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* Low light-to-energy conversion efficiency
* Large plot spaces required to assemble solar farms
* Variability of weather conditions
* Fabrication pollution.
Although contamination related to solar energy systems is less
compared to other sources of energy, solar energy can produce
environmental impacts related to the GHG emissions associated with panel manufacturing, transportation and installation.
Additionally, certain hazardous materials and products are used
during the manufacturing process of solar PV panels, which can
negatively impact the ecosystem.
Wind is an abundant but variable resource for producing
electricity. Wind-generated (eolic) electricity also can be used
to power water electrolysis systems to produce H2 gas and O2
gas. Wind energy offers a number of advantages over other energy sources; however, it too must overcome several challenges.
One advantage is that windpower is often a cost-effective energy
pathway. When wind turbines are used onshore as opposed to
offshore, they are one of the lowest-priced energy sources available today, with an estimated electricity production cost of $1/
kWh-$2/kWh (after tax credits are applied).
Wind is a cleaner fuel source compared to hydrocarbons. It
does not contaminate the air compared to power plants that use
coal or natural gas, which emit CO2 , particulate matter, SOx and
NOx. These emissions lead to negative effects such as acid rain,
smog and greenhouse effect. Like solar energy, wind energy is
considered to be a green and sustainable energy source. In fact,
wind energy can be viewed as a variation of solar energy because
wind is basically produced by solar heating of the atmosphere.
As long as the sun shines and the wind blows, the energy inherent in them can be harvested. However, windpower and solar
energy find challenges to operating under extreme weather conditions. Wind turbines can be noisy and affect the aesthetic of a
landscape. Wind farms can also impact local wildlife, such as birds
and bats that may fly into moving turbine blades. Additionally,
the production of wind turbine blades can be fairly carbon-intensive. The lifespan of these blades is about 15 yr-20 yr. After their
lifecycle is complete, some wind turbine blades can be recycled,
but others must be landfilled because they are non-recyclable.
Biological pathways. Methods employing biological avenues
also have been used to create green and sustainable H2 . One
method that shows potential is microbial biomass (organic matter) conversion. In this process, microorganisms break down
biomass by consuming and digesting its components, releasing
H2 gas as a byproduct. This pathway is not in use commercially at present; however, research funding will likely propel the
technology over the mid- to long term, and biomass conversion
could see large-scale commercialization in the future.
A related method to biomass conversion is photobiological
production. This process uses microorganisms in conjunction
with sunlight to transform water and organic matter into H2
gas. This pathway is still in the early stages, but it shows promising long-term potential as a highly sustainable H2 production pathway.
Finally, certain types of algae will also produce H2 gas as a
byproduct of photosynthesis, requiring only sunlight, carbon
dioxide (CO2 ) and water. Researchers in algal H2 production
(sometimes referred to as " olive " H2 ) are using a series of genet24

Q2 2021 | H2-Tech.com

ic modification techniques to increase H2 production efficiency
in certain algal subsets.
H2 gas also can be produced from municipal solid waste,
landfill gas, biogas and waste gas from water treatment plants.
These alternative routes do not necessarily lead to green H2 production; however, they add a certain level of sustainability to the
entire process of H2 production.
H2 production cost implications. The cost of H2 production
in present commercial applications can vary greatly. The lowest
H2 costs are associated with non-renewable processes-predominately gray H2 from steam methane reforming (SMR). The cost
of H2 production from SMR ranges from approximately $1/lb-
$2.5/lb. Future costs using the same method will likely achieve
$0.75/lb. If carbon-capture-and-sequestration equipment is in
place, $0.11/lb-$0.2/lb should be added to the final cost.
Electrolysis of water in the U.S., using the local electrical
grid, would produce H2 at $3/lb-4/lb. Future costs using the
same method are estimated at around $1.5/lb-$2/lb. Windpowered water electrolysis generates H2 at approximately $3/
lb-$5/lb. Future costs using the same pathway are estimated
at $1.25/lb-$1.65/lb. The cost of solar-produced H2 via electrolysis is presently at $4/lb-$8/lb. Future costs using the same
route are estimated at $1/lb-$2/lb.
At present, the cost of H2 production from biomass pathways
is approximately $2.5/lb-$3.5/lb; however, large-scale production of H2 using biomass is estimated to cost as little as $0.8/
lb-$1.5/lb in the future. H2 production via nuclear thermal conversion of water can achieve a cost of $1.05/lb-$1.5/lb. However, nuclear-powered H2 production technology is not presently
considered to be a sustainable or renewable H2 production pathway, and is included here only for comparison purposes.
Takeaway. Sustainable H2 production methods pose many
challenges for the future. To start, the term " sustainability " as it
pertains to H2 production must be accurately defined, and metrics should be in place to quantify the true sustainability of a
given H2 production pathway.
Most H2 production pathways have a carbon footprint and
produce an impact to the ecosystem, regardless of their assigned
color. Some H2 production pathways are more sustainable compared with others. However, to be able to claim a sustainable
(or fully sustainable) H2 production method, the complete production sequence should be evaluated-from the mining and
manufacturing of the raw materials for equipment manufacturing, transportation and installation, to the H2 production itself
in addition to storage, transportation and point of use.
At present, wind- and solar-powered water electrolysis are
the most sustainable H2 pathways, despite the carbon footprints
generated by the construction of their facilities. Nonetheless,
H2 is an energy source with minimal impact to the ecosystem,
and it will only become greener and more sustainable with better technologies, materials and methods.
DAVID ENGEL has more than 20 yr of experience in a variety of
areas of chemical engineering and chemistry. He is the inventor in
21 U.S. invention patents and the author/presenter of more than
100 technical papers and conference presentations. Dr. Engel is
the Managing Director of Nexo Solutions Companies and heads
the Board of Directors for Exion Systems. He holds a BS degree
in industrial chemistry and a PhD in organic chemistry.


H2Tech - Q2 2021

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