Technology Tracker

Advancements in the solar and wind power segments

Of late, the solar segment has shifted from being a subsidy-driven model to a competitive bidding one. The market has matured and is witnessing aggressive bidding for capacity by developers. It is resulting in the discovery of lower tariffs. This has made way for cheaper solar components, higher capacity inverters with better monitoring systems, module-level power electronics (MLPE) that enable greater synergies and hybrid inverters, etc. Meanwhile, in the wind segment, the need for higher turbine capacities and greater power efficiencies is driving significant changes in major turbine components. The main design drivers for wind turbine technology are suitable wind speeds at project sites, grid compatibility, aerodynamic performance, acoustic performance, visual impact and an impetus to offshore wind energy. This has led to an increase in hub heights, longer blade lengths, larger rotor diameters, and improvements in drivetrain technology for effectively handling larger wind turbine capacities. A look at the key technology trends shaping the solar and wind power segments…

Solar

Monocrystalline technology: The solar revolution began with thin-film technology; however, over the years, crystalline-silicon (monocrystalline and polycrystalline) increased its market share to become the most popular form of solar photovoltaic (PV) technology. While initially polycrystalline had an edge, monocrystalline has gained considerable share due to its higher efficiency (it is 2 per cent more efficient than polycrystalline and thin-film technologies) and higher average power output of 4-8 per cent. Earlier, polycrystalline was the preferred option because it could be combined with multilayered solar cells. It was useful for distributed solar PV systems and it cost less as compared with monocrystalline modules. However, the continuous decrease in the wafer thickness of monocrystalline modules has reduced material costs, without compromising on module efficiency, thus increasing the utilisation of monocrystalline modules.

Bifacial technology: Bifacial solar modules that capture sunlight from both sides of the panel have emerged as a technology of preference globally. 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 due to higher costs. However, better energy generation combined with greater system efficiencies has reduced the capital and operational costs, leading to an increase in bifacial module deployment. Further, various production processes are being developed to bring down manufacturing costs; these efforts are resulting in different bifacial cell architectures such as BiSoN, ZEBRA and PANDA.

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.

MLPE: Power optimisers are increasingly being integrated with string inverters at the module level, one at each solar panel. This helps in mitigating the shading effect to some extent by conditioning the power before sending it to string inverters, thereby improving the performance of solar plants. Microinverters are being used in the residential and commercial segments to convert DC power to alternating current (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 utilised for reducing the 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, such as the integration of solar trackers with inverters and other balance of system (BoS) components, are aimed at cost optimisation of solar plants.

Enhanced inverter capacities: In line with global trends, Indian developers are increasingly favouring 1,500 V DC inverters over 1,000 V DC inverters. Higher voltage improves DC output, necessitating shorter wires and fewer inverters, which help in reducing the overall BoS cost. Also, string-level monitoring systems, cloud-based systems, and consistent I-V curve monitoring systems are being deployed for improving inverter and plant efficiency, leading to a lower levellised cost of energy.

Wind

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 testing their 3 MW-plus WTG prototypes. Larger turbines generate more energy and compensate for the higher balance of plant costs, thus minimising the cost of energy. Larger WTGs reduce the total number of turbines required at a wind farm and 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 attaining higher efficiency. Although these installations require a larger area, tower heights for nearly all the recently launched models are being 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. A gearbox is responsible for enhancing the rotational speed of blades, and is one of the most expensive parts of a WTG. The moving parts of a drivetrain suffer significant wear and tear, and this can have a considerable impact on the WTG’s performance. Hence, R&D is concentrated on improving the efficiency of drivetrains 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 being developed. However, since most of the demand for drivetrains and motors in India is fulfilled through imports, the industry is at present focusing on improving domestic manufacturing capabilities.

Energy storage

One of the main limitations of solar and wind energy is the intermittency in power generation. Thus, energy storage is expected to play an important role in the balancing requirement with the increase in renewable energy capacity. As per the India Energy Storage Alliance, the market for energy storage will grow to over 300 GWh during 2018-25 and India is expected to attract investments of over $3 billion in the next three years.

Wind-solar hybrids

Wind-solar hybrids are ideal for addressing some of the inherent issues of stand-alone solar and wind power systems. Wind and solar energy have complementary generation patterns that can be used to produce a near-constant source of energy throughout the day. This not only leads to greater transmission efficiency but also results in significant capital and operational savings. Since the roll-out of the National Wind-Solar Hybrid Policy in May 2018, few pilots have come up. The first commercial wind-solar hybrid plant, comprising a 28.8 MW solar farm and a 50 MW wind plant, was commissioned in early 2018 by Hero Future Energies. In the first mega tender of wind-solar hybrid projects, conducted by Solar Energy Corporation of India (SECI) in December 2018, two companies won the bid – SB Energy for 450 MW at Rs 2.67 per unit and Adani Green Energy for 390 MW at Rs 2.69 per unit. The tender was undersubscribed by 150 MW. More recently, in April 2019, under Tranche II, Adani Green Energy and Renew Power submitted bids to develop projects totalling 900 MW.

The way ahead

Net, net, a decline in technology costs can further increase the adoption of variable renewable energy technologies and their integration into the grid. In the past year, investments in the downstream segment have been on the lower side, leading to fewer installations; meanwhile, upstream activity in the manufacturing segment has remained vibrant.

Moving ahead, with the advancement and adoption of storage technologies, higher economies of scale can be achieved in the renewables segment.

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