Distance between solar panels?

[DragsterDriver]

May sound daft but-

 

if I had panels on the main house and garage roof which is detached- is there a problem with distance between the arrays?

 

Currently the plan is :

 

4.2kw on the garage roof with a 3.6kw inverter to “keep me in g98 regs?” but I’m thinking more is better?

 

[joth]

I assume you mean to share one inverter between both arrays?

The main constraint is the distance from array to inverter. This is high voltage DC cable, needs armouring if not left fully visible. Too long a run will cause losses, especially if it's on a short "string" of panels (which means lower delivered voltage, hence line voltage drop takes a greater proportion of the output).

In general Voltage drop can be minimised by using thicker core cable, but MC4 connector limits how far you can increase PV cores.

 

Ours is about 10m, from house roof to garage. What sort of distance are you thinking?

 

[SteamyTea]

15 minutes ago, joth said:

This is high voltage DC cable, needs armouring if not left fully visible. Too long a run will cause losses, especially if it's on a short "string" of panels (which means lower delivered voltage, hence line voltage drop takes a greater proportion of the output).

Losses are not too bad on the DC side, usually 4mm² cable, so don't worry about that too much.

Somewhere on here we discussed the 16A phase limit, and I can't remember what was the answer e.g. installed capacity or inverter capacity.

Worth remembering that a 2 string inverter cannot take the full 3.6 kW_p though one string, and strings cannot be too unbalanced.  The manual will say what is possible.

One way around it is to use micro-inverters and then run AC cabling back to the consumer unit.

[DragsterDriver]

16 minutes ago, joth said:

I assume you mean to share one inverter between both arrays?

The main constraint is the distance from array to inverter. This is high voltage DC cable, needs armouring if not left fully visible. Too long a run will cause losses, especially if it's on a short "string" of panels (which means lower delivered voltage, hence line voltage drop takes a greater proportion of the output).

In general Voltage drop can be minimised by using thicker core cable, but MC4 connector limits how far you can increase PV cores.

 

Ours is about 10m, from house roof to garage. What sort of distance are you thinking?

 

Thanks!

 

I'm hoping to have a ‘plant room’ in the garage with everything ducted from there to the house which is 7m away. So the house panels would be maybe 20m from inverter? 
 

looking at the energy situation now I’m leaning toward more panels and a storage battery  

[SteamyTea]

43 minutes ago, DragsterDriver said:

looking at the energy situation now I’m leaning toward more panels and a storage battery

Ideally you want batteries charged from the most productive modules i.e. south facing, optimal inclination.

That will reduce the amount of modules needed and reduce the exporting of power.  The East-West split PV systems 'to spread the load' can now be done from the batteries.

Though batteries, on power delivery, are still limited by the inverter, and may not work too well with very small loads i.e. just lighting, assuming you only have a few watts of lighting on, not kW, like the olden days.

Edited September 26, 2021 by SteamyTea

[DragsterDriver]

26 minutes ago, SteamyTea said:

Ideally you want batteries charged from the most productive modules i.e. south facing, optimal inclination.

That will reduce the amount of modules needed and reduce the exporting or power.  The East-West split PV systems 'to spread the load' can now be done from the batteries.

Though batteries, on power delivery, are still limited by the inverter, and may not work too well with very small loads i.e. just lighting, assuming you only have a few watts of lighting on, not kW, like the olden days.

I think what I need is somebody to design a system. I’m not bothered about MCS so we can fit the panels and electrician wire stuff- but it needs to all work together properly

 

roof is south facing.

 

this is what’s been suggested:

 

 

[SteamyTea]

1 minute ago, DragsterDriver said:

this is what’s been suggested:

Have you run it thought PVGIS

[DragsterDriver]

4 minutes ago, SteamyTea said:

Have you run it thought PVGIS

Nope-

never heard of it before!

[SteamyTea]

9 minutes ago, DragsterDriver said:

Nope-

never heard of it before!

It is the sanity checker for PV.

East Anglia is pretty good for production.

[DragsterDriver]

12 minutes ago, SteamyTea said:

It is the sanity checker for PV.

East Anglia is pretty good for production.

it’s flat and exposed around this bit of it- any kind of heat and it’s like working in Nevada. 

[Sandybay]

Would it be possible to fit a 3.68kw system that could export to grid, and another 3.68kw system that just charged batteries? 

Or would it be possible to fit say a 6kw system, limit 3.68kw to grid, and fit a battery storage system for the remaining output? 

Do buildhub members find solar pv with battery storage offers a good return of investment over time? 

Thanks. 

[SteamyTea]

1 minute ago, Sandybay said:

Would it be possible to fit a 3.68kw system that could export to grid, and another 3.68kw system that just charged batteries? 

Yes, but then integrating the battery storage into your home wiring may be a challenge.

2 minutes ago, Sandybay said:

Or would it be possible to fit say a 6kw system, limit 3.68kw to grid, and fit a battery storage system for the remaining output? 

Yes, it is what diverters do, but it is still a grey area about allowing a larger than a nominal 4 kW_p system be limited by the inverter (you can search for the thread about it, it is on here somewhere).  Alternatively ask your DNO if you can connect a larger system.

4 minutes ago, Sandybay said:

Do buildhub members find solar pv with battery storage offers a good return of investment over time

I don't have PV, but with batteries, it is all about load time shifting.  It is similar to using E7.

Now my E7 price has just gone up to 12p/kWh, so if the amortised cost is lower than that, then it is worthwhile.  But you need to take into account what else you could have done with that cash i.e. put it towards an electric car, you will loose all of your capital either way, except the EV may have some value in a decades time.

[Sandybay]

OK thanks, just looking into all potential options that offer the best future proof system, if that's possible ?

[ProDave]

13 minutes ago, Sandybay said:

Would it be possible to fit a 3.68kw system that could export to grid, and another 3.68kw system that just charged batteries? 

Or would it be possible to fit say a 6kw system, limit 3.68kw to grid, and fit a battery storage system for the remaining output? 

Do buildhub members find solar pv with battery storage offers a good return of investment over time? 

Thanks. 

The DNO's system assumes that all you generate might be exported so they size to allow for that.  So if you want more than 3.68kW then you need permission.

 

Now your second battery charging system would be allowed as an off grid system if the items that the batteries powered were on a separate off grid circuit and there was no way the batteries could discharge into the grid.  You could argue until you are blue in the face that you will not discharge the batteries into the grid and they will only be discharged when you have high power loads running, but they won't believe you unless you have a type approved "G98 relay" even if such a thing were available.

 

I only have 4kWp of panels and have concluded batteries for this amount of power are not required, I can self use 95% of what I generate without. 

[Sandybay]

Thanks, 

So may not be worth the lager pv system, as you really need to be using all you are producing to get maximum value, as payback from grid is minimal, and an additional battery system would only mean more going to grid I guess?

[SteamyTea]

15 minutes ago, Sandybay said:

OK thanks, just looking into all potential options that offer the best future proof system,

A diesel generator.

[Sandybay]

? 

 

[Conor]

For my soalredge system, max string length is 100m.

[TonyT]

Isn’t it just a volt drop problem so increasing the csa of the conductor would let the distance be greater.

[ProDave]

Just now, TonyT said:

Isn’t it just a volt drop problem so increasing the csa of the conductor would let the distance be greater.

Yes.  And volt drop on the DC side is not an issue, the MPPT controller adjusts for that with no problems.  It is volt drop (rise) on the ac side that has to be limited otherwise the inverter trips or power limits on "over voltage"

[joth]

11 hours ago, ProDave said:

volt drop on the DC side is not an issue

Well it's a loss of efficiency, which could become an issue if there's too much

 

[SteamyTea]

Stop speculating and start calculating.

 

https://photovoltaic-software.com/solar-tools/voltage-drop-calculator-dc-ac

[DragsterDriver]

So- is there such a thing as a designer who will sort your system for a fee?

 

 

[SteamyTea]

1 minute ago, DragsterDriver said:

So- is there such a thing as a designer who will sort your system for a fee?

 

 

I could do it, and have the qualifications to back it up.

But it is not worth doing it.  Not as if I could charge you £1500 consultancy fee.

 

what you need to do is break down the system into each element, then see what is the most efficient and the least efficient, then aggregate the lot and compare prices.

It is what spreadsheets were made for.

[patp]

If you are in East Anglia then I cannot recommend Spartek https://www.spartek.co.uk/ more highly. The owner of the company, Lee, is a genius on electricity and all things solar powered. Because of this he is crazy busy carrying out contracts for London Boroughs etc. You are welcome to view our system which is nearly ready to go.