The Energy Resilient Vehicle (Part 3)
This is the 3rd of a series of blogs that explains the concept of the Energy Resilient Vehicle. This blog goes into some details about what the ERV is and how the EV manufacturers can make ERVs. The next blog will take a view of the advantages to the state of California if ERVs become the mainstream.
1) Use cases
Public Safety Power Shutoffs / Wildfires
When PG&E announces that a PSPS event is upcoming the driver has time to fully charge the EV. When the actual power is cut the EV can provide emergency power to the home for 3-5 days. This will avoid that the homeowner has to discard food contents of fridges and freezers often in the amount of $300-$500 per PSPS event. And in October we had 3 PSPS events!. Furthermore, the homeowner has the peace of mind that there will be light in the house, power to charge critical medical devices and power to charge the cell phones (so they can be used if the cell towers have power).
Earthquakes occur spontaneously and charging of the EV cannot be planned before an earthquake occurs. However, if power is cut and the EV is at home and charged or partly charged it can still provide power to the house as described above.
2) All electric vehicles are born to “bi-directionality” internally
When you depress the accelerator in an EV DC energy is flowing from the battery to the electric motor (EM) – the green arrows. However, before it reached the EM it has to be converted to AC, this is done by the inverter. See simplified diagram below.
When the foot is taken off the accelerator the EM will break the car by reversing the energy flow which flows back to the battery in form of regenerative energy – the red arrows. However, before the energy can be returned to the battery it must be converted from AC to DC. This is done by the rectifier. Voila, every EV is born to bi-directional power flow. Battery -> Electric Motor (outgoing power flow from DC to AC through inverter). Electric Motor -> Battery (incoming power flow from AC to DC through rectifier/charger).
The diagram below shows a typical power flow of a Tesla Model S. As can be seen by the orange and green curve the power is bi-directional.
3) The analogy between the car and the phone
The good old fashioned AT&T telephone was invented for making telephone calls. With the invention of the car phone and later the cell phone it was possible to move around with the phone. Later the first smartphones were introduced – spearheaded by Nokia, These could add text messages and simplified internet connections for limited internet browsing via the WAP (Wireless Application Protocol). With the introduction by Apple of the iPhone in 2007 that all changed. The telephone had become mobile and could be used for many functions: telephony, texting, browsing, emails, video, photography, music etc (see figure below).
Up till now the ICE (Internal Combustion Engine) vehicles fulfill one single purpose: transportation. With the introduction of the EV this has not changed. The EV can be charged and the energy can only be used for transport. So to say, the energy is trapped in the battery for one purpose only. With the bi-directional ERV this changes in analogy to the telephone – the ERV becomes multifunctional. The energy in the battery can be used for transport, emergency services, mobile power, energy services serving the business, home or stabilizing the grid. The energy is no longer trapped in the battery for transport but can be used for a multitude of value adding services.
4) The analogy between the Internet and the E-Mobility (ERV)
The key word during the internet revolution was: bandwidth, bandwidth, bandwidth, and the internet required a lot of it. However, the internet could only scale to what it has become now, if technology could drive the cost of bandwidth to almost zero.
The keyword now – in the transition to renewable energy and increased electrifications – is energy storage, energy storage, energy storage. But how can we make the cost of energy storage almost free or at least much lower costly?
The owner of an EV will buy the EV including the battery with the purpose of driving the EV. However, it is only driven for a few hours every day. Why not share the battery between transport and energy services? This would drive the marginal costs of using the battery for emergency power services dramatically down. For the state of California the cost of providing emergency power to households would also go dramatically go down.
5) What it takes to make an EV bi-directional externally
For DC charging the inverter is located in the EVSE (Electric Vehicle Supply Equipment). The EV manufacturers Nissan and Mitsubishi have already shown that is is possible to implement DC bi-directionality in their EVs even in “low cost” EVs.
For AC charging there are principally two ways to make the EV bi-directional to the outside:
A.Integrated solution.Use the existing internal EV inverter/rectifier system already on-board inside the EV.
B. Separate solution. Change the existing on-board charger to a bi-directional charger/inverter.
Option A is the solution pursued by Renault (unfortunately does not market its EVs in California).
Option B is pursued by Honda. Actual Honda cars are operating in the CEC (California Energy Commission) funded INVENT project (Intelligent Electric Vehicle Integration) at the UCSD campus.
Both case A and case B requires relative low cost components and some engineering efforts. Considering that the larger EV manufacturers are typically producing many hundred thousand EVs in a series the engineering costs can be amortized over many EVs. The total costs should be considerably less than what it cost to put catalytic converters on the cars in the 90ties.
Just in November 8, 2019: “BMW has just announced Bidirectional Charging Management – BCM research project brings together companies and institutions from the automotive, energy and scientific sectors. Electric mobility in tomorrow’s world – a question of give and take. Green light for the Bidirectional Charging Management (BCM) consortium research project led by the BMW Group: electric vehicles enable more efficient use of green energy while also boosting power supply reliability. Testing of the first 50 BMW i3 cars equipped with bidirectional charging technology (i.e. that are capable of back-feeding) is expected to start under real-world everyday conditions in early 2021.”
6) The ultimate ERV – The California school buses
There are over 25,000 school buses in California. In the USA there are 480,000 compared to 70,000 transit buses.
Electric school buses would be examples of perfect ERVs. They are large and have room for large batteries (+100 kWh), are driven only 180 days a year, for 4-8 hours a day, non-operation for long time (summer, holidays, weekends and nights) and have predictable routes every day. They could provide substantial community emergency power in case of power cuts for example 10 school buses could provide 1 MWh+ emergency power to critical community functions.
Trials have already been underway in California since 2014.
In July 2014, the California Energy Commission approved a $1.4 million grant for the deployment of six V2G school buses. These buses were 1996 model-year diesel Blue Bird buses, EV-converted with 96 kWh batteries, 150 kW EPC Power Corp on-board inverters and Nuvve 22 kW bidirectional chargers. In June 2019 a new vehicle-to-grid (V2G) pilot for 10 electric school buses was approved with a budget of $1.7 million. CPUC noted that it would be the first V2G pilot in the California Independent System Operator (CAISO) market utilizing 25 kW bi-directional chargers.
7) The cost of the bi-directional EVSE
It is not enough that the EV is bi-directional the EVSE must support bi-directional power flow as well. The figure below shows the two different ways to charge an EV (orange color). In the AC charging system the EVSE provides AC power to the on-board charger which in turn converts the AC to DC and via the Battery Management System (BMS) feeds the energy into the battery.
In the DC charging system (on the right) the AC to DC conversion is built into the EVSE and as such can be shared by many cars.
In case of bi-directionality (the green arrows) an inverter must convert DC from the battery to AC to the grid. The inverter can be located in the EV (on-board) or in the EVSE (off-board). Locating the inverter in the EVSE (off-board) transfers the cost to EVSE. This cost is today quite high. For example typical bi-directional EVSEs cost upward of $8,000.
Using the already integrated inverter in the EV used for feeding power to the electric motor (on-board) reduces the additional cost for the EV substantially. But more importantly the cost of the bi-directional AC EVSE is much lower – in the range of $1,000+. Such technology is already commercially available today e.g. the Nuvve Powerport charger that provide up to 99 kW (3 phase) at low cost.
So the way to achieve a low cost bi-directional solution is to go AC and as is show later the international standards to support this will be available in 2020.
8) Why EV manufacturers should implement external AC bi-directionality
Cost: In quantity this will only add some few hundreds $ per EV for ; less than the cost of a catalytic converter. However, the cost of a bi-directional AC EVSE will go down dramatically. Example: today a bi-directional DC charger @10 kW typically sells for $8,000+. The cost of AC bi-directional EVSE today is in the range of $1,000+!
Weight: Integrated solution – Case A: the added weight will be negligible; Separate solution – Case B: This may increase the weight with 5 – 10 kg, but with maturing charger/inverter technology and increased integration this weight should go substantially down.
Volume: Integrated solution – Case A: the added volume will be negligible; Separate solution – Case B: This will increase the volume, but with maturing charger/inverter technology and increased integration the volume should substantially decrease.
Performance: For emergency use (energy resilience) in case of cutting power or earthquake this will only be activated few times per year and have no effect on battery health and will make sure local grid is protected (anti-islanding). However, it will greatly help California in its preparedness for mitigating natural disasters.
9) The international standards
The CHAdeMO protocol between the EV and the EVSE already supports bi-directional power flow to day.
The IEC 15118-20 standard communication protocol supported by the European and North American car manufacturers will support bi-directional power flow functionality and be released in 2020.