Storing Wind

Technologies to address intermittency issues

Renewable sources of power such as solar and wind may be environment friendly, but they do not promise a constant and predictable stream of power. The sun does not always shine and the wind does not always blow. Thus, if renewables are to become a bigger part of India’s energy mix, they require energy storage.

The biggest disadvantages of wind energy are its weather dependency and fluctuating nature, which make wind power forecasting very difficult. The goal is to reduce the difference between forecasted and actual wind power generation. A solution to this is wind energy storage.

A new report from Navigant Research in late 2019 examined the role of energy storage in wind integration, covering existing and upcoming projects, the competitive landscape and expected market growth. The report, titled “Optimizing Wind Power Plants with Energy Storage”, aimed to provide an in-depth analysis of the drivers and challenges for the growing market. It stated that while the rise of combined solar plus storage projects is driving the growth of the energy storage industry, energy storage for wind integration has still not gained traction.

“The link between wind and energy storage remains far less established than storage for solar PV owing to both technical and economic factors,” says Alex Eller, senior research analyst at Navigant Research. “Although combined wind plus storage projects offer similar benefits and potential, little development has taken place thus far for these combined projects.”

Energy storage market

Recently, an analysis by research agency Wood Mackenzie revealed that the global energy storage market is set to grow from approximately 4 GW of annual deployments in 2019 to more than 15 GW in 2024. According to the analysis, the market will be characterised by stabilising supply chains, and mature and experienced players by the end of the decade. However, there will be a greater possibility of disruption from new technologies and policies.

“Costs have fallen, direct incentives and clean energy targets are proliferating, and competitive markets and vertically integrated electricity providers are beginning to recognise the potential of energy storage. In the next decade, the already consolidating web of manufacturers, developers, investors and integrators will compete for their slice of this burgeoning industry, carving out mature supply chains and propelling cost reductions. As they do, continued policy and regulatory efforts will be key to driving the market upside,” the analysis states.

Ajay Shankar, a fellow at TERI, explained to CNBC that the key issue for India and the rest of the world were the costs related to electricity storage. “These have been declining rapidly. The expectation is that they will continue to fall quickly. India is taking the first steps towards deploying storage technologies and getting experience of managing such systems,” he said. When costs of storage decline sufficiently, large-scale deployment would be feasible and the use of fossil fuels would then start declining.

Technical aspects

With the help of a developed calculation model, battery application has been analysed as a backup for 400 MW of wind farms dealing with power fluctuations. The results of the analysis have shown that the use of NaS (sodium sulphur) battery systems to compensate for power fluctuations at wind farms is possible. This considerably increases the reliability of wind power output and improves reserve energy management.

Further, battery size, forecasting errors and the forecasting horizon play an important role in the optimisation of the battery application. From a technical point of view, though the use of batteries as a backup for large wind farms is necessary, the economical evaluation of the present and future applications has to be analysed.

If the actual power output of the wind farm is higher than forecasted, the battery will be charged, whereas if the power output is lower than the forecasted power, the battery will be discharged to cover the difference. Thereby, the wind power output is always as planned, that is, it is the forecasted amount. Thus, the actual charging state of the battery is very important for its operational use.

India tender oversubscribed

In August 2019, the Solar Energy Corporation of India (SECI) issued a tender for setting up 1.2 GW of renewable projects connected with the interstate transmission system (ISTS), with a guaranteed peak power supply (Tranche VII). Projects were required to have at least two components – an energy storage system (ESS) and a renewable energy generating system. The renewable energy generating component could be a solar system, a wind energy system, or a hybrid system of the two technologies. In its tender, SECI specified that projects selected will be eligible for two-part tariffs – peak tariff and off-peak tariff. Energy generated during off-peak hours will be eligible for a flat tariff payment of Rs 2.70 per kWh while energy generated during peak hours will be purchased at a tariff discovered through the e-reverse auction.

In December 2019, SECI extended the bid submission deadline from November 29, 2019 to December 16, 2019, and revised the tariff for hybrid power developers during off-peak hours to Rs 2.88 per kWh. It also revised the required earnest money deposit to Rs 750,000 per MW from Rs 600,000 per MW.

SECI has now successfully concluded the world’s largest renewable energy-cum-storage tender, allocating 1.2 GW of renewable energy capacity to two of India’s leading developers, Greenko Energy Holdings (900 MW) and ReNew Power (300 MW). As per the tender conditions, the developers are required to supply firm renewable energy throughout the day, and bid separate tariffs for supplying power during peak (11 hours in a day) and off-peak hours.

Greenko Energy Holdings has secured rights to develop 900 MW of capacity at a peak period tariff of Rs 6.12 per kWh and an off-peak period tariff of Rs 2.88 per kWh. ReNew Power secured a capacity of 300 MW with a peak period tariff of Rs 6.85 per kWh and an off-peak period tariff of Rs 2.88 per kWh. To meet the firm supply of 1.2 GW, developers would be required to have a storage capacity of 3,000 MWh.

During the technical bidding round, Greenko Energy had bid for 900 MW, ReNew Power for 600 MW and HES In-frastructure for 120 MW. While ReNew Power halved its bid in the financial bidding round, HES Infrastructure did not participate at all.

While ReNew Power is not known to have worked on any large-scale energy storage projects, Greenko Energy Holdings is perhaps the most experienced in this field. The latter is working on two renewable energy-cum-storage projects in Karnataka and Andhra Pradesh. For each of the projects, the company will set up 2 GW of solar and 2 GW of wind energy capacity. The project in Andhra Pradesh will have a pumped hydro storage capacity of 8,000 MWh, while that in Karnataka will have 9,600 MWh.

Greenko Energy Holdings, which bought out SunEdison’s India assets, is backed by the likes of Singapore government-backed group GIC and the Abu Dhabi Investment Authority (ADIA). ReNew Power, one of India’s leading renewable energy companies, counts Goldman Sachs, ADIA, the Canada Pension Plan Investment Board, and the Global Environment Fund as its investors.

According to Mercom’s India Solar Project Tracker, SECI has tendered 12.2 GW under ISTS Tranches I to VIII and has auctioned about 6.44 GW under ISTS Tranches I to VI. SECI has been issuing unique tenders to offset the intermittent nature of renewable energy and promote local manufacturing. In October 2019, it issued a tender to procure 400 MW (2×200 MW) of renewable energy on a round-the-clock basis. Recently, the Ministry of New and Renewable Energy also came up with a draft plan to supply round-the-clock power from renewable (solar, wind and hydro) projects, which would be complemented with power from thermal projects.

Recommendations

As per Navigant Research, a Guidehouse company, the following actions are recommended to accelerate sector growth:

  •  Wind plus storage project developers need to explore new revenue streams to address reduction or outright elimination of subsidies for wind plants.
  • Wind and energy storage operators must invest in robust software to effectively pair the technologies with accurate wind output forecasts and market pricing.
  •  Wind farm developers should partner early with leading storage providers to identify cost-effective sites for potential projects and viable revenue streams.
  •  Stakeholders should maximise the use of existing transmission networks.

Conclusion

In conclusion, even though the rise of combined solar plus storage projects is reshaping the energy storage industry, both technical and economic factors contribute to the slow development of wind plus storage projects. Despite the limited number of combined wind plus storage projects, the pairing of these technologies is critical to achieve greater reliance on renewable energy generation. Since incentives for wind plants are also being reduced and phased out, leading wind developers need to explore energy storage. Wind integration thus provides opportunities for new technologies and business models. Finally, wind plus storage use cases are expected to expand as the grid evolves.

 

 

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