Problem Objectives
The electric grid is facing two issues – unfavorable renewable energy peaks and a projected significant increase in peak loads due to electric vehicles. Our project seeks to address both of these concerns.
- Design an economically favorable compressed air energy storage system that can store and release energy generated by renewable sources.
- Scale this energy storage system to meet the user needs of grid operators within the context of projected electric vehicle growth.
- The system’s ability to store and release energy is not time-of-day-dependent.
- The system’s ability to store and release energy is not geographically-dependent.
Compressed Air Energy Storage System Overall
Constraints
- The system must generate at least 1320 W of power. This is the power required to meet Level 1 EV charging requirements. In order for our design to meet the needs of our stakeholders, EV manufacturers and owners, power output must meet this threshold.
- The system’s run time is longer than 30 seconds. Having a prototype that can run for more significant periods of time enhances the system’s modeling and demonstration capabilities.
- The system’s loudness while in operation is less than or equal to 90dBs. This is a safety consideration, exposure to noise over 90dBs for extended periods of time can lead to hearing damage.
- The system’s design components are easily sourced, inexpensive, straightforward to assemble, and integrated with each other. Our prototype serves as a model for a larger, utility-scale compressed air energy storage system. Because of this, we would like our prototype to be easily imagined and replicated on a larger scale. We, therefore, want the system to run on components that are accessible at larger pressure or power capacities (ie: larger pressure vessel and air motor) and are not uniquely fitted to our prototype’s scale.
Metrics
- Total round trip efficiency of 50 percent
Subsystem Metrics and Constraints
Heat Exchanger
Constraints
- Storage capacity is sufficient to store 80% of the heat of compression from the compressor. Being able to store this much heat of compression ensures that the heat exchanger design is advantageous to the efficiency and adiabatic design goal of the overall system.
- Useful life with regular maintenance of 20 years. Because the heat exchanger is the only subsystem that we are designing ourselves, we want to ensure that its design is cognizant of the maintenance and longevity of its lifespan.
- The system’s length of high-pressure piping is minimized to 1 foot. For safety considerations.
Metrics
- 5 percent pressure drop from both pipe and valve effects
- Effectiveness of 80 percent
Compressor
Constraints
- Compressed air is stored at a minimum of 100psi. Compressed air is stored at high pressure to allow for regulated release at 100psi for as long as possible so that the system’s run time and power output can be maximized.
- Compressor is vertical and weighs less than 200 pounds. We want our prototype to be portable so that it can be demonstrated and potentially implemented in various spaces. To do that we wanted to make sure the pressure vessel, the largest component, was on wheels and designed so that it could safely be moved.
- Compressor has two compressing stages. Intercooling between compression stages allows for more heat extraction and therefore higher efficiencies. The two-stage design also makes the high-temperature air stream more accessible for the heat exchanger piping.
Metrics
- At least 70 percent mechanical efficiency
Expander/Generator
Constraints
- Vibration of the air motor is limited to 0.1in/sec. This is the acceptable vibration of an air motor so that the system is safe and losses to vibration are limited. We are currently designing a housing prototype to constrain vibrations.
- Airflow less than 90 cfm. Limiting the airflow discharge rate enables the system’s run time to be longer.
Metrics
- At least 80% mechanical efficiency for the expander
- At least 90% generator efficiency