Energy Storage System (ESS) has been known to mankind since few years now. However in the decade, a considerable amount of money has been spent in upgrading existing and/or developing new systems.
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.
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:
RAMP RATE CONTROL & OUTPUTRAMP RATE CONTROL & OUTPUTSMOOTHENING
A ramp may be defined as an event in which there isA ramp may be defined as an event in which there isa change in power in a fixed time frame. If the changein power is positive, this event is known as ramp-upevent. Similarly if the change in power is negative, it isknown as ramp-down event. The rate at which this rampevent occurs is known as ramp rate, which is usuallyconsidered for a minute and hence its unit MW/minute.The conventional power producers (due to their abilityto control input fuel) have a considerable control overtheir ramp rates. However the renewable energy sourcesdue to uncontrollable factor such as cloud cover, suddenchange in weather conditions may have significant effecton its power output. It is seen that close to 30 – 80% ofpower 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 andsupply ratio is maintained at almost all the times. In caseof sudden spike or surge in power, congestion in electricconductors may damage the grid. The ESS in such casecan release or absorb energy thus reducing the speed ofvariation 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 generationcompensates of spikes and sags so that the generationremains within the scheduled range.
India has had a typical power consumption curve witha peak consumption (which is normally much higherthan base demand) almost between 8 am to 12 pmand from 6 pm to 10 pm. This means that the gridoperators/ generators need to produce extra power tokeep the demand within limits. While few (generating)plants can provide such extra power (like hydro power)instantaneously, other plants need adequate time tostart their extra generating assets. Few plants also havespinning reserves up running continuously to provideextra power as and when needed. Renewable plants nowin order to supply (almost) constant source of powerhave (generally) battery or any other form of ESS. Thishelps renewable energy plants to mitigate the extra load.Known as Peak Shaving, it also helps the end consumermeet its demand from the ESS while curbing the needof purchasing energy at higher tariffs. This enables thatthe customers who install on-site generating and ESSequipment receive power at reduced rates year round.
FREQUENCY AND POWER-FACTOR FREQUENCY AND POWER-FACTOR REGULATION
Both frequency and power factor are important gridBoth frequency and power factor are important gridindicator. While frequency indicates the exact matchbetween demand and supply, power factor indicatesthe quality of power flowing through the grid. ESSensures stability in grid by dispatching or absorbingactive power as and when required. This ensures thatthe share of renewable energy in the entire energy mixof country is increased to a substantial amount. Theoperation of ESS however here are dependent on thenumber and frequency of variations in the grid power.These variations are typically of short duration whichensures ESS regulates the grid power by maintaining itwithin permissible limits.
With almost major power consumer and renewableWith almost major power consumer and renewableenergy producer states (like Maharashtra, Gujarat,Andhra Pradesh, Tamil Nadu) drafted out the Deviationsettlement mechanism for renewable energy generators,the usage of ESS has become mandate. This regulationshall applicable to both existing and upcoming plantswithin these state. In these regulations, the generatorhas to give a day ahead and three days ahead scheduleeach 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 theyhave forecasted, they would be charged with a fixedpenalty. While there are software’s and models availablewhich could predict the expected generation but not with expected confidence limits. This sets the path ofwith expected confidence limits. This sets the path ofESS which would be of prime importance once theseregulation are in full effect across the country.Let us all pledge to make solar energy the primarysource of energy in the near future.
Figure 1: Capacity Of Global Cumulative Storage Installations
(Source: Bloomberg New Energy Finance)
Figure 2: Ramp Rate Control With Use Of Storage
Figure 3: Peak Shaving
(Source: Google images)