Solar charging my EV - who is good at maths?

ASA201

Solar EV Maths Challenge….  

I’ve already posted this on a Facebook group but I’m not sure anyone understood what I was trying to ask so I’ve tweaked some of the below slightly! 

 

So who is good at maths?  

I’m on Intelligent Octopus Go’s Fixed 12m and trying to work out the optimal way to do some EV charging from my solar during periods where to charge the EV from the grid would be at the Day Rate.   

So this would be a day of nice bright weather, when I’ve plugged in, and not got any or insufficient daytime slots to charge the EV…

Important to note I have a small 2kw system that was in the property when I moved in so based on other power draws in the house it’s unlikely I’ll ever have 1.4kw excess being pushed to the grid which is the minimum amount required before the EV will commence charging.    Therefore I need to utilise a percentage of grid top up to reach the 1.4kw but the more I need to provide the less incentivised doing this becomes.   

 

Here’s my workings so far:

 

Import Costs from Grid

 

Day rate: £0.2621 per kWh (inc VAT)

Night rate: £0.0700 per kWh (inc VAT)

 

Export prices to Grid (Deemed FiT Tarriff so aggregated amount is my overall ‘sell’ rate per kWh)

 

Generation Rate: £0.2286 per kWh

Deemed Export Rate: £0.0714 per kWh

½ of Deemed Export Rate: £0.0357 per kWh

Aggregated: £0.2643 per kWh

 

If I were to set my Zappi charger to use 70% Solar against the 1.4kWh required to start charging this would mean I would need to draw 30% from the grid.  30% of the day rate of £0.2621 comes in at £0.078, so less than a penny more expensive to draw from the grid in this fashion if my calculations are correct. 

 

Meantime I’m maximising the solar that I’m generating in the house, and still getting the generation and deemed export elements of it so in a way ‘double bubble’ as if I weren’t using that surplus it wouldn’t give me double the payment, it would just go ‘lost’

 

If I were to drop the leaf to say use 60% solar against the 1.4kwh required to start charging this would mean I would need to draw 40% from the grid.  40% of the day rate of £0.2621 comes in at £0.104 which is 3.4p more expensive to draw from the grid in this fashion. 

 

Again in this scenario I would be maximising the solar that I’m generating in the house, and still getting the generation and deemed export elements of it but drawing more from the grid at the higher cost rate.  So I think it is best to stay with my 30% grid draw calculations. 

 

Am I missing something though or does this seem right?

QrizB

Ohme's "solar boost" as part of a smart charging schedule gets you 7p/kWh for daytime import on IOG. I don't know if you get the same with a Zappi?

sheenas

I think your are make things far to complex. No idea how big your ev battery is, but with the size battery you have, its going to take all week to charge the car. If you still want to go ahead why not just set the car to use a 100%, so when the car is plugged in all the export electricity will charge the car. 

MWT

QrizB said:

Ohme's "solar boost" as part of a smart charging schedule gets you 7p/kWh for daytime import on IOG. I don't know if you get the same with a Zappi?

No, that wouldn't work with a Zappi, and to be honest I'm not at all sure it should do that on Ohme either, unless it is only happening when a smart schedule is in place, in which case yes, that works with Zappi...

... but recently at least, if I connect after 11:00am I'm getting a lot of daytime slots on the Zappi anyway, but I'd usually avoid doing that as it is more profitable to export the solar at 15p rather than 'saving' 7p by putting the solar into the car.

ASA201

sheenas said:

I think your are make things far to complex. No idea how big your ev battery is, but with the size battery you have, its going to take all week to charge the car. If you still want to go ahead why not just set the car to use a 100%, so when the car is plugged in all the export electricity will charge the car. 

Does this mean the maths challenge is too complex? 

Do you mean why don’t I set the car to only charge when 100% solar (minimum 1.4kw) can be sent to the Zappi from the solar?    If so I tried to answer that when I explained: 

“Important to note I have a small 2kw system that was in the property when I moved in so based on other power draws in the house it’s unlikely I’ll ever have 1.4kw excess being pushed to the grid which is the minimum amount required before the EV will commence charging.    Therefore I need to utilise a percentage of grid top up to reach the 1.4kw but the more I need to provide the less incentivised doing this becomes.”

ASA201

MWT said:

... but recently at least, if I connect after 11:00am I'm getting a lot of daytime slots on the Zappi anyway, but I'd usually avoid doing that as it is more profitable to export the solar at 15p rather than 'saving' 7p by putting the solar into the car.

…and hopefully in my case you can see why I would want to put the solar into the car given I’m not on a SEG

MWT

ASA201 said:

MWT said:

... but recently at least, if I connect after 11:00am I'm getting a lot of daytime slots on the Zappi anyway, but I'd usually avoid doing that as it is more profitable to export the solar at 15p rather than 'saving' 7p by putting the solar into the car.

…and hopefully in my case you can see why I would want to put the solar into the car given I’m not on a SEG

How does your deemed export compare to your actual export?

The rate you are getting is low compared to the SEG rate.

QrizB

ASA201 said:

MWT said:

... but recently at least, if I connect after 11:00am I'm getting a lot of daytime slots on the Zappi anyway, but I'd usually avoid doing that as it is more profitable to export the solar at 15p rather than 'saving' 7p by putting the solar into the car.

…and hopefully in my case you can see why I would want to put the solar into the car given I’m not on a SEG

Like you, I'm also on deemed export so any surplus solar electricity is fair game!

Petriix

I switched from deemed exports to metered export payments and now earn 15p per kWh for 80% of my generation. I charge the EV overnight for 7p per kWh along with running other appliances. I'm ~ £150 better off per year. 

QrizB

MWT said:

QrizB said:

Ohme's "solar boost" as part of a smart charging schedule gets you 7p/kWh for daytime import on IOG. I don't know if you get the same with a Zappi?

No, that wouldn't work with a Zappi, and to be honest I'm not at all sure it should do that on Ohme either, unless it is only happening when a smart schedule is in place, in which case yes, that works with Zappi...

To answer this point, yes. If we plug the car in at say 10am and ask it to be charged by 8am the following day, we might get charging slots for the coming overnight period. Then Solar Boost will kick in at say 12pm and it will start charging with any import at Intelligent rates.

Curiously it ignores any "% charged" target we might have set and will carry on solar boosting until the car is full of we manually intervene.

Edited for typos.

MWT

QrizB said:

MWT said:

QrizB said:

Ohme's "solar boost" as part of a smart charging schedule gets you 7p/kWh for daytime import on IOG. I don't know if you get the same with a Zappi?

No, that wouldn't work with a Zappi, and to be honest I'm not at all sure it should do that on Ohme either, unless it is only happening when a smart schedule is in place, in which case yes, that works with Zappi...

To answer this point, yes. If we plug the car in at say 10am and ask it to be charged by 8am the following day, we might get charging slots for the coming overnight period. Then Solar Boost will kick in at say 12pm and it will start charging with any import at Intelligent rates.

So if you start exporting is that the trigger for the 'Solar Boost' to start? ... or might you be exporting for a while and then the Solar Boost cuts in at a point where, presumably, Octopus have given Ohme an indication that there is capacity to be used...