Li-ion solutions are both scalable and flexible in their power-to-energy ratio. The flexibility enables MTR-type solutions for high-power smoothing, medium-power options for shaping renewable output to meet a forecast, and high-energy systems for shifting of renewable energy to periods of peak load.
Lithium-Ion Energy Storage for PV System in Puerto Rico
Jim McDowall | Saft
Can you give us a brief overview of the PV project in Puerto Rico that will be using Saft’s lithium-ion (Li-ion) energy storage technology?
The Coto Laurel PV facility has an ac rating of 10 MW, and under PREPA’s Minimum Technical Requirements (MTRs) and Agreed Operating Procedures (AOP) must be equipped with an energy storage system (ESS) rated at least 3 MW continuous and capable of providing peak power of 4.5 MW for one minute. The ESS comprises three Saft Intensium Max 20P Li-ion battery containers and an Ingeteam power conversion system. Ingeteam is also providing a site controller that will dispatch the battery power as required by the MTRs.
Knowing PV energy is variable in nature, how does Saft’s energy storage technology overcome the challenge of integrating renewable energy into existing grid?
Under the MTRs the ESS must control the ramp rate of the facility to no more than 10% per minute. The output of a 10 MW PV array could drop by 70 to 80 percent in about a minute, so the ESS has to discharge in a way that ramps the net facility output down smoothly over seven or eight minutes. The high-power design of the Intensium Max 20P is optimized for such short-duration discharges. In addition to ramp-rate control, the MTRs also require the ESS to provide 1 MW of frequency response, discharging to raise the facility output when the frequency is low and charging when the frequency is high.
How does Puerto Rico’s remote island location impact integration of renewable energy sources?
Island grids lack the inertia of mainland networks and are susceptible to disruption, such as could be caused by simultaneous uncontrolled ramping of several renewable facilities (or a single facility in a smaller grid). The ramp-rate control requirement of the MTRs ensures that each facility ramps at a rate that is compatible with fossil-fueled generation on the island, while the frequency-response requirement complements the governor response of those generators to maintain frequency stability. The MTRs are appropriate for island grids but would not be useful for renewable-energy facilities on the mainland because of the sheer size and inertia of such large networks.
What are the benefits of Li-ion solutions for renewable energy storage?
Li-ion solutions are both scalable and flexible in their power-to-energy ratio. The flexibility enables MTR-type solutions for high-power smoothing, medium-power options for shaping renewable output to meet a forecast, and high-energy systems for shifting of renewable energy to periods of peak load. The scalability provides solutions for anything from small residential units up to multi-megawatt systems.
Is there a limited or optimum project size that best suits Li-ion solutions for renewable energy storage?
No. The scalability described previously is achieved through modularity, both in the battery and in the power conversion, and system expansion simply involves adding more modules.
How costly is Li-ion storage and how does it payback the initial costs to the utilities?
The cost of a Li-ion ESS is quite variable depending on whether it is designed for high power for a few minutes, high energy for several hours, or something in between. In the case of an ESS in Puerto Rico payback is achieved by adding a few cents to the price paid by PREPA under the power purchase agreement, still allowing PREPA to save money compared to its traditional generation. The cost of generation in island grids is typically quite high, so the use of energy storage for renewables integration or for spinning reserves normally provides an attractive return on investment.
Saft’s Intensium® Max 20P high-power Li-ion battery containers are providing ramp-rate control and frequency response for a 10MW PV facility in Puerto Rico. Can you share details about the role of ramp-rate control and frequency in renewable energy integration?
Under the MTRs the ESS must control the ramp rate of the facility to no more than 10% per minute. The output of a 10 MW PV array could drop by 70 to 80 percent in about a minute, so the ESS has to discharge in a way that ramps the net facility output down smoothly over seven or eight minutes. The high-power design of the Intensium Max 20P is optimized for such short-duration discharges. In addition to ramp-rate control, the MTRs also require the ESS to provide 1 MW of frequency response, discharging to raise the facility output when the frequency is low and charging when the frequency is high.
Are utility companies on board with renewable energy integration of is there resistance to this advancement?
Most utilities recognize the need for increasing the share of renewable energy, and indeed many are mandated to do so because of renewable targets set by governments. The storage ownership model can differ, however, with PREPA requiring facility developers to provide the storage and others, such as Kauai Island Utility Cooperative in Hawaii, opting for utility ownership. The main difference is that in the PREPA model the storage operates in a highly structured manner, and only when the facility is producing energy, while utility-owned storage can be used more flexibly, responding to frequency deviations whether or not a renewable facility is in production.
Which parts of the US are you finding the most open and why?
The most open areas are those with the most to gain from storage, notably island systems—whether geographical islands like Hawaii or electrical islands like Alaska. In the mainland, any part of the grid with high penetration of renewables can benefit from storage, and we have seen this with forward-looking utilities like San Diego Gas & Electric deploying storage on microgrids and high-penetration feeders.
About Jim McDowall
Jim McDowall has worked in the battery industry since 1977 and is currently in the position of Business Development Manager with Saft, primarily associated with grid systems. Involved in the energy storage market since 1998, Jim was a Director of the Energy Storage Association for 14 years and is a past Chair of the organization. Jim is a Senior Member of IEEE and is Standards Coordinator of the IEEE Stationary Battery Committee, the Chair of two of its working groups, and a past Chair of the main committee. Jim is a frequent speaker at energy storage conferences and related events.
The content & opinions in this article are the author’s and do not necessarily represent the views of AltEnergyMag
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