Hydrogen As An Energy Carrier

-Zubin Shresthainfo@windpowernepal.com

Hydrogen factsLightest Most abundantColourlessOdourlessNon-toxicNon-carcinogenic gasNot found by itself on Earth but in its

molecular form combined with anotherchemical as a compound (e.g. water, methane)

How can it be produced?Water electrolysis using any power source including

wind, solar, nuclear powerGasification of CoalAs a by-product from reforming natural gas/biogas

with steamFrom gas or biomass-derived alcohols

ElectrolysisUsing electricity to split water into hydrogen &

oxygenReaction takes place in electrolyzersDecomposition of water (H2O) into oxygen (O2) and

hydrogen gas (H2) due to an electric current being passed through water

ElectrolyzersConsist of an anode and cathode separated by an electrolyte

producing an electrically conducting solution when dissolved in water

Three types of electrolyzers: PEM (Polymer Electrolyte Membrane) Alkaline Solid Oxide

PEM Electrolyzer: Electrolyte is a solid speciality plastic material Electrons flow through external circuit and hydrogen ions

selectively move across the PEM to the cathode Combine with electrons from external circuit to form hydrogen

gas Operates at 70°-90°C

Alkaline Electrolyzer: Use of liquid alkaline solution of sodium or potassium

hydroxide as the electrolyte Transport of hydroxide ions through the electrolyte from

cathode side to anode side Operates at 100°-150°C

Solid Oxide Electrolyzer: Use of solid ceramic material as the electrolyte Selective conduction of negatively charged oxygen ions

at elevated temperatures Operates at much higher temperatures for the

functioning of solid oxide membranes : 700°-800°C

The ProcessHydrogen gas produced at cathode (-ve)

Reduction reaction with electrons from cathode given to hydrogen cations

2H+(aq) + 2e- H2 (aq)

Oxygen gas produced at anode (+ve)Oxidation reaction giving electrons to the anode2H2O (l) O2 (g) + 4H+

(aq) + 4e-

Overall Reaction : 2H2O (l) 2H2 (g) + O2 (g) Twice the amount of hydrogen molecules produced

than oxygen moleculesProduced hydrogen gas has twice the volume of the

produced oxygen gas (assuming equal temp. and pressure for both gases)

The VerdictHydrogen production via electrolysis can result in zero

greenhouse gas emissionsOffers opportunities for synergy with variable power

generationAllows for flexibility to shift production to best match resource

availability with system operational needs and market factorsPossibility of the elimination of curtailing excess energy from

renewable energy generationGrid electricity is not environmentally friendly, energy

intensive, and is not an ideal source for electricity for electrolysis

Renewables integrating hydrogen production through electrolysis is a possible option to overcome these limitations

StorageUsually stored in a liquid or gas stateLiquid hydrogen kept at temperatures bordering on -

253°C in highly insulated tanksAs a compressed gas underground at pressures up to

150 bar (15MPa)Gaseous hydrogen storage is simplest and most

extensively employed for both large and small scale storage

Steel cylinders or special composite material tanks (Li, Mg, C based) are capable of holding the gas at 700 bar

Typical storage: < 1.5% wt H2 , >98.5% wt of cylinderIncrease of % wt of H2: lighter cylinders at higher

pressuresHigh cost of materials required for storageHigh amount of energy is required to liquefy hydrogen

Hydrogen CompressionHydrogen gas requires much larger tanks for its

storage compared to hydrocarbons due to its poor energy density by volume

As a compressed gas usually at pressures up to 200 bar (3000 psi)

Increasing gas pressure improves the density by volume, making for smaller, but heavier container tanks

Compressed hydrogen storage can exhibit very low permeation

Special composite material tanks are capable of holding the gas at 700 bar

Compressed hydrogen is conventionally stored at near-ambient temperatures

“Cold” (sub-ambient but >150K) and “Cryogenic” (150K and below) storage being investigated to achieve higher H2 densities at reduced temperatures

Cost of current compressed gas systems is dominated by composite materials & processing with a significant impact from balance of plant (BOP) components

Hydrogen compressors increase the pressure on the hydrogen and can transport it through a pipe

Approx. 15% of the usable energy from the hydrogen is lost on compression using today’s compression technologies

Also reduces the volume of hydrogen gasExamples:

Electrochemical hydrogen compressor Hydrogen supplied to the anode Compressed hydrogen is collected at the cathode Energy efficiency up to and even beyond 80% Pressures up to 700 bar

Linear compressor Piston moves along a linear track to compress the working fluid Used under cryogenic conditions

UtilizationTo provide electricity and heat through its use in fuel

cellsFuel cells generate electricity from an electrochemical

reaction where oxygen and hydrogen combine to form water

Electricity produced used in a variety of applicationsHeat produced as a by-product used for heating and

cooling purposes

Why Hydrogen?A clean energy carrier produced from any primary

energy sourcePros of Hydrogen as an energy carrier:

Security of Energy Supply Air Quality & Health Improvement Greenhouse Gas Reduction Ensures Economic Competitiveness

Hydrogen SafetyKnowledge gaps have existed for several decades

regarding: Conditions of ignition Flame acceleration Structural protection Ventilation

Public perception and confidence in hydrogen relies on credibility, transparency, and individual benefit

Exhibits wider limits of flammability, high detonation sensitivity, and relative low ignition energy if mixed with air, in comparison to conventional fuels

Codes & Standards regarding Hydrogen Safety: Safety distances Design of buildings & containers for housing hydrogen

equipment Earthing & lightning protection Materials & components used in hydrogen systems

Risks & ChallengesMixtures of hydrogen in are flammable over a wide

range of compositionsEnergy required to ignite a hydrogen/air mix can be

very lowBurns with a flame that is invisible in daylightSmall molecule that can leak very easilyIf released and ignited, it burns with a rapidly moving

flame

ConclusionSophisticated battery for energy

storageHigh potential as a relatively

clean fuel of the futureNegative net energy i.e. it takes

more energy to produce it than it contains

Very low calorific valueRequires larger and heavier fuel

tanksExtraction methods are extremely

energy intensive (e.g.. Electrolysis of water)

Thank You

WindPower Nepal is looking for technical assistance to find out if Hydrogen could be used as a Cooking Fuel in Nepal. For further

information, please write to us at info@windpowernepal.com