Solar quote confusion

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I’ve been getting in quotes for a solar system and wow it’s confusing! I’ve only used MCS installers and the range is huge - from £6800 for 5.4kw to £4200 for 2.9 kw.
No one seems to quote for the same size and I’ve been trying to compare based on £ per watt (installed value, not produced) which gives me £1.44-£1.26 per watt.
Is this reasonable? I live in a bungalow and there’s nothing odd about the roof. The systems themselves seem similar (longi or Ja solar panels).
Any suggestions on how I can benchmark? I’d normally want quotes in a similar range but I can’t seem to get them to produce similar system designs!
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2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 2.5kw inverter. 28MWh generated, long-term average 2.6 Os.
£1.00 per watt installed is often a benchmark to aim for. Doesn't matter if it goes a little above this...
Benchmarking by £ per watt is sensible (I went ahead with my installation partly based on that) but bear in mind that 5.4kW of panels with only a 3.68kW inverter isn't going to make full use of all the potential generation. (In the same way that for example, 4kW of panels with a 3.68kW inverter will make use of nearly all the potential generation.)
As you go bigger, the price per Wp should fall. My sister had an install last week of 10.3kWp and that was just under £8.5k (but there was already scaffolding in place).
For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
Install 2: Sept 19, 600W SSE
Solax 6.3kWh battery
2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 2.5kw inverter. 28MWh generated, long-term average 2.6 Os.
Quote 1: £11,000 / 6035w/ £1.82 per watt (INCLUDES BATTERY)
17x 335 W Monocrystalline Panels (not specified)
1x 6kw inverter (not specified
1x 9.6kwh battery
software etc
scaffolding
Quote 2: £4200 / 2920w/ £1.44 per watt
Solaris 3Kw inverter
8x JA Solar 365KW Panels
Renusol mounting system
Tigo TS4 Optimisers
Install, Scaffold etc
Quote 3: £6500 / 5400 watt/ £1.20 per watt
15 x SolarEdge P401 Optimisers.
Mounting equipment for roof installation with cable flashings.
1 x Generation Meter. Connection agreement application & processing.
Scaffolding etc
Install 2: Sept 19, 600W SSE
Solax 6.3kWh battery
Do you have a rough idea of many panels can fit on your roof(s)? And will they all have the same orientation?
The Solaredge system concerns me slightly, as it's pushing the kWp to inverter size to the limit, and possibly starting to get wasteful regarding capping. Also, if you don't have shading and are using one roof, then Solaredge may be overkill - but please note, Solaredge is brilliant, I have two systems using it, so if needed, and/or the PV is across two different orientations, then I can understand it.
I think what jumps out at me the most is the difference between a 6kW inverter in one quote, and a 3.68kW inverter in another. It would make a lot more sense to know if you can (hopefully) exceed the 3.68kW cap, or not, otherwise it's hard to judge what might be best.
For general PV advice please see the PV FAQ thread on the Green & Ethical Board.