Upscaling the solar generation on our property 2

[openspaceman]

Openspaceman, I missed your last post so,

I don't know where your getting that 30A number from either.

Maybe panel fuse rating ?

Yes, I took that to be a worst case.

Thanks all for the input and I'll get on to the fuses.

Frame on the flat roof today and there will be no clearance to work if it is flat so I'll probably have to start at 45 degrees and wait for comments from planners. Also the bottom Airy point on the panel nearest to the party wall will not be reachable on top, so I'll have to make a clamp that can tighten from underneath.

[nowty]

Openspaceman, I missed your last post so,

I don't know where your getting that 30A number from either.

Maybe panel fuse rating ?

Yes, I took that to be a worst case.

Thanks all for the input and I'll get on to the fuses.

Frame on the flat roof today and there will be no clearance to work if it is flat so I'll probably have to start at 45 degrees and wait for comments from planners. Also the bottom Airy point on the panel nearest to the party wall will not be reachable on top, so I'll have to make a clamp that can tighten from underneath.

For info, the fuse rating of the panel is only to protect a new string being added to a multi string system where if you connect it the wrong way around, you can blow all the bypass diodes in the panels in the new string from the sum of currents in the existing strings. Not something you need the worry about.

[openspaceman]

Have I got this correct that if I have one of those battery disconnect fuses between the panels and charge controller and between the charge controller and battery I need not use a separate isolator as pulling the fuse handle does the job?

[nowty]

Have I got this correct that if I have one of those battery disconnect fuses between the panels and charge controller and between the charge controller and battery I need not use a separate isolator as pulling the fuse handle does the job?

You could.

But you don't need a fuse on the Panels to Charge Controller (CC) side so I would prefer a DC rotary isolator there. The CC to Battery side definitely needs a fuse, mainly to protect the battery in case of a short circuit within the CC.

[openspaceman]

Just an update on this, after failures for two electricians to arrive I went DIY, not pretty but working.

Rather than use a busbar I paralleled the negative of the battery by piggy backing a cable and lug at the inverter, I made a new cable with lugs for the positive and brought it out from the inverter to the fuse terminal and piggy backed the original battery positive terminal there, so no bare terminals.

Here is where I got an unwelcome surprise, with the new 1785W PV array isolated and Victron charger wired up I gently closed the fuse cutout, fat blue spark as it made gentle contact so I pulled back. I then sat and thought about what I could have done wrong for a few days.

I decided to connect just a tractor battery to the charger and there was still a bit of sparking, must have been inrush current activating the smart charger. All set up at 12V and seemed okay so I connected the PV. It was overcast but it ran at a few tens of watts before reaching float.

I left it for a few days doing little but on 11/1/23 I worked up enough courage to reconnect the 48V system, with PV isolated. Again it sparked as I made the connection but I pushed the fuse home and went in to the app and reconfigured the charger for the 48V LiPo battery. All seemed to work fine and throughout the dull day the SE facing system was producing half that the 4kW SW facing strings, so about right.

Yesterday it was sunny most of the day and the charger had to self "curtail" as the battery approached 75% full and I had set the charger voltage to 53.8V. It supplied 2.31kWh into the battery while the original system produced 5kWh.

It did confuse the Growatt webpage which showed zero export from battery most of the day but nothing untoward happened.

I remain a bit worried that in high sunshine I could technically exceed the 104A maximum charge rating of the battery as summing the two strings gives a theoretical 113A but as the panels are at 90 degrees I doubt it could happen and by summer I shall have enough excess to switch out the new string.

One thing is that the new panels shade a corner of the original array and this will affect my FIT receipts.

Finally because I was worried about the effect the direct PV to battery would have on the growatt inverter I had made an application to the DNO for a further 2kW installed generation, bringing me up to 5.6kW. I received an acceptance confirmation a couple of days before I connected everything up as above.

I have till Janury 5th 2024 to make up my mind what to do next and install it all.

[openspaceman]

But you don't need a fuse on the Panels to Charge Controller (CC) side so I would prefer a DC rotary isolator there. The CC to Battery side definitely needs a fuse, mainly to protect the battery in case of a short circuit within the CC.

Nowty I have all that but as the panels cannot produce more than 37.5A at 48V should I replace the current 80A fuse with something smaller to protect the battery if the charger shorts internally?

I over specified most of what I did on the grounds the labour saving of DIY offset any extra costs and to be sure.

[nowty]

But you don't need a fuse on the Panels to Charge Controller (CC) side so I would prefer a DC rotary isolator there. The CC to Battery side definitely needs a fuse, mainly to protect the battery in case of a short circuit within the CC.

Nowty I have all that but as the panels cannot produce more than 37.5A at 48V should I replace the current 80A fuse with something smaller to protect the battery if the charger shorts internally?

I over specified most of what I did on the grounds the labour saving of DIY offset any extra costs and to be sure.

The CC should give a recommendation in the documentation to the fuse size, you could drop it to 50A but 80A sounds fine to me, in a short circuit the 80A fuse is gonna blow and should be well within spec of your DC cables.

A calculation was done on an earlier message, for the max current to the batteries from both charging sources which showed the max battery charging was unlikely to be exceeded. The CC should also have a max current limit setting you can set if you want to limit it to say 30A to keep some more headroom or if you end up adding another PV string to it.
https://camelot-forum.co.uk/phpBB3/view ... =20#p19092

Glad its working for you.

[openspaceman]

Thanks for the reassurance Nowty

[nowty]

Here is where I got an unwelcome surprise, with the new 1785W PV array isolated and Victron charger wired up I gently closed the fuse cutout, fat blue spark as it made gentle contact so I pulled back. I then sat and thought about what I could have done wrong for a few days.

A lot of us have been there and I still wince when connecting a new inverter to a battery bank.

You can use a low value resistor to initially connect up to avoid the spark but I rarely have one handy.

Some of the newer BMS in the Pylontech batteries are so paranoid they actually shut down thinking there is a short circuit so you have to use the resistor method.

[openspaceman]

It is nearly a year since I have had my 1785W battery charging array running, it has produced an extra 962kW and enabled me to go 236 days between 3rd March and 3rd November without buying electricity other than the daily ~1/3kWh import that seems to be a result of the poor integration of the mishmash of components. We are currently buying about half our electricity needs.

After discussion here I was on the point of ordering a 5kW Victron Multiplus to sit between the grid and my current 4kW Fit system with the intention of adding 10-13kWh of Pylontech batteries and 1600W of PV. The idea being the multiplus would keep the FIT system generating in the event of a power cut and if I get around to running islanded with a DC generator. I would have to live with a 5kW maximum load.

My worry is would the multiplus cope with being pushed by 4kW of excess power from the PV once the battery is full and with no draw from the house?

Further my supplier is now suggesting it would make the FIT system non compliant and this should only run in parallel with the multiplus, which means the fit system would not generate when off grid.

Any thoughts?