Fuel for thought

The transition to economical and effective low-carbon and low-emission energy carriers and fuels may include biofuels, hybrids and battery-electric options, but long-term options could also include different battery systems or chargers, and hydrogen or ammonia variations.

But why change? Transition is not sustainable if we lose employment. To be sustainable, the change must be financially effective and environmentally sustainable. Petro-fuel imports have exchange fluctuations and imported inflation – and then we burn it. This impacts the taxpayer in a range of ways, from health to the balance of payments and taxation. Is there a better way?

Could we build local electrical generation, train local people to operate and maintain these assets and then use the electricity to replace the imported fuel? This could provide a career and a lifestyle, reduce emissions, and improve effectiveness and efficiency.

Why electrify?

Everything needs electricity, whether that is biofuels, hydrogen or batteries. We already have networks, so why not improve those? An important point to consider is that flexibility beats perfection. Perfection only exists at that snapshot in time. When conditions change, the solution is no longer perfect. The future is changing, so being flexible offers the greatest advantage to the widest range of scenarios – whether that is climate change or power demand. We need a range of generation options – wind, solar and marine – and a system to deliver and store power.

Storage options

We need to consider our storage options, and factor in major changes that might be coming. We also need to consider how efficient these options are now, and how efficient they’re likely to be in five years’ time.

A nuclear fuel option for transport in Aotearoa is unlikely to succeed from an environmental concern, a political/country framework and the lack of skills. Therefore, the top contenders are:

• liquid fossil fuels such as petrol and diesel
• pressurised fossil fuels such as LPG or CNG
• synthetic alternatives to the fossil fuels
• gravity or thermal store
• in-ground compressed air
• electricity and batteries
• electricity and hydrogen.

The decision filter

In a seismically active country, a gravity store that relies on converting potential energy to kinetic energy is a real challenge (and very costly). Aotearoa does not have deep mining skills with steel ropes. Thermal storage is still being developed. This country has no large mining caverns and no large salt caverns for compressed air.

Synthetic fuels may be considered a suitable transition step (and would defer asset replacement). The feedstock for those synthetic fuels could be biomass. However, that still leaves a tailpipe emission. Based on zero tailpipe emission as a key criteria, we are effectively left with electricity/batteries or electricity/hydrogen.

Legislative and political considerations

Batteries and chargers are already installed daily. These still have to comply with the relevant legislation, such as NZECP34 and AS/NZS3000 but they are a well-known aspect. Bulk installation of flow-batteries (in the TWh range) may need careful consideration for environmental and resource consents, but nothing that would prove impossible.

On the other hand, legislation still has to be amended for hydrogen, which requires an approved handler for hydrogen (Class 2 hazardous goods). This also requires leak detection, handling/compression requirements and blast walls. These requirements differ by country and are still evolving.

The rapidly changing technology and options

Technology is changing quickly and new options continue to become available. Battery chemistries are progressing rapidly, with 12 major new types. These range from lithium (with reduced rare-earth metal compositions), sodium and iron with a variety of specific energy densities and advantages and disadvantages (including flammability, weight, charge rates and toxicity). It’s now possible to purchase battery electric passenger vehicles with ranges in excess of 1,000km, and a new breed of battery electric freight trucks can achieve 670km with a gross vehicle weight of 49 metric tonnes. Drag coefficients are down to 0.276 – a spectacular improvement.

Charge rates of up to 16c (this means the charge rate is 16 x the battery discharge rate) are in development in the mining industry, while freight trucks today charge with twin feeds at 870kW giving a 400km range boost in 35 minutes.

But don’t underestimate the impact of a lack of skills on both the future technology and the transition (think coal). In public transport, diesel mechanics have been trained on battery electric buses, enjoying a new career path plus the issue of a laptop instead of a pipe-wrench.

Something that might develop more is a type of battery swap system – a modular system where a battery tray (and associated battery management system) can be replaced and updated to newer high-performance batteries.

The challenges

The difficult metrics are chemistry, specific energy density and degradation. For vehicles, this includes lithium nickel cobalt manganese oxide (NCM/NMC, also called ternary batteries) which have low cobalt cathodes and higher energy density. Also, lithium iron phosphate battery (LiFePO4, LFP battery).

For grid-connected storage, a flow battery (consisting of two liquid electrolytes that only discharge when in the energy cell but are inert when separated is ideal for long period storage).

Hydrogen is currently expensive to manufacture, but perhaps a breakthrough will come by 2030. However, there are still maintenance and replacement costs (such as membranes/gaskets and valves).

Life span is another issue. Over time, the capacity of the battery decreases, and some batteries have a limited number of charge cycles. Many commercial manufacturers guarantee their batteries for eight years, so you know it will match the required range/operations at that point.

Capital cost must also be considered. The battery chemistry and production process will determine the capital cost.

Hydrogen as an energy carrier will add specific capital costs, including selected materials such as gaskets to deal with the reactive nature of hydrogen gas under pressure. Hydrogen embrittlement occurs with some metals, and leakage can be a big problem.

Upstream infrastructure demands are another issue – is there available capacity at the selected site, or is additional grid reinforcing required?

There is also the matter of generation to wheel efficiency. The operating cost will be impacted by the efficiency of converting electricity to kilometres. The sensitivity is important, so a lower efficiency process using an intermediate energy carrier (such as hydrogen) will be greatly impacted by an energy cost rise when compared to a more efficient process.

Storage and range are additional factors. The most efficient vehicle is lightweight, so reducing the mass of the battery or fuel tanks can pay dividends, but may also reduce the range. When comparing technologies, consider all aspects. For battery systems, include the weight of the electronics, charge ports and the like. For hydrogen, include the weight of the tanks (carbon wound epoxy), fuel cell, heaters, controls and filler ports, as well as the battery.

Most fuels and batteries are flammable, so protection from impact is essential. Some energy carriers such as hydrogen require infrastructure such as storage tanks, compression and leak detection. All need fire detection and early warning capabilities.

Whole-of-life cost and emissions must also be considered, although this is tricky as not all data is available regarding manufacturers (including their scope 3 emissions). The logistics of getting things to New Zealand plus in local infrastructure, workshops and operations must all be factored in.

While it’s exciting to see technology rapidly advance, we will see winners and losers in the field ahead as we transition to low-carbon transport energy options.

Kristian Jensen CMEngNZ CPEng is Technical Director – Industrial & Utilities at WSP.

This article was first published in the December 2024 issue of EG magazine.