There is little doubt that renewable energy – be it from solar, wind or other sources – is becoming increasingly common as the world transitions towards a low or zero carbon energy future.

Renewable energy accounted for 27.7% of Australia’s total electricity generation in 2020 and continues to play an ever growing part of the energy mix.

While further growth is likely, storage is needed to store excess energy for the times when there’s no sun or wind.

The leading contenders for energy storage – particularly for transport and grid-scale systems – are green hydrogen, which is produced by using renewable energy to power electrolysers that turn water into hydrogen and oxygen, and any of the different flavours of lithium-ion batteries (LiBs) that store electricity directly.

Grid and stationary power

Storing renewable energy on the grid-scale has been gaining significant interest in recent years with batteries taking an early lead.

Examples of grid-scale battery systems include the 300 megawatt (MW) Victorian Big Battery and the 100MW system in South Australia that Elon Musk famously promised would be installed and made operational by Tesla 100 days from contract signing (he was successful, in case you’re wondering).

There are significant advantages to using batteries for grid storage.

As demonstrated by Tesla, implementation as a bolt-on to existing projects or even the grid in general can be incredibly quick as long as the impetus is there to do so.

This same ease of implementation also lends itself to having the ability to be scaled up rapidly when required.

Such systems can also store electrical energy with a remarkable level of efficiency and can be quickly fed back into the grid when required.

Battery systems for home use have also been making significant headway with companies such as Tesla and LG offering their respective solutions.

The use of hydrogen as a grid-scale energy storage solution is still very much in its infancy compared to its counterpart, but it does offer some significant advantages.

As a gas, hydrogen can also be stored in depleted hydrocarbon reservoirs at much lower costs than batteries.

ADX Energy (ASX:ADX) is planning to use depleted reservoirs in Austria to store hydrogen produced in summer using renewable energy for sale in winter, essentially creating a hydrogen battery.

The company estimates that each reservoir can store about 500 times more energy than the largest Tesla energy storage Mega Pack (about 200 megawatt hours) at a much lower price.

The stored hydrogen, which represents enough power for 20,000 households for one year, can be burnt for heating or fed into fuel cells to generate electricity.

A Boston Consulting Group study also found that green hydrogen has great potential in industry as well as in heavy goods, air and sea traffic.

Companies are also starting to develop hydrogen storage systems for home use with at least one company developing a (somewhat hefty) system with a built-in electrolyser, hydrogen storage tank and fuel cell.

Transport shootout

On a smaller scale, most car manufacturers have lined up behind battery electric vehicles with plans to introduce dozens if not hundreds of new models.

Musk famously dismissed hydrogen fuel cells as being “mind-boggingly stupid” while Volkswagen group chief executive Dr Herbert Diess noted last year that there is no clear alternative to battery electric vehicles for the foreseeable future.

Part of this is due to BEVs being at least a decade ahead of their hydrogen fuel cell (FCEV) counterparts as the technology was more suitable for mass rollout that allowed manufacturers – especially European companies – to comply with carbon dioxide emissions regulations.

The lower cost of building battery recharging infrastructure compared to hydrogen refuelling stations has also meant that the former far outstrips the latter. And that does not include (admittedly slow) recharging from regular power points.

Taking the entire supply chain into consideration, BEVs also benefit from higher efficiency.

From generating the power in power stations, transport and then storing the electricity in the batteries, BEVs enjoy an efficiency of between 70% to 80%.

hydrogen fuel cell electric battery efficiency comparison
Pic: Volkswagen

In contrast, FCEVs are inefficient as electricity is needed to power the electrolysers that crack water into hydrogen and oxygen before the resulting gas is sent to storage. The hydrogen will then need to be converted into electricity in the fuel cell, which results in a further loss of efficiency.

Taken together, FCEVs are only between 25% to 35% efficient.

While hydrogen is likely to remain more inefficient compared to batteries, it does have some significant advantages over its competitor.

One of these is energy density. Hydrogen can store more energy per unit weight and volume compared to batteries.

Refuelling is also quick, taking no longer than refuelling petrol or diesel does now.

Verdant Earth Technologies general manager sustainable energy Mike Haywood told Stockhead that while batteries are purely storage mechanism, hydrogen cells can produce electricity for much longer periods of time and were equal to transport fuels for baseload power.

“They (FCEVs) can be refuelled very quickly while BEVs can only really operate for a few hours per day between recharging. It is also interesting to note that quick charging batteries substantially reduces the life of the battery,” he explained.

“Batteries also have a much shorter lifespan that H2 and there is presently little to no recyclability of the lithium in a battery. A lithium-ion battery will often only discharge 70% of its energy as it becomes inefficient and does not discharge to zero.

“Due to the dual power source, the batteries in FCEVs are much smaller than the ones required for 100% EV. EVs additionally have problems under load so you cannot tow caravans, etc, as that just destroys the distance that you can travel between recharges.”

The quick refuelling is particularly valuable for commercial vehicles that cannot afford to take significant amounts of time out of their work shifts to recharge.

Car manufacturers such as Toyota, Honda and Hyundai are promoting FCEVs, though they also have their respective BEVs.


Bitter rivals or working hand in hand?

Rather than being an all out royal rumble, the future of energy storage to bring about the net zero future is likely to see both hydrogen and batteries working in tandem if this Finnish study is anything to go by.

The study demonstrated the technical feasibility of an off-grid residence using solar photovoltaic panels to generate power, which will be used to first charge the battery system for short-term energy storage and for controlling peak demand before it is used to power the electrolyser to produce hydrogen for seasonal storage.

The battery is also used for all overdemand, limiting the unnecessary sudden powering on and off of the fuel cell.

On the transport front, batteries are likely to remain dominant for consumer EVs while hydrogen fuel cells could become the power source of choice for commercial vehicles where range and ease of refuelling are essential.

Longer term, for vehicles a similar setup could be used with a fuel cell recharging the battery that powers the electric motor, allowing for both the immediate power available from batteries and the ease of refuelling of hydrogen.