The Puerto Rico Electric Power Authority (PREPA) identified its island condition and the relatively large size of its generating units as main factors leading to unacceptable system performance (blackouts) when
generation deficiency occurs. A team composed of the University of Puerto Rico at Mayagüez, PREPA and Raytheon/Westinghouse was created to evaluate possible solutions to Puerto Rico's rapid response spinning reserve insufficiency under generation deficiency conditions.
We proposed a three-part study to determine:
Phase IA - the energy requirements (size) of an energy storage unit that will support Puerto Rico's electrical system with rapid spinning reserve to prevent a blackout under generation deficiency conditions;
Phase IB - the technical and economic parameters required to design a Superconducting Magnetic Energy Storage (SMES) system to meet the previously mentioned energy storage requirements; and
Phase IC - an operational and economic evaluation of alternative energy storage technology such as SMES and Battery Energy Storage Systems (BESS) to achieve the most economical solution to Puerto Rico's electric power system rapid response spinning reserve insufficiency under generation deficiency conditions.
Phase IA study showed that the energy storage unit needs to store 60 MW, bringing the total amount of stored energy in Puerto Rico’s system to 80 MW (including the 20 MW BESS actually in use). If generation deficiency, of the order of 400 MW, occurs the energy storage units will provide rapid response spinning reserve. The energy storage units must provide 80 MW for at least 5 minutes to prevent under frequency load shedding. This scenario presumes the San Juan repowering units are allowed peak-firing action.
Phase IB study produced a SMES conceptual design for a 10-MW pilot plant and cost/weight/size estimates for the pilot plant and the full-scale rapid spinning reserve application. The final conceptual design package include information such as: an overall system description (magnet, PCS, refrigeration, etc), an overall system drawing and layout, subsystem drawings and layouts, interfaces, weigt/volume and cost, full specification and protection for the magnet, design basis, capabilities and operating characteristics of the Power Conditioning System, design basis, description and ratings for the refrigeration subsystem, design basis, layout for vessel and pumping systems for the vacuum system, the system operating characteristics and design envelope, fringe field calculations, cost/weight/volume estimates and component availability (off-the-shelf or developmental).
Phase IC study produced an economic comparison, based on present value calculations, between a 60 MW BESS, a 60 MW SMES, a 60 MW SMES plus diesels as well as cost estimates for a 10 MW SMES pilot plant, a 50 MW SMES and a 70 MW SMES.
The combined results of our study show that the 60 MW SMES option alone will not be a solution to the rapid spinning reserve insufficiency under generation deficiency conditions problem. This is so because the electric system requires a 60 MW injection for at least 5 minutes. The SMES unit becomes uneconomical if it is required to discharge for longer than one (1) minute. A BESS unit will solve the problem since it can sustain the required discharge for more than 5 minutes.
A SMES plus diesels option, a combination that will keep the required power output over a five minutes period or more, will also solve the problem. The SMES plus diesels solution present value was calculated as $133,004,974. The 60 MW BESS present value was calculated as $101,523,044 ($31,481,930 less than the SMES plus diesels solution.) The most economical of the solutions considered is the 60 MW BESS.
For the complete report contact Dr. Agustin Irizarry (agustin@ece.uprm.edu)