technology of preference. These modules deliver almost 50 per cent more power output than conventional monofacial modules, according to the US-based Electric Power Research Institute. Earlier, their uptake was limited by their higher costs. However, better energy generation combined with greater system efficiencies and hence, lesser capital and operational costs have led to an increase in bifacial module deployment. Further, various production processes aimed at lower manufacturing costs are being developed, resulting in different bifacial cell architectures such as BiSoN, ZEBRA and PANDA.
Greater focus on R&D for enhanced module efficiency: R&D is currently focused on improving the conventional silicon solar cells. To this end, high efficiency passivated emitter rear contact (PERC) cells, passivated emitter rear locally diffused (PERL) cells, passivated emitter rear totally diffused (PERT) cells and heterojunction technology (HT) are being enhanced to make them bifacial. New-generation perovskite solar cells that entail relatively low production costs are also being improved upon for greater efficiencies.
Module-level power electronics (MLPE): Power optimisers are being increasingly integrated with string inverters at the module level, one at each solar panel. This mitigates the shading effect to some extent by conditioning power before sending it to the string inverter, thereby improving the performance of the solar plant. Microinverters are being used in the residential and commercial segments to convert DC power to AC power at the module level, without the need for an additional string inverter. Smart modules (modules integrated with power optimisers) and AC modules (modules integrated with microinverters) are being used to reduce installation time and costs.
Hybridisation in inverters: Battery-based inverters to manage solar PV intermittencies and provide power backup are gaining traction. These can work in grid-connected, off-grid as well as stand-alone modes owing to their inherent ability of being able to run on both battery and electricity. Smart hybrid inverters are being increasingly used to automatically switch between different power sources and bring in more flexibility. Recent design innovations are aimed at cost optimisation of solar plants by integrating solar trackers with inverters and other BoS components.
Enhanced inverter capacities: In line with the global trend, Indian developers are increasingly favouring 1,500 V DC inverters over 1,000 V inverters. Higher voltage improves DC output, necessitating shorter wires and fewer inverters, which help in reducing the overall BoS cost.
Efficient monitoring in inverters: String-level monitoring systems, cloud-based systems, and consistent I-V curve monitoring systems are being increasingly deployed to reduce maintenance costs and achieve higher yields. This helps in increasing inverter and plant efficiency, leading to a lower LCoE.
Thicker coatings for mounting structures: The thickness of the coating (whether GI coating or GL coating) on mounting structures determines the level of protection provided against environmental conditions. Hence, to reduce corrosion and bring down life cycle costs, advancements are being made to increase the coating thickness.
Solar power cables: Both copper and aluminium are commonly used as conductor materials in solar installations. Although slightly more expensive, copper is a better conductor as it carries more current and does not lose its strength during bending. For insulation, electron beam, cross-linked polymers that do not melt even at high temperatures are gaining ground. Another upcoming trend is that of using solar hangers or hooks to hold the cables in the air, an upgrade over the costly and time-consuming procedure of burying power cables in a restrictive underground conduit. Pre-connectorised cable solutions are also increasingly being deployed to save time and ensure reliability.
With the increasing demand for clean energy, even the mature wind power segment is witnessing a technological transformation. The need for higher turbine capacities and greater power efficiencies is driving significant changes in the major components of wind turbines. The main design drivers for wind turbine technology are wind speeds at project sites, grid compatibility, aerodynamic performance, acoustic performance, visual impact and offshore considerations. This has led to increasing hub heights, longer blade lengths and larger rotor diameters, and enhanced drivetrain technology to effectively handle larger wind turbine capacities.
Larger wind turbines: The average size of wind turbine generators (WTGs) has increased over the years due to a growing demand for larger WTGs with higher capacities and longer blades. This has led to the phasing out of smaller turbines to make way for WTGs with capacities of over 2 MW, which are more suited for low wind sites in India. Some manufacturers are also testing their 3 MW-plus WTG prototypes. Larger turbines generate more energy and compensate for the higher balance of plant cost, thus minimising the cost of energy. Larger WTGs reduce the total number of turbines required at a wind farm and hence decrease the operations and maintenance cost during the project life.
Manufacturers are constantly working on increasing the rotor diameter and tower height of their wind turbines for higher efficiency. Even though these installations require a larger area, tower heights for nearly all recently launched models have been increased.
Improved drivetrains and motors: Drivetrains convert the kinetic energy of wind into electrical energy and are hence, a key component of a WTG. A drivetrain comprises components such as the bedding, gearboxes, brakes and a generator. The gearbox is responsible for enhancing the rotational speed of the blades, and is one of the most expensive parts of a WTG.
The moving parts of a drivetrain suffer a significant amount of wear and tear, which can have a considerable impact on the performance of the WTG. Hence, a lot of R&D is concentrated on improving the efficiency of this component so as to handle larger capacity turbines. Improvement in permanent magnet synchronous generators by reducing the content of rare earth metals in permanent magnets is expected to drive down capex, making them ideal for larger turbines. Superconductor-based generators, which can lead to significant weight and cost savings, while also reducing resistance losses, are also being developed. However, most of the demand for drives and motors in India is fulfilled through imports and hence the industry is at present focusing on improving domestic manufacturing capabilities.
Other focus areas: A lot of research is being done to improve the performance and reliability of blades. These design innovations are focused on increasing the energy capture capability of blades. For instance, gently curved tips have been designed to take maximum advantage of all wind speeds. Various kinds of aerial wind turbine designs are being explored and developed to make use of higher wind speeds at greater heights. Manufacturers are also developing bladeless wind turbines, which significantly reduce the manufacturing costs of WTGs and are also expected to be safer for birds.
India is gradually moving towards achieving its 175 GW renewable energy target by 2022, primarily through solar and wind power additions. The entry of a large number of international players and manufacturers will bring in more technology innovations focused on efficiency improvements, to lower the delivered cost of energy. It is expected that going forward, the slightly higher prices of these technologies will be offset by increased generation over the project lifetime.