Hybrid System

[yebaws]

I would like to install a hybrid (battery charging, grid connected) system at my property. I'd like some advice please about what is possible with my setup.

System I'm looking at has the following:
 

• 4.5kw panels
• 2 x Pylon 3.5kWh US3000C Li-ion Battery - 48V Lithium
• Solis Energy Storage 3.6kW Hybrid 5G Inverter with DC switch for On Grid Hybrid for 48V batteries

Panels would be ground mounted, about 100m away from CU in house. There is an existing SWA cable run from its own circuit on the CU to the installation point of the panels. Batteries and inverter would be installed outside, near the panels, in a suitably weatherproof enclosure. DNO Meter is about 50m away from house in the opposite direction (SWA cable from DNO meter to house CU)

I appreciate a significant voltage loss given the cable length, but this will be more than compensated for by the extra generation (house is mostly shaded and cable runs up a steep bank to where it is rarely shaded.)

Given that I don't want to run any more cables owing to the practicality of doing this, what are the possibilities / limitations of my setup?

I appreciate that the cabling setup won't allow me to have critical load capacity, but can the system still basically work as intended - ie charge batteries with surplus power in the daytime and then run down the batteries when demand from the house outstrips supply as load increases / pv generation decreases?

Thank you.

[ProDave]

The voltage drop may be a real problem.  What size is this 100M cable?

 

The problem is when an inverter is generating, it is seen by the inverter as voltage rise, and most will either shut off completely or limit their output if the voltage they see is too high.

 

You would be better off with long runs of DC cable from the panels and the inverter much closer to the house.  On the DC side it will be voltage drop from the panels and will only result in a small loss of power it won't cause issues with tripping inverters.

[SteamyTea]

55 minutes ago, yebaws said:

Panels would be ground mounted

Have you planning permission for them?

[yebaws]

1 hour ago, ProDave said:

The problem is when an inverter is generating, it is seen by the inverter as voltage rise, and most will either shut off completely or limit their output if the voltage they see is too high.

Could you clarify please? Can't quite grasp that concept.

And would it be possible to use the existing (3 core) SWA cable for a DC run?

And could the system work as intended (battery charging).

Thanks again

[ProDave]

7 minutes ago, yebaws said:

Could you clarify please? Can't quite grasp that concept.

And would it be possible to use the existing (3 core) SWA cable for a DC run?

And could the system work as intended (battery charging).

Thanks again

Lets start with the size of the existing SWA cable and length as accurate as you know it.

[jamieled]

I'm not an electrics guru. But, if it helps I have a very similar setup without the batteries. 70m run from house CU to inverter, mounted on the frame for the panels. 20m or so to external mater box from house CU. 

 

It all seems to work fine. The AC cable from the house CU to the inverter/panels is probably overkill in diameter terms but the additional cost was not much if I remember rightly.

[yebaws]

57 minutes ago, jamieled said:

I'm not an electrics guru. But, if it helps I have a very similar setup without the batteries. 70m run from house CU to inverter, mounted on the frame for the panels. 20m or so to external mater box from house CU. 

 

It all seems to work fine. The AC cable from the house CU to the inverter/panels is probably overkill in diameter terms but the additional cost was not much if I remember rightly.

Thank you. No beating real world experience.

[yebaws]

1 hour ago, ProDave said:

Lets start with the size of the existing SWA cable and length as accurate as you know it.

will go and have a look

[Dillsue]

2 hours ago, yebaws said:

Thank you. No beating real world experience.

But.... the problem, as prodave mentioned, is voltage rise and that is specific to your situation. It depends not only on your cable length/size but on the power(current) you are trying to push down the cable and the supply voltage to your house. UK supply voltage can legitimately be anywhere from 216-253vac. If you start with a high voltage you havent got to cause much of a rise to go outside those limits, but thats somewhat up to you and/or your electrician. The problem is if you get too much of a rise your inverter can trip. If you are charging batteries then thats unlikely to be a problem, but once the batteries are charged on a sunny summers day, it could be a problem.

 

Best to get your electrician to look at things and do some calcs for you

[yebaws]

SWA cable is 3 core 6mm2 conductors.

 

Total length ITRO 120m, but could be anything from 70m to get reasonable light if necessary (120m best for light)

[Onoff]

5 hours ago, SteamyTea said:

Have you planning permission for them?

 

That's what hedges are for!

[yebaws]

38 minutes ago, Dillsue said:

But.... the problem, as prodave mentioned, is voltage rise and that is specific to your situation. It depends not only on your cable length/size but on the power(current) you are trying to push down the cable and the supply voltage to your house. UK supply voltage can legitimately be anywhere from 216-253vac. If you start with a high voltage you havent got to cause much of a rise to go outside those limits, but thats somewhat up to you and/or your electrician. The problem is if you get too much of a rise your inverter can trip. If you are charging batteries then thats unlikely to be a problem, but once the batteries are charged on a sunny summers day, it could be a problem.

 

Best to get your electrician to look at things and do some calcs for you

Thanks. Problem is that I can't get a sparky to look at this for me. Jobbing sparkys are busy enough "jobbing" and don't want to take on anything more complicated, solar PV guys are busy enough doing simpler installations and aren't interested either. That's why I'm here...

Might just end up putting in panels and worry about batteries later

[ProDave]

35 minutes ago, yebaws said:

SWA cable is 3 core 6mm2 conductors.

 

Total length ITRO 120m, but could be anything from 70m to get reasonable light if necessary (120m best for light)

That is borderline.  you are likely to get in the region of 10V drop, but as this is a supply cable not a load cable, that will be 10V rise.  So if your supply measures at 240V that would push you up to 250V.  If (as is common here) your actual supply voltage is 245V it would push you over the normal limit of 253V

 

 

[Dillsue]

6 minutes ago, ProDave said:

If (as is common here) your actual supply voltage is 245V it would push you over the normal limit of 253V

 

We run at no load voltage of 250vac. I was told a while back our DNO runs it high to get more power through the system rather than lower us to UK spec of 230vac with increased current and the need for beefier cabling everywhere.

 

Starting at 250vac means our original 4kw system pushes the house over 253vac and the new system way beyond that.

[yebaws]

2 hours ago, Dillsue said:

 

Starting at 250vac means our original 4kw system pushes the house over 253vac and the new system way beyond that.

But that's not an issue? Will check my voltage, although I appreciate it can vary. I guess highest voltage would be at peak periods?

[yebaws]

2 hours ago, ProDave said:

That is borderline.  you are likely to get in the region of 10V drop, but as this is a supply cable not a load cable, that will be 10V rise.  So if your supply measures at 240V that would push you up to 250V.  If (as is common here) your actual supply voltage is 245V it would push you over the normal limit of 253V

 

 

What about the feasibility of using the SWA cable as a DC cable and putting the inverter at the other end (near the house)?

[yebaws]

2 hours ago, ProDave said:

If (as is common here) your actual supply voltage is 245V it would push you over the normal limit of 253V

See you're in the Highlands. Me too and quite remote, so I guess probably similar voltage? Can't really test just now as I'de need to turn off the main switch and that would upset everybody in the house....

[Dillsue]

51 minutes ago, yebaws said:

But that's not an issue?

If the voltage goes too high it will trip the inverter which probably would be an issue.

 

I just reread what you originally said and spotted that youve got another 50m of cable to the DNO service connection which will give you additional voltage rise over whatever your DNO is giving you.

 

Not sure if the Solis inverter has a similar feature but Solaredge HD wave inverters have a power control function that can be voltage controlled so as the voltage rises the power generation is throttled. That would keep voltage in check.

 

Another option could be to put in zero export limitation so the inverter will only supply battery charging and the house load and throttle generation if theres no charging or house load. That would remove any voltage rise caused by the 50m from house to service connection.

[TonyT]

Don’t you need CT’s around the tails too, so some sort of comms cable.

 

I would personally install a duct from a to b to facilitate all power and comms..

[yebaws]

12 hours ago, TonyT said:

Don’t you need CT’s around the tails too, so some sort of comms cable.

 

I would personally install a duct from a to b to facilitate all power and comms..

Not an easy job unfortunately. Must be a reasonable way to do it wirelessly in this day and age, although it may mean a different inverter. Anybody have any experience of these: https://www.solaredge.com/uk/products/communication/wireless-gateway#/

[Radian]

17 minutes ago, yebaws said:

Not an easy job unfortunately. Must be a reasonable way to do it wirelessly in this day and age, although it may mean a different inverter. Anybody have any experience of these: https://www.solaredge.com/uk/products/communication/wireless-gateway#/

There seem to be too many regulatory hurdles to overcome to allow type-approved inverters that can have built-in wireless sensing like this.

[Ronski]

20 hours ago, yebaws said:

But that's not an issue? Will check my voltage, although I appreciate it can vary. I guess highest voltage would be at peak periods?

 

Actually voltages will be at there highest when there is the least load, so between midnight and five.

 

6 hours ago, yebaws said:

Not an easy job unfortunately. Must be a reasonable way to do it wirelessly in this day and age, although it may mean a different inverter. Anybody have any experience of these: https://www.solaredge.com/uk/products/communication/wireless-gateway#/

 

It has to be via cable connection for the CT clamp for an inverter, WiFi connection is not permitted.

 

PS I just put in 25mm SWA to my garage, a distance of about 20 meters, simply because I wanted minimal voltage drop for the solar array and battery system, and the whole house will also be running through it.

[Dillsue]

Youd only need a CT if going down the route of export limitation to keep voltage in check. 

 

If running additional/upgraded power/comms cables isnt an option then choices to keep things above board seem to be-

Use an inverter with voltage controlled power throttling

Run DC down the SWA and have the inverter at the house rather than with the panels, subject to the 6mm/120m cable being up to it and having the correct voltage rating.

 

Obviously lots of other solutions that may not keep things strictly above board.

[yebaws]

12 minutes ago, Dillsue said:

Youd only need a CT if going down the route of export limitation to keep voltage in check. 

I thought that the CT was necessary in order for the charge controller to work out whether there is a surplus of power from the PV (ie which direction the current is flowing - from or to the grid) so that it knows when to start diverting power to charge batteries? Yes, a quick search shows plenty of wireless solutions

[Dillsue]

Yes, I think youre correct- I forgot you want batteries aswell.  

 

If the CT is for battery charging I think a wireless CT is fine. I think that a cabled CT is only mandatory where your export limition is part of a G99/G100 compliant system. Definitely worth checking before you commit to any scheme.