Fuel and efficiency
Set a flat heat rate or a heat rate curve that describes efficiency across load levels. Add fuel cost per unit of energy input, any cost per unit of electricity output, and an hourly running cost.
Technologies
Generator and genset modelling
Fuel-powered generators, or gensets, provide resilience within microgrids and behind the meter, or peak generation and contingency reserve within the wider grid. They can run on gas, diesel, biofuel or hydrogen. Gridcog models them alongside solar, battery storage and grid supply, with fuel costs, efficiency and emissions, so you can size them and see when they should run.
When diesel rose from A$1.60 to A$3.00 a litre, the optimal design for a 10 MW industrial site in New South Wales cut diesel capacity by 1 MW and added about 9% more solar and 21% more battery.
For a 100 MW UK data centre on a 50 MW grid connection, 20-year opex was £1,135m with solid oxide fuel cells against £1,412m with gas gensets, but the model assumed fuel cell capex five times higher per kW.
In Ireland, a 25 MVA data centre would need 90 MW of 4-hour battery storage to meet Ireland's proximate generation rule for data centres, against 29 MW of gas turbine capacity.
What is a genset?
A genset is a fuel-powered electricity generator, typically a diesel generator or gas turbine. It can also run on renewable fuels, as biogas generators and hydrogen fuel cells do. Gensets provide resilience within microgrids and behind the meter, or peak generation and contingency reserve within the wider grid.
What are generators used for?
| Use | What the generator does | How Gridcog runs it |
|---|---|---|
| Backup and off-grid supply | Meets whatever load is left after solar, wind and batteries | Unserved Load mode |
| Peak shaving | Runs when it's cheaper than importing from the grid, for example in network peak demand periods | Co-optimised mode |
| Microgrids | Provides firm capacity, and spinning reserve or fault current where the system needs it | A Must Run minimum output alongside either mode |
| Firm on-site supply | Covers demand a constrained grid connection can't, for example at a data centre | Co-optimised mode with the site's import limit |
| Capacity markets | Earns availability payments in markets that accept gensets | Capacity Market settings on the asset |
How does Gridcog model a generator?
As an optimisable asset on the site, interval by interval. Gridcog decides when the genset runs against the site's load, the other assets, the grid connection and every price signal the site faces, using the fuel cost and efficiency you set.
Operating limits
Set a minimum operating load, ramp up and ramp down rates, a maximum energy output per week, and a Must Run minimum output, for example to hold spinning reserve or provide fault current.
Dispatch modes
In Unserved Load mode, the genset follows whatever load the other assets can't meet, as in an off-grid site. In co-optimised mode, it runs only when that's cheaper than importing from the grid.
Emissions
Set an emissions intensity in tonnes of CO2e per MWh, and compare the emissions of each design alongside its costs.
Solar, storage and constrained connections
Model gensets with solar, batteries and a limited grid connection, and compare generator sizes in alternative scenarios to find how much firm capacity the site needs.
Any fuel
Add generators regardless of fuel type: diesel, gas, biogas or hydrogen fuel cells, each with its own efficiency, ramp rates and costs.
Modelled in Gridcog
How do fuel prices change the role of a backup generator?
They can turn it from a money-saver into a reliability-only asset. Gridcog Senior Energy Analyst Scott Bosman sized solar, diesel and a battery for an industrial site in New South Wales at two diesel prices. At the higher price, the generator stopped running to cut network charges and ran only when nothing else could meet the load.
Scott Bosman
Senior Energy Analyst
Read Scott's analysis: rising fuel costs and the shift to energy resilience
10 MW industrial site, New South Wales, Australia
- Site
- Near 24/7 demand on a 5 MW grid connection, so on-site generation has to cover the rest
- Assets
- Solar, diesel generation and a 4-hour battery, with sizes optimised for each scenario
- Scenarios
- Diesel at A$1.60 a litre (before the 2026 price shock) and A$3.00 a litre (after)
- Costs
- CSIRO GenCost capex; retail, network and environmental charges; a 20-year model
- Optimal design
- At A$3.00, 1 MW less diesel capacity, about 9% more solar and 21% more battery
- Generator's role
- At A$1.60, it ran in network peak demand periods and to avoid unserved load. At A$3.00, only to avoid unserved load
- Share of supply
- The generator's share of the site's energy fell from 3% to 1%
- 20-year cost
- The A$3.00 design was about A$15m more expensive, because extra hardware and higher network costs outweighed the fuel and retail savings
Sizing a generator, or working out when to replace one?
Model your site in GridcogShould a data centre choose a fuel cell or a gas genset?
Pete Tickler
Chief Product Officer
It depends on whether you need efficiency or flexibility. Gridcog Chief Product Officer Pete Tickler modelled a 100 MW UK data centre on a 50 MW grid connection, with co-located solar and storage, supplied by either solid oxide fuel cells (SOFCs) or gas gensets.
| Gas-fired genset | Solid oxide fuel cell | |
|---|---|---|
| Maximum electrical efficiency | 40% | 60% |
| Ramp rate in the model | 20% per minute | 1% per minute |
| Capex | £1,000/kW | £5,000/kW |
| Emissions | 0.5 kg CO2e per kWh | 0.37 kg CO2e per kWh |
| 20-year opex in Gridcog | £1,412m | £1,135m |
| Suits | Flexible supply that ramps with prices, solar output and the battery | Steady baseload supply, with lower 20-year opex and emissions |
| Watch out for | Lower efficiency means more fuel per kWh, and higher grid import costs and emissions over 20 years | Capex in a different league; slow ramping means less response to prices and solar |
Who is planning to replace diesel generation with Gridcog?
Community microgrids, Western Australia
AMPERES and Amboranj Power
With ageing diesel power stations in remote First Nations communities nearing the end of their lives, AMPERES and Amboranj Power are using Gridcog to build the case for community-owned solar farms and battery storage. With Amboranj Power's support, Djarindjin Aboriginal Corporation secured A$5m in funding from JTSI for the Lower Carbon Grants Program.
‘Excel spreadsheets and back-of-the-envelope calculations only take you so far.’
Who models generators in Gridcog?
Data centres, large energy users, microgrid developers and the consultants who advise them.
Frequently asked questions
Model the site's load with its solar, battery and grid connection first, then see what's left. In Unserved Load mode, Gridcog runs the genset to meet whatever the other assets can't, so you can see how often it runs and at what output. Compare generator sizes in alternative scenarios against their capex, fuel and the amount of unserved load.
When it's cheaper. In co-optimised mode, Gridcog runs the genset only when its fuel and running costs are lower than the cost of importing, including network demand charges. In Scott Bosman's New South Wales model, diesel at A$1.60 a litre ran in network peak periods; at A$3.00 it no longer paid to.
Often in part, but not always completely. In Scott Bosman's industrial site model, higher diesel prices shifted most of the generator's work to solar and storage, but the site still kept diesel for reliability in low-renewable periods. Gridcog shows how much generator capacity a site still needs once solar and storage are sized.
Yes. Gridcog's genset asset covers fuel-powered generation of any fuel type, including biogas generators and hydrogen fuel cells, each with its own heat rate, ramp rates, running costs and emissions. Pete Tickler's data centre model compared solid oxide fuel cells with gas gensets this way.
Yes. Set each generator's emissions intensity in tonnes of CO2e per MWh and compare designs on emissions as well as cost. In Pete Tickler's data centre model, a solid oxide fuel cell emitted 0.37 kg CO2e per kWh against 0.5 kg for a gas genset. Both run on gas, so neither is zero-carbon on its own.
Where the market allows it. Gridcog lets you assign capacity markets to a genset, with the auctions, prices and de-rating factors set in the Gridcog Library, so availability payments sit in the cashflows alongside fuel and running costs. Compare that income with the cost of keeping the generator available.
Request a live demo
Model your generators in Gridcog
Request a demo and we'll show you how Gridcog sizes and dispatches generators with solar, storage and the grid.
The team behind Gridcog
Fabian Le Gay Brereton
Chief Executive Officer & Co-Founder
Previously co-founded Greensense, acquired by ERM Power (now Shell Energy).
Pete Tickler
Chief Product Officer & Co-Founder
Co-founded Greensense and led digital innovation at ERM Power (now Shell Energy).
Genna Boyle
Chief Commercial Officer & Head of EMEA
More than 10 years in energy strategy, trading and renewables, with senior roles at Battery Optimiser and Limejump.
.png)
