Electric Versus Hydraulic Outputs in Modular Power Systems Which Architecture Delivers the Highest End Use Efficiency
Electric Versus Hydraulic Outputs in Modular Power Systems Which Architecture Delivers the Highest End Use Efficiency
A turbine produces shaft power. What matters commercially is how much useful work arrives at the load after conversions. This article compares two architectures for modular systems: generating electricity and then running hydraulics, versus driving a hydraulic pump directly from the turbine. It also compares electric motors to hydraulic motors for end use efficiency and recommends when to standardize on electrical architecture versus dedicated hydraulic modules.IntroductionIn a modular supercritical CO2 power platform, you can package outputs as electricity, hydraulic power, or both. The key engineering question is not which output looks simpler, but which delivers the highest end use efficiency for the actual load profile.The cleanest way to evaluate this is to start with the same input: turbine shaft power at the coupling, then quantify the conversion losses to the final actuator or motor output.This article compares:1. Turbine shaft power to electricity to hydraulic power2. Turbine shaft power directly to hydraulic power3. Electric motor versus hydraulic motor efficiency at the load4. Whether modular architecture should standardize on an electrical bus or offer dedicated drivesAll efficiencies below are typical real world ranges for industrial grade equipment, not ideal lab values.Definitions and AssumptionsWe will use a normalized basis of:100 units of turbine shaft power available at the output couplingThen compute delivered hydraulic power and delivered mechanical power at the actuator or motor.Typical component efficiencies assumed:Electrical chain:Generator: 96 to 98 percentPower electronics inverter and rectifier: 97 to 99 percentElectric motor: 93 to 97 percentHydraulic pump driven by motor: 85 to 92 percentHydraulic chain:Mechanical coupling gearbox belts coupling: 98 to 99 percentHydraulic pump driven directly: 85 to 92 percentHydraulic motor: 85 to 92 percentValves hoses filtration losses vary strongly with design and are often the hidden penaltyArchitecture 1Turbine Drives Generator Then Electricity Runs a Hydraulic PumpShaft to Hydraulic Power at the Pump OutletEnd to end efficiency from shaft power to hydraulic power is approximately:Generator 0.97Power electronics 0.98Electric motor 0.95Hydraulic pump 0.90Overall: 0.97 times 0.98 times 0.95 times 0.90 equals about 0.81So from 100 units of turbine shaft power you deliver roughly:80 to 82 units of hydraulic power at the pump outlet in a well designed systemThis is surprisingly strong. Modern generators, drives, and motors are highly efficient.Additional hydraulic losses beyond the pumpOnce you distribute that hydraulic power through valves hoses and control blocks, real delivered power at the actuator can fall depending on throttling and pressure drop. Systems that use load sensing and variable displacement pumps can keep this penalty modest. Systems that rely on throttling control can waste large fractions as heat.Architecture 2Turbine Drives a Hydraulic Pump DirectlyShaft to Hydraulic Power at the Pump OutletEnd to end efficiency from shaft power to hydraulic power is approximately:Coupling 0.99Hydraulic pump 0.90Overall: 0.99 times 0.90 equals about 0.89So from 100 units of turbine shaft power you deliver roughly:87 to 90 units of hydraulic power at the pump outletWhat you gainYou remove the generator, power electronics, and electric motor losses. The direct drive approach is typically about:6 to 12 percentage points higher efficiency to hydraulic power at the pump outletWhat you give upYou lose flexibility. Hydraulic output is not as universally usable as electrical output, and long distance distribution of hydraulic power is generally poor compared to electricity.Which Is More Efficient at the End Use LoadThere are two separate questions:1. Which is more efficient to produce hydraulic power at the pump outlet2. Which is more efficient to deliver useful work at the actuator or motorFor producing hydraulic powerDirect turbine to pump is more efficient.Direct shaft to pump: typically 87 to 90 percent to hydraulic powerElectric chain to pump: typically 78 to 82 percent to hydraulic powerFor delivering useful mechanical work at the loadIt depends on the type of load control.Hydraulic systems can be very efficient when:Load is heavySpeed control is handled with variable displacement or load sensingShort hoses and low pressure dropsDuty cycle demands high peak power burstsHydraulic systems are less efficient when:Control relies on throttling valvesHigh standby pressure is maintained for long periodsLong hose runs or complex manifolds existHeat rejection is largeElectrical systems excel when:Variable speed is frequentPart load dominatesRegeneration is valuableDistribution distance is longYou want simple controls and telemetryElectric Motor Versus Hydraulic Motor EfficiencyComponent levelElectric motor efficiency: typically 93 to 97 percentHydraulic motor efficiency: typically 85 to 92 percentHowever, that comparison is not fair unless you include the required upstream equipment.System level comparison for rotary loadsElectric bus to shaft at the load:Inverter 0.98Motor 0.95Gearbox optional 0.98Overall: commonly 0.90 or higherHydraulic bus to shaft at the load:Pump 0.90Motor 0.88Plumbing and valves often 0.95 or worseOverall: commonly 0.75 to 0.85 in well designed systems, and can be lower in throttled systemsResult:Electric motor systems are typically more efficient overall for distributed rotary loadsFor linear actuationHydraulics can be competitive for very high force short stroke, especially where packaging and peak power matter. But electric linear actuators with ball screws or roller screws can be highly efficient and easier to control, particularly at partial load.Is Electricity More Useful Than Hydraulic Power in a Modular PlatformFrom a product strategy standpoint, electricity is usually the better primary output because it is:Universally compatible with loadsEasy to distribute and scaleEasy to control and meterEasy to store in batteriesEasy to integrate into microgridsHydraulic power is better treated as:A dedicated module for specific loadsPumpingCompressionHigh force actuationShort duration peak power burstsRecommendation for a Modular Infinity Turbine Style SystemBest default architectureStandardize the platform around an electrical DC bus or AC output as the primary product.Then offer two optional secondary pathways:1. Electric to hydraulic moduleUse generator output to drive a motor pump package when hydraulics are needed. This will usually deliver 78 to 82 percent shaft to hydraulic power, with the highest flexibility and simplest standardization.2. Direct drive hydraulic moduleFor sites where hydraulics are the dominant product and electrical export is secondary, offer a direct turbine to pump module. This maximizes hydraulic efficiency at 87 to 90 percent shaft to hydraulic power.Why dedicated drives can winIf the customer explicitly values hydraulic output as the primary commodity, direct drive is both:More efficientLower component countPotentially lower capex and maintenanceWhy electric standardization usually winsIf the customer values multiple loads, variable duty cycles, storage, or distribution, electrical architecture is the better default. You can always convert electricity to hydraulics locally with acceptable losses. The reverse is usually not true without added complexity.ConclusionIf the turbine is already producing shaft power, driving a hydraulic pump directly is more efficient than generating electricity and then running a motor driven pump. The direct drive advantage is typically 6 to 12 percentage points at the pump outlet.However, electricity is generally more useful than hydraulics in a modular system because it is easier to distribute, store, control, and integrate across many load types. For most modular deployments, the best design is an electrical standardized platform with an optional hydraulic module, plus a dedicated direct drive hydraulic option for customers who are hydraulics first.If you want, I can redo the math using your target module size and assumed component vendors, for example 25 kWe modules and a 50 to 150 kW hydraulic package, and compute delivered power, heat rejection, and cooling requirements for both architectures.
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