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Comment by KaiserPro | Hacker News Reader

I have a solar system in my house in london. 5kw, 13kwhr battery. I am self sufficient from end of march to october.

I recently got a second hand electric car. I bought an EV plug (total fucking ripoff. its a fucking plug with a contactor, RCD and a CAN interface. no way is that worth fucking £600)

It has some basic control to allow me to charge from excess solar. What is not easy to do is charge at night without draining the house battery. Its fine for me, because I have Home Assistant, with enough fiddling I can get all the systems to talk to each other to play ball. (to add to the complication, I'm on a variable rate tariff, so price can be negative or £1 a kwhr)

I would really love a "house power API" that would allow a "controller" to locally control the power behavior of all the things in a house. Because at the moment, a "normal" person wouldn't be able to charge their car and have house batteries and have solar, and optimise for cost.

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If your electrical installation allows it: You can connect your ev plug before the battery so that it does not drain the battery. You can do this by placing the fuse/connection before the measurement clamps for the battery. Somewhere in between your mains connection and your battery/solar system.

This way the battery does not see the load and does not provide power to your EV.

That way you can still use excess solar (before you inject it into the mains) to charge your car + you do not pull power from your battery :)

The ideal solution is for the battery to have a third set of clamps to measure the EV. But as I don't have installer access to the software (centrally managed for the win) I'm not sure thats possible.

I might ask to see if thats possible. I probably need more panels to cover the winter load.

Would be interesting to know how London compare to Sweden. Electricity here are generally about twice to four times more expensive during the winter than during the summer, and energy consumption is about twice the amount during winter compared to summer. On average people here spend around 75% of the total energy bill during winter.

Generally people are on fixed rates that are updated yearly. Its pretty "new" to get variable rates here.

https://agilebuddy.uk/historic/agile

has some historic prices. We still use gas for heating, so there isn't so much seasonality for consumption. (there is, but not in the same way).

What does affect price is wind. you can see in december there were both record high prices and record low. The more wind we have the cheap power becomes. so in winter its generally quite cheap, but then also it can flip and become very expensive, because gas imports are expensive.

> no way is that worth fucking £600)

Liability coverage, and UL certification (or UK/EU equivalent), for the company is. Though see perhaps:

* https://en.wikipedia.org/wiki/OpenEVSE

> I would really love a "house power API" that would allow a "controller" to locally control the power behavior of all the things in a house.

With regards to EV and the grid, see perhaps:

* https://en.wikipedia.org/wiki/ISO_15118

* Also: https://www.ampcontrol.io/post/what-are-ocpp-iec-63110-iso-1...

For an (industrial) electrical communication protocol, perhaps:

* https://en.wikipedia.org/wiki/IEC_61850

Midnight Solar are the OG company in off grid and they have a "waste not" feature from way back that triggers any device when the parameters you set are reached, ie: float voltage, and/or other things, like a second set point where power would be sent to a third load, like the grid or water heating. https://www.midnitesolar.com/ hard core techies, even had the pleasure of detailing my inadvertant and unsucessfull attempts to melt one of there controlers.......literaly had a main lug get loose, and the panels arc melted the lug to slag, and it lived. in any case, there web site has a wealth of info on what is possible, and to look for elsewhere

Midnite Classics are great... But the web APIs seem to be deprecated. Do you know of any tools that can get data off them?

nothing other than what is published in the manuals, there is a link to a third party software for monitoring the clasics, but if you want the inside story, call them....they answer the phone and speak many dialects of techinese there latest offering is a game changer "the 1" it does everything 11kw of 600 volt solar in, to any kind of 48 volt battery, and grid tie, and single,split phase and 3 phase 208 volt ac out, one box 98 lbs, 5k list you can install 200 % extra solar for low light, or norther locations specs are wild https://www.midnitesolar.com/productPhoto.php?product_ID=766...

We have https://www.myenergi.com/ for our car charger and it seems to be able to integrate batteries, charging and panels like you suggest, only you have to go all in. We have parts of it and are tempted to use more, but the lock-in angle is a bit off-putting

Yeah I have a Zappi, but as you know its got no local API, and it doesn't like getting warm. However it _cant_ control my battery directly, because its made by tesla. (I mean thats also my fault....)

I have also heard that if you go all in it works much better. It does have the nice feature of diverting to other devices instead of the grid, and giving priority to certain devices.

If your rates can go negative you should be charging the car and house batteries at that time if possible and then selling back to the grid at peak times. Does your home assistant get real-time rate data and can it facilitate that?

I mean, it's a bit more than a contactor and an RCD, it also has PEN fault detection because TN-C-S is how most of us are wired up to the grid.

Then for use with smart tariffs like IOG there's a microcontroller, cloud gateway for them to hook into for OCCP to turn on and off the charger when the grid is cheapest/greenest etc.

So £600 is about right, once you add in R&D, certification, profit margin, warranty claim % etc.

> Then for use with smart tariffs

I wish it had all of that. I would actually pay for that. The Zappi from myenergi promises much but fails to deliver.

That's odd - I've got the Zappi and it works perfectly with Intelligent Octopus Go. Plug the car in, have a HomeAssistant automation that detects this and sets the "charge to add" on Octopus and enjoy the car being charged the next morning.

I always recommend hardwiring it though, rather than relying on Wifi through a brick wall.

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