Home Battery vs an Electric Car?

Before diving into todays post, quick reminder that tomorrow we will be meeting with a bunch of internet strangers and talk money in the La Place, in de Meern. Hope to see you there!

In this post from not to long ago, I looked at our expiring energy contract, dynamic energy contracts and energy trading using a home battery. I got a lot of feedback on this post, primarily offline. Very useful stuff though! It actually made us think again about a few issues and risks with the home battery for trading energy. Another thing that popped up was the electric car as a home battery. Time for a follow up post.

Home Battery vs an Electric Car? The Grid

Home Battery for Energy Trading – Risks

Besides the already elaborate assessment made in the previous posts. Some insider information (from people working for several Dutch power distribution companies) highlighted the following main risks:

  • The lower-voltage part of the network might actually suffer from additional home batteries being used to push currents around. The use of home and commercial battery systems are thus very much on the radar of power distribution companies. And not necessarily in a good way. Depending on popularity and impact, there might be restrictions coming in certain areas in the coming years. This could potentially negatively affect your ROI of the home battery (especially when used for trading)
  • The prices of commercial batteries are dropping pretty fast, and they are already much lower than the €400-600/kWh we pay as (residential) consumers. The number and size of potential commercial systems are far larger than the current impact and size of residential home batteries (and the ability to use them for energy trading). For now, the home battery (with energy trading options) seems to be an interesting investment. But this can turn around pretty quickly once commercial parties get in the game of balancing the grid (the potential connection requests for commercial battery systems already outpaces the total requirement for the grid). It is thus somewhat uncertain if you can completely earn back (and make money with) your home battery. I’m not saying that it’s not possible, but there will likely be hurdles in the future.

Our thoughts

In short, right now, a home battery with energy trading can be a good investment. It’s just really difficult to make an educated guess about the future and if you can recoup the investment and even make some money in the long run. For ourselves, we have decided for now to wait and see what the energy market does. The available funds will be dropped into index funds for now, which seems a lower risk investment.

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Home Battery vs an Electric Car? The Leaf!

The alternative: an electric car!

But what about an electric car? They have batteries too, right?! Can you use these batteries for you home? Unfortunately, there are currently very few models available that can both charge and discharge via your energy box / connection. Today, you pretty much have the choice between the Nissan leaf (or EV200) and the Mitsubishi Outlander. This is purely due to the CHAdeMO-plug, which in combination with a special converter, allows you to supply to your house (and national grid). The more common CCS-plug, in combination with existing software / converters, does not allow for discharge of a car to your home at this time.

Having said that, there are obviously many car manufacturers that are investigating the options for vehicle-2-grid (V2G) / Vehicle-2-Home (V2H) capabilities or their cars. Unfortunately, there is no standard yet, also software & battery warranty are issues and there are no confirmed roll-out of V2G/V2H as far as I could find. But this will certainly change in the (near?) future.

So let’s look at the Leaf and the Outlander for now. The Leaf has a battery between 24kWh and about 62kWh in the new models. The outlander is only about 12-14 kWh. For sake of having a reasonable comparison to the home batteries reviewed in the previous post (which were 20kWh), I’ll stick to the Leaf.

The Leaf

Scouting the world wide web I found the cheapest 24kWh Leaf for about €4.500, a model from 2012 (12 years old) with under 173.000km. An average charge holds about 75-100km for this Leaf model. Assuming you charge every 50km or so, you have had about 3500 cycles of loading and unloading (out of about 7000-ish). Based on this age and usage, you’d probably have 60-80% capacity left. At 70% you would have about 17 KWh in storage capacity left (which you can use for about 80-90% or so = 14-15kWh in real terms of practical storage). If you want to use for storage the cost is thus ~€265/kWh (based on 17 KWh and €4.500 purchase price).

In order to connect your Leaf to your house, you need a special converter that support loading and unloading. These don’t come cheap. Most I could find were around the €5.000 mark. The total costs would this be starting at about €9.500 for 17kWh or capacity. This is thus about €550/kWh. This is about the same price as the battery systems for sale at the moment, and you even get a free (old) car as a bonus!

Yeah or Nea?

Okay, so buying the car to use only as a home battery might not be financially the smartest thing to do. Firstly because you buy an older battery system, which comes with risks and general wear. Secondly, the purchase price of a new system is about the same (or less) in cost per kWh (albeit without the free car).

You can furthermore likely not use the car battery for trading purposes. I am however not a 100% sure about this. But the converter would have to be linked to he trading app by a dynamic energy provider, which might be difficult or not possible at all.

You could use it as a regular storage option for electricity, where you store from your solar panels during the day (or load with cheap energy from the grid) and supply back during more expensive times. Unfortunately, this still can’t be done economically (as pointed out in the the previous post) for the simple reason that the electricity price differences are too low to earn enough respective to the storage capacity and cost of the battery, In short, the purchase costs has to be (at lot) lower (and we also need to get rid of the Salderingsregeling). Would this be the case for newer models with larger batteries?

Home Battery vs an Electric Car? Just a pretty picture of the Grid

Newer options

The cheapest 30kWh model was already €8.500. Model was from 2016 (8 years old). Had about 155.000km on the odometer. So likely still about +80% of battery capacity = 24 KWh. If you want to use for storage the cost is thus ~€350/kWh. Including converter you’d be looking at €13.500 or €560/kWh.

The cheapest 40 kWh model is about €12.000. This model is from 2019 (5 years old) and has about 138.000km. One should have about 85% of battery capacity left = 34kWh. If you want to use for storage the cost is thus ~€350/kWh. Including converter you’d be looking at €17.000 or €500/kWh.

The cheapest 62 kWh model is about €15.000. This model is also from 2019 (5 years old) and has about 135.000km. Again, one should have about 85% of battery capacity left = 53kWh. If you want to use for storage the cost is thus ~€280/kWh. Including converter you’d be looking at €20.000 or €380/kWh. This is starting to look promissing and is actually cheaper than the cheapest home battery set I reviewed (from Zonneplan = actual cost after BTW recoup = €8.300 for 20 Kwh = €415/kWh).

Discussion

Home Battery vs an Electric Car? At this time I think it’s safe to say, that a stand-alone battery system is likely a better option that buying an old car for the battery itself. However, if you already need a car (or second car), getting a newer Leaf (with larger battery pack) and bi-directional converter might actually make some financial sense. It works even better with solar panels obviously. And you do need a dynamic energy contract and software to automatically charge and discharge based on energy prices. At least this way you can recoup part of the costs of the car (and benefit from the dynamic energy prices, which are lower than most fixed term contracts)

We currently still have a hybrid (Prius +), which has been extremely useful for the renovations of the past 4 years. I can move up to 3m pieces of wood and load full size gypsum plates, and still close the boot. Also our big dog has enough room in the back and the car is also really good for long road trips. So we have no desire at the moment to switch to a full electric car. However, our the renovations are almost complete and the dog likely won’t last more than 5 years from today, so changing to an electric car, that we can use as a home battery is very much part of our plans in the future. But as we want to keep it to one car only, we would like to get one with a bit more range (and thus larger battery pack).

Do you already have an electric car? Have you connected it to your home, or are you planning on it once it is possible?

9 thoughts on “Home Battery vs an Electric Car?

      1. Interesting, have you found real use cases for those converters and dynamic contract with energy trading? For this work, the trading software would need to have its own controller device or gateway and would need to communicate with the converter.

        Also, using the car battery for this purpose will accelerate the battery depreciation, and if an additional car is purchased, there will be additional costs with insurance, maintenance, and soon, road tax.

        However, for a primary car, or like in my case, I already own a 62Kw Leaf, this is something to consider indeed.

        1. Hey Diogo,

          There is a long thread on Tweakers (also lot’s of noise, so you have to skim through it a bit) here: https://gathering.tweakers.net/forum/list_messages/2230992 with people that have the Zonneplan battery with energy trading. The software Zonneplan use is really a blackbox and you have no control over it. Also the business model is pretty murky, so you don’t know where they earn their money and how much (and where you take the risks instead of them).

          Now, you currently cannot do energy trading with your car battery. As you indeed need this proprietary software to control charging and discharging (and a way to connect this to your converter). You could only use the battery for balancing your own use and earn some money based on the day-ahead prices (which are a lot less lucrative). That being said, you could do a calculation to see if the differences in energy prices, combined with your large car battery, could become financially viable (assuming the cost of the expensive converter and maximum one or two daily loading and unloading cycles).

          1. Yeah, and considering the battery sits in a car, which is supposed to be eventually used to what a car a is supposed to do, having control of charging and discharging is important. Otherwise, the software may decide to discharge the battery in a days/times that I need to use the car.

            But without a software to control when to charge and discharge, it is going to be a lot of manual work.

            Something I am thinking currently is to have (perhaps DIY) a way to manage the solar panels and the car charger according to the dynamic energy prices. Turning-off the solar panels when energy price is negative, and charging the car when price is low/negative.

            This seems to require small investment, only a switch for the solar panels and an integration with the car charger.

          2. In principle that software is not supposed to be that complicated, the day-ahead prices are available on line, solar power production can be coupled to weather forecasts and setting some thresholds should be doable. But I hear what you say, it won’t be a good thing that the charge/discharge cycles start to determine when you can use the car.

            Good luck with the tinkering and let me know how it goes!

          3. Ah, Cheesy, thnx for the follow up! I was just wondering to go the other route, (not a car but a battery) because, as Diogo says, a car ‘s gotta do what a car ‘s gotta do . In our case, take one of us somewhere at night, leaving the other one powerless 😉
            For us, the trading option is also a bit too uncertain. I was thinking just to use more of our own power (become a bit more Sovereign, next to our vegetable garden ;-)) So we are starting to look into the smart options for our heat pump (seems to have it, but the plumber doesnt want to install it because… Electricity is not his thing… that maybe is a tip if you are looking for your heat pump).
            For Diogo: doesn’t Home Energy / Home Wizard have possibilities to switch large appliances like cars on and off depending on the dynamics prices (day ahead)? Maybe something to look into….

          4. You have a vegetable garden?! You sovereign rebel! 😉
            For us the power grid is still simply too stable to warrant the need for a battery at home. But if that changes, we would definitely start to consider a sizable battery that can run the household for a day or more (even in winter).

  1. Anna H, yes I checked the HomeWizard sockets, but they are meant to devices with low current, not a car or solar panels. There are Wifi circuit breakers available, but I don’t know if it is possible to connect and control them via a custom solution, like my own software or something like HomeAssistant.

    I’ll keep investigating this, for now, I don’t have time to build something from scratch, but maybe using or integrating with an existing home automation tool like HomeAssistant maybe an option.

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