Energy Storage – a key ingredient for renewable energy system

Tuesday, July 07, 2015
Krishna Magar
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Energy storage has been the most challenging task to handle from the beginning of the human race, and they have continuously been trying to store more energy effectively and efficiently. Energy can be used either directly through the sun or indirectly, storing it for future use, from ancient time to balance its supply and demand. Energy storage systems can be broadly categorized as mechanical, electrical, chemical, biological and thermal. Nowadays, renewable energy deployment and policies to modernize the electricity production and consumption are propelling numerous advances including increased battery storage. This technology stores energy in the form of chemical and can be located at the point of end users or at the grid level. Its use can allow for greater amount of renewable electricity into the grid and as well as contribute in system reliability.

The cost of batteries has been falling day by day along with the advancement in technology, and such batteries have become safer and more efficient. However, battery storage system needs to overcome various barriers to become the main line of energy. The rapid growth in variable renewable energy like Solar and Wind is changing the conventional electricity system into modern type of electricity system. At high levels of penetration, variable renewable energy increases the need for resources that contribute to system flexibility. This ensures that system stability is maintained by matching supply and demand of electricity. Battery storage is one of the options for enhancing system flexibility in these circumstances by managing electricity supply fluctuations. In multiple application areas around the world, batteries have been used to aid integration of renewable energy.

Lead acid battery has been around for over 100 years. It is popular mainly due to its low costs & widespread availability. Large-format lead-acid designs are widely used for storage in backup power supplies in telecom towers, high-availability settings like hospitals, and stand-alone power systems. As Lead Acid is a proven technology and relatively cheaper, they are still used in majority of starting-ignition-lighting applications such as car battery. However, its low energy-to-weight ratio and a low energy-to-volume ratio became its constraint for its use in places where weight is the major concern. Also it is not very environmentally friendly as the electrolyte and the lead content can cause environmental damage.

Lithium Based batteries are quickly becoming a reasonable replacement for Lead-Acid batteries. In applications where weight is a consideration, Lithium batteries are among the lightest options available. Lithium-Ion batteries and Lithium Polymer batteries are the most energy dense of the Lithium batteries, but they are lacking in safety. The LiFePO4 (also known as Lithium Iron Phosphate) batteries are the safest type of Lithium batteries as they will not overheat, and even if punctured they will not catch on fire. LiFePO4 has the highest cycle life and also most environmental friendly battery.

In May 2015, Tesla CEO Elon Musk unveiled its new product “Powerwall,” who imagines the world on the road to “enabling zero emissions power generation.” He believes that the “Powerwall” will help to start to wean the world off fossil fuels. It is a backup power source not much different from the generators. Another top battery manufacturer BYD, a Chinese company, also offers eco-friendly, sustainable and safe Energy Storage System, which has been widely recognized. Based on advanced Iron (Fe) based battery technology, intelligent battery management system, reliable power conversion system, BYD provides integrated containerized solution.

The use of battery storage in remote areas presents one of the ripest applications for expansion. Diesel generation is costly and polluting, and fuel imports create supply risk, among many things. More renewable energy with batteries at the grid level and at the production site can decrease the necessity of diesel generation, increase clean renewable energy supply and enhance system reliability and stability. The declining costs of solar PV systems and batteries are revolutionizing this market. The combination of solar PV systems and batteries is still more expensive in many areas than retail electricity prices. However, this combination will become cost-competitive in some areas over the next few years in an environment where retail electricity prices are increasing.

In conclusion, batteries are already facilitating the transition towards renewable-based power systems in remote areas and in urban areas for emergency backup systems. Cost falling down are not merely parameter that will determine the attraction towards different battery storage systems. Instead, the attraction and value of battery storage technologies for renewable integration will depend on creating an appropriate low carbon ecosystem with significant interplay among policy, regulation, business models, and consumers.

(Disclaimer: The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of WindPower Nepal Pvt Ltd.)

Specifications Lead Acid Li-ion LiFePO4
Specific energy density(Wh/kg) 30-50 150-190 90-120
Cycle life(80% discharge) 200-300 500-1000 1000-2000
Charging time(hours) 8-16 2-4 1 or less
Self-discharge/month(room temp) 5-15% <5% <5%
Maintenance requirement 3-6 months Not required Not required
Safety Fair(presence of toxic materials) Low(risk of fire and explosion) Excellent (no risk of fire/explosion)
Environment Concern Very dangerous Very dangerous Most Enviro-friendly

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