Study Finds Electricity Beats Hydrogen for Power Storage

Study Finds Electricity Beats Hydrogen for Power Storage/Delivery

Aug 28 - Power Engineering

A new study finds that major applications for hydrogen envisioned in hydrogen economy scenarios could be more efficiently accomplished with technologies that use electricity directly. It concludes that in key roles envisioned for hydrogen as an energy carrier - namely transmission of remote renewable resources, storage of intermittent renewables or for use in vehicles electricity offers options that are more energy efficient and might preclude massscale emergence of hydrogen technologies.

The study - Carrying the Energy Future: Comparing Hydrogen and Electricity for Transmission, Storage and Transportation - was issued by the Institute for Iifecycle Environmental Assessment and was funded by the John D. and Catherine T. Macarthur Foundation. It found that energy penalties incurred in manufacturing hydrogen place it at a competitive disadvantage compared with electricity.

"The first and most important understanding about the proposed hydrogen energy system is that hydrogen is not an energy source," say study authors Patrick Mazza and Roel Hammerschlag. "It is an energy storage medium and carrier. And like the only other commonplace energy carrier electricity - hydrogen must be made." The study compares the actual energy available when hydrogen and electricity carriers are employed and finds that electricity delivers substantially greater end-use energy.

Advocates of hydrogen portray it as a means to transmit abundant renewable energy resources located distant from markets, such as sunlight in the Southwestern U.S. or wind in the Great Plains region. Electricity generated in solar panels or wind turbines would be converted to hydrogen via electrolysis, a process that uses electrical current to break the bonds of hydrogen and oxygen in water. Electricity would be recovered through electrochemical reactions generated when hydrogen and oxygen join in a fuel cell.

However, when energy penalties are taken into account, says the study, only 4555% of original energy remains compared to 92% if transmitted as electricity. Therefore, electrical transmission provides roughly twice the end-use energy.

"Although hydrogen is seen by some as a medium to store energy generated by intermittent renewable sources such as sun and wind, making power available on demand, other energy storage technologies deliver comparatively more energy," says Mazza. "Hydrogen storage returns around 47% of original energy, while advanced batteries return 75-85% and established pumped hydroelectric and compressed air technologies return about 75%. A wind farm which stores at 47% efficiency would require 160 turbines to generate the amount of useful energy produced by a 100 turbines which store at 75% efficiency."

The study concludes that even though the use of hydrogen as clean vehicle fuel is the most prominent of its foreseen uses, relative inefficiencies of hydrogen compared with direct electricity play out in vehicle technology too. "Using electricity to charge electric vehicles (EVs) provides twice the miles per kWh than employing electricity to make hydrogen fuel," says Mazza. "While conventional wisdom has it that the EV is a technological dead-end, hobbled by limited range and extended recharging times, advanced battery technologies could substantially extend ranges and meet the needs of a more substantial share of the market than is commonly understood. Lithium ion batteries developed for portable electronics are now working in prototype EVs that go nearly 250 miles between charges."

The relative inefficiency of hydrogen as opposed to electricity has implications for global warming emissions. The study calculates CO2 emission reductions from employing renewable energy in various applications. Directed to displacing electricity generated by advanced technology coal plants, renewable electricity eliminates 2.6 times more CO2 than if it is used to displace gasoline by making hydrogen fuel for cars. Charging EVs removes twice the CO2 of making hydrogen fuel. The study calculates similar results for use of natural gas, which also has been proposed as a source of hydrogen energy.

These results strongly suggest that priority use for new renewables should be to eliminate demand for coal-fired electricity, say Mazza and Hammerschlag. They say if that is not an option, use the power to charge EVs.

The study distinguishes between hydrogen and fuel cells. While a hydrogen fuel system is hindered by multiple inefficiencies, fuel cells can form an important part of highly efficient systems that convert biofuels or fossil fuels to electricity. Fuel cells can operate as stationary electrical generators, potentially at significantly higher efficiencies than central power stations or other distributed generators. Emergence of a substantial fuel cell market is in no way conditioned on mass application in vehicles or development of a hydrogen network.

The study recommends that hydrogen and electricity advocates focus on complementary development that can support both pathways. This includes rapid expansion of renewables, improvement in hybrid vehicle technology, vehicle-to-grid applications that employ parked vehicles as grid energy storage, and development of biomass supplies from which liquid vehicle fuels and hydrogen can be made.