Valve Regulated Lead Acid Battery Evaluation under Peak Shaving and Frequency Regulation Duty Cycles

Overview

The study asks how suitable lead-acid technology is for grid storage services and how known degradation mechanisms (sulfation, water loss, positive active-mass shedding) map to each service. Test modules were six-cell C&D SHC 12-200FT lead-carbon AGM VRLA, 172 Ah at the C10 rate to 1.8 V/cell at 25 °C, 60 kg. Two modules ran peak shaving at different discharge rates and two ran 24-hour frequency regulation in different SOC windows, with periodic capacity and pulse-resistance tests. Duty cycles followed the PNNL/Sandia energy-storage performance protocol; the data cover 28 months for one duty cycle and 18 months for the other three.

Peak shaving at 50% DoD was 730 W for 1.2 h (PS 2-h) and 246 W for 3.8 h (PS 8-h), recharged at 265 W to 14.1 V then CV, about 2 cycles per day. The frequency-regulation signal was normalised to 1090 W (C1 rate at 50% SOC), about 3.9 kWh of discharge throughput per 24-h energy-neutral cycle, run in 80-60% and 57-37% SOC windows.

Results: FR-cycled batteries degraded more than PS-cycled batteries over the same time; the 57-37% SOC FR module degraded most, while PS modules recovered capacity after an initial drop. No module showed significant temperature rise, so dry-out was not a major failure mode. Capacity loss per energy throughput ranked FR (57-37)% > FR (80-60)% > PS 8-h > PS 2-h, following the potential for sulfation; FR (80-60)% spent 3.5× longer below 70% SOC than PS 8-h. Higher resistance during charge limits maximum power for energy-neutral services such as frequency regulation.

Limits: four modules, one product (lead-carbon AGM) and 28 months for one duty cycle against 18 for the others, with no repeats, so measured differences come from a small sample. The results bear directly on proposals to use VRLA UPS strings for grid services.

Key points

1. Test modules: six-cell C&D SHC 12-200FT lead-carbon AGM VRLA, 172 Ah at the C10 rate to 1.8 V/cell at 25 °C, 60 kg.
2. Duty cycles followed the PNNL/Sandia energy-storage performance protocol; the data cover 28 months for one duty cycle and 18 months for the other three.
3. Peak shaving at 50% DoD: 730 W for 1.2 h (PS 2-h) and 246 W for 3.8 h (PS 8-h), recharged at 265 W to 14.1 V then CV, about 2 cycles per day.
4. The frequency-regulation signal was normalised to 1090 W (C1 rate at 50% SOC), about 3.9 kWh of discharge throughput per 24-h energy-neutral cycle, run in 80-60% and 57-37% SOC windows.
5. FR-cycled batteries degraded more than PS-cycled batteries over the same time; the 57-37% SOC FR module degraded most, while PS modules recovered capacity after an initial drop; no significant temperature rise was seen.
6. Capacity loss per energy throughput ranked FR (57-37)% > FR (80-60)% > PS 8-h > PS 2-h; FR (80-60)% spent 3.5× longer below 70% SOC than PS 8-h.
7. Higher resistance during charge limits maximum power for energy-neutral services such as frequency regulation.

Using it in design

• When considering VRLA UPS strings for grid services, account for frequency regulation (especially in a low SOC window) degrading batteries much faster than peak shaving, with capacity loss tracking internal resistance rise.
• For a grid-service duty, keep the SOC window high and limit time spent below 70% SOC as the sulfation indicator.
• Verify UPS backup autonomy periodically with capacity and internal-resistance tests after grid-service cycling.

Who should read it

Energy and electrical engineers evaluating the use of VRLA-based UPS strings for grid services.

Document contents

1. 1. Introduction
2. 2. Failure Modes for Lead Acid Batteries (2.1 Flooded Batteries, 2.2 VRLA Batteries)
3. 3. Experimental Setup (3.1 Module Specification, 3.2 Test Protocols: reference performance capacity test, DC current pulse test to measure internal resistance, peak shaving duty cycle test, frequency regulation duty cycle test)
4. 4. Results and Discussion (4.1 Reference Performance Test Results, 4.2 Pulse Resistance Test Results, 4.3 Degradation Analysis)
5. 5. Conclusions

Related standards

• IEC 60896-21
• IEC 60896-22
• IEEE 1188
• IEEE 1679

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Publication details

Authors

Nimat Shamim; Vilayanur V. Viswanathan; Edwin C. Thomsen; Guosheng Li; David M. Reed; Vincent L. Sprenkle

Publisher

Energies (MDPI AG)

Year

2022

Volume

15

Issue

9

Pages

3389

Document language

English

Source type

Scientific

Access

Open licence — downloadable

DOI

10.3390/en15093389

Licence

CC BY 4.0 — share with attribution

Licence evidence

www.mdpi.com

Citation