Energy Storage System (ESS) has been known to mankind since few years now. However in the decade, aconsiderable amount of money has been spent in upgrading existing and/or developing newsystems. This is partly because of the fact that such systems are poised to double six times only in the next 15 years i.e. from 2016 to 2030 reaching almost up to 125GW/305GWh (Figure 1). ESS is simple terms means any system/technology which is capable of storing excess energy and releasing it when required. The types of ESS available in the market are of electrical, mechanical, thermal, chemical, etc. in nature. The storage type today with maximum market penetration are batteries. While we informed you on the technicalities of battery storage in our previous blog “Importance & Reliability of storage”, we thought it was important to educate our readers on what actually would be the role of ESS (and how would they help such plants) with reference to renewable energy power plants. Additionally with various Indian states drafting the Deviation settlement mechanism regulation this year, it can be easily assumed that ESS would be of prime importance to all the renewable energy generators for various reasons. This blog hence aims to educate its readers on role of ESS and its importance to the national grid.

Figure 1: Capacity of global cumulative storage installations (Source: Bloomberg New Energy Finance)

ESS as we mentioned above is of great importance to both Solar Photovoltaic (PV) and Wind energy generating plants. A main reason that is attributed to this is that both these generating sources are intermittent in nature. ESS thus helps such sources in following ways:

1. Ramp rate control & Output smoothening: A ramp may be defined as an event in which there is a change in power in a fixed time frame. If the change in power is positive, this event is known as ramp-up event. Similarly if the change in power is negative, it is known as ramp-down event. The rate at which this ramp event occurs is known as ramp rate, which is usually considered for a minute and hence its unit MW/minute. The conventional power producers (due to their ability to control input fuel) have a considerable control over their ramp rates. However the renewable energy sources due to uncontrollable factor such as cloud cover, sudden change in weather conditions may have significant effect on its power output. It is seen that close to 30 – 80% of power output in a minute may be lost in such cases. Ramp rate are usually of prime interest to grid operators, as they are the ones who ensure that the demand and supply ratio is maintained at almost all the times. In case of sudden spike or surge in power, congestion in electric conductors may damage the grid. The ESS in such case can release or absorb energy thus reducing the speed of variation at the injection point. Also as evident Figure 2, the ESS also helps to smoothen the power output i.e. it compensates of spikes and sags so that the generation remains within the scheduled range.

Figure 2: Ramp rate control with use of storage (Source: Saft)

2. Peak Shaving:India has had a typical power consumption curve with a peak consumption (which is normally much higher than base demand)almost between 8 am to 12 pm and from 6 pm to 10 pm. This means that the grid operators/ generators need to produce extra power to keep the demand within limits. While few (generating) plants can provide such extra power (like hydro power) instantaneously, other plants need adequate time to start their extra generating assets. Few plants also have spinning reserves up running continuously to provide extra power as and when needed. Renewable plants now in order to supply (almost) constant source of power have (generally) battery or any other form of ESS. This helps renewable energy plants to mitigate the extra load. Known as Peak Shaving, it also helps the end consumermeet its demand from the ESSwhile curbing the need of purchasing energy at higher tariffs. This enables that the customers who install on-site generating and ESS equipment receive power at reduced rates year round.

Figure 3: Peak shaving (Source: Google images)

Frequency and Power-factor Regulation: Both frequency and power factorare important grid indicator. While frequency indicates the exact match between demand and supply, power factor indicates the quality of power flowing through the grid. ESS ensures stability in grid by dispatching or absorbing active power as and when required. This ensures that the share of renewable energy in the entire energy mix of country is increased to a substantial amount. The operation of ESS however here are dependent on the number and frequency of variations in the grid power. These variations are typically of short duration which ensures ESS regulates the grid power by maintaining it within permissible limits.

With almost major power consumer and renewable energy producer states (like Maharashtra, Gujarat, Andhra Pradesh, Tamil Nadu) drafted out the Deviation settlement mechanism for renewable energy generators, the usage of ESS has become mandate. This regulation shall applicable to both existing and upcoming plants within these state. In these regulations, the generator has to give a day ahead and three days ahead schedule each day. Such forecast could only be changed 8 times & 16 times (For Gujarat – number may vary state-wise) for solar & wind energy generators in 96 time blocks (15 minutes each) per day. Above such revisions and/or if a generator generates more/less energy than they have forecasted, they would be charged with a fixed penalty. While there are software’s and models available which could predict the expected generation but not with expected confidence limits. This sets the path of ESS which would be of prime importance once these regulation are in full effect across the country.

Let us all pledge to make solar energy the primary source of energy in the near future.

RAHE ROSHAN HAMARA NATION