Shed solar on a budget

[drjim]

So last year I got a couple of panels and a chinese microinverter that sticks a few watts into my somewhat large electricity sucking household with lots of computers, network switches, xboxes and fridges, even before we get the washer and dishwasher going. They are mounted in a south Easterly direction on a shed roof the wrong side of the house so shaded in the morning. Noticeable watts monitored by a home made emonPi. They actually feed via a 13A plug into the downstairs ring main (or rather a spur in the shed!), and the watt monitoring is done via an esp8266 on a board from Mottram Labs as the MCB is at the other side of the house.

So I am working on an upgrade and the self explanatory "project baseload"

I'm headed on a short road trip tomorrow to pick up a total of 8 250w panels, four the same, another matched pair and two randoms. All have similar numbers on the stickers and can probably be stuck together in combinations or even one big string.

I have a couple of enecsys 200w sim-200-72 inverters that I got for very little off ebay last year, but couldn't decide if they were doing anything with the original panels so got the microinverter thing from China. I was contemplating using them on a couple of these panels, but they are probably best binned I guess in the context of 2kw. They are now effectively free though!

I am planning to build a new shed with attached gazebo, it will again be SE facing as garden geography simply doesn't work for due south. Should be able to get 6M of panels in a line on there. I do have lots of SE facing roof at high level and some lower but shaded by next door and a tree, so bits and bobs in different locations might be the best bet. As such my microinverters might be useful for now. I also wondered about vertical on the back of the house which gets hammered by the sun in the summer making it too hot in those rooms, so shading the brickwork would be beneficial as well.

I'm looking for a cheapish inverter to set up with at least the four identical panels as a string, I reckon I need an approved G98 one for my initial setup for the DNO, so all the older secondhand stuff on ebay is a bit of an issue. Anyone got any tips??

[richbee]

I guess it depends if you want to add batteries using the original inverter, so a Hybrid inverter, or if you will add the batteries separately as AC coupled charger.
There are loads of options from Solis, Growatt, Givenergy with varying prices depending on the output you want.
I've got a Sunsynk 3.6kW hybrid inverter, with 5.6kW of PV and 10kWh of batteries, most of which was fitted by an accredited MCS installer (I added the 2nd battery later).

The problem often seems to be that you install the first part, then find out how good it all is, and wish you had gone bigger to start with .

I've since added shed solar with a Hoymiles microinverter, but kind of wishing I had gone for eg. 5kW inverter in the first place with required G99(?) approval for more export.

If you want to cover ASHP, EV charging etc in the future, I would try to make it as flexible as possible to start with

[nowty]

There are currently loads of brand new Solis inverters on ebay for under £200 which would suit your panels.
The smaller ones will start up with just 60V.

[drjim]

Good points there.

Progress today, a little road trip produced 7 panels.



2 of these, one has a damaged MC4



4 of these, still have cardboard corner protection on so unsure if actually been used



And lastly one of these



The voltage/current figures are all near enough I reckon I can just string them together.

Oh £100 for the 7 panels

Panel 8 was elsewhere and sold before I got there.

[nowty]

Nice, they will work fine together.

[drjim]

I have two 240w panels from last year so might add them all together. Just bagged this off ebay...

blag

I'm not back at work till Monday so might challenge myself to get this up and running before then!

One annoying obstacle is that the MCB is now in the utility room and everything is sealed up/decorated so getting a cable in there for a proper feed is tricky. Plus no spare breakers. I had the idea of feeding to the boiler room where the immersion heater circuit has a lovely 6mm cable to feed it, and connect solar to that. If I add a solic/EDDI/whatever for "project hot water" it could sit there just need to extend the sensor cable. My thinking being the load going into the immersion would have no way to overload the 6mm cable from the board. Would save getting expensive sparky in - or for that matter buying any bits at all!

[nowty]

That grid tie inverter looks fine, G98, a low V start up and wide operating MPPT range.

The grid tie inverter really needs to be on a separate circuit.

The loading on the 6mm cable is not the issue. The issue is, if there is a fault with the immersion(s), this would normally trip the MCB. But if your adding reverse power flow via the grid tie inverter on the same circuit, the MCB may not trip because it does not see the full fault current flow. The fault remains and increases risk of fire.

There are arguments for very small scale solar, like 500W (2A), is so small it’s irrelevant so could be used on an existing circuit. This is legal in some other European countries. But you’re talking about maybe 1.5kW or 2kW so the current is not so trivial.

[drjim]

Nowty

Thanks for explaining that, I'll simply have to get another board fitted. Mind you my incomer has an isolator in it so if I asssume I am competent I can just isolate the supply and fit a small CU with some henley blocks. More faff to get the cables to the right place, but it's better to do it right.

Or what if I fit a "garage CU" on the end of my 6mm immersion feed cable, and have the solar and immersion on separate breakers, that'd be a LOT easier than trying to get cables through various inaccessible voids...

Jim

[nowty]

I guarantee you will be bitten by this renewable bug and before you know it, you'll be fitting batteries, exporting back to the grid, etc, etc. I'd preferably be henley blocking it off the incomer and then you can easily upgrade the small CU for other renewable shenanigans, more PV, battery inverter, EV charger, etc.

I get you on your second idea, as that appears to mitigate the main problem and allow the new local MCB to the immersion to trip without seeing reverse power flow from the inverter sub circuit. Not sure how it measures up on the leccy regs though.

[drjim]

I'm going to speak to my sparky tomorrow, I think henley and a new consumer unit is the plan. Just trying to work out what the best route to get a cable out there is so we can get the right cable sorted before he comes.

I reckon it'll be a medium size CU rather than small!