Energy Storage Considerations: Applications, Issues And Solutions

Solar Panel, wind turbines and Li-ion Battery Container With Blue Sky Background. Energy Storage System.

With daily changes in technology, ways and methods of how we use energy are changing. With increase in the power requirements for smaller devices it has become important to improve the density of energy storage in these devices. With these improvements has also come a wider array of applications for power storage on the electric grid and in electric vehicles (EVs). Energy storage is being increasingly investigated for its potential to provide significant benefits to the interstate transmission grid, and perhaps to local distribution systems and thus to retail electric customers. While energy storage is seen as an enabling technology with the potential to reduce the intermittency and variability of wind and solar resources, energy storage resources would have to be charged by low or zero emission or renewable sources of electricity to ensure a reduction of greenhouse gases.

As a flexible power source, energy storage has many potential applications in renewable energy generation grid integration, power transmission and distribution, distributed generation, micro grid and ancillary services such as frequency regulation, etc.

Advanced energy storage provides an integrated solution to some of the most critical energy needs: electric grid modernization, reliability, and resilience; sustainable mobility; flexibility for a diverse and secure, all-of-the-above electricity generation portfolio; and enhanced economic competitiveness for remote communities and targeted micro-grid solutions. Storage technologies strengthen and stabilize the grid by providing backup power, leveling loads, and offering a range of other energy management services. Electric vehicles (EVs) are also poised to become an integral part of this new grid paradigm as their batteries both draw power from and supply it back to the grid (when beneficial) – while eliminating tailpipe emissions.

To understand this topic in detail, let’s read on what our experts have to say…

The Need: 

Electricity grid is an instantaneous demand-based system where the supply and demand have to be matched at every instant. Constant adjustment has to be made on the supply side to mitigate predictable or unexpected changes in the demand. Energy storage can play an important role in this balancing act and make the grid more reliable and flexible. 

Renewable energy, when connected to the electricity grid, creates more uncertainty in the supply side due to inherent variability of irradiance and wind speed. Storage coupled with PV/wind or a hybrid system minimizes the uncertainty of these natural resources by backing up the power when the supply is more than demand and discharge when it is less.

The main intention of a C&I (Corporate & Industrial) customer is to reduce its electricity bill. There are a few challenges including peak load demand charge, penalty on low power factor and power cut that need to be addressed and BESS (Battery Energy Storage System) provides a scope to address all these issues.

The Applications: 

BESS applications in Utility scale are mainly two types, viz. Energy Application (MWh) & Power Application (MW). 

Energy Application can be further subdivided into

1) Energy Arbitrage, in which, battery is charged from renewable energy during high generation and discharged during higher tariff. 

2) Micro-Grid, where the battery is used in parallel to other sources (e.g., PV/Wind/DG etc.) in no electricity zone or island.

Power Application, on the other hand can be subdivided into 

1) PV Smoothing, where intermittencies of PV generation have to be mitigated at a specified instant. Due to the very fast response time of BESS almost in mSec, it is able to achieve the goal. 

2) Ancillary Service, due to voltage or frequency variation in Indian grid, it is required to pump (or absorb) reactive or active power from grid respectively. BESS can serve the purpose of providing the extra amount of active/reactive power and stabilize the grid.

Apart from that, in C&I applications, maximum demand charges which are proportional to the maximum load (in Watt) for a certain period of time is to be paid by consumers. BESS can supply the peak power for that period thereby reducing the electricity bill. This application is called Peak Shaving. Load factor (a ratio of average load and peak load) can also be improved in this way and many DISCOMs provide incentive for high load factor. Many times, C&I customers also have to pay a penalty for low power factors. Instead of using separate active power factor correction devices, BESS can serve the purpose by pumping/absorbing reactive power to the grid. Moreover, having a black start facility of BESS gives an edge to replace DG’s used for power cut scenarios.

The Issues: 

Key challenges for the widespread deployment of electric energy storage can be divided into two parts, viz. Technical & Non-Technical.

Technical issues of BESS can be categorized as 

1) Life cycle: Li-ion battery, which is the most commercially available battery has a life cycle of 4000-5000 cycles. Considering 1 cycle per day, the battery has to be completely replaced after 10-12 years. Hence, considering a 25-year life of the plant, this creates a huge operational cost.

 2) Efficiency: Round Trip Efficiency (RTE) of most of the commercially available batteries are in the range of 65-85%, which forces the developer to use higher rating at the Beginning of life (BOL). 

3)  Degradation: Battery is degraded @ rate of 1.5-2% every year. Hence, throughput from the battery is very low after 10 years. 

4)  Specific Energy: Sp. Energy varies in the range of 10-150Wh/kg for different battery technology. 

5)  Safety: Li-ion Batteries have the potential to be dangerous and hence, safety is a big concern. 

6) Disposal: From the EVs sold globally in 2017 alone, the waste from the spent lithium-ion batteries could be about 250,000 tonnes, or a half a million cubic metres. This is again a growing concern. 

7) High C-rating: Not all battery technologies are available with high C rating (>2C).

Here, one thing to address is that Li-ion comes with high efficiency (~85%), high Sp. Energy (~120Wh/kg), but having low life cycles and low safety. Whereas technologies like Flow battery are high in safety and life cycle (>10000) but have low Sp. Energy (10-20Wh/kg) and very low efficiency (~65%). Hence, there is no One-Stop solution for all.

Non-technical issues are 

1) Regulatory Barriers:  without any compensation or regulatory mandate, developers are unwilling to make any capital investment

 2) Cost Competitiveness: Actual Energy storage cost (e.g., battery) contribution is 70-75% of the total ESS solution cost.

The Solution(s): 

Awareness is growing across the world which pushes the policy makers to make regulations favouring uptake of BESS. Let us consider Germany’s primary control reserve (PCR) market. Participants in this market generate revenue by winning a weekly auction and receive remuneration for providing capacity to balance the grid. 

Now, battery price is reducing continuously and rapidly.  Lithium-Ion battery prices fell by 80% from 2010-2017 (Source: Bloomberg New Energy Finance, Lithium-ion Battery Price Survey) and falling continuously. Several new technologies are coming in (e.g., Vanadium Redox flow battery, Zinc-air battery) which have a high life cycle, considerably high efficiency and can be a cheaper alternative. Using EV batteries in stationary storage application even though they no longer meet EV performance standards.

Conclusion: Though “storage” and “renewables” are often seen to be equivalent, energy storage isn’t just about integrating intermittent wind and solar output: battery solutions, which can be deployed rapidly and with pinpoint precision, can be used to make the overall grid more efficient and resilient, regardless of the generation sources. This makes the storage story all the more compelling. For these reasons, storage markets are developing much faster than anticipated and battery storage is getting supercharged around the world, riding on the wave of falling battery prices and expanding demand. 

By Subhamay Ganguly, AGM- Energy Storage & Innovation, Amp Energy India

India has set itself a renewable energy (RE) target of 175 GW and 450 GW for 2022 and 2030, respectively. With the country bracing up to meet these targets, and given the intermittent nature of RE, energy storage systems (ESSs) are required to balance the grid. 

The most commonly used storage technologies in the Indian grid are pumped-hydro (~96% of the total storage installed) and battery storages. Other storage technologies that can be used are compressed air, flywheels, hydrogen storage, supercapacitors, superconducting magnetic energy storage (SMES), and thermal energy storage (which includes water heaters, ice storage, chilled water storage, and molten salt-based storage). 

Applications of energy storage

ESSs have a wide variety of applications in the grid. The four main applications are ancillary services, bulk energy services, transmission and distribution infrastructure services, and customer energy management. 

Ancillary services support the smooth and stable operation of the grid by maintaining the grid voltage and frequency within permissible limits (voltage support and frequency regulation). They also manage sudden fluctuations in the load by adjusting the power generation according to demand (load following). Other ancillary services include spinning reserves and black start. Spinning reserves are standby generators that support the grid during a power shortage. When there is an unexpected power outage (partial or total blackout of the grid), the system is restored through a black start. ESSs installed at the generation and transmission level can provide these ancillary services.

Bulk energy services include variable RE integration, seasonal storage, and energy arbitrage. ESSs can store excess energy and supply it when needed, thereby managing RE intermittency and integrating more RE into the grid. Also, ESSs can cater to the seasonal mismatches in demand. Energy arbitrage is the storage of energy in large-scale energy storage devices when the electricity price is low and its sale when the price is high, leading to revenue generation. 

The use of ESSs in the transmission and distribution network helps in delaying upgradation of the network, while easing congestion. It is also useful in city limits where acquiring land for laying high voltage lines is a hassle.

Customer energy management services include using ESSs to provide quality and reliable power, reducing peak demand, and time-shifting customer demand to off-peak periods.

ESSs at different levels of the network

ESSs can be classified based on the duration of the discharge of power as short-term (seconds to minutes), mid-term (minutes to hours), and long-term storages (hours to days). Table 1 shows the suitability of different energy storage technologies for various applications and their levels in the network.

The Way Forward

The major challenge in the adoption of ESSs in the grid is their cost. Hence, to improve profitability, a single storage device may be used for different applications, leading to multiple revenue streams. In addition, our energy market and regulatory framework should incentivise storage-specific projects.

By  Dr Ammu Susanna Jacob – Senior Research Engineer, Center for Study of Science, Technology and Policy (CSTEP) 

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