Winter is coming - solar project review

[Guillaume.l]

Hi there.

I am sharing here my project of upgrading my solar energy system to get advice from knowledgeable peoples from this forum. There is a real possibility that I have misunderstood some things and planning something crazy. Any correction of comment will be greatly appreciated.

Context:

I am located in Europe, near Mediterranea, in an area that has excellent potential for solar (> 1600 kWh / kWp / year).

I already have a small self consumption installation running since a few years. Around 2400 kWp of second hand panels with enphase micro inverters (M215) that produce around 3000 kWh / year. In summer, we generate 14kWh/day with this array. We are consuming around 30 kwh/ per day in average, so there is room for more solar power.
Main consumers at home are swimming pool filtration (mostly in summer), water heater and (small) electric vehicle.
nearly 95% of current production is self consumed by running load based on available power with home automation system, and routing surplus to water heater.

I am pretty convinced that electricity price will be high in future, so I am seeing solar a good use of some money I have available that is currenlty being eaten by inflation.

Objective:

1. Have fun with DIY project
2. Increase solar power to 5 kWp to cover most of our electricity need. I am not after going off grid. That would be cool, but not really make sense economically to my opinion and don't want to be in darkness when I will blow something on my system
3. Install battery system to optimize self consumption of solar energy I produce
4. In case solar was not enough to top it off during day, be able to charge batteries at night to take advance of cheaper electricity cost,
5. have UPS capability, especially to be able to keep pellet stove running in case of blackout (winter is coming)
6. Be able to charge batteries while being in off-grid mode (in case thing go really bad this winter)
7. Use grid to run home when batteries are flat and no solar available
8. Use grid when home need more power than inverter can provide

The plan

Plan is to build AC coupled system because of the flexibility of wiring. DC coupling would be quite complicated to install in my home. Being in series with grid vs parallel to grid means bigger inverter, but necessary to have UPS fonctionnality.

I am still not sure if current sensing clamp is necessary in this configuration. Neither If it will be possible to avoid back feeding to grid when batteries are full. I am not supposed to feed back excess powder to grid, but energy company is not measuring (yet), so not a big deal.

Looking at power curve of house, I am confident that 99% of time we are under 5kw. Yet, once in a time we have temporary surge in power use over 5kW for few minutes. Not sure though if powerAssist functionality of Victron can use AC from grid when demand is higher than what inverter can provide. Only using battery to assis AC is mentionned in documentation.

Victron multiplus-II 5000 W 48V, wired in series with grid would be heart of system. My understanding is that max solar power I can install is 5000 Wp to respect 1:1 rule. Or is the limit of solar constraint by charger ? This limitation only applies to off-grid situations.

A GX device is apparently needed for this setup. My plan is to use raspberry Pi running venus OS to save some money here. Interface between raspberry-pi and multiplus would be MK3-USB interface. Not sure here if

Battery will be self assembled LiFePO4 .16S 280Ah. Still not sure about BMS. Currently leaning toward JK-BMS. Still not clear is it would be doable to read value from BMS from raspberry pi to feed it to openhab.

 

[mr-manuel]

Hi,

I have planned a similar setup but with Enphase IQ7. Are you sure that the M215 Microinverters are able to frequency shift?

You have to pay attention, that a MultiPlus II 48/5000/70-50 in offgrid mode can handle 5.000 VA (not W!) for 30 minutes and 9.0000 W for 2 minutes. The continuous output at 25 °C is 4.000 W. The charger is limited to 70 A (depending on battery cells and voltage it can be from 2,65 V * 16 cells * 70 A = 2.800 W to 3,2 V * 18 cells * 70 A = 4.032 W. 2,65 V is the lowest voltage per cell you should use for a LFP cell). As lowest cell voltage I use 2,9 V so I have 3.248 W max. for the panels that are connected to the AC Out. The max. panel number obiously changes from summer to winter.

If you are drawing to much power in offgrid mode, than the inverter shutdown itself, so nothing breaks.

I attach you the datasheet with my notes for more details (it's for the GX device, but it doesn't matter). It took me a while to get all this informations. For the 1:1 rule you can also look here: https://www.victronenergy.com/live/ac_coupling:start

In offgrid mode you also have to think, that a completely AC coupled system cannot start if the batteries are empty. Therefore you should connect some panels with a DC charger to the battery, or at least have a DC charger so you can connect it in emergency. When the batteries are loaded a bit the whole system can start and charge again over the Microinverters.

If you are connected to the grid you are limited to 50 A from the transfer switch of the multiplus.

The schematics you attached will not work completely. The grid meter of the Enphase has to be between AC Out and Main panel. Else in grid mode the MultiPlus and Envoy tries to regulate the load.

If you don't want to use the MultiPlus GX device it should work the the MK3-USB as you said. For the BMS a lot of people (including me) is using the JK-BMS. You can take a look to the Off Grid Garage: https://off-grid-garage.com/bms-communication/

Should you have a Envoy-S you can also integrate it in Venus OS through a dbus driver I wrote: https://github.com/mr-manuel/venus-os_dbus-enphase-envoy

To turn on the water heater you could also use Node-RED which is included in the Venus OS Large image. So you can directly turn on/off something like a Shelly 1PM.

I hope I could help you What is the current state of your project?