Hi from SW UK

[PROTEU5]

Just joining, having been watching all the videos on YT for the last several years.

I have finally got around to sorting the house out, and am on here to look for some PV solutions.

We have built a dormer roof on the second floor (3rd for US) , which is 5m x 4m, along with a 14.5m^2 shed, that is about 5m away from the main property. The dormer is flat, but south facing, the shed roof is on a 13° pitch and SSW facing. I am looking to place the PV array on both, but would like to converge them in a battery bank by the main consumer unit. I am not wanting to connect them to the grid, just set them up as a UPS, which we can run the house on, and for it to switch to grid if necessary.

My main question is, would this seem feasible, and what is the best way to maintain the cells on the flat roof please? It isn't the easiest to reach, aside from building a scaffold tower.

Many thanks for anyone's input in advance, and apologies if it seems like a daft question.

 

[OffGridForGood]

I don't think it is Daft at all, more like 'first draft'.
Welcome to the community. Since no one replied yet I will start.
Most PV panels will not do well set dead level (horizontal) and many require some slope in their installation instructions just to maintain a clean surface using rain to clear any leaves, dirt bird droppings etc.with your third floor roof being inconvenient to access this is quite important. So my first comment would be the dormer PV should be planned to be on a tilted rack mount to achieve at least the min slope required. Additionally since your latitude is significant, you will want those PV units tilted anyway in order to gain any winter sun you get. Without using an adjustable tilt, many designs use your latitude as your tilt angle. A starting point at least for you to consider.
Your 14.5sqm shed roof (150sqft) at only 13-degree pitch (from horizontal likely?) is about 3:12 pitch and very low for your latitude (good in July poor in Dec). If you can design the racking to increase the angle here as well, would likely be advisable. Again your latitude angle may be a decent starting point. Assuming the shed roof is more easily accessable, you may consider an adjustable rack here that you change angle for winter/summer.
As to your question about feasible and run the house on - well you don't provide any information for us to comment on this.
Starting point is the house loads you have historically, by season/month
Individual peak loads you may have, especially large loads you may want to run. Pay attention to resistive loads (ie heating elements) vs induction loads(motors).
One thing to look up for your area is the incoming solar potential available by month/week/day - several good resources on this site and others, and often available from local sources/government agencies. From others in the UK we often see a 7:1 ratio of solar potential between long sunny summer days and short cloudy winter ones it seems, making non-grid-tied systems a challenge. I have seen some EU users opt for grid tie and average their PV collection to meet annual use. That is, they collect a years' worth of energy using PV mostly during May-Sept months, and then use the "banked energy" during winter without much PV coming in, and avoid batteries (the expensive part of most systems) altogether.