If you're going to be storing the energy in batteries for your own use, then it makes financial sense to max-out the roof with panels which will last the rest of your life.

The cost of solar panels (per kW) and the cost of LiFePO4 cells (per kWh) has halved in the past 2years.

You need to weigh that against promises/predictions from the energy sector and government that the UK's move to Net Zero will save each household £100's per year.

On Friday (13th), DESNZ formally announced that the new National Energy System Operator (NESO) is to assume responsibility for all British energy supply systems from 1st October.

I've been talking with staff who will transfer to NESO next month, I've attended the National Grid public consultations on future energy strategy, and I've read the relevant planning documents for the Great Grid Upgrade

Connections Reform, phase-3

Electricity Ten Year Statement (ETYS, Dec 2023)

RIIO-ED3 Network Price Controls from 2026 onwards (Ofgem proposals)

If those strategies are going to reduce consumer bills, then it's extremely well hidden as to how it can be achieved!

Investing in privately-owned generation gives you greater resilience against the 'market reform' we will be required to fund...
... investing in storage-batteries is better still.

@transparent at the minute I’m getting cheap electricity, 7p from 11.30-5am, my batteries, 10kw last until 4pm where I feed it all back to the grid for 15p. I need to reconfigure that as winter kicks in but doubt my batteries will take me beyond noon. So definitely more solar panels and I have been sourcing box steel to make a frame to mount them on my garage. Purchasing ready made or ballast boxes is expensive so using my engineering skills and tools makes sense to make them. I can also face them direct south as well at present my panels are south west. 

batteries are expensive and mine as you know are modular and I just sit another on top and off we go but it’s the cost.  I know you touched on home assembled ones but it’s confusing since mine are linked by some kind of computer cable to somewhere. So no idea how I could integrate the ones you mention with mine. 

but its infectious all of this and almost a hobby. 

but back to the panels, I have the thermal solar on there and I want to max out without shading so thinking less of the more powerful panels would work better for me. I doubt I could put more on that flat roof for the original string due to shading but the sun room roof could take two on ballast boxes, it’s single ply plastic covering it but overal weight of ballast might be an issue.

Posted by: @david999

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I know you touched on home assembled ones but it’s confusing since mine are linked by some kind of computer cable to somewhere. So no idea how I could integrate the ones you mention with mine. 

The only reason for that 'computer cable' will be to transfer status data from the battery so that it can be viewed using the App for your inverter.
If you unplug it, I fully expect everything to continue running!

There are several better reasons why a communication cable would be beneficial, but I have never known any manufacturer who has offered such functionality as these:

• ensure that the max & min voltage settings on the BMS are configured just beyond the preferences you've set on the inverter
• transfer fault/alarm messages, and interpret them so that the relevant ones will reduce the charge (or demand) current being imposed by the inverter
• cross-check the charge current against inverter losses in order to report an accurate State of Charge (SoC)

Based on the experiments I've done here, you can simply ignore the communication cables and add further LiFePO4 batteries in parallel to the existing one.

Most BMS units have their own App through which you can view its parameters and current status.
In practice you'll probably do that for a week, and then ignore it.
The BMS will happily continue protecting your cells for years to come! 😀 

@Transparent do you have any calculations to what the roof load can take. Some of those larger capacity panels come in a bit weightier?

I have a copy of the Span Tables from the appendix at the end of Building Regs Approved Document Part-A.

Those tables are no longer attached to the free PDF of Part-A.
But I retained them from an earlier version.

The three relevant parameters are:

• span of each timber
• distance between the timbers (usually 400mm)
• thickness of each timer (eg 150 x 47mm)

Of course you'll also need to state whether we're discussing a flat or a pitched roof!

There are sometimes ways to increase the permitted load.

When renovating my ex-farmhouse, I added support to the perlins and ridge on the main pitched roof.

The ridge of the hipped roof was originally supported by two queen-post trusses.
But I added an additional post at the mid-point of each truss.
So that halved the span of each.

The brown wall on the first floor was timber with lathe & plaster.
I added a vertical 100x100mm square support at the point where the queen-post truss crossed the building.
That took the load at the centre of the truss and transferred it to the block wall below.

Building Regs surveyors are meant to be impartial, and not give advice.
A local one here told me to ask "If I were to make this hypothetical alteration, would that be likely to impact on you approving the works?" 😉 

For your amusement, here's a photo showing one of those square supports on the landing, prior to being 'boxed in'.
The paint colours date from around 1973, although the farmhouse itself is 1937.

The arrow points to a 60mm hole in the ceiling, directly below the queen-post truss.

That's where I inserted a bottle-jack to lift the centre of the truss by a few mm and insert the square support timber below it.
The truss was then lowered onto the support and bolted to it.

(You don't learn this sort of stuff on a BTEC course!)

@transparent i had a similar problem when I took the ceilings down after my roof blew off to discover no steels fitted for the  dormer conversion. It’s all brick walls on the lower level so weeks of moving walls about upstairs to support the roof.  Much nicer now but a pain. The wind loading worries me but it’s so much stronger than before. So not just cowboy heating folk around, there were so called joiners with spurs 50 years ago.