As battery owners and operators seek to maximise the returns from their assets, they simultaneously face the Herculean challenge of managing degradation. This remains one of the most prominent challenges in the industry, where assets are expected to last around 15 years before reaching End-of-Life (EoL).

Degradation manifests itself in several ways leading to reduced energy capacity, power, efficiency and ultimately return on investment.

Put simply, battery degradation is a serious economic problem which will vary according to how the battery is used. It is therefore essential to monitor factors which drive degradation. These include temperature, ramp rate, average State of Charge (SoC) and Depth of Discharge (DoD).

Analysing the impact of these factors is vital to assessing the cost-benefit of decisions to charge or discharge a battery in response to different market signals.

This is especially important as single/multi-service batteries have the option of participating in a variety of markets, such as frequency regulation or the Balancing Mechanism (BM), and each market can have a different risk level according to the asset’s load profile and cycling behaviour.

Back to basics: what ‘exactly’ is a charge cycle?
Unfortunately, and confusingly, the industry has different definitions for what ‘a cycle’ actually is. In commercial documents, such as warranties, a cycle is calculated via energy throughput. This tallies the energy going in/out of the battery and divides total energy throughput by capacity. Even though this is a relatively simple calculation, it actually only tells you the number of ‘Equivalent Full Cycles’, or EFCs.

EFCs do not quantify DoD, which factors how deep charge cycles are. As can be seen below, EFCs would be unable to distinguish 1 cycle of 100% DoD vs 2 cycles of 50% DoD vs 10 cycles of 10% DoD. Cycle depth is completely ignored in EFCs! For this reason, KiWi Power utilises the Rainflow algorithm as a tool for profiling each ‘real cycle’ in terms of DoD.

The stationary energy storage industry, with batteries as the prime mover, has enjoyed a series of record years of deployment across North America, Europe and Asia in particular, but what comes next after that first wave? What are the challenges still posed for the ‘mainstream’ adoption of cost-effective energy storage technologies in a modern, low-carbon grid?

PV Tech Power, the downstream solar industry journal from our publisher Solar Media, has reached its fifth ‘birthday’ and Volume 20 of the quarterly magazine, out now, includes a special report on energy storage. In addition to some excellent technical papers and guest submissions, every edition of the magazine has for more than five years brought you the latest news and feature articles from writers and industry experts at PV Tech, Energy-Storage.news and our other channels including energy transition site Current± and Solar Power Portal (UK).

It’s got the usual great solar PV industry analysis on everyone’s favourite topics, technologies and gripes. From bi-facial modules in a post-trade tariff environment, to president Emmanuel Macron’s attempts to revive French solar makers, to the impact of digitalisation on the solar industry, PV Tech Power 20 has it covered across its mammoth 126 pages. Better understanding of corporate solar PPAs, the ‘terawatt opportunity’ of floating PV, utility-scale solar site safety and much more, from the worlds of solar technology, business and inevitably, policy.

But this issue’s Special Report focuses squarely on energy storage, with no less than seven feature articles and technical papers looking at everything from the policy and regulatory initiatives that still need to happen, to bankability and profitability of ESS, system technologies and architecture, all the way to recycling and end-of-life care for batteries. Additionally, Energy-Storage.news’ contributed section of the journal, Storage & Smart Power, returns once again, with feature articles on the UK’s recent blackouts and how batteries can help maintain system stability, the role of flexibility in smarter energy networks and finally a fascinating technical paper on the role batteries can play in delivering a ‘synchronous grid takeover’.

Knowledge transfer between academia and industry has the potential to affect a lot of change for a small off-grid solar company like M-KOPA Solar, a Kenya-based company and 2015 recipient of the Zayed Future Energy Prize. This is why Harini Hewa Dewage joined M-KOPA Labs, the research branch of M-KOPA, in November of 2016 as its battery technology specialist.

She has been connecting academia to industry in the battery storage sector ever since.

Now Battery Research Lead for M-KOPA Labs, Dewage believes in the mission of M-KOPA: providing access to energy through high-quality solutions that are affordable for all. As of November 2018, M-KOPA has over 700,000 total households subscribing to their services. But while typical businesses or nonprofits working in the low-cost distributed solar industry focus on the potential for solar power to support lights, M-KOPA has worked to meet demand for larger appliances such as TVs or refrigerators.

“Coming from the western world, we have this idea that access to energy is being able to get lightbulbs and light,” explained Dewage. “And I think that’s a fantastic first move to be able to displace candles and kerosene for light, but I think where you see people’s quality of life really improve is with access to appliances and other services.”

At M-KOPA, Dewage believes in giving people not just access to lighting, but the full range of what energy can provide. She explained that a common assumption is that if you ask people what’s the first appliance they want, it would be a fridge or a washing machine. While those two appliances are important, however, the first appliance most people want is a TV.

But with larger appliances, it requires more battery understanding and development. And that is where things get tricky.

“Any problem you have on a smaller battery it might be magnified on a larger one by the sheer fact that you have more cells,” said Dewage. “But also new challenges will appear. For example, as your pack increases in size you might have to put in cooling systems, you might have to manage, you know, thermal radiance better within the pack.”

“Any problem you have on a smaller battery it might be magnified on a larger one by the sheer fact that you have more cells,” said Dewage. “But also new challenges will appear. For example, as your pack increases in size you might have to put in cooling systems, you might have to manage, you know, thermal radiance better within the pack.”

The energy storage market enjoyed another record year for deployment in 2018, according to a new study by Navigant Research.

The news is not so surprising for a growth sector that is just finding its feet. However, while that growth is driving energy storage into new applications and in increasing volumes, the geographic distribution remains concentrated in just ten countries. Those being U.K., France, Germany, U.S., Brazil, India, China, Japan, South Korea and Australia.

Navigant expects these countries to install 1,242.1MW of energy storage in 2019, which it predicts will represent 80% of the market all in all.

As costs fall and the regulatory goalposts shift (in a positive direction) more and more use cases become economical in more territories.

Most new energy storage markets start off with systems providing short-duration discharges that provide services to the grid such as recalibrating the frequency. These are often rewarded through specifically designed market structures.

“In terms of applications for new utility-scale energy storage projects, solar plus storage has emerged as a major opportunity and driver of new growth,” says Alex Eller, senior research analyst at Navigant Research. “The rapidly falling costs for both technologies have made combined solar plus storage plants economically competitive against conventional fossil fuel plants in a growing number of markets, which allows a solar plant to be a predictable resource for grid operators.”

With around 100GW of solar installed annually the scale of that particular opportunity is significant.

Discharging batteries storing renewable electricity to meet peaks in demand instead of starting up natural gas peaker plants is proving increasingly economical. U.S. developer Fluence has commissioned research that found the economics could work not just in the very peakiest moments of demand but further down the shoulders of these peaks as well.

Storage facilities, particularly battery-based storage can also deliver extremely fast start-up times responding to momentary fluctuations on the grid that can trigger blackouts.