Evaluate gas turbine part-load performance against the electricity your site will actually consume during each development phase. Request configuration-specific heat-rate curves, minimum operating limits and auxiliary loads. Then compare dispatch arrangements on delivered energy, fuel use, starts and reserve requirements before committing to equipment sized for the final buildout.
A turbine can fit the eventual campus and still be a poor fit for its opening years. The difficult purchase decision is whether to reserve that capacity now, install smaller blocks in stages, or combine generation with another source while demand develops. A nameplate comparison cannot settle it.
This guide sets out the information an industrial buyer should request and how to compare the answers. Start with the gas turbine equipment hub, then qualify the exact offered package against the operating schedule. Availability is useful only when the equipment can serve the demand that arrives.
Key Takeaways
- Build a load profile for each development phase, including site auxiliaries and credible delays to occupancy.
- Keep turbine minimum load, emissions-compliant load and whole-plant turndown separate.
- Compare fuel use across the expected operating schedule; full-load heat rate is only one input.
- Evaluate multiple units against reserve and restart requirements before assuming they improve the operating case.
- Attach the agreed performance curves, exclusions and acceptance method to the equipment offer.
Start with the load that arrives first#
Ask the project team for an electricity-demand profile that the generating plant can use. For a data center, distinguish IT demand from the cooling, electrical losses and other facility loads needed to support it. For an industrial site, identify the process equipment that runs continuously and the production steps that create peaks.
Keep a chronological demand series alongside the load-duration curve. A load-duration curve sorts demand from highest to lowest and shows how long each level occurs. It loses the sequence of events. That sequence matters when an arrangement needs time to start another unit or cannot repeatedly stop and restart between nearby peaks.
Inputs for a phased-demand assessment#
| Input | What the buyer should supply | Equipment decision it changes |
|---|---|---|
| Initial operation | Expected demand profile and date of first usable power | Capacity needed at opening |
| Expansion | Timing, scale and confidence of each load addition | Whether to install capacity together or in stages |
| Low-demand periods | Overnight, weekend, maintenance and delayed-occupancy cases | Minimum-load exposure and shutdown strategy |
| Demand changes | Largest credible load additions and removals | Controls, reserve and transient assessment |
| Reliability duty | Loads that must survive a unit outage and permissible interruption | Online reserve, storage and backup arrangement |
| Site conditions | Ambient range, elevation, fuel and cooling assumptions | Site output and auxiliary requirements |
Produce a delayed-expansion case as well as the expected case. If the next building opens later, the plant may spend longer operating below its intended load. Put that exposure into the comparison before treating future demand as committed revenue or guaranteed utilization.
The power procurement and interconnection roadmap provides the wider scheduling context. For this decision, assign an owner to every demand assumption. A turbine vendor cannot resolve uncertainty about when tenants occupy the building or when an industrial process becomes operational.
Request a performance map with a defined boundary#
Part-load efficiency describes how efficiently a generating arrangement converts fuel into electricity below its stated full-load output. Heat rate expresses the fuel energy required per unit of electricity; a higher heat rate means more fuel energy for the same electrical delivery. Keep its heating-value basis consistent throughout the comparison.
The EPA combustion-turbine technology chapter, section 3.4.3, explains why part-load efficiency can fall. Its historical example curve is useful background, but it does not establish the performance of an offered used unit. Request the applicable OEM or qualified supplier curve for that unit's configuration and condition.
Required fields for comparable performance curves#
| Field | Required clarification |
|---|---|
| Equipment identity | Model suffix, generator, combustion system, package and installed upgrades |
| Electrical basis | Frequency, voltage, power factor and gross or net measurement boundary |
| Fuel basis | Composition, lower or higher heating value, and gas or liquid operation |
| Operating points | Output, heat input and auxiliary consumption at the requested load levels |
| Environmental basis | Ambient temperature, humidity, elevation and inlet/exhaust losses |
| Equipment condition | New, clean, expected as-delivered or tested condition; degradation allowance |
| Maintenance basis | How the proposed starts and cycling affect inspection and service assumptions |
| Constraints | Permitted operating range, emissions basis and minimum time or operating restrictions |
Make the supplier identify which auxiliaries are included. A curve measured at generator terminals and a curve measured at the site's delivery point can describe different amounts of useful electricity. Gas compression, cooling and other plant equipment may change the relationship further as load changes.
Do not apply an unexplained percentage allowance to convert every curve into site performance. Request the calculation boundary and the actual loads. If the supplier cannot provide part-load evidence at the proposed opening demand, record that portion of the offer as an unresolved project assumption before selecting the unit.
The LM6000 dossier is a starting point for identifying a family. The offer still needs its exact variant, package and operating curves; the family name alone cannot supply those answers.
Separate plant turndown from turbine minimum load#
Minimum load can refer to several different limits. A turbine may sustain operation at a load that is outside its specified emissions range. A combined-cycle plant may have a minimum imposed by steam-system conditions or by the arrangement of operating units. A percentage without that boundary is incomplete buying information.
GE's September 2025 LM6000 factsheet illustrates the distinction. The table uses its PC SPRINT column. Values retain the OEM's indicative rating basis; the final row shows editorial arithmetic. Confirm the steam-system layout and operating-unit sequence separately.
Published LM6000 PC SPRINT plant-turndown example#
| Field and basis | 1×1 combined cycle | 2×1 combined cycle |
|---|---|---|
| Reference net plant output | 66.5 MW | 133.8 MW |
| Plant turndown: minimum load | 37.0% | 18.0% |
| Listed frequency offering | 50/60 Hz | 50/60 Hz |
| Rating basis | ISO conditions; natural gas | ISO conditions; natural gas |
| Published boundary | Inlet/exhaust losses included; balance-of-plant equipment excluded | Same stated boundary |
| Implied minimum output: editorial calculation | 66.5 × 0.37 = 24.605 MW | 133.8 × 0.18 = 24.084 MW |
The lower percentage produces a similar absolute minimum because the plant denominator is larger. Compare that minimum with opening demand. The derived decimals are arithmetic on rounded OEM inputs. They retain the datasheet boundary and establish neither a turbine-only limit nor electricity delivered after excluded site loads.
Installed hardware also matters. GE's 9E enhanced-turndown offering describes a combination of fuel-staging hardware and control software for specified combustion systems. This is an OEM upgrade description, not evidence that an older offered machine already has the capability.
Require separate answers for minimum sustained operation, minimum emissions-compliant operation and the lowest output the complete site arrangement can use. If surplus generation would need export, establish whether that export is available. An unapproved export assumption can make an otherwise attractive low-load plan unusable.
Use the simple-cycle and combined-cycle comparison to establish which complete plant arrangement the performance data describes.
Compare unit arrangements against the same duty#
Multiple generating units may allow some equipment to operate at a more favorable load while other equipment remains stopped. That option brings additional equipment, auxiliaries and maintenance interfaces. It also changes the response when an operating unit trips. Compare the complete operating arrangement before assigning a benefit to modular capacity.
Define how many units are online for each demand interval and why. If the site requires immediate reserve, a stopped unit may not satisfy the requirement during its restart interval. Storage, a utility connection or other generation may bridge that interval, subject to their own capabilities and availability.
Count spare capacity at the required ambient condition and delivery point. Name the source that carries the load immediately after a trip and the source that restores reserve later. Those responsibilities may sit with different equipment. A spare turbine awaiting startup should have an explicit role in that sequence.
Arrangements to evaluate in the same bid comparison#
| Arrangement | Potential reason to consider it | Evidence needed before selection |
|---|---|---|
| Larger unit installed early | Capacity available for planned expansion | Opening-load performance and delayed-expansion exposure |
| Several smaller units | Ability to change the number of operating units | Dispatch schedule, restart timing and shared-system dependencies |
| Generation installed in phases | Capacity follows committed demand | Later equipment availability and expansion interfaces |
| Turbine plus storage | Support during transitions or brief changes in demand | Power, energy, controls and recharge requirements |
| Broader technology mix | Different equipment serves different duties | Consistent site, fuel, reliability and lifecycle assumptions |
Siemens Energy describes multiple-unit and island-mode arrangements on its SGT-800 product page. Treat those as configuration options. The SGT-800 dossier can support initial screening, while the supplier defines the arrangement that is actually included in the offer.
Evaluate gas engines, diesel generation, solid-oxide fuel cells and solar with storage on the same required service where they are credible candidates. None should receive assumed reserve, fuel availability or operating flexibility that another option must demonstrate. The fuel-cell and gas-turbine comparison provides a separate starting point for that broader shortlist.
Calculate fuel use across the operating schedule#
For each interval, multiply delivered electrical energy by the corresponding heat rate on a consistent boundary and fuel basis. Add the intervals to obtain operating fuel energy. Account separately for startup fuel, shutdown sequences and any fuel consumed while producing no useful electrical output.
The example below is editorial arithmetic. Its energy and heat-rate inputs are invented solely to show the method; they describe no OEM model, quotation or SecondWatt transaction. Both cases deliver the same annual electrical energy, and every heat-rate input uses lower heating value, or LHV.
Illustrative annual fuel-energy comparison#
| Operating interval | Delivered energy | Case A assumed net heat rate | Case A fuel energy | Case B assumed net heat rate | Case B fuel energy |
|---|---|---|---|---|---|
| Lower-demand operation | 50,000 MWh | 10,000 kJ/kWh | 500,000 GJ | 11,000 kJ/kWh | 550,000 GJ |
| Higher-demand operation | 100,000 MWh | 9,000 kJ/kWh | 900,000 GJ | 9,000 kJ/kWh | 900,000 GJ |
| Total | 150,000 MWh | Energy-weighted below | 1,400,000 GJ | Energy-weighted below | 1,450,000 GJ |
| Energy-weighted heat rate | Same delivery in both cases | 9,333.33 kJ/kWh | — | 9,666.67 kJ/kWh | — |
The conversion is fuel GJ = electrical MWh × heat rate kJ/kWh ÷ 1,000. The lower-demand row for Case A therefore gives 50,000 × 10,000 ÷ 1,000 = 500,000 GJ. Its annual weighted heat rate is 1,400,000 × 1,000 ÷ 150,000 = 9,333.33 kJ/kWh.
50,000 GJ — In this illustrative comparison, Case B consumes that much additional annual fuel energy despite having the same higher-demand heat rate as Case A.
The example isolates one difference. It is not an economic ranking. Add the actual fuel-service terms, startup consumption, maintenance effects, capital scope and auxiliary boundary before comparing costs. A simple arithmetic average of the two heat rates would give the wrong annual result because the energy quantities differ.
For cogeneration, evaluate useful heat against a separate thermal-demand profile. Solar's cogeneration description identifies electricity and useful thermal energy as distinct outputs. Credit heat only where the site can use it at the required conditions. The Taurus 60 dossier can help identify an equipment candidate; it does not establish a heat customer or the value of recovered energy.
Test the operating plan when demand changes#
Steady-state curves do not show whether the site can move between operating points successfully. Request the control sequence for starting another unit, transferring load, losing the largest operating source and returning to normal operation. Define the permissible interruption and voltage/frequency behavior with the facility's electrical designer.
Keep the analysis tied to the loads that must continue. A backup arrangement adequate for controls and orderly shutdown may not carry the operating facility. Likewise, storage sized for a brief transition may be unsuitable for an extended period before another turbine becomes available. The backup-power procurement discussion addresses that separate equipment role.
Challenge shared dependencies. Separate turbines may rely on the same gas-compression equipment, control-power source or cooling system. Count those dependencies when describing reserve. More generating units do not automatically create independent supplies to the facility.
Repeat the operating analysis after a material change to demand, fuel, ambient assumptions or available equipment. Retain the original case so the procurement team can see why the preferred configuration changed. Otherwise, successive supplier revisions can quietly compare different projects under the same bid title.
If the operating plan includes restart without grid support, define the separate gas turbine black-start duty and its auxiliary requirements.
Put the operating evidence into the purchase package#
Ask each shortlisted supplier to return the same demand schedule with its proposed dispatch and equipment arrangement. Require marked exceptions. A response that omits an operating interval should remain visibly incomplete in the comparison, even if its full-load performance is attractive.
Agree how the relevant performance will be checked. ASME's public PTC 22 description covers thermal-performance testing of open-cycle gas-turbine plants and engines, including corrected power and heat rate. If acceptance covers a complete combined-cycle plant, specify the applicable plant-level method separately. Transient performance needs its own assessment.
Specify measurement boundaries, instruments, correction methods, equipment condition and the treatment of uncertainty with the responsible test engineer. Separate a performance shortfall from a changed site assumption. Define who resolves each and what evidence closes the issue before the final acceptance milestone.
For used equipment, attach the configuration record and agreed inspection scope to the same submission. An assumed upgrade or missing control function can invalidate a dispatch plan even when the turbine's mechanical condition is acceptable. State who supplies, installs and commissions any required adaptation.
Advance an offer when opening demand, the minimum operating range and the reserve arrangement fit together on documented assumptions. If the comparison needs an unconfirmed export route, an unspecified upgrade or demand that has no committed date, price and resolve that dependency before selecting the equipment.
SecondWatt provides independent equipment intelligence and connects buyers and sellers; it does not take equipment into inventory. Send the demand profile, target operating mode and proposed development phases to info@secondwatt.com to discuss the information needed for a qualified equipment enquiry.
FAQ: gas turbine part-load performance#
Does running at half load use half the fuel?#
Do not assume a proportional relationship. Fuel use depends on the applicable part-load heat rate, auxiliary consumption and operating boundary. Obtain the curve for the exact configuration and calculate the fuel energy at the required electrical output. A full-load fuel figure alone cannot answer the question.
Is minimum load the same as emissions-compliant load?#
They can describe different limits. Ask the supplier to identify sustained mechanical operation and the emissions-compliant operating range separately, including fuel and ambient conditions. For a complete plant, also establish which generating units and supporting systems must remain online at the quoted minimum.
Are several smaller turbines always better for phased demand?#
No. They may improve the match between operating capacity and demand, but the comparison also includes additional equipment, auxiliaries, maintenance, restart timing and reserve requirements. Evaluate the actual dispatch arrangement and shared dependencies. The preferred choice can change when the expansion schedule or reliability duty changes.
Can a full-load datasheet support an annual fuel budget?#
It can support an initial reference point. An annual estimate also needs the expected energy delivered at each operating condition and the corresponding heat rate. Include startup and other non-generating fuel consumption separately. Use the same heating-value basis and electrical measurement boundary throughout the calculation.
Does adding a battery solve a low-load mismatch?#
A battery can support specific transitions or shift energy within its power and energy limits. Its usefulness depends on the mismatch duration, charging opportunity, controls and required reserve. A sustained difference between generation and demand needs an explicit operating strategy; adding storage does not by itself establish one.
What should a used-turbine seller provide first?#
Request the exact unit and package identity, installed upgrades, condition evidence and available performance records. Share the intended demand profile so the seller can identify applicable curves and limitations. Use that exchange to define missing information before relying on a generic model-family performance claim.