Energetica India Magazine: september 2020

31 energetica INDIA- September_2020 ENERGY STORAGE battery modules, we eliminate voltage at the terminals until the system is fully engaged and the BMS can confirm that all cables are correctly installed. There is no voltage or power to the terminals as long as the contactor is open. Con- tactors also reduce the risk by isolating the modules as single units no matter how large the overall system size. The element of crew safety of our techni- cians and the operation staff cannot be overstated in terms of benefit to our customers. Instead of relying on spe- cially qualified technologists, we can now train the customer’s engineers to do maintenance. This design decision was not free, but it is the right way to go to improve overall safety and reduce costs for our customers. Figure 2: Sterling PBES patentedeVent system showing path of gas extraction in a single cell thermal event. Image courtesy Sterling PBES. Cost Another critical part of the design of a battery is not the actual battery itself, but the space the battery operates in. The added costs of necessary safety systems can be significant. Most bat - tery suppliers off-load these safety mea- sures onto other contractors and by not including them in the quoted price of the battery. These add-on systems are critical to the performance and safety of a battery and are therefore included in every Sterling PBES system deployed. Another benefit of liquid cooling is the ability to predict the lifespan of our sys- tems. Air cooled batteries are dependent on the ambient temperature to manage the overall life of a lithium battery. Even a small increase in battery room tem- perature has a significant reduction in calendar life. In contrast, liquid cooling maintains the temperature of the cells at a fixed range eliminating the impact of ambient temperature on lifespan. Size and Cost The other significant feature of any system is the percentage of energy available on a continuous basis. On air- cooled designs, the continuous rating is about 70%. This means that if 1MW of energy is required, a battery of 1.4MWh of capacity will operate at 1MW load - a larger, heavier system that is significant - ly more costly to install and maintain. If we assumed that the battery system cost $100/kWh, then a 1.4MWh battery adds $140,000 to the capital cost of the system. With Sterling PBES CellCool, the battery can operate at an average continuous rate of 300%. A 1MWh system can now be met with a 350kWh battery; much smaller, much lighter, and much less costly to install, with only a $35,000 bud- get needed. Figure 3: Advanced technology: Patented Cell- Cool TM liquid cooling reduces risk and increases lifespan. Image courtesy Sterling PBES. Sustainability A battery that can last for ten years is a pretty amazing thing, but it will like- ly not match the lifespan of the power generation system it is supporting. This equates to battery system replacement Figure 4: CellSwap TM battery reconditioning re- duces cost and increases sustainability. Image courtesy Sterling PBES. Where to next? Commercial needs will continue to drive improvements. Gone are the days when a battery was a fire and forget proposition. They are now an integral part of the overall system design and can provide significant ROI when deployed thoughtfully and with care. Modern batteries can provide safe, reliable service for decades and, when integrated correctly, reduce the system size and cost of any renewable grid energy system every five or ten years. In analyzing a system, our engineers realized that the most significant reason for ESS replace - ment was the fact the cells will age with time and use. With Sterling PBES CellSwap TM the cells of a battery module are able to be re- placed within 30 minutes. Cell swap means that the battery system life span is now the same as that of the power generation system. With this inclusion, the design of the battery system is now in line with market requirements. Recycling will have an increasingly prominent role in decision making in coming years. This is part of the benefit of a cell swap; we can recycle the lithium cells at a very low cost because only the cells are replaced – the other hardware is reused. While often overlooked, it is necessary for any company that uses ESS in commercial operations to include this operational expenditure in their im- pact analysis.