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Researchers developing DC micro smart grid for charging EV fleets; Li-ion, redox flow batteries and renewables

Up to 30 electric vehicles at a time can recharge in Fraunhofer IAO’s parking garage. Click to enlarge.

A team from Fraunhofer Institute for Industrial Engineering IAO, together with Daimler AG and the Institute for Human Factors and Technology Management at the University of Stuttgart, is developing both the charging infrastructure and the energy management systems required to manage large fleets of EVs in a project called charge@work.

The aim of charge@work is to design a micro smart grid (MSG) capable of supplying the EV fleet with electricity produced exclusively from renewable sources. This year will see the installation of a photovoltaic unit and a small wind power system at the Fraunhofer Institute Center Stuttgart IZS, where up to 30 electric vehicles at a time can recharge at AC charge spots in the Fraunhofer Campus parking garage.

EV charging at IZS
Up to 340 kW are consumed when all 30 charging spots are occupied—equivalent to ~20% of the load of the Institute Center, with a staff of 1,500.
“Charging an electric vehicle fleet poses high requirements on the energy system. Setting up an EV charging infrastructure of this kind is impossible without smart charging and load management.”
—Hannes Rose

In addition, a lithium-ion battery storage unit will be added to the basement and a redox flow battery to the roof as temporary storage of energy. A 30-meter-tall wind turbine delivers 10 kW. Since it operates on a vertical rather than a horizontal axis, it does not have to be oriented to wind direction. The MSG can be run in island mode in parallel to the grid operated by the local energy provider.

The MSG is designed as a direct current (DC) grid.

Photovoltaic facilities and battery storage devices both use direct current. We settled on a DC design for our micro smart grid to avoid the losses that occur when transforming alternating current (AC) into DC.

— Dipl.-Ing Hannes Rose, head of the Mobility Innovation Lab at the Fraunhofer Institute for Industrial Engineering IAO

In addition to the energy management software, the IAO scientists are also setting up a simulation environment in which to lay out their MSG and play out various scenarios, such as different weather conditions.

Rose sees a host of advantages in decentralized power generation, but none more significant than being able to secure supply.

As Germany continues to move toward a new energy economy, increasing demand is being placed on the country’s power grids. Wind and photovoltaic facilities generate electricity intermittently, which doesn’t always match customer demand. The grid has to compensate for these fluctuations, increasing the risk of power outages. We can counteract this risk by establishing decentralized supplies of electricity and by optimizing the way we manage our energy. And doing so also serves to increase our independence from energy price trends by largely eliminating the need to import electricity.

—Hannes Rose

The IAO scientists now plan to create a testing environment that will allow industrial companies, systems providers, public utility companies, communities and distributers to explore the potential of micro grids.

Over the next two years, the Micro Smart Grid innovation network is to provide interested parties with an opportunity to work up new kinds of smart grid configurations and operating strategies. Using the Fraunhofer micro smart grid demonstrator, the project partners can test their hardware and software components. They can also investigate options for allowing other consumers to connect to the MSG—whether, for example, to run a building’s air conditioning system or to integrate other production facilities.

Our long-term goal is to bring individual local grids together to form a large smart grid.

—Hannes Rose

Researchers will be presenting a virtual model of the smart grid at the Hannover Messe from 7-11 April 7-11 at the joint Fraunhofer booth in Hall 2, Booth D18.

The project "charge@work" is one of more than 40 initiatives in the “LivingLab BWe mobil” program to demonstrate the merits of electric mobility. It is being sponsored by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety as part of the federal government’s agenda to promote electric mobility in Germany.

Supported by the state of Baden-Württemberg and the Stuttgart region, more than 100 partners from business, science and public sectors are conducting practical research into electric mobility under the auspices of the state government of Baden-Württemberg as part of the LivingLab BWe mobil promotion program. Daimler AG is involved in ten such promotion projects.

As part of its efforts in charge@work, Daimler is making 260 electric vehicles available to employees, with more than 170 charging points at five Daimler plants in Stuttgart.



Better grid load management will become common place when justified with larger EVs fleet. This is one of the early application. More will follow.

Roger Pham

An H2 filling station can be built in exactly the same way, all DC network, for a lot less cost. No storage battery needed, and H2 storage is 1/20th the cost of battery per kWh basis. The electrolyzer can put out up to 350 bar of pressure, meaning that only a single stage 2:1 compression will be needed to 700 bar standard pressure. Instead of parking spaces and charging sockets for 30 charging BEV's, only 1-2 H2 fillers (dispenser) will be needed, since a FCV will pull up and takes a few minutes to fillup and leave instead of having to park for much longer.


Leave, and go where? This is a charge at work plan, the drivers are still stuck at the site foe 8 hours even if their cars are filled up.

Roger Pham

Good point, ai vin. However, look at each dedicated charger and meter and charging post per car per day...not cheap! What ever happened to just a single power cord or power socket per parking spot? Perhaps when that many cars are charged at one time, the power drain on a facility or on the RE infrastructure including battery storage is substantial, such that close monitoring is required.

By contrast, one single H2 filling post with one single nozzle can serve 100's of cars per day. Who could've predicted that BEV charging insfrastructure can potentially be more complicated and more costly than H2-filling infrastructure? Of course, I did, many years ago!


Just because the cars are left on the charger for 8hr doesn't mean they have to be charging. With a smart grid the building can draw on their storage capacity as well as its own. With more storage capacity you can increase your RE generation potenial.


The buffering batteries can be recharged during very low consumption periods at lower cost.

So could H2 storage system.

Difficult to predict which technology will prevail for Extended range electricifed vehicles.

Both technologies could co-exist for a few décades.


True. The fact is FCVs are BEVs. A FC works best by producing energy at a constant output but a car's energy use is variable so a FCV is well served to include a battery pack. Commutes to work tend to be short - well within the range of even a small pack, FCs (with their quick fill) are better for longer trips.

A charge@work/mall/school plan allows you to cover your daily driving needs while H2 stations placed near highway onramps will meet every other.


BTW: Better late than never.

"German energy giant RWE has taken a massive loss of €2.8 billion – it’s first loss in 60 years – after admitting it got its strategy wrong, and should have focused more on renewable and distributed energy rather than conventional fossil fuels.

RWE, like other major German utilities, has spent much of the past decade fighting against the country’s “energiewende”, the energy transition that is seeing it dump nuclear energy and transform the electricity system of Europe’s biggest manufacturing economy to one dominated by renewables.

Last night, Peter Terium, who has been CEO for less than two years, conceded that the company had got it wrong. He admitted that the change in electricity markets, which has seen earnings from conventional generation gutted by the impact of solar and wind energy, was “unstoppable”. It was now time to change strategy, and focus on what the electricity market will look like in the future."


Europe should follow Germany's lead and become less dependent on Oil and Gas from Russia (and others) as quickly as possible.

The use of Solar, Wind, other alternative clean energy sources, improved energy storage units, BEVs, FCEVs, improved buildings etc can do it. That's what Germany has been doing.

Another huge benefit for humanity, would be a progressive crash for Oil and NG prices. All the saved $$$$B could be used for better things in life than building huge cities in the ocean with petro-dollars.


New Battery Technology Could Provide Large-Scale Energy Storage for the Grid

The result is a battery that Cui and his colleagues claim is able to retain 83% of its charge after 40,000 cycles, which compares more than favorably to Li-ion batteries of 1,000 cycles.

Roger Pham

Panasonic NCA 18650 is already capable of 5,000 full DOD cycles with only 18% loss of capacity, at reasonable cost, calculated to be at 1.5 cent/kWh for battery amortization cost. This will make stored RE very cost competitive with other means of power generation. If charged twice daily at less than full DOD, it will last for more than 10 years, at which time batteries generally will age and will not be effective.

So, unless Stanford/Cui's battery will not age after 20-30 years, the 40,000 cycles won't be much of an improvement.

Roger Pham

However, no battery can provide the vast capacity for seasonal-scale energy storage like H2 can. This is because seasonal energy storage only goes thru 2-3 cycles/year, so the battery must be very cheap per kWh of capacity to do this. For example, H2 bulk storage using underground caverns only cost pennies per kWh of capacity that will last for decades if not centuries.

Let's say it costs 50 cents/kWh for bulk H2 storage, and one cycle per year for 50 years, then the storage cost per kWh of H2 will be only 1 cent. If 2 cycles/year over 50 years, then the storage cost per kWh of H2 will be 0.5 cent. No battery can be built for 50 cent to a dollar per kWh of capacity.

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