Techniques
Along with major techniques as discussed above, there are some techniques which are attaining a commercial stage. One of the techniques is ‘Airborne Wind’ in which flying turbine devices which have 90% less mass than traditional wind turbines are used (IRENA 2016). At 300 m above altitudes, these turbines can generate power from the low‐speed winds. This technique covers a range of concepts such as rigid wings and airborne rotors. This technique can generate electricity at a lower cost due to less material usage, low capital expenditure and higher energy production compared with conventional turbines (IRENA 2016).
Apart from innovations in technologies, developments are also taking place in operation, maintenance and services (IRENA 2016). Due to higher growth rate in offshore wind turbines, there is a need of advances in the technology systems to keep track of turbines and to avoid failures. One such operation and maintenance tool is ‘Condition Monitoring Systems’ which help operators to forecast any problem with the working of wind turbines or failure of any components so that replacement can be done in advance to avoid any accident (Froese 2017).
2.3.3 Hydropower
Energy resulting from the running water is termed as hydropower. Harnessing energy from water is one of the ancient methods used by the Greeks to run wheels for grinding grain. It is an inexhaustible and clean source of energy without consumption, pollution, emission of waste gas and other wastes. Utilizing hydropower is one of the efficient ways to achieve low‐carbon emission and meet the Paris climate goals. Its contribution in power generation is maximum among all renewables, World's largest hydropower plant in China – ‘Three Gorges Dam’ with 22.5 GW capacity is a great example of this renewable source. First time in the history, contribution of hydropower reached just 50% in the year 2018 due to more growth in solar and wind energy sector. In recent times, its growth rate (2% in 2018) continued to slow, with only China adding a substantial amount of 8.5 GW in 2018, as per IRENA report (IRENA 2019f). Hydropower plants are classified into two types, namely with dams and reservoirs or without. Hydropower plants with dams and reservoirs produce electricity at a large scale while the other type produces at a smaller scale.
Hydropower technology has reached a mature level as compared with other renewable sources, namely solar and wind. Thus, advances in identification and implementation of radical design which can change the operative method of hydropower have less potential. However, development of new methods in design, planning and operation of a hydropower station still has many opportunities (Kougias et al. 2019). Recent advances in the hydropower sector show increment in efficiency, flexibility of operations, durability and cost reduction of installation, operation and maintenance. Developments in technologies are needed for this sector to respond to changing climate conditions, expanding markets and variabilities of electrical power systems. Further, novel developments for upgradation and refurbishment of current facilities in hydropower are required in accordance with the environmental standards.
2.3.3.1 Flow Control Technologies
The flexibility in electricity generation from the wind and solar renewable source poses some challenges on power generation from hydro. To fulfil the demand of variable energy production along with limited capability for energy storage, hydraulic turbines need to operate at a wide range and changing conditions (Valero et al. 2017). Recently, some developments have taken place in control technology to reduce the flow instabilities which occur due to self‐induced instability in the operation of hydro turbines. Several techniques have emerged which decrease the flow instabilities in hydro turbine operation. These comes under passive and active control techniques (Kougias et al. 2019). Number of techniques are reported under these two types of control technologies. Some other techniques have also been reported by a recent research known as ‘Magneto‐rheological control techniques’ (Trivedi et al. 2015) which uses magneto‐rheological brake to mitigate flow instability along with the decreasing speed of the runner.
2.3.3.2 Digitalization of Hydropower Plants
Hydropower plants were established and designed decades ago, so to meet today's requirement of variable energy demand and face the present environment conditions, they need digitalization of operative methods used in existing plants. Present hydropower plants also require developments with respect to flexibility which can be done by providing storage capacity and advanced system services. However, practically there are some hydrodynamic phenomena which are associated with the working of hydropower plants which leads to limit their flexibility. Digitalization in the hydro sector will change the methodology for design, development, operation and maintenance of new hydropower plant projects. Thus, renovation and digitalization of various equipment of existing plants offer the opportunities of enhanced operations. These developments will increase the lifespan of power plants along with increased efficiency and power production (Kougias et al. 2019). The effect of digitalization can be best understood by the projected increase in capacity of the world's 1225 GW installed hydropower by 42 terawatt‐hour (TWh) annual production. This increment will help in achieving the low‐carbon emission and thus maintaining a balance in the ecosystem. On the basis of recent advances reported by various research groups for digitalization of hydropower plants, one of the studies (Kougias et al. 2019) concluded that a ‘Digital Avatar’ of hydropower plant dynamics can be developed by following a multidisciplinary approach which covers the hydraulic machinery, electrical power systems and its associated control and components fatigue modelling.
2.3.3.3 Evolution in Hydroelectric Energy Storage
Continuous increase of variable renewable energy (solar and wind) in electrical power system (EPS) leads to advances in the field of energy storage. For energy storage, pumped‐storage power plant (PSPP) is a well‐developed technology with continuous improvements taking place in PSPP (Kougias et al. 2019) in order to reduce response time for transition mode i.e. from pump to turbine and vice versa. Recently, two technologies are evolving under PSPP which can play an important role in fast energy storage systems, namely flywheels and supercapacitors (Sarasúa et al. 2016; Gevorgian et al. 2017). Synergy between fast energy storage systems and hydropower operation permits an improved frequency control in EPS. Integration of these technologies into the operational hydro plants can be easily done in a span of a few months which can provide advantages in voltage control in the proximity of the hydro plant. Coordinated operation of fast energy storage systems and hydropower plants is also possible for one or set of hydro plants which are connected to the transmission power system in other geographical locations. As an example, globally, by the end of 2017, total installed hydropower capacity including pumped storage was 1267 GW (IHA 2018) as evaluated by International Hydropower Association. Now, assume that every operational hydro plant and PSPP are connected by fast energy storage systems with 5% (assumption) of the installed capacity, then new 65 GW fast energy storage systems are needed to be manufactured and installed across the world.
A new concept in pumped energy storage is emerging, known as underwater pumped hydro energy storage (UPHES) owing to advance research in the energy storage area. Its technical feasibility was investigated between 2008 and 2011 (Kougias et al. 2019). In contrast to the PSPP, it is not restricted to specific geographical locations. In UPHES, sea acts as the upper reservoir while a hollow deposit situated at the seabed is the lower reservoir. Seawater enters the deposit, which in turn drives the turbine and leads to electricity production.
2.3.3.4 Technology Evolution: Small‐Scale Hydropower Plants
Construction of large‐scale hydropower plants poses a great threat on the environment, balance of ecosystem and the life of aquatic species. Small‐scale hydropower plants offer a solution to these persisting problems with large‐scale hydropower plants. Further, small hydro plants do not disturb the flow of the river to generate electricity which makes them environment‐friendly. At present, small hydro plants are not profitable; however, it can become cost‐effective with the usage of digitalized operation and control technologies (Kougias et al. 2016a) along with combination of other variable renewable energy technologies (Kougias et al. 2016b).