The challenge of what to do with electric car batteries that have degraded over time has been solved in a novel way that also holds the promise of helping to reduce instability on the grid.
The innovation sees the reuse of 24kWh lithium-ion battery packs from Nissan Leaf cars in combination with power electronics to deliver an energy storage technology that has multiple applications across industrial, commercial and residential settings. The unit could bring wide-ranging benefits including securing continuity of supply, avoidance of peak energy tariffs, and a reduction in the reliance on expensive fuels such as diesel to compensate for poor grid networks in developing countries.
From Nissan’s perspective, the energy storage technology provides a cost-effective ‘second life’ for batteries that have degraded after several years’ use in its Leaf vehicles. “Second-life batteries maintain more than 70% of their initial capacity at the end of the ownership cycle and we see that as available capacity,” says Robert Lujan, global electric vehicle director at Nissan. “More than 200,000 Nissan EVs have been sold since launch. That represents multiple gigawatt hours of energy storage capacity.”
The technology combines power electronics and control software, renewable energy and stationary storage into a single, packaged system. The first module to be deployed will combine the Leaf batteries with an uninterruptible power supply (UPS) from power management specialist Eaton, with integrated solar photovoltaics, to create an energy storage and control package. This will allow customers to manage energy consumption and supply while connected to, or independent of, the grid.
The Eaton UPS acts as the brain of the system, with the second-life batteries providing the storage capacity. Fabrice Roudet, program manager for data centre automation solutions at Eaton, says: “This is not simply the combination of batteries and bi-directional inverters, it is the creation of multiple capabilities in a single packaged unit. The technology provides uninterrupted high-quality power, energy storage and supply of energy off-grid. The UPS is programmed to select the optimum mix of power sources according to load, grid constraints and availability of renewables.”
If installed with solar photovoltaics, as suggested by Nissan and Eaton, the technology could work in several ways, depending on various factors. During early mornings, when renewable energy is not available and the batteries are not fully charged, the energy control centre could use the grid to power the load. When the sun begins to shine and renewable energy is available, the control centre could then be used to power load or charge the batteries.
When the sun is shining and batteries are fully charged, the energy control centre could feed the load directly with renewable energy, thereby reducing costs. During peak periods, when solar produces more energy than needed by the load, the control centre could inject the available energy to the grid. If grid demand was very high, the energy stored in the batteries could also be released to further support peak shaving.
“This is a totally integrated solution,” says Roudet. “With the integration of the photovoltaics, for example, the connection is not just via an input on the UPS. We connect it inside the UPS on the DC bus which acts to minimise the losses on the system. It doesn’t make sense to spend time and money developing a system to save energy which itself is not efficient.”
The first working demonstration of the system has been installed at a Nissan office in central Paris. The office’s energy is switched from grid to batteries to power lighting and other electrical circuits.
“The technology has been validated at the Paris site and there is a system in operation at one of our facilities in Lausanne in Switzerland,” says Roudet. “These represent market-ready technologies. We have a proven product that we will start installing at customer sites early this year. We think the market for second-life energy storage systems is massive.”
Roudet thinks there will be applications across industrial, residential and commercial settings. “The sweet spot depends on energy market incentives, and that differs from country to country. The quicker the return on investment, the more likely people are to invest. So I think maybe commercial buildings, particularly those with mission-critical use, will come forward first.”
In terms of system lifecycle, car battery capacity would usually degrade by around 25% over several years of standard automotive operation, and it is at this point that they would be considered for second-life energy storage use. Nissan says that, depending on their usage, the batteries in the energy storage unit would then be expected to last between five and 10 years.
At present, Nissan is planning to reuse 24kWh battery packs, but this output could be doubled as Leaf battery technology develops. The company says it might also consider manufacturing batteries for energy storage use at its plants in Sunderland, the US and Japan, should enough demand exist.
The development of the energy storage product could also change the economics of electric car ownership, says Nissan, as the value of degraded batteries increases. While disposal of spent batteries has always been considered a cost, in future there would be real value for the car owner at end of life.
“If the Leaf battery pack is worth several thousand euros, regardless of the value of the car, then that could really start to challenge consumer perceptions around electric car ownership,” concludes Lujan.
Trials of electric vehicles as ‘energy hubs’
Nissan has also teamed up with power company Enel to develop a vehicle-2-grid (V2G) system that will allow drivers of Leaf electric vehicles to operate as individual ‘energy hubs’ with the ability to use, store and return excess electricity to the grid.
The agreement will bring the first grid-integrated vehicles to countries where regulation allows sufficient market incentives. Denmark will host the first set of trials, with Germany, the Netherlands and other northern European countries following suit.
The V2G technology allows electric vehicles to be fully integrated into the electricity grid. The system works by allowing Nissan Leaf owners to connect to charge at low-demand, cheap tariff periods, with an option to then use the electricity stored in the vehicle’s battery at home when costs are higher, or even feed back to the grid to generate additional returns.
Nissan says there is enormous potential for electric car fleets to be used as energy hubs. In France, for example, where there are 38 million vehicles and where the current electricity generation capacity is 130GW, in a future where all cars are EVs or plug-in hybrid electric vehicles, their grid integration could generate
a virtual power plant of up to 380GW.
Nissan Europe chairman Paul Willcox says: “As the energy and automotive sectors converge, the opportunities for enhanced energy management have never been stronger. V2G technology underscores Nissan’s commitment to the entire
EV ecosystem – it goes way beyond driving.”