question

@SolarBonanza

It's possible your colleagues just guess. Hopefully educated ones, but they may not have the deeper knowledge to pass on the real technicals.

Trouble is, offgrid can be a very personal thing. Many are prepared to 'schedule' their loads, but then then you might have a client who isn't prepared to do that, and wants the same load capacity as he's used to from an ongrid switchboard. He'll pay for that privilege.

I live offgrid and love it. I find a 5kVA Multiplus adequate for all the normal household water heating appliances like washers, etc. But I don't run them together. Never know when the water pressure pump might run, but I might still run a vacuum cleaner or a power tool at the same time without issues.

Solar calcs usually follow, and then battery sizing (often dependent on inverter size)

There's a bunch of stuff in the Downloads section of the Victron website. I won't link them, I want you to look yourself.

If you want to really get involved, you could sign in to Victron Professional and do their training courses. Even become 'Victron certified', online.

We don't normally encourage individual design enquiries here, but in your case I'd like to help out if I can. Try to keep to specific issues if possible, the broader the harder it gets.

Sizing of Solarpanels, Batteries and maybe Windmills depend on more factors you can ever imagine.

I am in Estonia where usually December/January we have only 0,2 Sunhours a day but you have to clean the Solarpanels. In addition I use several Windmills. In the beginning of my Off-the-Grid adventure, I calculated the Batteries from the material lifespan (20 years) divided by the 1500 cycles at DOD 60 which give me roughly 5 days.

I calculated, that I need maximal 8kWh a day, hence 40kWh in 5 days. With s DOD60 I get 66,6kWh. Divided by 24V give me 2780Ah. Since not a normal person can install a 2V cell of 170kg, I choose to install 4 battery sets and the smallest cell I could use wad 735Ah with 39kg.

Hence in total 24V and 2940Ah.

This was in 2017, but in the meantime, i was ablebto reduce the power consumption to 4-5 kWh and I usually have 7-10 days autonomy, if I absolutely have no sun and wind.

However, now my organic farm was growing and I need additional 175kWh Batteries, and additional 12kWp of Solarpanels. And of course installed in a way for easy cleaning. However, my Fronius Primo 8.2-1 and the panels are 100% winter optimized, hence they will be in an angle of 80-90° standing up.

Then, Off-the-Grid also mean, cooking with LPG and heating with wood/LPG.

Hotwater can be made with a LPG Instant Heater, however, a Boiler with Double-Heatexchanger (I use it) could be the bettet option, since in the summer you can use a solarcollector and in the Winter the Wood/LPG heater.

As you can see, in an Off-the-Grid system there are MANY things to consider and this is based on experuence. Probably the main reason why your sub-contractor do not tell you how to dimension the system. This knowledge can be pure money if you are very good.

I do not know, where are you located, but i wish you good luck.

P.S.: In Estonia the weather is absolutely unpredictable and while everything was working fine between 2017 and 2021, since 2022 I have a period where I was forced to run a GenSet in August 2023 two times. This winter I have unexpected solarenergy while 2022/2023 it was datk as hell, BUT I got unexpected windenergy and three windmills (2x 2000W, 1x 700W) simply charged my batteries in 3 days full and I used the excesd energy to heatup my 200l boiler and when it reached 72°C i continued pumping the excess into my 200l (will be changed to 500l) heating buffer.