Is north facing solar a complete waste

In a word - yes.

In a few words. Depends on what you want from it. If you put a very large array in (6Kw+) you might do ok with it on sunny days. But you'll never make your money back on the investment. If you take it that on a cloudy day in summer my 6kw array might manage 1.5kw during the peak of the day - you can imagine a north facing array won't do much more I would think on a sunny day.

Maybe try one of the calculators online and see what it says though? Personally I wouldn't bother.

https://www.seai.ie/tools/solar-electricity-calculator/

Have a similar setup - 60sqm of roof - which is 'extremely flat' but pitched slightly (1:80) North.

Could I get tilted mounts or something which would unlock the potential of the surface area?

emmet02 since it's 1:80 it's essentially flat and while pitching the panels would definitely improve your production, roofs which are essentially flat have reasonable production by default, even north facing. If you want a bit of math and a longer explanation.

How much less efficient are north-facing solar modules? (solarpowerworldonline.com)

Ideally you would want solar facing south, but in reality the pitch of the roof is a huge determining factor. You can "get away" with low pitched roof facing north much better than say your average 30-40 degrees roof.

Going back to

https://re.jrc.ec.europa.eu/pvg_tools/en/#PVP%20that's%20the%20calculator%20for%20Europe

and plugging in 5Kwp one facing due north with a 5 degrees pitch, and the other due south with 5 degrees roof pitch....they are as you can see pretty close.

Course the steeper the roof the bigger the difference between the north and the south.

Hmmm - maybe the buckets (Renusol) would work on a 1:80 roof?

Is it worthwhile to add some north facing panels to a system which is primarily south facing? I.e. a couple of panels on North side of house to supplement the south?

30 degree angle.

I've no idea, to answer your question. I have no system right now. Just all in its planning infancy!

Yup I'd tend to agree with you there unkel, though the article i linked was more for the math around the production rather than the return on investment aspect....but as you say, panels have come down a lot since then. In 2018 and 2019 alone they came down a ton. That said, I'd still advise caution there with north facing panels.

If you have an existing array, then it's not so bad. You already have a "sunk cost" for inverter and possibly battery and the extra panels is more likely to give you something useful to add to existing production. However, if all you have is north available to you, and especially if you have more than 15-20 deg slope, I'd think you'd be better off investigating alternative solutions. Ground mounted array or perhaps 4-5 panels on the side of your house? Or spend the money on a ground source heat pump (if applicable for your house - not all houses are a good fit).

I know, I know I'm a kill joy (LOL).... but sometimes while as much as i like to see Gretta happy, a nod to the fiscal side of things is necessary.

On an east-west facing roof is there good value in having arrays on both sides?

I'd echo what graememk said above and add some more info as someone who has an exactly east/west split (1.4 Kwp East/3.8 Kwp west). Definitely 100% they are worth it. In fact for some consumers like me, they are better than south facing. I'll explain below. Sure as graememk mentioned above.... in winter, when the sun rises in the south east (very slowly) and then gets to 15 degrees elevation at noon due south and sets in the south west, you don't get much production as the panels are never really facing the sun being orientated east/west. Some real life figures for you.... is that I generated 56kwhr on a 5.3 Kwp system (which was 6% over forecast) for December. Not a lot. If those panels were all south facing I'd have produced 130Kwhr. So you can see the benefit of a south panel in Winter. Nearly 2.6x the generation

However, from March to Oct the East/West split works out very well. You end up getting 2x peaks during the day. one about 8-9am and the other about 3-4pm. (The times of these peaks do move during the year as the sun changes) That 2nd peak in the afternoon is helpful to charge a battery to get you to ride through the evening until night rate comes on.

In high Summer of course (May-Aug) the sun is even rising in the North east, so your East facing panels will start to produce from as early as 5-6am - and with the long days your west panels are producing right up to 8-9pm. South facing panels will only come fully on stream much later in the day, and reduce production at 5-6pm (roughly)

If you consume leccie at breakfast (8am) and again later in the day when you come home from work that split works out very well. Overall an east/west split generates about 85% yearly what a south facing one does, so technically south is "better" but there are some advantages as mentioned above.

I think the general feeling is that south, east and west are "no brainers" for a solar installation. With those orientations, you'll get your money back in approx ~10 years (give/take) depending on what the price you paid for it of course and your consumption. North facing panels requires some further thinking.

It's workable if the angle on your roof isn't too steep. Ideally you'd want to have a roof which has less than 15 degrees slope. From the previous picture you posted Manion, I think that you angle is way higher than 15 degrees, so for you I think you'd suffer. However, the one option you still have available to you is if you can remove the middle man and install the panels yourself (like some of the regulars here have done) you can "load up" on panels to make up for the lack of (efficient) generation with sheer volume of panels. Panels are reasonably cheap these days (circa €200/panel, sometimes less even).

You will suffer pretty poor generation in winter, but in summer you'll do ok. Your payback timeline will probably (I'll ballpark) 20+ years, but as unkel says.....it's not all about money and payback. Sure payback is important, but knowing that your doing the right thing for the environment is worth something too.

If it was me, I'd probably investigate alternatives. For example can you vertically mount some panels on your south facing wall? Angle them 10 deg from the vertical plane. Something like this guy is doing. Maybe 5-6 of these panels with the rest (bulk) facing north then you could be on a real winner.

Wall Mounted Solar, worth it? - YouTube

Just a thought.

The grant eligibility requirements have changed very recently (Jan1st?) or they will be changing very soon as announced in the last budget. You no longer need a house built pre 2011 to avail of the grant.

That said, while I think the grant is a great incentive....it's not totally "free money". I've seen people quoting prices to install a system without a grant which were very reasonable. The logic is that the suppliers sort of "up the price" cause they know you are getting the grant, so they build that into the price. Basically you can get fleeced if your not careful.

Aside: That price of €14,695 is (how shall i put this?) ..... let's go with "a lot" for a 6Kw system! That system should (ballpark) cost €8500-€9000 or there abouts. (this is without grant applied)

Adding a 5Kwhr battery that would be €10.5-€11k. So the quote you have is probably €3k+ over what you should be paying if you shop around.

If you can avail of the grant, that would be of course €3k less, so you can expect to pay (ballpark) in about the €8.5-9K mark for a 6kwp system and 5kwhr battery. There's a whole quote thread you should read.

Domestic Solar PV Quotes 2022 - Page 9 — boards.ie - Now Ye're Talkin'

If all your panels were north facing, I'd probably add 50% to the panels and look for 9Kwp, as you won't be efficient but this really is down to you and your consumption. I reckon you'll still be in under €12-13K.

Obtaining the grant is useful, but I've seen people get bigger systems saving themselves €5-6K by shopping around.