Geothermal Power Plant Step-Up Transformer: How to Size a GSU for Flash and Binary Units, Why H2S and 45 °C Powerhouse Air Change the Specification, and What Load Rejection Demands

The answer first: a geothermal GSU is sized on generator MVA and then re-rated for 45 °C air, H₂S and altitude

A geothermal generator step-up (GSU) transformer is sized from generator MVA at its rated power factor — typically 1.05–1.10 × generator MVA, with 8–12% impedance at 33 kV — not from the plant's nameplate MW. The number that surprises most first-time buyers is the house load: a flash-steam plant consumes 8–18% of its gross output, and a binary ORC plant with air-cooled condensers consumes 15–30%, so a 25 MW unit needs a 3–6 MVA auxiliary transformer as well as a 30–35 MVA GSU. What separates a geothermal GSU from a hydro or wind GSU is not the electrical duty but the environment: 100–1,000 ppmv hydrogen sulphide in the steam, 45–50 °C powerhouse air, altitudes of 1,500–2,700 m, and volcanic-zone seismicity. Because a geothermal plant runs 7,500–8,000 hours a year at baseload, no-load and load losses are worth roughly USD 6,000–8,000 per kW capitalised, which is why a cheap transformer is the expensive choice here.

Key takeaways

• Size the GSU on generator MVA × 1.05–1.10 at 0.85–0.92 power factor, then check the auxiliary load separately: flash plants 8–18% of gross, binary ORC plants 15–30%.
• H₂S at 100–1,000 ppmv attacks copper, silver and zinc, so specify tin-plated copper, stainless 316 hardware, ISO 12944 C5-M paint or a sealed IP55 tank, and a desiccant breather — not a standard painted tank.
• IEC 60076-2 rates liquid-immersed transformers for 40 °C maximum ambient; a 50 °C powerhouse costs roughly 8–10% of rating unless you move up a cooling class (ONAN to ONAF) or up a size step.
• Load rejection and islanded operation, not normal loading, set the tap range and the over-excitation limit: specify ±8 × 1.25% OLTC, 110% continuous over-flux and a witnessed load-rejection test.
• At 8,000 h/yr and USD 0.07/kWh, each kW of total loss is worth about USD 7,000 over 25 years — a 0.1 percentage-point efficiency gain on a 40 MVA unit is worth more than a typical price difference between two suppliers.

Where do transformers sit in a geothermal plant? Four duties, four specifications

A geothermal power station is electrically simple and environmentally hostile. Power flows from an 11–15 kV generator through a GSU to a 33 kV collector or a 115–220 kV grid connection, while a much smaller auxiliary system feeds the pumps and fans that keep the cycle alive. The four transformer duties below are often quoted as one line item in a tender, which is exactly how plants end up with an undersized auxiliary unit and an over-painted GSU.

The GSU and UAT are the two units that matter commercially: together they are typically 6–9% of the mechanical and electrical package cost of a flash plant, and they are the two items whose failure stops generation completely. A wellhead transformer, by contrast, is a distribution-class unit that has to survive being fed through kilometres of cable in a hot, humid, sulphurous wellfield.

How do you size a geothermal GSU in five steps?

The sequence is fixed: generator electrical output, power factor, margin, impedance window, and then the environmental re-rating that most templates forget.

Step 1 — generator MVA, not plant MW. A 30 MW steam turbine generator at 0.88 power factor and 11 kV delivers 34.1 MVA at its terminals. The turbine's rated MW is a thermal figure; the transformer sees apparent power.

Step 2 — apply the margin. Use 1.05–1.10 × generator MVA to cover voltage and frequency excursions, short-time overload during load rejection, and the fact that generators are often re-rated upwards after a turbine upgrade. For the 34.1 MVA example, the requirement is 35.8–37.5 MVA, which lands on a 40 MVA standard rating.

Step 3 — fix the impedance window. On a 33 kV collector the GSU impedance is normally 8–12%; on a 115–220 kV connection, 10–14%. Lower impedance reduces voltage dip on motor starting and improves load-rejection behaviour but raises the LV fault current that the generator breaker and the generator itself must withstand. Check the resulting fault level against the generator's sub-transient reactance and the switchgear rating using the method in our short-circuit current calculation guide.

Step 4 — re-rate for the site. A powerhouse at 1,600 m with 45 °C air is not the IEC reference condition. Apply the ambient correction (roughly 1% of rating per K above 40 °C for oil-immersed units, more for dry-type), the altitude correction above 1,000 m, and the cooling-class decision: moving from ONAN to ONAF1 typically recovers 20–25% of rating for 1–2% additional loss.

Step 5 — round to a standard rating and check the losses. Choose the next standard size after derating, then evaluate no-load and load loss at 8,000 h/yr with your own energy price. The arithmetic is in our sizing and budget formula guide; the loss-capitalisation table later in this article shows why a 40 MVA unit at 99.45% and one at 99.30% are not the same purchase.

Flash steam or binary ORC: how does the cycle change the transformer?

The conversion technology decides the generator speed, the voltage, the auxiliary load and the operating pattern — all four feed the transformer specification.

The practical difference is where the money goes. In a flash plant, the GSU dominates and the technical argument is about impedance, load rejection and corrosion. In a binary plant, the auxiliary transformer and the condenser fans dominate: on a 15 MW air-cooled ORC unit at 40 °C site ambient, fan power alone can reach 1.5–2.5 MW, which is a 2,000–3,150 kVA auxiliary transformer before any pump load is added.

How much parasitic load does a geothermal plant actually carry?

Parasitic load is the single most useful number for sizing the auxiliary system, and it varies more between plant types than between manufacturers. The ranges below are from operating flash and binary plants and from vendor performance guarantees; treat them as design ranges, not standards.

Size the UAT on connected load with a 1.15–1.25 margin, not on measured average demand: the cooling system is designed for the hottest day, and that is the day the transformer is also derated. Two half-size UATs with a tie breaker are common in plants above 30 MW, because losing the auxiliary supply during a GSU outage otherwise means a full shutdown rather than a forced cooling-down period.

Why does hydrogen sulphide decide half the specification?

Geothermal steam carries H₂S at 50–1,000 ppmv, and condensed steam turns it into a weak acid solution with pH 3–4 in the presence of CO₂. The result is a corrosion environment closer to a chemical plant than to a power station, and it attacks exactly the materials a standard transformer uses.

What fails first. Bare copper busbars and flexible connections darken and form conductive corrosion products; silver-plated contacts tarnish into high-resistance films; galvanised cable trays and zinc-rich paint fail within a few years; aluminium LV links pit; standard nitrile gaskets harden. Failure mode is rarely dramatic — it appears as rising contact resistance, hot spots on thermal imaging, and eventually a Buchholz trip from decomposed paper.

What to specify. Tin-plated copper for busbars and tap links; stainless steel 316 or hot-dip galvanised hardware with a defined coating thickness; ISO 12944 C5-M or C5-I paint system (typically 240–320 µm total dry film) on the tank, or a sealed, welded cover with no breathing path; a desiccant or membrane breather rather than an open conservator; IP55 enclosures for the OLTC drive cabinet, marshalling box and fan control; and copper-free or tinned terminals in the cable box. For coastal geothermal fields — Iceland, Kenya's Olkaria, New Zealand's coastal fields — add salt to the H₂S and specify the higher severity.

What to inspect. Ask for the paint system datasheet with batch numbers, salt-spray test reports to ISO 9227 (480–720 h for C5), and a photograph record of tank welds and busbar plating before tanking. In operation, add a quarterly thermographic survey of the cable box and tap changer compartment: it finds H₂S-induced contact resistance long before a DGA trend does.

What does 45–50 °C powerhouse air do to the temperature rise?

IEC 60076-2 rates liquid-immersed transformers at a maximum ambient of 40 °C, a daily average of 30 °C and a yearly average of 20 °C. A geothermal powerhouse in Turkey, Kenya or Indonesia routinely sits at 45–50 °C at the transformer bay, because the turbine hall is hot by design and ventilation is often an afterthought. Two corrections follow.

Rating. As a working rule for oil-immersed units, derate about 1% of rating per K above 40 °C ambient at the same winding-rise limit, which is 8–10% for a 48–50 °C bay. The exact figure depends on the load profile and the hot-spot limit; IEC 60076-7 gives the loading and ageing calculation, and a 10 K rise in hot-spot temperature roughly halves insulation life.

Cooling class. The cheapest answer is usually not a bigger core but a higher cooling class: an ONAF1 rating typically recovers 20–25% over ONAN for 1–2% additional loss, and ONAF2 another 10–15%. Fans add 2–15 kW of auxiliary load, noise and a maintenance item in a sulphurous atmosphere — specify fan motors to IP55 with stainless fasteners and a spare set of blades.

Dry-type units behave differently: IEC 60076-11 gives an altitude correction above 1,000 m and a hard ambient limit depending on the insulation class. A Class F cast-resin unit rated 40 °C ambient cannot simply be installed in a 50 °C electrical room at 1,800 m and expected to deliver nameplate. Either derate it by 10–15% or specify Class H with a higher design ambient. See insulation class and high-altitude and high-temperature derating.

How do you choose the cooling method and calculate the derating?

Geothermal plants use three cooling arrangements: sealed ONAN for small units, ONAN/ONAF for GSUs up to about 60 MVA, and OFAF or ODAF above that. The choice trades capital cost against auxiliary power, noise and maintenance in a corrosive atmosphere.

Radiator fouling is the underestimated item. In a geothermal bay, dust, silica scale and sulphur deposits cut heat transfer by 10–20% within a few years, which is why design margin of at least 10% above the calculated duty is standard practice, and why some operators specify removable radiator banks or an air-to-water cooler with cleanable tubes. Our cooling methods and temperature rise guide covers the class definitions in detail.

How do you specify a GSU for load rejection and islanded operation?

Load rejection is the design case that separates a GSU from a distribution transformer. When the grid-side breaker opens at full output, the generator's terminal voltage rises, the frequency rises until the turbine governor reacts, and the transformer sees an over-flux condition (V/f above design) for a few seconds. In islanded operation on a rural 33 kV collector — common in Kenya, Turkey, Indonesia and the Philippines — the GSU may also have to carry a weak network with a large voltage swing.

Over-excitation. Specify 110% of rated voltage at rated frequency continuously and 125% for at least one minute, per the over-excitation capability in IEC 60076-1. Ask for the calculated flux density at 110% and confirm it stays below saturation for the core grade supplied.

Tap range. An OLTC of ±8 × 1.25% (17 positions) on the HV winding is the usual geothermal specification; ±10% is not enough where a weak collector swings by 8–10% between wet and dry seasons. The tap changer must be specified for the full load current at the lowest tap and for the harmonic content of the load.

Load-rejection test. Require a witnessed factory test or a documented site test at 100% load with the grid breaker opening, recording terminal voltage, frequency and transformer winding temperature for 10 s. This is a system test, not a transformer test, but the transformer's over-flux and short-time thermal capability are what it proves. In plants with a bypass to the 33 kV collector, also specify the parallel-operation conditions in our parallel operation guide.

What impedance and short-circuit strength does a GSU need?

Impedance is a three-way compromise between fault level, voltage regulation and load-rejection behaviour, and geothermal plants push it in an unusual direction because the generator is often small relative to the grid.

Typical window. 8–12% on a 33 kV GSU, 10–14% at 115–220 kV. Below 8% the LV fault current rises towards the generator's contribution plus the grid's, which can exceed the generator breaker rating; above 14% the voltage dip on auxiliary motor starting and the reactive consumption become painful on a weak collector.

Short-circuit strength. Specify compliance with IEC 60076-5 with a 2 s thermal duration and a demonstrated ability to withstand the calculated asymmetrical peak. Geothermal units are often single-generator stations, so the GSU's LV side sees nearly the full generator fault contribution — check that the LV winding's radial and axial support is designed for it, and ask for the short-circuit test report rather than a calculation note.

Parallel operation. Where two GSUs feed one 33 kV bus, impedance mismatch above 10% of the mean causes unequal load sharing and circulating current. Specify impedance tolerance of ±7.5% of the declared value and match the X/R ratio, not just the percentage.

How should the tap changer be specified for a geothermal plant?

Most geothermal GSUs use an on-load tap changer on the HV star point, because the plant must hold the collector voltage while the grid voltage moves and the generator runs at constant output for months. A de-energised tap changer is a false economy here: the wellfield cannot be restarted quickly, and each tap change on a DETC means a shutdown.

Range and step. ±8 × 1.25% is the default; ±10 × 1.5% appears on weak rural collectors with seasonal swing. Step size matters more than total range for voltage holding: 1.25% keeps the busbar within ±1% of target.

Type. Vacuum OLTCs are now standard above 33 kV for maintenance interval (200,000–300,000 operations) and because arcing in oil produces acetylene that shows up in DGA. In a remote plant with a 6–12 month maintenance cycle, that difference is worth the price premium.

Accessories. Motor drive with local and remote control, tap position indication to SCADA, an OLTC oil compartment with its own breather and oil filter, and a separate DGA sampling point. Our OLTC versus off-circuit tap changer guide covers the price premium and the maintenance trade-off.

Which vector group and earthing arrangement should you use?

The standard geothermal GSU connection is YNd11: generator-side delta, HV star with the neutral brought out and solidly earthed at the substation. The delta on the generator side blocks zero-sequence currents and third harmonics from reaching the generator, and the earthed star gives the grid a reference and a path for earth faults.

Generator neutral. Earthing is handled on the generator side with a resistor or a distribution transformer plus resistor, limiting earth-fault current to 5–15 A for a large unit. If the generator is delta-connected (rare above 10 MW but common on small binary units), an earthing transformer is required on the generator bus.

Why not Dyn11 on a GSU. Dyn11 is the distribution answer; it forces the HV neutral to be isolated or earthed through a reactor and gives no path for a grid earth fault at the plant. Where the grid operator requires an effectively earthed system, YNd11 (or YNyn0 with a delta tertiary on autotransformers) is the compliant choice.

Check with the grid code. Some operators require the GSU neutral to be earthed through a reactor to limit single-phase fault current, and some require a zig-zag earthing transformer at the 33 kV bus. Fix this in the basic design stage, not after the transformer is ordered — a neutral bushing and a neutral CT cannot be added to a sealed tank cheaply.

What do bushings, creepage and seismic requirements look like on a geothermal site?

Three site conditions push the HV termination beyond a standard specification: humidity and sulphur, altitude, and earthquakes.

Creepage. Specify 31 mm/kV (phase-to-phase) for a heavily polluted or coastal geothermal site, against 25 mm/kV for a light-pollution inland site. Composite silicone bushings are preferred over porcelain in H₂S and salt atmospheres because the hydrophobic surface sheds contamination and resists shattering under seismic load. Above 72.5 kV, condenser-graded bushings with test taps and a power-factor measurement at commissioning. See our bushing selection guide.

Altitude. Above 1,000 m, external insulation must be corrected: the withstand voltage of an air gap falls roughly 1% per 100 m, and the correction is applied to the bushing's external creepage and to the clearance to the tank and to earth. A 1,800 m site needs one insulation level higher in practice, which is why a 33 kV GSU for a Kenyan or Turkish highland field often carries 36 kV-class bushings with extra creepage rather than standard 36 kV units.

Seismic. Geothermal fields sit in volcanic and fault zones — Iceland, Turkey, Kenya, Indonesia, New Zealand, California. Specify seismic qualification to IEEE 693 (or IEC 60068-3-3) at the site's design spectrum, with anchored base plates, restrained radiators, flexible bus connections and bushings qualified as a mounted assembly rather than as individual components. Ask for the shake-table report, and confirm the anchorage design is included in the foundation drawing package.

What about harmonics from downhole pumps and cooling fans?

The GSU itself carries almost pure fundamental current: the turbine generator produces a clean sine wave. The harmonic problem lives on the auxiliary system, where VFD-fed downhole pumps, cooling-tower fans and NCG compressors draw 25–45% current THD from 6-pulse front ends without reactors.

Where it lands. On the UAT, harmonic currents raise winding eddy-current loss and hot-spot temperature. A transformer loaded to 80% of nameplate with 35% THD and no K-factor rating can run above its insulation class limit. Specify a K-factor of 13 (moderate) or 20 (heavy) for auxiliary transformers feeding VFD groups, or derate a standard unit by 15–25%.

Where it is measured. At the point of common coupling, against IEEE 519-2022 or the local grid code; at the drive input, against IEC 61800-3. If the plant is islanded, the harmonic distortion at the 33 kV bus is set by the plant's own loads and the GSU impedance, so a higher-impedance GSU filters slightly better but regulates worse.

Mitigation order. Line reactors or DC-link chokes first, then a passive filter for a dominant 5th/7th pattern, then active filters. Our transformer harmonics guide covers the loss calculation and the K-factor selection.

How is a geothermal GSU different from a hydro, wind or solar GSU?

All four are generator step-up transformers, and all four are specified from generator MVA. The differences are in duty cycle, environment and loss economics, and they change the design in concrete ways.

Compared with hydro, the geothermal GSU has fewer starts but a much harsher atmosphere; compared with wind and solar, it has no converter on the GSU side, so harmonic specification moves to the auxiliary system. The detailed requirements for the other three are in the hydropower GSU guide, the wind farm step-up guide and the solar PV step-up guide.

Which protection and monitoring should be included?

A geothermal GSU normally runs unmanned, so protection must be complete and monitoring must be trendable remotely. The standard package is:

• 87T transformer differential with harmonic restraint and CT supervision — the primary protection for winding faults.
• 63 Buchholz relay (or sudden-pressure relay on sealed tanks) with alarm and trip stages, plus an oil-surge trip on the OLTC compartment.
• 26 / 49 top-oil and winding temperature indication with alarm, trip and fan control stages; fibre-optic winding sensors on units above 40 MVA.
• 51G / 51N backup overcurrent and earth fault, plus restricted earth fault on the HV star winding.
• 71 gas and oil monitoring: online DGA or a scheduled sampling point, moisture in oil, and an OLTC operation counter. Our DGA guide explains the gas ratios that matter.
• Partial discharge measurement for units above 72 kV, and bushing test taps for capacitance and tan-delta trending at each service interval.

Alarm philosophy matters as much as the device list: in a remote plant, a winding-temperature alarm that is not trended becomes a trip. Export the analogue values to SCADA with a 15-minute resolution and set the alarm at 10 K below the trip point. Protection device selection is covered in our protection devices guide.

What tests and documentation should you require before shipment?

Routine tests to IEC 60076-1 are the minimum: winding resistance, ratio and vector group, impedance and load loss, no-load loss and current, applied and induced overvoltage, insulation resistance, and partial discharge for units rated 72.5 kV and above. For geothermal duty, add the following, and make them witness points in the inspection and test plan.

Documentation should include the loss-capitalisation calculation signed against measured values, the paint and plating batch records, the bushing and OLTC type-test certificates, the seismic report, and a shipping procedure with nitrogen padding and impact recorders. Nitrogen-padded oil shipping and the 15° tilt limit are described in our transportation and installation guide; the wider checklist is in the pre-shipment inspection checklist.

What does a geothermal GSU cost, and what is loss capitalisation worth?

Prices below are indicative FOB China bands for 2026, for oil-immersed GSUs with OLTC, ONAN/ONAF cooling, C5-M paint and standard tests. They exclude freight, erection, seismic qualification if charged separately, and any grid-code-specific type tests.

Loss capitalisation is where a geothermal buyer can out-negotiate a standard tender. At 8,000 operating hours per year, a 25-year life and a 6% discount rate, the annuity factor is about 12.8, so 1 kW of total loss at USD 0.07/kWh is worth roughly USD 7,200:

That is several times the price difference between two qualified suppliers. Evaluate bids on price plus capitalised loss, and hold the supplier to the measured loss with a penalty per kW above the guaranteed figure — the standard approach is described in our total cost of ownership guide. A 0.15 percentage-point efficiency improvement on a 40 MVA unit, worth about USD 430,000 capitalised, is usually achievable with a better core grade and a larger conductor cross-section.

What are the five specification mistakes most common in geothermal projects?

1. Sizing from MW instead of MVA. A 30 MW unit at 0.88 pf needs 34 MVA before margin; templates that divide MW by 0.8 and stop there arrive at 37.5 MVA and then buy a 31.5 MVA unit to save money. The result is a transformer running at 108% of rating on a hot day.

2. Ignoring the 45–50 °C bay. A unit that passes its temperature-rise test at 40 °C ambient is not the same unit at 50 °C. Specify the design ambient in the data sheet and require the derating calculation in the offer.

3. A standard paint system and an open conservator. H₂S finds every unpainted edge, every galvanised tray and every silver-plated contact. C5-M paint, tinned busbars, stainless hardware and a sealed or membrane-breathed tank cost 3–6% more and avoid a decade of thermographic surprises.

4. A de-energised tap changer on a baseload plant. The saving is small against the loss of voltage control on a weak collector, and every tap change becomes an outage.

5. Buying on price without loss capitalisation. At 8,000 h/yr, a 0.15-point efficiency difference is worth more than the entire commercial gap between two bids. The same logic applies to the auxiliary transformer, where a K-factor rating avoids a derating that costs more than the K-factor itself.

Frequently asked questions

Can a standard distribution transformer be used as a geothermal GSU?

No. A distribution transformer is rated for a 40 °C ambient, a cyclic load and a modest fault level; a GSU must carry generator fault current, tolerate load rejection with 110–125% over-flux, and hold voltage through an OLTC. The insulation level, impedance and short-circuit strength are all different. Using a distribution unit as a GSU is occasionally seen on 1–3 MW pilot binary units, and it usually ends with a failed short-circuit test or a burnt LV winding.

How much auxiliary power does a 25 MW geothermal plant need?

For a flash plant with a wet cooling tower, expect 2.5–4.0 MW, or 10–16% of gross; with an air-cooled condenser, 3.5–5.0 MW. A 25 MW binary ORC plant with air-cooled condensers can reach 5–7 MW. Size the auxiliary transformer at 1.15–1.25 × connected load, and remember the transformer is derated on the same hot day the fans draw maximum power.

Why is YNd11 preferred over Dyn11 for geothermal GSUs?

YNd11 gives the grid an earthed star point with a solid earth-fault path, blocks zero-sequence and third-harmonic currents from the generator, and matches the standard generator protection arrangement. Dyn11 leaves the HV neutral unavailable and is used on distribution systems, not on generator step-up duty.

How often should geothermal transformer oil be tested?

Annually for DGA, moisture and acidity in the first two years, then every six months if the trend is rising, plus after any through-fault, load rejection or OLTC overhaul. In high-H₂S fields, add a copper-corrosivity (ASTM D1275) check at each sampling, because sulphur attack shows up in oil before it shows up in gas.

Is a dry-type transformer ever used in a geothermal plant?

Yes, for indoor auxiliary and station-service duty where oil is a fire risk — but not in the turbine hall. Cast-resin units need clean, ventilated air; H₂S and dust foul the windings and the 45 °C ambient erodes the thermal margin. Where a dry-type unit is unavoidable, specify Class H insulation, IP54 enclosures with filters, and a design ambient 5 °C above the room's measured maximum.

Does 50 Hz versus 60 Hz matter for a geothermal GSU?

Only if the unit is relocated. A transformer designed for 50 Hz can run at 60 Hz at the same voltage with lower flux and slightly higher impedance, but a 60 Hz unit run at 50 Hz needs the voltage reduced by 50/60 to avoid saturation. The V/f rule and the relocatable-unit checks are in our 50 Hz versus 60 Hz guide.

Sources / 资料来源

Source: IEC 60076-1 — Power transformers, Part 1: General.
Source: IEC 60076-2 — Power transformers, Part 2: Temperature rise for liquid-immersed transformers.
Source: IEC 60076-3 — Power transformers, Part 3: Insulation levels, dielectric tests and external clearances in air.
Source: IEC 60076-5 — Power transformers, Part 5: Ability to withstand short circuit.
Source: IEC 60076-7 — Power transformers, Part 7: Loading guide for mineral-oil-immersed power transformers.
Source: IEC 60076-10 — Power transformers, Part 10: Determination of sound levels.
Source: IEC 60076-11 — Power transformers, Part 11: Dry-type transformers.
Source: IEC 60214-1 — Tap-changers, Part 1: Performance requirements and test methods.
Source: IEC 60137 — Insulated bushings for alternating voltages above 1 000 V.
Source: IEC 61800-3 — Adjustable speed electrical power drive systems, Part 3: EMC requirements.
Source: IEEE 519-2022 — Recommended practice and requirements for harmonic control in electric power systems.
Source: IEEE 693 — Recommended practice for seismic design of substations.
Source: IEEE C57.91 — Guide for loading mineral-oil-immersed transformers and step-voltage regulators.
Source: ISO 12944 — Corrosion protection of steel structures by protective paint systems.
Source: ISO 9227 — Corrosion tests in artificial atmospheres, salt spray tests.
Source: IRENA, Renewable Capacity Statistics 2024 — global geothermal capacity of about 16 GW.
Source: IRENA, Renewable Power Generation Costs in 2023 — geothermal LCOE range of about USD 0.06–0.11/kWh.
Source: QDTB Engineering Team — geothermal and ORC project experience, 2015–2025 (parasitic-load ranges, price bands and delivery periods are industry experience values, not published standards).