Our research focuses on advanced energy storage solutions to allow for increased penetration of renewable electricity generators beyond the widely-stated value of 20% by nameplate capacity. Each renewable resource is unique with regard to both geographical and time characteristics. The following are a few recent project examples. Some are models and data-analysis based, while others are experimental projects.

Repurposing EV batteries at a grid storage: mixed battery array

There are millions of electric vehicles (EV) traveling the roads today, with exponential growth in numbers. Each vehicle has a lithium-ion battery pack rated 24 – 100 kWh in size. While the batteries will age and reduce in performance, there will likely be a significant capacity remaining when the vehicle reaches end-of-life (wrecked, worn-out, corroded). Our project takes used EV batteries from Nissan, Tesla, GM, Enerdel and others to characterize their performance in grid storage applications such as frequency regulation and peak shaving. We are presently mapping their performance (kW, kWh, energy efficiency, thermal response) and will create a new stacked-service control strategy for a mixed-battery-array. Such an array is a regionally located conglomerate of used EV batteries from different marques and models. The following is a pilot mixed battery array of Nissan and Enerdel on a multi-channel 100 kW power cycler.

High-voltage grid storage cell balancing

Battery storage for the electricity grid is maturing to higher voltages, now up to 800 VDC. In this project we built an air cooled battery pack composed of 360 lithium-ion cells in 2P180S configuration. The pack is fully instrumented and sits on a blower-deck. Using this battery we are evaluating the imbalance characteristics and necessary currents and duration of balancing to insure safe pack operation in long series strings. In the below screen the pack is disconnected (no HV PPE) and we are taking some IR measurements.

Model predictive control of commercial building systems

Commercial buildings use a high proportion of electricity to be well-lit and functioning. We have developed new Model Predictive Control strategies to influence building HVAC operation and take advantage of the natural thermal mass storage of buildings. These new control strategies enhance occupant comfort while saving both energy and peak electricity demand. This integrated well with new building technologies such as integrated solar and heat-pumps.

Techno-economics of energy storage

Energy arbitrage is an exciting opportunity for storage. While it is presently not as profitable as frequency-regulation service, a competitive and market driven energy arbitrage service will solve problems such as peak-shaving, mid-day PV curtailment (peak generation), and over-night wind turbine curtailment (low load). We have laid out a “recipe” in one of our publications for assessing services technical and economic viability. It progresses through the following table of parameters, and arrives at a comparison of wear cost (effectively depreciation) vs energy efficiency and energy purchase price. The chart can be used to quantitatively assess arbitrage and gauge the important of high-efficiency and low-purchase price.