Solar array 50/30kw viability

Just trying to work out the viability of the following scheme. Keep reading that the ship has sailed and am sure it is no longer a show stopper but I got the returns to not look disastrous.

So flat roofed agri/commercial building approx 350m2 roof, facing SW.

Initial calcs say around 50kwh worth of space available but conflicting advise on most economical size installation. Have read that over 30kwh requires export meter but read elsewhere that under 50kwh doesn't require. Perhaps one website out of date?

Building had 3 phase connection due to previous use.

30kwh system cost around £40k
Tariff income £3k
Export income £600
according to websites.

9% return before insurance, can't really see any other costs which aren't DIY'able.

Ok not setting the world alight but an income nether the less. I suppose the show stopper is the need to replace after 20/25 years? Although will the economics stack up better or worse then? If you had a spare 40k lying around would you do it?


  • Martyn1981Martyn1981 Forumite
    12.5K Posts
    Part of the Furniture 10,000 Posts Name Dropper Photogenic
    Hiya, just some thoughts;

    I also understand that 30kWp+ requires an export meter.

    I'd have thought the price seems high, as domestic installs (if you shop around) can start to go sub £1k/kWp at around 6 or 7kWp, so would have thought cost less than £30k.

    Tariff income seems too high at £3,000. Assuming you get good generation of say 1,000kWh per kWp, that's 30,000kWh's pa. With the 10-50kWp FiT tariff at 4.19p (4.12p from 1/10/17) that comes to £1,257.

    If you are estimating export at £600, then assuming you get approx 5p/kWh, that's about 12,000kWh of export, leaving around 18,000kWh's of saved import (is that about right?). I don't know what you pay, but that might be £1,800 pa.

    Long term, hopefully the panels will last 30yrs+. Though the inverter(s) will most likely need replacing. Not much else to go wrong.

    Maybe if you get the cost down to £20k or so, though perhaps the flat positioning is adding costs, not really sure, just sounds like a lot. For domestic installs scaffolding adds a lot, perhaps 10% of costs, not sure if you need any?

    Rather than guess on generation, as this is such a big install, why not try out PVGIS (see section 5 of the FAQ's, link in my auto sig), if the system is too big for the site, then just put in 3kWp and then multiply results by 10, for a quick guestimate.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
This discussion has been closed.
Latest News and Guides