SMART CHARGING 104: Electric car can power your house via Vehicle-to-Home (V2H) smart charging

Isn't it annoying when you get paid so less for the solar power you feed into the grid? - and a few hours later, you have to buy back the same electricity at a much expensive rate? Wouldn’t be better to temporarily store the electricity locally and to use it yourself later?

That exactly is the use case offered by vehicle-to-home (V2H) smart charging. So far, people use dedicated batteries (like Tesla Powerwall) for this local storage ;  but using V2H charger technology, your electric car can also become such a power storage, and as an emergency power back-up!.

Replacing 'static' wall batteries with a more sophisticated & larger capacity 'moving' batteries (EV) sounds great!. But how does it work in real life?, Won't it affect EV's battery life?, How about EV manufacturers’ battery warranty? and is it really commercially viable?. This article may explore answers for some of these questions.

How does Vehicle-to-home (V2H) work ?

The electric vehicle is charged by solar panels on the roof, or whenever the electricity grid tarrif is low. And later during peak hours, or during power outages, the EV battery is discharged via V2H charger. Basically, the battery of electric vehicle stores, shares and re-purposes energy when needed. 

Below video demonstrates the operation of V2H technology in real life with a Nissan Leaf.

This V2H technology is just one among the various levels of vehicle-to-grid integrations; V2H is all about self-consumption, not to be confused with Vehicle-to-Grid (V2G) which lets the EV also to feed in to the grid for monetary benefits. (Also read: different possibilities of integrating electric vehicles into power grid: V1G, V2G , V2B and V2H).

Advantages / Use cases of V2H 

“Can I power my house with electric car?”, “Can EV battery power my house?, “Can I use my Nissan Leaf to power my house?”, these were the most searched phrases on internet, during when Pacific Gas and Electric Co. turned off power to 800,000+ homes in Northern and Central California to prevent Wildfire in October 2019.

And the answer is technically “Yes”, Vehicle-to-home technology lets you to power your House with your electric car and address some more use cases / advantages, listed below.

1. EV as an emergency power supply for home:

Even in well-developed countries, there can be unexpected power outages due to simple infrastructure / equipment failures to big natural calamities. Recently (Oct 2019),  Pacific Gas and Electric Co. turned off power to 800,000+ homes in Northern and Central California to prevent Wildfire. Isn't it?

Under these circumstances, the electric vehicles that support vehicle-to-home (V2H) can act as an emergency power back-up. During the 2011 Tohoku earthquake and tsunami, Nissan sent 66 numbers of  Nissan Leafs to the north-eastern coast of Japan which acted as the primary power supply for many days!.

2. Reduce electricity consumption during peak hours

As the number of electric vehicles constantly increasing, and when all of these EVs are plugged-in simultaneously for charging, they could increase the peak demand on the grid, contributing to grid overload and create the need for upgrades at the distribution level.

EVs that support V2H gives the flexibility, to deliver electricity during peak hours (thus saving peak-time prices & fines) and take charge whenever the electricity rates are cheap.

3. Possibility to use large capacity home appliances at the same time

Many modern homes at old cities do not have the possibility to grid upgrade, thus limited to use small capacity home appliances. Even if they buy a large ones, they will not be able to use them at the same time.

I have seen at least a couple of homes in Amsterdam, where you cannot use the dish washer and dryer at the same time, though these houses have the best possible load arrangement wiring per phase. Electric vehicles with V2H can act as a buffer in these cases to provide the extra capacity, without going for a need to upgrade the grid connection.

4. Effective use of natural energy & self-sustainable living

Vehicle-to-home provides a perfect combination of two of the most promising technologies – electric mobility and solar power. By storing the energy generated by solar panels into the batteries of electric cars and re-use it for home consumption could not only avoid grid imbalances, but also helps to lead an eco-friendly life style.

Is Vehicle-to-home (V2H) commercially viable?

At present, most of the smart home owners install solar panels and storage batteries which enable them to increase self-consumption of solar power. A typical home storage battery (4 - 7 kWh) costs about $5000. This is the cost you’ll save since the EV’s battery becomes the storage; there is no need to invest in a separate storage battery as well it’s costly installation.

In addition, typical home storage batteries have a capacity of only 4 to 12 kWh, whereas an electric vehicle has a larger capacity of minimum of 10 to 100 kWh batteries. That means, you can use home appliances for a longer time, even up to a week.

There are numerous case studies and pilot projects validating the commercial viability of vehicle-to-home (V2H) and vehicle-to-grid (V2G) bidirectional charging. However, the results of each report hugely vary; some of them show a profitable business case, and some just conclude bidirectional charging as an unnecessary errand.

Having said that, there is no standard calculation that can show the exact impact of V2H; you should always work-out the cost based on how you want to use V2H. If you intend to use it only as an emergency power-back-up, the cost of battery degradation would be minimal. But when you intend to substitute your EV as the main battery storage to work with solar panel, the cost of battery degradation could be significant.

It is also necessary to think about how much time the car will be available at home (during day to charge from solar panels and at night to discharge to home appliances). And how much load/capacity you want to power-up with the EV battery.

Won’t V2H / V2G degrade EV battery life ?

Since inception, the battery degradation and thus the economic viability of V2H/V2B/V2X bidirectional operations has always been on debate.

The rate of degradation of EV battery depends on how you use them. There are multiple factors such as how often and how much you discharge (discharging current), at what temperature, - to what capacity throughput, at what state of charge (SoC) of the battery and depth of discharge (DoD), decide the degradation of the battery.

(a) – (b) as a function of temperature and State of Charge; and battery degradation during cycling (c) – (d) as a function of swing in State of Charge and current (Ref: Science-direct Uddin et al., 2017a).

Say for example, the battery degradation rate will be much higher at extreme SoC (< 20% or > 80%) than at discharging in 30-60% of SoC. Charging/discharging at extreme temperatures (cold as well warm) will degrade the battery faster than in room temperature. However, together with a smart battery management systems running intelligent “optimization algorithms”, the V2H could help to balance battery degradation vs benefits.

In short: Vehicle-to-home V2H , or any other form of battery discharge/recharge will degrade battery life of the electric vehicle. So perhaps, “how much is the degradation” and “whether it is worth the benefits you get?” should be the questions and calculations you may need to do.

Which EV manufactures support V2H ?

As far as I know, Nissan (Leaf & e-NV200), Renault (Zoe) and Mitsubishi (Outlander) are the only battery electric vehicles - BEV that support vehicle-to-home technology.

In addition to these BEVs, Fuel cell vehicles (FCV) also support V2H:  Toyota's MIRAI and Honda Clarity also provide V2H solutions by generating electricity using hydrogen and supplying electricity to homes. Both the MIRAI and Clarity are capable of delivering 9 KW electricity, that can power a typical household for up to 6-7 days!.

V2H capable chargers & technologies:

CHAdeMO Vs CCS: As you may see from the list of EVs above (Nissan, Renault, Mitsubishi, Toyota and Honda), for now only the Japanese electric vehicles, thus CHAdeMO fast charging connectors provide V2H capabilities. However as ISO 15118-20, the newer vehicle to grid communication interface standard coming out, this can extend V2H capabilities to the CCS fast charging connectors too.

DC vs AC V2H chargers: you may also notice that not many V2H chargers that support AC charging. It is because the implementation of V2H or any form of vehicle-to-integration is easier with DC chargers, than regular AC charging.

Electric vehicles need a power converter that converts the direct current (DC) stored in their batteries into the alternating current (AC), that can be feed into the grid.

➤ In case of DC (dis-) chargers, this DC-AC power converter is located inside the charging stations. Therefore, the location-dependent grid codes can be programmed into the controller of the charging station that manages the power flow to and from the grid.

➤ In case of (AC disc-) charging, this DC-AC power converter that manages the power flow is located “on-board”, that is inside the EV. This means that the external charging station needs to provide the EV with all the necessary location specific information on how to feed energy back to the grid. For detailed explanation, please check this page at V2G clarity (Credits : Dr. Marc Mültin)

Regulations and standards around this grid codes communication are not clear yet ; hope the ISO 15118 communication protocol address this issue with AC discharging too.

How about EV manufacturers’ battery warranty?

Consequent to the battery life degradation, car manufacturer’s warranty for battery is one of the main factors that has been blocking the V2H (or any V2G bidirectional) solutions.

Industry-wide EV manufacturer’s warranty is around 160,000 km driving with a minimum remaining capacity of 70% for eight years (Reference warranty statements of Nissan, Renault, BMW, & Tesla). However, Nissan is the only EV OEM who has declared that V2H / V2G use will not void the warranty of its car battery.

As the EV makers have more insights in to the capabilities and safe-operating range of their batteries, they can design a better battery management systems for their EV, that guarantees warranty period including V2H operations. Honda-Europe and BMW are reportedly testing V2H charger capabilities, but not sure when/whether they will release a commercial solution like Nissan Leaf.

Electric vehicles are already changing the way we commute, and now with Vehicle-to-Home smart charging, EVs can change the way we consume electricity too!. Not to forget, these vehicle to grid integrations will challenge traditional businesses of utility companies and require meaningful commitment from car OEMs as well. What do you think of this shift? Where will it lead us to?