The Reality of Replacing Diesel Generators with Natural Gas, Energy Storage, Fuel Cells & Other Options

Overview

The paper evaluates alternatives to diesel generators for 24-hour backup and narrows the field to natural gas gensets, Li-ion BESS and PEM fuel cells. They are compared on emissions, cost, footprint, start-up time and technology maturity. The evaluation basis is a 1 MW load, 24 hours of backup, 4.7 hours of outage per year and 1 hour of maintenance per month.

The conclusion is that there is no clear drop-in successor to diesel. The most practical routes are natural gas generators or sustainable diesel fuels (biodiesel, HVO). Li-ion BESS suits runtimes under about 4 hours, not 24. PEM fuel cells look promising for long runtimes if hydrogen supply matures. Numbers make the comparison concrete: a diesel genset starts and accepts load in under 10 seconds, while natural gas takes 10 to 45 seconds. Lean-burn natural gas emits about 425 kgCO2e/MWh, roughly 40 percent less than diesel, and rich-burn about 637, roughly 11 percent less. A PEM fuel cell on grey hydrogen sits around 946 kgCO2e/MWh.

Diesel occupies about 11 m2/MW including a 24-hour belly tank for a 1 MW unit, and its annual maintenance costs about 9 to 10 thousand dollars per MW. The study is a general technology assessment rather than a product comparison, so local fuel supply, permitting and costs must be rechecked for each project. The results can be used directly in a design tool: fuel type, start time, footprint per MW and kgCO2e/MWh can be kept as catalogue fields. In a Tier III or higher design where genset start time exceeds 10 seconds, UPS runtime has to be increased. A carbon calculator can also take the emission factors in the paper as defaults.

Key points

1. Diesel genset starts and accepts load in under 10 s; natural gas 10-45 s (lean burn averages about 45 s to 100 percent load)
2. Diesel footprint is about 11 m2/MW including a 24 h belly tank (1 MW unit)
3. Lean-burn natural gas about 425 kgCO2e/MWh (about 40 percent below diesel); rich-burn 637 (about 11 percent below)
4. Grey-hydrogen PEM fuel cell about 946 kgCO2e/MWh
5. Evaluation basis: 1 MW, 24 h backup, 4.7 h/yr outage, 1 h/month maintenance
6. Diesel annual maintenance is about 9-10 thousand dollars per MW
7. Li-ion BESS is practical for runtimes under about 4 h, not 24 h

Using it in design

• Keep fuel type (diesel, HVO, natural gas, fuel cell, BESS) as a field in the generator catalogue
• Add start time, footprint per MW and kgCO2e/MWh as catalogue fields
• In a Tier III or higher design, increase UPS runtime if genset start exceeds 10 s
• Use these emission factors as defaults in the carbon calculator

Who should read it

Designers and decision makers on projects with emissions or permitting limits on diesel standby plant.

Related standards

• NFPA 110
• ISO 8528
• EPA Tier 4
• IEC 62282

Publication details

Authors

Allegia Wiryawan; Carsten Baumann

Publisher

Schneider Electric

Year

2022

Document number

WP 14

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation