The add‑on helping gas turbines claw back 5%–25% of lost summer output

On hot days, gas turbines sag. Output typically drops about 0.3%–0.5% for every 1 °F (0.6 °C) rise above ISO (International Organization for Standardization) conditions, according to Turbomachinery Magazine. In practice, a simple‑cycle or CCGT (combined cycle gas turbine) unit rated at 15 °C (ISO ambient) can lose roughly 3%–8% output at 27 °C (80 °F) and ~7%–17% at 38 °C (100 °F) (Power Engineering). Large‑frame engines shed less than aeroderivatives.

Indonesia rarely sees ISO conditions. Daily averages run 27–33 °C with up to ~90% relative humidity (RH), per Universitas Indonesia (lib.ui.ac.id). Those losses bite hardest during summer afternoons, when wholesale prices can jump to ~$50–100/MWh (Power Engineering).

Enter TIAC ([turbine inlet air cooling](https://beta.co.id/en/blog/heat-is-stealing-megawatts-turbine-inlet-air-cooling-is-how-ccgts-get-them-back)): techniques that chill the air before it hits the compressor, hiking density and restoring output. The menu spans evaporative pads, high‑pressure fogging, and mechanical chillers. Each trades capital, water, and auxiliary power for megawatts.

Ambient temperature derating curve

The rule‑of‑thumb sensitivity—roughly 0.3%–0.5% drop per 1 °F above ISO—sets the context (Turbomachinery Magazine). By 27 °C (80 °F), many turbines shed ~3%–8% of output; by 38 °C (100 °F), ~7%–17% (Power Engineering). Aeroderivative machines, with higher pressure ratios, lose more than frame engines; they can see roughly double the percent loss per °C rise, making them strong candidates for inlet cooling (Power Engineering).

Wetted‑media evaporative cooling

Evaporative pad systems pull inlet air through continuously wetted media; the phase change cools air toward the wet‑bulb temperature (the limit set by humidity), typically capturing ~85%–95% of the dry‑bulb/wet‑bulb spread (Gas Turbine World). In arid climates, gains can be 10%–15%; in high humidity, the boost shrinks (often under 10% and approaching zero near 100% RH) (Gas Turbine World).

Capital costs are low—about $15–$20 per kW of turbine capacity (Gas Turbine World; Turbine Inlet Cooling Association). Operating cost is mainly makeup water and a small fan/pump load; there is no significant electrical parasitic beyond pump power. [Water quality control is essential](https://beta.co.id/en/blog/the-unglamorous-water-rule-that-makes-turbine-inlet-cooling-pay) to prevent scaling and pad fouling (Gas Turbine World). Plants often pre‑condition pad feedwater with a softener to remove calcium and magnesium that drive scale formation.

High‑pressure fogging systems

Fogging injects ultra‑fine water droplets upstream of the compressor; the mist evaporates in flight near the compressor face, cooling without contact pads. Performance is similar to wetted media—cooling toward wet‑bulb—with tighter control over atomization and spray rate. Reported power gains are comparable to pads (TICA).

Installed cost typically lands in the same $15–$20/kW range (Gas Turbine World; TICA), but requires high‑pressure pumps. Water usage mirrors the evaporated fraction; excess mist is captured in a drain pan. There are no refrigerants, and parasitic load is limited to pump power. Benefits drop in high humidity, as with pads. To protect compressor blades and nozzles, operators frequently polish fogging water using a mixed‑bed deionizer for very low TDS and silica, and house prefilters in stainless cartridge housings for sanitary, high‑pressure service.

Mechanical refrigeration chillers

Vapor‑compression or absorption chillers deliver sub‑wet‑bulb cooling, reaching ~45–50 °F (7–10 °C) inlet air even in high humidity, subject to OEM dew‑point/icing limits (Power Magazine). Absorption chillers, typically steam‑driven, similarly provide sub‑dew‑point cooling without electric drive.

Capex is high—about $150–$185/kW of turbine capacity (Gas Turbine World). One F‑class example required a ~2,330 RT (refrigeration ton) chiller—roughly $1–2 million—for an 83 MW turbine (TICA; TICA). Electric chillers draw substantial auxiliary power—roughly 0.65–0.8 kW per RT—plus condenser/cooling‑water pumps; net parasitic can run ~30% of the additional output (Power Magazine). Absorption chillers eliminate electric load by using steam (often extracted from the turbine exhaust) but carry higher capital, need hot steam, and require large cooling towers with their own water use.

Cooling tower water chemistry for these systems often relies on targeted biocides to control biofilm and on scale inhibitors to reduce mineral deposition, sustaining chiller and tower performance.

Hybrid and two‑stage configurations

Designers sometimes combine methods—e.g., pre‑cooling air to wet‑bulb with evaporative media to trim the chiller load and water usage, or using two‑stage “super‑evaporative” or indirect setups. Such hybrids can deliver the highest annual gains but at higher cost and complexity, and often more water (MDPI; MDPI).

Observed performance gains

On a ~90 °F (32 °C) day, TIAC can add 5%–25% of nominal capacity, depending on method and humidity. Gas Turbine World reports “5% to 25% of turbine nameplate rating” increase on a 90 °F day (Gas Turbine World).

Case in point: Los Angeles (87 °F/31 °C dry‑bulb, 64 °F/18 °C wet‑bulb). An 83.5 MW frame CT derated to 75.3 MW (10% loss) uncooled; evaporative cooling lifted it to 81.3 MW and fogging to 81.9 MW (~8%–9% gain), nearly erasing the 10% drop. A 42 MW aeroderivative fell to 34.1 MW (24%); evap raised it to 39.9 MW and fog to 40.4 MW (gain ~6–7 MW, almost reclaiming the 24% loss). In both, fogging slightly outperformed media; chilling to ~45 °F would approach ISO, less the chiller draw (TICA).

Literature echoes this pattern: a Middle‑Eastern CCGT study found water‑cooled chillers delivered a 14.3% output increase vs 6.9% for wetted media (ResearchGate). Analyses show fogging and media recover most hot‑day losses but flatten as ambient wet‑bulb rises (TICA). Dry climates and higher‑compression (aero) machines see larger percentage gains; marine/aero turbines can lose roughly double the % per °C of a frame engine (Power Engineering).

Humidity effects in Indonesia

In humid tropics, pure evaporative cooling is constrained. Gas Turbine World notes gains are “under 10%” in high humidity (versus ~15% in dry air), and at ~90% RH evaporative effect can vanish (wet‑bulb equals ambient) (Gas Turbine World). In Jakarta‑like conditions (30 °C and 70%–80% RH, wet‑bulb ~24–26 °C), a pad might cool by only 4–6 °C—worth a few percent—while fogging or two‑stage setups can dig deeper.

Fogging water makeup often comes from RO (reverse osmosis) or demineralized sources. Coastal plants commonly rely on seawater RO for reliable low‑salinity makeup, and pretreat surface intakes with ultrafiltration to protect downstream membranes and nozzles.

Capital and water requirements

Capex: evaporative pads and fogging are very low—typically ~$15–$20/kW installed (Gas Turbine World; TICA). For perspective, adding a new turbine is about $750,000/MW (TICA). Mechanical chillers come in far higher at ~$150–$200/kW (vapor compression), with absorption also high (Gas Turbine World). One reference assumes ~$19,000 per MW for wetted or fog cooling, versus $750,000/MW for a new turbine (TICA), making TIAC 10–50× cheaper per MW gained than building new capacity (TICA).

Opex: evaporative and fogging systems mainly consume water and small pump/fan power. Water usage scales roughly with air mass and humidity change. Hybrid studies show absorption chillers can use far more water than pure evaporative TIAC—about 2.4× in one case (MDPI). Fogging evaporates the designed mist with no recirculation pond; no refrigerants are involved, and parasitics are a few percent of turbine output.

Chillers: electric systems often draw roughly one‑third of the added output (e.g., every +3 MW can cost ~1 MW of chiller/pump power), reducing net gain but acceptable when prices are high (Power Magazine). They also require cooling towers (with blowdown makeup), though not for the inlet air itself. Absorption units remove electrical draw but have lower COP (coefficient of performance) and higher tower water flow needs. To maintain water quality in these circuits, plants use metered chemical feeds via a dosing pump and broader cooling tower chemical programs.

Revenue, fuel, and emissions effects

Increased capacity: each extra percent of turbine output translates to added generation value without additional capital equipment and with only slight fuel rise. At an electricity tariff of $0.048/kWh (Saudi industrial rate) (MDPI), 1 MW continuously added yields ~$42,000/year revenue. A 10% boost on a 100 MW turbine (+10 MW) at this price is ~$8.4M/year. In Indonesia, peak wholesale prices may exceed $50–70/MWh, magnifying the value (Power Engineering).

Fuel consumption: inlet cooling increases mass flow, so absolute fuel burn rises; however, output rises more, improving heat rate (kJ/kWh). Studies show slightly higher turbine fuel consumption with TIAC but overall efficiency gains that reduce heat rate by a few percent.

System and CO₂: added CT output can displace peakers or older units, cutting system fuel and CO₂; emissions tend to fall roughly in proportion to output gains achieved with TIAC (Gas Turbine World).

Economic thresholds and payback

Evaporative systems deliver short paybacks thanks to low capex despite humidity limits; mechanical chillers require higher prices to justify. One techno‑economic study finds cooling only pencils out above ~$0.05–$0.08/kWh (ResearchGate).

Because TIAC’s capital per MW of recovered capacity is so low, paybacks often run 1–3 years in high‑value applications. “Figure 9 in [46] (excerpted)” shows incremental cost per 1 MW of gain: TIAC is 10–50× cheaper than adding a new uncooled CT. For water supply resilience, some operators add compact brackish‑water RO to ensure consistent TIAC makeup independent of municipal sources.

Indonesia‑specific considerations

In Indonesia’s hot‑humid climate, TIAC can still recover essential capacity. Although evaporative gains are humidity‑limited, fogging and combined systems remain effective, recovering roughly ~5%–10% of base output in many cases. The low capex of fog/media (tens of millions IDR per MW) makes them attractive. Regulatory constraints primarily concern water sourcing and drift disposal; no special Indonesian laws prohibit TIAC, but plants must treat blowdown water and consider local water rights.

For microbial control in recirculating evaporative stages, many facilities add non‑chemical barriers such as ultraviolet disinfection. Where ultra‑pure polishing is needed—for example, near‑zero silica before fogging—the continuous, chemical‑free option is electrodeionization (EDI).

Cost‑benefit summary and examples

Gains: up to ~10%–15% output in humid tropics (more in dry heat), at ~$15–$20/kW (Gas Turbine World; TICA).

Costs: evaporative/fogging—low capex, modest water use, near‑zero parasitic beyond pumps; mechanical chilling—high capex (~$150–$200/kW) and ~30% parasitic of the gain, but largest absolute increase (Gas Turbine World; Power Magazine).

Payback: with summer peaks, TIAC paybacks can be very fast. A 50 MW additional peak output at $0.05/kWh is worth ~$22M/year; even at one‑third utilization, this can offset a multi‑million‑dollar TIAC investment. Studies find paybacks of a few years or less for evap/fog when prices exceed ~$0.05–$0.08/kWh (ResearchGate; MDPI).

Key metrics: on a 100 MW GT, fogging might add ~6–10 MW on a 33 °C day, costing ~$0.5–1.0M (at ~$15–$20/kW). At $0.05/kWh and 50% utilization, an extra 7 MW yields ~$1.5M/year, implying ~1‑year payback. Chilling to ~15 °C inlet might add ~20 MW but cost ~$30–35M; net output and margin can still justify it when prices are high. All figures depend on local climate and prices; detailed hourly analysis of weather and tariffs refines ROI (TICA; MDPI).

Sources and technical references

Authoritative reviews and case studies underpin this comparison. Gas Turbine World reports 5%–25% output gains and capex spanning $15–$185/kW for TIAC types (Gas Turbine World; Gas Turbine World). A 2023 survey summarizes expected performance by method (ResearchGate; MDPI). Power‑sector analyses provide cost and parasitic effects (Power Magazine; Power Magazine), while TICA compiles economics and real‑world plant data (TICA; TICA). These quantitative sources support all performance, cost, and water‑use figures cited above.