Categories - Renewable Energy
Sub Categories
- Wind Energy - 46 projects
- Hydro Energy - 14 projects
- Bioenergy - 6 projects
- Geothermal Energy - 12 projects
- Photovoltaics and Solar Energy - 69 projects
Topics
geothermal, solar-cells, pvoutput, wave-energy, wind-turbines, aircraft, aerodynamics, potential-flow, offshore-wind-platforms, process-simulation, sunsynk, inverter, deye, seabirds, offshore-wind, migratoryspecies, collision-risk, bifacial, rotorcraft, optics, raytracing, amrex, ecp, exascale-computing, boundary-element-method, balkonkraftwerk, scada, wind-power, aeroelasticity, marine-renewable-energy, fault-detection, modelica-library, openfoam, openmdao, geothermal-energy, mhkit, scr-2609, snl-visualization, dweet, freeboard, modbus-sungrow, sungrow-inverter, aeroacoustics, vortex-methods, vpm, vtol, crne-solar, duramat, outback-mate, packets, renogy, renogy-rover, slack, slack-bot, solarthing, degradation, solcast, chakra-ui, inverse-modelling, meshing, hoymiles, solenso, tsun, multiphysics, finite-difference-time-domain, defects, electronic-structure, materials-design, semiconductors, scr-1551, energy2d, aeronautics, structural-dynamics, structures, photovoltaics-dashboard, exawind, les, low-mach, hydropower-model, custom-cards, water-wave, hut23-425, compliance, low-carbon-systems, scr-1647, simulink, wec-sim, wind-farm, pv-simulator, shading-effects, cloud-motion-prediction, generative-models, photovoltaic-power, probabilistic-solar-forecasting, sky-images, stochastic-video-prediction, halide-ion-migration, perovskite-solar-cells, solax, non-governmental-organization, detection-boxes, detector-model, keras, model-detection, photovoltaic-panels, yolo3, heatexchanger, photovoltaic-systems, pv-modules, unsupervised-machine-learning, scr-2927, beam-irradiance, flight-simulation, sun-position, operations-maintenance, simpy, cheminformatics, density, equation-of-state, heat-capacity, molecule, solubility, surface-tension, thermal-conductivity, vapor-pressure, viscosity, circularity, circularity-metrics, lifetime, mass-flow, repair, reuse, multiphase-transport, fermentation, flash, heat-exchanger, structural-geology, unit-operation, balkonpv, ecosystem-models, phenotyping, boundary-element, hydrodynamic-coefficients-viewer, mesh-processing, meshviewer, mplstereonet, fractures, fracture-mechanics, geothermal-reservoirs, golem, moose-framework, irradiance, ninja, fracture, borehole-image-analysis, bem, bemt, nuclear-waste-repositories, porous-flow, reactive-chemistry, simulation-modeling, soil-vapor, subsurface-hydrology, subsurface-remediation, solar-concentrating-systems, coupled-heat-mass, carbon-sequestration, modbus-tcp, modbus-rtu, huawei-solar, huawei, sofar, sol-ark, solarman, solis, home-assistant-integration, biochemical-process, bioprocess, biorefinery, centrifuge, distillation, propeller, plates, structural-engineering, agroclimatology, agroclimatology-data, nasa-power, weather-variables, semiconductor, amr, actuator-line, radiance, scr-2490, ocean-wave-energy-converters, potential-flow-theory, wave-structure-interaction, deeplabv3, deepsolar, inception-v3, network-planning, neurips-2020, pv-systems, solar-panels, borefields, sizing, bioreactor, rotor, turbines, systems-engineering, wisdem, blade-element, ray-tracing, airfoils, rigorous-coupled-wave, transfer-matrix-method, ste, analysis-framework, beam-section, buckling, cylinders, design-of-offshore-steel-structures, dnv-os-c101, dnvgl-os-c101, dnvgl-rp-c201, dnvgl-rp-c203, fatigue-analysis, girder, gui-based, naval-architecture, plate-thickness,
Projects
Contributors
LucidityCrash [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
octopus, octopus-agile, octopus-energy, deye, inverter, sofar, sol-ark, solar, solarman, solis and 1 more
allx [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
deye, inverter, sofar, sol-ark, solar, solarman, solis, sunsynk
Ben Agricola [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
deye, inverter, sofar, sol-ark, solar, solarman, solis, sunsynk
Harald Funk [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
deye, inverter, sofar, sol-ark, solar, solarman, solis, sunsynk
Tommaso Toniolo [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
deye, inverter, sofar, sol-ark, solar, solarman, solis, sunsynk
Harald Funk [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
deye, inverter, sofar, sol-ark, solar, solarman, solis, sunsynk
agirilovich [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
deye, inverter, sofar, sol-ark, solar, solarman, solis, sunsynk
Stefan van der Walt [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
photovoltaic, semiconductor, solar-cells, spec-0, spec-1, spec-4, numerical-methods, closember, astronomy, classification-hierarchy and 18 more
Víctor Pont [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
home-assistant-integration, huawei, huawei-solar, modbus-rtu, modbus-tcp, solar-energy
Iñigo Martinez Lasala [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
home-assistant-integration, huawei, huawei-solar, modbus-rtu, modbus-tcp, solar-energy
Kev [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
home-assistant-integration, huawei, huawei-solar, modbus-rtu, modbus-tcp, solar-energy
Marcin Kornat [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
home-assistant-integration, huawei, huawei-solar, modbus-rtu, modbus-tcp, solar-energy
Breina [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
home-assistant-integration, huawei, huawei-solar, modbus-rtu, modbus-tcp, solar-energy
Johannes Hoppe [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
geojson, django-file-upload, django-storages, file-upload, auth0, django-authentication, noauth, otp, password, unit-testing and 11 more
Dexter Rautenbach [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
custom-cards, deye, inverter, powerflow, solar, sunsynk
Sven Op de Hipt [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
custom-cards, deye, inverter, powerflow, solar, sunsynk
fboundy [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
battery, givenergy, givtcp, octopus-energy, prediction-model, solar, deye, inverter, sofar, sol-ark and 3 more
Aliaksei Hirylovich [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
deye, inverter, sofar, sol-ark, solar, solarman, solis, sunsynk
Fabrizio Romanelli [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
deye, inverter, sofar, sol-ark, solar, solarman, solis, sunsynk
Ian Bell [email protected]
OST Projects: 1
Categories: Emissions, Renewable Energy
Sub Categories: Carbon Capture, Photovoltaics and Solar Energy
Topics:
fluid-properties, thermodynamics, closember, ipython, notebook, repl, spec-0, binder, genetic-programming, symbolic-regression and 4 more
John McLear [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
home-assistant-integration, huawei, huawei-solar, modbus-rtu, modbus-tcp, solar-energy, community, forum, nodebb, socket-io and 1 more
Malte Gerken [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
home-assistant-integration, huawei, huawei-solar, modbus-rtu, modbus-tcp, solar-energy, geography, russia, distributed-computing, pydata
Evert Amssoms [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
home-assistant-integration, huawei, huawei-solar, modbus-rtu, modbus-tcp, solar-energy
Mathieu Delsaut [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
classsification, reunion, measurement-data, photovoltaics, solar, solar-energy
dvegaa20 [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
climate-change, non-governmental-organization, organization
David Goodman [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
crne-solar, outback-mate, packets, pvoutput, renogy, renogy-rover, slack, slack-bot, solar, solar-energy and 2 more
cibinjoseph [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
acoustics, aeroacoustics, aerodynamics, aircraft, cfd, computational-fluid-dynamics, rotorcraft, vortex-methods, vpm, vtol and 3 more
rymanderson [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
acoustics, aeroacoustics, aerodynamics, aircraft, cfd, computational-fluid-dynamics, rotorcraft, vortex-methods, vpm, vtol and 11 more
Shaun J.V.Nieuwenhuizen [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
custom-cards, deye, inverter, powerflow, solar, sunsynk, hacs, hacs-custom, hacs-integration, solis and 1 more
Bradley Muller [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
custom-cards, deye, inverter, powerflow, solar, sunsynk
slipx06 [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
custom-cards, deye, inverter, powerflow, solar, sunsynk, esp32, esphome-config
Shabara [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Hydro Energy
Topics:
hydrodynamics, marine-renewable-energy, simulink, snl-applications, wave-energy, wec-sim, scr-1647
basti122303 [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
custom-cards, deye, inverter, powerflow, solar, sunsynk
Jason Madigan [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
varta, varta-storage, custom-cards, deye, inverter, powerflow, solar, sunsynk
MiniBlister [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
custom-cards, deye, inverter, powerflow, solar, sunsynk
virtualj [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
custom-cards, deye, inverter, powerflow, solar, sunsynk
Roger Bergua [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
aeroelasticity, wind, wind-energy, wind-farm, wind-power, wind-turbine
Kyle Pressel [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
amrex, atmospheric-modelling
adamwise95 [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
amrex, atmospheric-modelling
Rahimi [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Bioenergy
Topics:
bioreactor, inverse-modelling, meshing, openfoam, postprocessing
giray98 [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
Kyle Pressel [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
amrex, atmospheric-modelling
WilliamRichardJohns [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
amrex, atmospheric-modelling
Clint Cecil [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Bioenergy
Topics:
Nathan Hillson [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Bioenergy
Topics:
Jenni Rinker [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
aeroelasticity, wind, wind-energy, wind-farm, wind-power, wind-turbine
Tom [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
continuous-profiling, developer-tools, find-bottlenecks, observability, profiling, pyroscope
Matthias Geier [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
scr-2609, closember, notebook, ipython, repl, spec-0, numerical-methods, dataviz, ipython-widget, quiver and 32 more
jainprana [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Bioenergy
Topics:
bioreactor, inverse-modelling, meshing, openfoam, postprocessing
Mark Bruggemann [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Hydro Energy
Topics:
marine-renewable-energy, mhkit, quality-control, wdrt, asyncio, hdf5, multi-dimensional, scientific-data
David Österberg [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
closember, ipython, notebook, repl, spec-0, operations-maintenance, simpy, wind-energy
David Whiteside [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
Milo Davis [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
Peter Lieven [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
balkonkraftwerk, esp32, hoymiles, platformio, solar, solenso, tsun
Simon Letzgus [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
renewable-energy, scada, wind-energy, wind-power
Simon Leszek (TUB) [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
renewable-energy, scada, wind-energy, wind-power
Stefan [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
home-assistant-integration, huawei, huawei-solar, modbus-rtu, modbus-tcp, solar-energy
suvanbanerjee [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
nowcasting
braddf [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
nowcasting
Alex Kinley [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
19danderson [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
djanders19 [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
guillencampa [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
mattEhall [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
benzman [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
balkonkraftwerk, esp32, hoymiles, platformio, solar, solenso, tsun
Malik Hassanaly [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Bioenergy
Topics:
bioreactor, inverse-modelling, meshing, openfoam, postprocessing
Jeffrey Harris [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
wind-energy
Nathan Moore [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Geothermal Energy
Topics:
Tanushree [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Geothermal Energy
Topics:
wenchao.yu [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
aeroelasticity, wind, wind-energy, wind-farm, wind-power, wind-turbine
Sergiu Deitsch [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
asciidoctor, assembly, build, build-system, build-systems, build-tool, build-tools, cplusplus, docbook, dolphin and 7 more
mborsetti [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
airports, iata-codes, icao-codes, markdown-parser
Bumseok Lee [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
cfd, ecp, exascale-computing, exawind, les, low-mach, wind-energy
Liao [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
openmdao, systems-engineering, wind, wisdem
Herbrax [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
Andrew Simms [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Hydro Energy
Topics:
marine-renewable-energy, mhk, mhkit, mhkit-documentation, mhkit-matlab, quality-control
cclintris [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
Chengcheng Ding [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
JulianColab [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
Mars Tan [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
xmingandrew [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
Kevin Hashimoto [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Bioenergy
Topics:
compliance, dds, low-carbon-systems
Prashanth [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Bioenergy
Topics:
compliance, dds, low-carbon-systems
prv-proton [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Bioenergy
Topics:
compliance, dds, low-carbon-systems
Kuan Fan [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Bioenergy
Topics:
compliance, dds, low-carbon-systems
tim738745 [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Bioenergy
Topics:
compliance, dds, low-carbon-systems
Mohammad Hamza [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
hpacella [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Wind Energy
Topics:
sandia-national-laboratories, snl-science-libs, cfd, ecp, exascale-computing, exawind, les, low-mach, wind-energy
stefanosalvador [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
balkonpv, photovoltaic, photovoltaics, powerplant, renewable-energy, solar-energy, sustainability
Georg Ledermann [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
photovoltaic, photovoltaics, photovoltaics-dashboard, senec, activejob, activerecord, mvc, rswag, swagger-ui
Georg Ledermann [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
photovoltaic, photovoltaics, photovoltaics-dashboard, senec, solar, csv-import, sungrow, car, emobility, renault-ze and 6 more
[email protected] [email protected]@5f0613ce-6e50-0410-beef-1d40ed1f67fe
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
solar, solar-concentrating-systems
[email protected] [email protected]@5f0613ce-6e50-0410-beef-1d40ed1f67fe
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
solar, solar-concentrating-systems
ilescener [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
solar, solar-concentrating-systems
manuel.jesus.blanco manuel.jesus.blanco@5f0613ce-6e50-0410-beef-1d40ed1f67fe
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
solar, solar-concentrating-systems
Dawann Dawann@5f0613ce-6e50-0410-beef-1d40ed1f67fe
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
solar, solar-concentrating-systems
[email protected] [email protected]@5f0613ce-6e50-0410-beef-1d40ed1f67fe
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
solar, solar-concentrating-systems
sergio.garayald sergio.garayald@5f0613ce-6e50-0410-beef-1d40ed1f67fe
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
solar, solar-concentrating-systems
Calama Consulting [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
photovoltaic, renewable-energy, renewables, solar-energy
Veronica Guo [email protected]
OST Projects: 1
Categories: Renewable Energy
Sub Categories: Photovoltaics and Solar Energy
Topics:
photovoltaic, renewable-energy, renewables, solar-energy, cables, impedance