My south-facing solar array is brilliant in the morning. By 2pm it’s declining. By 6pm it’s barely generating. Meanwhile the west-facing gable end of my house sits there catching the evening sun and doing nothing.

So I fixed that.

The data said there was a gap

Before spending anything, I looked at my half-hourly Octopus import data. I wanted to see how much electricity I was actually importing between 2pm and 9pm in summer — the window when west-facing panels would be generating.

The answer: 37.4 kWh total across the whole of summer (May–August). That’s tiny. The battery was covering almost everything.

But here’s the thing — the battery covering the gap is exactly why it’s worth adding west panels. Every kWh of evening generation from the west wall means the battery finishes the day more charged. That means Predbat needs to import less overnight. Less import = lower bills, even if the direct evening saving is small.

The real value of west panels in my setup is extending the charging window into the evening, giving the battery more to work with overnight.

The hardware situation

My existing setup:

Fox ESS H1 3kW hybrid inverter (serial: 60JH302047KC114)
8 × AIKO 455W south-facing panels on MPPT1
Fox ESS 10.3kWh battery
MPPT2 — completely empty

That last point is key. The Fox H1 has two independent MPPT inputs. MPPT1 is running my south panels. MPPT2 is spare. That means I can add a completely separate west-facing array with zero inverter cost — just wire it into MPPT2.

How many panels can MPPT2 take?

Fox H1 MPPT limits:

Max voltage: 600V Voc
MPPT operating range: 70–550V
Max current: 15A per MPPT

AIKO 455W panel specs:

Voc: ~44.8V
Isc: ~13.2A

In a series string (which is what you want for one string going west), the current stays at 13.2A regardless of how many panels. Voltage adds up per panel.

Panels	String Voc	Within limits?
1	44.8V	❌ Below 70V minimum
2	89.6V	✅
3	134.4V	✅
4	179.2V	✅ Sweet spot
6	268.8V	✅ (but over power limit on paper)

4 panels is the safe, clean choice. Well within voltage and current limits. The inverter handles MPPT1 and MPPT2 independently — the south and west arrays optimise separately.

The wall

Looking at the west gable end, there’s a large unobstructed brick section at first floor height. No shading from the roof until very late evening. The evening sun hits it beautifully — you can see it lit up golden from about 3pm onwards on a clear day.

The space comfortably fits 4 panels in a 2×2 arrangement:

Each AIKO 455W panel: 1,722mm × 1,134mm
2 wide × 2 tall: 2,268mm × 3,444mm
Fits the available wall space with room to spare

90° or 30°?

I looked at this carefully. The wall is at height — roughly 3–4m up. A 30° tilt would mean panels sticking out nearly a metre from the wall at that height. Significant wind loading, more complex mounting, and a scaffold tower needed anyway.

90° vertical wall mount is the right answer here:

Wind pushes panels into the wall — no uplift problem
Gravity works with you
Mount rails directly to the brick with rawlbolts
Panels hang on the rails with standard solar clamps
Clean, secure, permanent

Generation loss vs 30°: about 22% less annually. Over 10 years that’s ~£800 less value. But the simpler, safer mount is worth it at height, and the project cost is lower.

The rail system — 3 rails, not 2

For 2 rows of panels stacked vertically you need 3 horizontal rails:

─────────────────────────  ← Rail 1 (top)
│ Panel │ Panel │
─────────────────────────  ← Rail 2 (middle — shared by both rows)
│ Panel │ Panel │
─────────────────────────  ← Rail 3 (bottom)

The middle rail is the bottom clamp for the upper panels and the top clamp for the lower panels simultaneously. Standard solar mid-clamps sit on that rail gripping both.

Rail positions (AIKO 455W panels mount ~200mm from each end):

Rail 1: 200mm from top of array
Rail 2: 1,522mm from top (bottom of upper panels)
Rail 3: 3,244mm from top (bottom of lower panels)

Total wall height needed: 3,444mm. Use 2.5m aluminium solar rails, overlapped and spliced if needed.

Wind loading — take it seriously

At 90° vertical with 4 panels, you’ve got ~7.8m² of surface. In a 70mph Welsh storm that’s the equivalent of over 400kg of force. The weight of the panels alone (86kg) won’t hold them.

What you need:

M10 rawlbolts into brick along each rail — 4 per rail minimum, into brick not mortar joints. Fischer FBN II M10 from Screwfix. Each one holds ~4,000N — 4 per rail gives 16,000N capacity against a storm force of ~4,400N. 3× safety margin.
Proper solar end-clamps and mid-clamps — don’t rest panels in channels, clip them down positively.
SDS drill to get into the brick properly.

For a vertical wall mount, that’s all you need. No ground anchors, no diagonal bracing. The wall does the work.

Wiring

4 panels in series from the west wall → DC cable run into the loft → down through the wall to the Fox H1 → MPPT2 input.

Cable: 4mm² solar DC cable (red and black), rated for UV outdoors
Connectors: MC4 male/female — crimped properly or use pre-crimped leads
Run the cable along the wall in UV-rated conduit
Label both ends clearly: “WEST ARRAY MPPT2”

The Fox H1 will detect the new array automatically and start optimising it independently of MPPT1.

Cost breakdown

Item	Cost
4 × AIKO 455W panels	£80
3× aluminium solar rails (2.5m)	£45
End clamps × 8 + mid clamps × 8	£27
M10 Fischer rawlbolts (box of 12)	£12
4mm² DC solar cable (10m each +/-)	£22
MC4 connectors	£8
Scaffold tower hire (1 day)	£60
Total	£254

What it generates

Annual estimate for 4 × 455W vertical west-facing in Cardiff:

Month	kWh
June (best)	140
May–Aug average	~110/mo
Annual total	~810 kWh
Annual value	~£205

Payback at this cost: just over 1 year. Then ~£200/year free for the next 29 years.

The daily profile in summer is what matters most:

Before 2pm: barely anything (sun hasn’t got there yet)
2pm–4pm: ramping up
4pm–8pm: peak generation — exactly when your south array has faded and your evening loads are highest
After 8pm: tapering off

That evening window is where the real value is. The battery gets topped up from the west panels instead of drawing down — which means less overnight import from the grid.

Is it worth it?

At £254 all-in with a 1-year payback and 30 years of operation, it’s one of the best pound-for-pound solar investments you can make — especially when you already have a spare MPPT input sitting idle.

The only reason not to do it is if you don’t have a suitable west-facing wall. I do. So I’m doing it.

I’ll update this post with real generation data once the panels are up and running.

Have a spare MPPT input and a west or east-facing wall? The maths almost always works in your favour if panels are cheap. Feel free to get in touch if you want to talk through your own setup.

Project 2: Adding west-facing panels for free evening power