As the project comes to an end, flooded lead acid batteries were found to be the most reliable and economical solution. Each alternative studied has advantages over one another, but lead acid batteries were found to have the best overall characteristics. This evaluation was based on primarily on reliability, initial costs, maintenance costs, useful life and size.
One alternative that ranked well in relation to lead acid batteries was a hybrid system consisting of ultracapacitors and lead acid batteries. In this hybrid system, the ultracapacitors would only be sized to supply a momentary current used to trip the breakers. The lead acid batteries would only be sized to supply the continuous loads presented by relays and other control room equipment.
The price of the hybrid system discussed is comparable to the price of a system of a purely lead acid battery system. The m aintenance requirements of the hybrid system will also be similar to the requirements of a purely lead acid battery system. The reliability of the hybrid system is questionable because ultracapacitors are still a relatively new technology that hasn't seen the extensive field testing that lead acid batteries have seen. With costs comparable for the two systems and reliability somewhat uncertain for the hybrid system it is unreasonable to replace the present lead acid battery systems with this hybrid system. However, if ultracapacitor see more extensive field testing in the future and ultracapacitor prices come down this system may become a viable option.
A basic bench top test testing system was developed using ultracapacitors to show their effectiveness. A diagram of the bench top system can be seen below. The purpose of this test system was to understand some of the implementation considerations when using ultracapacitors.
Bench Top Diagram
See the final report for detailed analysis of reliability and alternatives along with a detailed final recommendation.