Page 44 - Energize April 2022

VIEWS AND OPINION

Could green hydrogen become the universal

fuel of the future?

While a lot of attention is given to the use of green hydrogen as a promising way to meet clean energy
requirements, it is important to consider the possible uses in terms of cost of production and overall
energy efficiency. Hydrogen is claimed to be the universal fuel of the future,

but with current technologies, this is a matter of debate.

ENERGIZE STAFFWRITER

here are two approaches to this issue: overhyped enthusiasm and cautious optimism. storage, the storage system would be fully
Irrespective of which approach is adopted, hydrogen will play a role in the power charged only once per annum. Over a ten
Tsector of the future. year lifetime the unit would cycle only ten
What has inspired this sudden interest in hydrogen? After all we already have hydrogen- times its maximum storage capacity. The
powered vehicles, hydrogen fuel cells and gas turbines which run on hydrogen and other unit price of seasonally storing electricity
hydrogen powered power systems. The difference is that all these rely on fossil-fuel-derived should thus be 180 times that of the
hydrogen, and the use of “green” hydrogen is cleaner. Green hydrogen is produced using daily storage. All this is very daunting
“green” power, which, at this stage comes from renewable energy. This has been possible for and close to physically impossible with
a long time so why the sudden increase in interest? current technology, so seasonal storage is
The answer to that question might be based on the characteristic of renewable energy impractical. On a smaller scale, daily and
(RE) systems which result in surplus generation. This is because all large RE systems have hourly storage face similar problems.
varying outputs. Because the energy is surplus to requirements it is also seen as being cheap Hydrogen storage has been suggested
or even free. as the ideal medium for seasonal storage,
There are two main RE technologies, solar and wind, and both have varying outputs. but the same factors apply as to other
Where the penetration of RE is low, this is not a problem because the variation can be technologies, and the fact that the round
balanced by other generating technologies. With high RE penetration however, variation trip efficiency of hydrogen storage is less
needs to be managed to match production with demand. than 50%, makes this a less-than-attractive
Variation in production can be from short term (i.e., hourly), mid-term (i.e., daily), or option.
long term (i.e., monthly or seasonally). It is well known that RE production varies from The next obvious solution is to install
season to season, with typical winter production differing from summer production. In the sufficient RE to meet demand during the
case of solar power, winter production is generally lower than summer production. But low generation season. This has been
with wind power, winter production can be higher or lower than summer, depending on made more attractive by the decreasing
geography. Some countries are fortunate in having a complementary wind/solar pattern, but cost of RE systems. However, if sufficient
South Africa is not. Electricity generation from both wind and solar is lower in winter than in capacity is installed to meet the demand
summer. during low production, then there will be
With a high penetration, where dependence on RE is high, this phenomenon has to be overproduction during the high period,
considered, and the production of RE during the period of lower production must meet the which could be seen as wasteful.
demand, because demand is usually higher during the winter months. Overprovision for daily demand is a
One way to solve the problem appears to be energy storage. When there is high common practice as it reduces the amount
production of RE, the surplus should be stored for use when production is low. This requires of storage required for daily operation, but
a huge amount of long term storage. For example, we would need 6000 GWh of storage also results in surplus production. Surplus
to cater for a 10% lower-than-average winter production in South Africa if we had 50% RE. electricity cannot be used elsewhere
The largest current storage is about 500 MWh. We would need 12 000 such units to provide than the grid, and when production
seasonal storage. exceeds demand this inevitably involves
The other factor not taken into account is cost of seasonal storage. The lifecycle cost curtailment, which leads to non-optimal
of storage is primarily capital, so the unit cost of storing or cycling (recycled) electricity use of plant and hence higher costs, unless
depends on how much electricity is cycled through the storage unit over its lifetime. For a another use can be found for the surplus
normal use storage battery, if we consider a 50% capacity cycle every day, for a lifetime of electricity.
10 years, the storage capacity would be recycled approximately 1800 times. For seasonal It is here that we meet an interesting

energize | April 2022 | 42