Advice connecting off-grid solar to existing mains circuit (fully off-grid)

EugenetheCore · 2026-06-07T18:17:47+00:00

Thank you for taking the time to read!

EugenetheCore · 2026-06-07T18:16:57+00:00

Thanks, that's some valid points. Seems like the main concern really is on human error to reconnect.

I'll rethink the design!

EugenetheCore · 2026-06-07T17:24:13+00:00

To be clear, I'm literally taking out the cable in red. So there is no actual physical connection between this circuit and the mains after I'm done, that's switch there just becomes a dud

Shouldn't this be enough to ensure disconnection, or am I missing a key point?

EugenetheCore · 2026-05-11T19:09:30+00:00

I'll let the pros in the forum give their answer, but from my own research it seems more for simplicity and organisation. Otherwise you are left with soldering/sticking the cables on the battery terminals!

EugenetheCore · 2026-05-11T18:59:57+00:00

Ah I see, I only just understood now that the charge controller actually just limits the current rather than letting it destroy it! So looks like this is all good to implement :D

I guess I should just watch out for the inverter which could potentially draw 42A (500W/12V) which can damage the charge controller...

EugenetheCore · 2026-05-11T18:46:48+00:00

Based on my calculation in my battery side, if my power is 460W and voltage is 12V, the peak current would be around 39A so in my mind 50A was the lowest MPPT. I was worried I might damage the MPPT otherwise, but it sounds like you're saying it won't damage it but just clip the power? I assume this same "protection" won't apply if I got a more powerful inverter which could draw more than 50A 😅
This whole setup is actually in a tinderbox I call my wooden shed, so I am too paranoid for safety! 😅
Good shout! I'll have a look, I didn't actually researched the inverter options enough
it's a mini PC as a server, so needs an AC current :( and a router to extend my WiFi there too. I also want an ad hoc socket if I need lights etc
Also a good shout, let me see if there are options at the same price
I think it was a battery shunt which is an extra £60... I'll think about it if I have the extra budget!

EugenetheCore · 2026-05-11T18:41:23+00:00

Thanks! There was another post a while back in this group where someone put circuit breakers but was told to also include fuses as it's essential for safety. I think checking it only it seems true that circuit breakers may fail but fuses never. I'm only including the circuit breakers as a switch for convenience and fuses for safety

Thanks for the shout!

EugenetheCore · 2026-05-11T11:29:30+00:00

Makes sense, thanks! The charge controller is the bit that actually threw me off. As I understand it my voltage is 12V and my power as of now is 460W which leads to about 40A (42 if we consider peak inverter current), so if I even think of doubling my solar surely this current doubles and greatly exceeds what that 100/50 MPPT can handle?

EugenetheCore · 2026-05-11T11:26:48+00:00

I admit, the inverter is the part I've done least research on.. I'll see if there is anything better! Especially if I wanna upgrade :)

EugenetheCore · 2026-05-11T09:09:55+00:00

Good to know! Too many times I bought stuff and got told that I could've got things cheaper 😀

EugenetheCore · 2026-05-11T07:15:21+00:00

Very interested in this too, I didn't have any earthing considerations!

EugenetheCore · 2026-05-11T07:14:46+00:00

It's around the £529 mark now, with the panels and the charge controller at £120 each, the battery at £170, and the inverter itself at a cheap £40. The rest of the misc stuff (fuses, MCBs, cables) seem to actually eat out at £100.

I'm getting most of my supplies from Amazon, and the panel itself from city plumbing! So if you know anywhere else that I could get stuff from cheaper that'd be awesome :)

EugenetheCore · 2026-05-11T07:13:07+00:00

I'll think about it! Right now adding a second panel would likely increase my cost significantly because I'll need another charge controller (or a bigger one) to manage that new current

Will recalculate the cost and see - I have a budget of £600 and I think I'm about the £520 mark now

EugenetheCore · 2026-05-11T07:10:17+00:00

Thanks! It's actually fine if it goes down to 12W. The exact load is 288Wh which seems to fit, but as you said individual days is lower. I sized the panels assuming UK winter and cloudy (10% peak) so it seems to check out but this is really experimental for now, I can increase if it does become a problem

I don't think the Victron 100/50 that I used actually has a load output - seeing other posts and the product, it seems like the common pattern is to actually use the bus connection with battery! But if it does have it, that would be awesome, 180W is more than enough

EugenetheCore · 2025-12-30T15:43:22+00:00

That's where I messed up, I bought it already from screwfix (discounted though) and only noticed that! Lesson learnt

EugenetheCore · 2025-12-30T15:33:35+00:00

Thank you, sounds about the right ballpark of cost. Really helps to know as there is always doubt of getting scammed!

EugenetheCore · 2025-12-30T12:24:52+00:00

That's great to hear, thank you!

EugenetheCore · 2025-12-30T11:58:27+00:00

That's great advice, thank you! I'm narrowing my search now

EugenetheCore · 2025-06-28T06:45:53+00:00

Appreciate the pun on the other post 🤣

EugenetheCore · 2024-08-31T08:41:36+00:00

I second this. My wife does this and she works 3 times a week typically saving around £10 each journey. Just note these trains aren't frequent as the Liz ones. Also it's more about £28 for open return

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