V2H Part2 - Learning to Use It
Chris Gilbert
Teething Issues
We’ve had our V2H charger a while now, but had a couple of teething problems around a software issue that have made it somewhat hard to figure out the best way to use it. We are one of the limited number of customers who have been given an export limit by the DNO (Distribution Network Operator) telling us how much electricity we are allowed to export to the grid at any time.
This limit for our house is 7.36kW, which includes any current solar export too.
Indra have had to come up with a novel software solution to support these dynamic export limits, and we had some problems with it tripping out the charger premateurely in the first few weeks (i.e. when we were exporting below the limit).
This seemed to be to do with beginning to charge our Tesla whilst the V2H charger was in load match mode, and the load on the V2H being quite high, though not actually exporting this power. This wasn’t what we intended - charging one car from another is an inefficient (although fun) idea. Unfortunately when it happened, it also required a remote reset, given DNO stipulations, so this meant we’ve not had a chance to really get to grips with the charger until now.
However, Indra have now fixed the issue, and the charger is operating as expected. This is one of the fun parts of being an early adopter to new technology!
Indra Smart Portal
Indra developed a website to control the settings on the V2H charger, to be able to monitor and switch modes. At the moment it’s fairly rudimentary, and has no mobile app available. It has enough settings and options to meet our needs though.
This is how it looks (when the car isn’t plugged in).
There’s also a graphical telemetry view of how you’ve been using the charger over the last day or week, which can show how you’ve been using your battery and grid power at different times of day. Here you can see the discharge on our battery and the subsequent charge cycle at 11:30pm.
Where the blue usage patterns are below 0, the power is coming from the car battery, and where they are above 0, the power is coming from the grid.
And here’s a longer view over the last week. As you can see we often use all available battery power during the day. This has made me much more conscious of wasting electricity - I’ve been going around the house turning off lights regularly!
In terms of the Leaf, Nissan stipulate that the lowest the battery is allowed to fall to is 30%. As such, once we discharge it that far, the charger will automatically start using only grid power again. It’s not currently possible to change this battery discharge setting, but Indra plan to add that feature in the future.
How We Use It
I’ve tried to keep things simple in the way we use the charger, but have had to make a few adjustments to fit our electricity usage patterns.
Winter Time
During late autumn and winter, there’s not a great deal of generation from our solar panels, so we are mostly importing electricity from the grid. A bright sunny day is a bonus, but don’t get too many winter days like that in these isles. As such, it doesn’t seem worth optimising for solar during the winter months at all. If it’s generating, then that will reduce grid/battery load a little.
Using Load Match & 6h Charge Window
Schedule - 6H charge at 11:30pm, then load match for the rest of the day. This means that the most expensive periods - around 7am-8am and 4pm-7pm are covered by the battery, and the car is charged to 100% by 7am. We don’t bother trying to load match during the night when it is cheap, and we avoid charging the other car from the Leaf battery.
We recently switched from Octopus Agile to Intelligent Octopus, as this works out quite a bit cheaper for us in winter. I’ve written another post on that and how I did the calculations. Technically the charger doesn’t support this tariff, but our other car (which is a Tesla) is supported by octopus, and as such we can use the cheap off-peak rates for the V2H charger too.
Summer Time
There’s a different calculation to be done in summer - charging the battery with excess solar may well be feasible, and perhaps just a top-up over night can be required on some days.
Load Match Only (no charging)
This schedule load matches between 5:30am and 11:30pm, which co-incide with the expensive hours on Intelligent Octopus. However, it only charges using excess solar with no help from the grid. This may or may not suit us in summer - I will have to find out.
Solar Only
A very similar setting to above, load matching between 5am and midnight.
V2H2G
There’s also an interesting setting option called V2H2G (Vehicle-To-Home-To-Grid). This exports anything beyond what you are using in your home to the grid. It allows you to take advantage of export tariffs to get paid
for the electricity from your battery at times of high demand. We are not on an export tariff yet, so I haven’t tried it, but plan to look at the option in the future.
Setting Your Own Schedule
At the moment it’s not possible to set your own schedules, and only to use those on the list. There are a lot of different options however, so it should be possible to find something to suit. It’s also possible to manually change the mode at any time.
How Much Electricity Can We Use?
One weekend in October, we had the good fortune of Octopus plunge pricing, which happens when there’s more power on the grid than can be used. It typically happens overnight when the demand is low, and there’s higher wind speeds, producing lots of surplus wind power.
In this case, for most of the night, negative wholesale prices were in place, producing a tariff of somewhere between -4p and 4p kWh. The upshot was we were going to be paid to use electricity. This was a great opportunity to charge two electric cars, do some loads of washing and drying and run the dishwasher.
In the past, we’ve tried to take advantage of this, but now having a V2H charger, we could also take advantage of these cheap rates by offsetting the next days power usage too!
After setting this up in the evening, and beginning to schedule everything to use our negative cost power, it suddenly occurred to me that I might have to worry about the maximum consumption on our DNO (main) fuse. This is the fuse that protects the house from drawing too much power from the grid. It’s rated at 80A, which I looked up as 18.4kW.
It was actually pretty possible to do this - two electric cars charging at 30A each, a washing machine, tumble drier, dishwasher and a small electric radiator were all running at this time!
To avoid the risk of blacking out our house until the next day, and waiting for a DNO engineer to come and change a fuse, I decided it would be sensible to reduce the charging speed. Both the Tesla app and the Indra Smart portal had options to do that, and I settled on slow charging the Leaf for 7 hours at 2kW, ensuring it would be fully charged by the morning, but without adding the extra full 7.7kW to the house load.
I think if we had a 100A fuse as fitted in newer houses, we’d be very unlikely to be able to reach this limit, but it was an interesting issue to have to think about!