Hello everyone!
I would like to share with you the result I achieved in charging my electric vehicles with my solar panels, using Homey as a management box. I would like to remind you that this way of doing things allows you to save the purchase of a specific management device which usually costs between € 500.- and 1000.-, and which in most cases never pays for itself. The method presented here goes a little further than simply charging when there is enough sun, and stopping everything when there is not enough. The goal was to vary the charging amperage according to the available current!
Initial situation
- a rather modest SolarEdge solar panel system (7 kW installed power), compatible with Homey
- a go-eCharger HOMEfix wallbox, compatible with Homey
- a 100% electric SKODA Enyaq that charges on a maximum of 3 phases / a 100% electric SKODA Citigo iV that charges on a maximum of 2 phases. Both vehicles are configured to accept maximum charging power. It is therefore the wallbox that manages the charging power, and not the vehicles
- As my installation is rather modest and my two vehicles do not charge with the same number of phases, I decided to configure my wallbox so that it only charges on one phase. This allows me to charge with less power but almost all year round, without having to wait for sufficient sunlight. It also allows me to use the same flows for both vehicles
- before starting, you have to note how much current the wallbox uses to charge, for 6 amps (A), 8, 10, 12, 14 and finally 16A (the maximum possible at my house). Here are the approximate values displayed by the wallbox for a single phase (these values will be used in the charge control flows):
6A : 1.43 kWh
8A : 1.9 kWh
10A : 2.34 kWh
12A : 2.78 kWh
14A : 3.33 kWh
16A : 3.78 kWh - the method presented here allows charging with solar power only. Another method that I developed initially allowed charging as soon as the cost of charging was equal to or less than the cost of charging at the low rate (i.e. at night at my home). However, I will not present this solution here, as it requires additional calculations to compare charging costs
- I am not an engineer, nor an electrician, nor a computer scientist, so I did the best I could, but it can surely be improved. My electrical vocabulary is also very approximate (power, voltage, etc, I confuse everything…). The main thing for me: it works exactly as I want it to, transparently, and I understand how it works (unlike specific boxes where you don’t always know how they “think”)
Calculation flows
These flows allow to calculate, every 5 minutes (you can obviously choose to calculate more often or less often…), the average current that is injected back into the electrical network, and that is therefore available to recharge an electric vehicle. The consumption of the house is already deducted (about 250W when nothing special is running in the house). Furthermore, the value is also calculated so as not to take into account the current used by charging a vehicle. If this were the case, it would become too complicated for the charge control flows. My goal was to obtain positive values when current is drawn from the grid, and negative values when sufficient current is produced to be injected into the grid. The value calculated by the last flow is the only one that will be used in the control flows
Control flows
The two first flows presented here are used to activate and desactivate (with a shortcut or a physical button) the solar charge.
The control flows
A flow to stop the charge when not enough sun anymore
A flow to stop the charge when battery is full (or 80%…)
On this picture, you can see the result of a charge (in blue) carried out on Monday with a small voluntary break around 1.45 pm and a not very regular sunshine (in green). You can see that the blue curve follows the green curve relatively well. I am personally very happy with the result:
I remain at your disposal for any question, remark or proposal for improvement 
