Think of an average household and you’ll notice that there’s a definite daily pattern in its energy usage. Millions of such households produce a similar pattern in an economy as well. Our usage is high in the morning, somewhat average during the day, maximum in the evenings and the lowest at night. Which means that our energy supply should follow a similar pattern since energy cannot be stored necessitating a variable energy supply. Yet, most of our energy systems can produce a steady stream of electricity and do not respond well to sudden changes – meaning that we’re either producing more or less energy than we need causing an enormous fall in energy prices or causing blackouts. And this is a major problem in an economy dependent on electricity. And then there’s the issue about the renewables.
You see while renewable based energy are slowly replacing the traditional coal (and sometimes nuclear) energy systems with clean and safe wind and solar alternatives, they are bringing with them an inherent problem that is unique to such systems. This is because except for hydroelectric power, most renewable systems depend on wind and solar energy that we haven’t been able to absolutely predict even with modern satellite based systems. This makes RE a source of intermittent power compared to the more stable coal and nuclear systems. This wouldn’t necessarily be a problem if both systems were to coexist in a way that one would counter the shortcomings of the other but that is not what’s happening. Since fuel for the RE systems are essentially free, in a capacity-based auction based on marginal cost (the cost to produce one extra unit of electricity), RE will always outbid coal and thus push the stable energy producers out of the market. This makes the market volatile and dependent on factors we have no control upon causing sudden changes in energy prices. For example, a great sunny and windy day produces so much power that the supply overtakes demand pushing energy prices to extreme lows and even sometimes to negatives as has been seen in England and Germany on many instances in the last few years. And this is exactly why experts and analysts think that we’ll soon be needing a proper storage option for electricity in the coming years.
The simplest Energy Storage System or ESS for short is an enormous battery and it works exactly how a backup battery or invertor system works in your house or in case of a grid-tied solar system. But even though we have had batteries around us for about almost a century, they are still very primitive and have largely been unchanged until the recent years. The advent of smartphones, laptops and other handheld electronics allowed for the evolution of battery technology from its primitive form as is found in your car to the sleek version we see today (unless you own a Tesla). While the Lead-acid batteries were bulky and less efficient, modern Lithium-ion batteries weigh only a fraction of them and can achieve high energy densities. This makes Li-ion a strong contender to be used in storage systems. But energy storage is just not batteries – the law of conservation of energy states that energy can neither be created nor destroyed but can only be transformed from one kind to another. This makes it possible to convert electrical energy to other forms that can be stored easily. For example, the most commonly used ESS (when used) is a Pumped Hydroelectric system – in such a system water is usually pumped from a lower basin to a higher basin during periods of excess energy in the grid and stored as potential energy. This water is released during peak periods to generate excess energy. Another system that has been used in many applications especially in solar thermal power stations has been through Molten Salt storage. Molten salt can retain thermal energy for longer periods of time compared to water and if the solar thermal energy during the sun hours can be stored in this medium it allows the energy generator to extend the generating hours from beyond the actual sun hours. Flywheels are a mechanical storage device which utilizes the property of inertia for a rotating mass to store and deliver energy as necessary. Flywheels have the added advantage that they can be easily used to clean up the frequency in a grid by utilizing it to counter frequency changes within the system. Other systems that have shown potential as ESS are Compressed Air Storage (stores air at high pressure in underground salt formations or depleted gas reservoirs) and Hydrogen based storage.
Hydrogen can be an effective storage and peaking power system – it can be produced from natural gas by Steam Methane Reformation to be burned cleanly as a peaking power utility and be created through electrolysis. The excess electrical energy is used to electrolyze water into Hydrogen and Oxygen which can then be stored in storage vessels and be burned to produce power as needed. The effectiveness of such a system increases through ‘economy of scope’ if a hydrogen based infrastructure is being put into place as it can have multiple uses in domestic and commercial heating and as a clean-burning transport fuel
Often the primary reason given for an ESS is to counter intermittent renewable production, but its scope extends far beyond that. For starters, it can be used as a sort of demand and supply management system to shift generation and consumption patterns form one period to another. What this means is that due to quite restrictive load patterns, generators are often forced to produce energy at periods when it is not economic to do so. The possibility of energy storage allows the generator to take advantage of the lucrative period to generate energy, store it and then sell it at the peak periods to increase plant profitability. This would be particularly beneficial to the coal-based energy generators who have seen their utilization percentages falling in the recent years. A storage system would enable them to counter that by allowing them to exploit their full plant potential by storing and dispatching energy to the grid as necessary without having to alter their generation patterns. Storage systems tied to RE systems would operate somewhat in a similar manner by allowing the generators to fulfill their supply commitment to the grid. An advantage of such systems in both these cases is that the shifting of the generation and usage patterns effectively smooths out costs in the energy system especially during the peak periods.
The primary use of an ESS is that it effectively acts as an enormous battery that can be used to provide backup power in case of power failures. This reduces the dependence on costly gas-based peaking power plants and oil-burning generators that also contribute to increased carbon emissions and which are generally used to provide back up in most economies. ESS is also perfect for providing a cold-start to an energy system if it is required in case of an emergency. [A Cold Start is when one or all generators have shut down due to some emergency and needs to be started from scratch. Usually in such cases hydroelectric with its easy availability of fuel and diesel generators are used as the starting system that would in turn provide the required power for the other systems to start up]. ESS can also act as a balancing and frequency modulating facility by storing the deviated energy from the grid and in turn feeding back a more refined power output. This would ensure an optimal utilization of the infrastructure facilities within the country.
These advantages make it possible for ESS to be owned and operated by a variety of owners within an energy system. A RE generator can build, own and operate a facility to adhere to its energy delivery obligations or a conventional generator may sell its energy bundled with non-conventional sources. A transmission licensee may own it as an additional facility and provide storage services as a supplementary to its transmission services with additional rates while a distributor may use it to flatten the demand curve and provide reliability to the sale of power. And based on the legal and policy framework, the ownership maybe varied and give rise to new and specific business opportunities. Such as consumers could own and operate such small community-scale storage facilities to allow them uninterrupted power and insulate them from upstream outages. Storage technology vendors can use this as an opportunity and provide storage facilities to generators, transmitters, distributers and the consumers for a small fee per MWh of power supplied or stored.
Then comes the question of the technology to adopt from the selection and for that we need to review each technology to determine its individual advantages and shortcomings. For example, even though hydroelectric based storage has usually been the go to solution for grid operators when it came to energy storage, it requires a very specific geography to operate and such formation may or may not be even available in a specific location. In India, the government has marked out locations that can be possible to build a pumped storage system and each of these regions come with their own land laws, environment regulations and other significant challenges that make it quite an uphill task. Moreover, with India aiming to source a large section of its energy from renewables means that these locations just won’t be enough to handle the amount of balancing/storage capacity that will be needed. And with countries pledging to shift towards a more carbon-free energy economy, the impact of renewables is only going to rise which will only mean more and more energy storage. And companies have been quick to jump at the opportunity. The major technologies to look out for have been Li-ion, flow-based and lead acid battery packs for some years now. While lead-acid battery packs are still in contention as far as large-scale systems are concerned, lithium-ion have steadily been gaining ground. There has been massive decline in their prices owing to the large-scale development in battery technology. About 145 GW of Lithium-ion based energy storage has come online in the US alone in 2015 and global technology research company Technavio projects demand in the segment could surpass 3 GW worldwide by 2020. Lead-acid will obtain a smaller share of the segment rising to about 990 MW worldwide by 2020. Tesla has been among the global giants betting on the Li-ion technology with a gigafactory dedicated to producing 35 GWh of Li-ion battery cells each year. Another technology that has been gaining ground are the flow-battery systems that run on the principle of having a charge carrier liquid medium running through the system that can be easily and quickly charged. ESS Inc. – an energy storage firm has developed a flow battery that can use iron and saltwater to create a simple, non-toxic battery that can function reliably over twenty thousand power cycles.
While the possibility of multiple usage for ESS might be an attractive possibility, several details both in determining public policy, energy prices, ownership and financing models need to be ironed out if India is to benefit from such a technology. For starters, the business models need to fit into the existing legal and regulatory framework with discussions on issues like the ownership of the stored energy, etc. The business model will also be complex with multiple uses as the ESS can act both as a load and as a supply which would mean a unique sharing of costs among the stakeholders. If it is used as a voltage stabilizer, the developer may negotiate some profit sharing with the transmission licensee from the compensation provided by the government for the same. Just like natural gas should the storage customer hold the ‘title’ of the energy in storage or should it just be a contract to a certain amount of storage as negotiated between the customer and the regulator because electricity, unlike gas is uniform irrespective of the generator or the transmitter. This might allow for large-scale facilities that could be shared which would reduce operational costs and increase profits. Unlike conventional or non-conventional generation, transmission and distribution facilities, the charges for storage options would be needed to be fixed based on specific charging, holding and discharge periods. The Indian government in its aim to source at least 40% of its electricity from non-conventional, renewable resources have finally woken up to the possibility of the inclusion of storage in its existing and upcoming renewable energy systems. A recent tender by Southern and Eastern Power Distribution Company of Andhra Pradesh Ltd. is for an ESS of 1 MW and 2 MWh capacity and other similar projects are in the pipeline in the country. The power distribution company of California has launched targets for 2015 and 2020 and have recently proposed storage mechanisms totaling 1325 MW.
While India is miles from announcing energy storage mechanisms, it needs to continue its discussions in the sector while promoting and involving national and international research into the sector. While it still does not have a well-established policy and regulatory framework, investor confidence can be increased through continued research through pilot-scale projects to gain valuable practical experience. The Indian government has recently issued a Discussion Paper based on Energy Storage Systems and how they can fit in the energy system where it asks questions that needs to be answered if we are to solve this puzzle. While researching this article three of those questions seemed extremely vital to me if ESS is to go mainstream –
Is ESS necessary or can it be replaced by alternative systems?
How will scheduling, energy accounting and open access issues be dealt with when the generation output and energy storage output are being measured at two different grid points?
Written by Sagnik Ghoshal