Is it worth putting PV panels on a North facing roof?

[Countrypaul]

We currently have 3.3kWp of PV panels on the south facing roof which cannot take any more, and we cannot put any on the north facing roof of the house. I am planning on building a large single garage approx 4 x 7.5m with a gable ended roof (to match the house) which like the house will have a south facing side and a noth facing side.I figure I could put 6 x 495W panels on the south facing roof, these may be grid tied (have to check whether we can do that) or a battery based solution. I dont want to interfere with the existing system as that is on FiTS and I can see little benefit in changing it. The existing inverter is in the "basement garage" which is only 4ft high but cool and well ventilated. The new garage will be about 3m behind the house and I will put 1 or 2 conduits in between the new garage and existing basement garage (for mains power, data, water and probably PV DC) so the new inverter/charge controller/??? is located in the basement garage along with any batteries.

In order to keep the garage style consistent with the house, the roof will have clay tiles. I am assuming the PV panel will be roof intergrated (like the house) which will also reduce the number of tiles required and the cost.

Would it be worth putting any additiona PV panels on the north facing roof of the garage?

[Stinsy]

I'm going with: yes!

Panels are cheap very very close to the price of tiles. North facing will give you a few precious kWh just when you really need them (bright-overcast conditions).

[Mart]

Yes, or no, depends!

I have PV on my WNW roof, but that's an easier decision.

My thoughts on N roofs is that it all comes down to the additional costs, which if low enough, may make it entirely worth doing. For instance if you spend £2k on the south roof, but the north roof will only cost another £1k, because its just the extra panels, no extra inverters, AC cabling etc then so long as the N roof can generate around 50%+ of the S roof, then it starts to make sense.

Quick check for my location and a S roof 1kWp would be 989kWh pa at 35d, but only 527kWh's facing N. At 25d pitch it improves significantly with the S roof at 970kWh's and the N roof at 614kWh. So you'll need to check PVGIS and see how the numbers and economics stack up.

But wait ...... there's more, while you are on PVGIS, check to see when you'll get the generation, as the N roof will have a massive summer bias, perhaps 12:1 (June v's Dec), whereas E or W is more like 7:1, and S 4:1, even 3.5:1 for steep pitches. So you'll generate most of that N roof leccy during the summer months when you may already have too much, or if sharing an inverter, it is already close to maxing out.

This may sound weird, but north facing PV shouldn't be dismissed, especially as PV panels get cheaper and cheaper, but we may not be there yet, and the issue might be more about when you get the generation, not how much you get?

S'pos there's no chance to go with a monopitch roof all facing south?

Have fun.



Edit - Good point Stinsy makes about poorer weather, as the larger kWp will help. I also should have mentioned that at the height of the summer the N roof will give you some early and late generation as the sun rises in the NE and sets in the NW.

[nowty]

I have some on my NE roof which I did myself with a second hand inverter so very cheap to install and yes its worth it if it can be installed cheap enough. If you make the roof angle on the garage shallow, its even better.

Practically nothing in winter but If its cloudy in summer, they generate almost as much as south facing ones.

[Countrypaul]

I had assumed the roof pitch of 42 degrees to match the house, but I'm not sure it has to be that steep. The fact the roof finish should match the house roof as far as tiles are concerned, might mean we can't drop below 35 degrees - I need to check that but sounds right. The idea of a mono pitch roof I don't think will work as I want to do this under permitted developmet, which limits roof height, coupled with the tiles limiting the angle makes things difficult. The garage will be built into a slope so one side (south) will be quite low from ground to eaves and the other quite high also south is likely to be only about 1m from the boundary.

4 metres wide with dual pitch roof at 45 degrees would mean two metres of height taken by the roof, so only 1/2 metre of wall on the south side above ground, but likely 2m on the north side. That 1/2m of wall will mean the PV panels are quite close to the ground which might also cause problems with shading due to bushes on the other side of the boundary.

[Mart]

Hiya Paul, nothing to do with PV, so to speak, but we built a side garage on our house about 5yrs ago, over the side drive. The planning laws in Wales had just changed so we could build to the boundary without planning permission, so long as the max height of the roof, and the height at the boundary were within set limits. I'm not saying the rules have changed elsewhere, but you never know.

Just checking on PVGIS for our location at 42d and it's pretty bad - S 42d gives 989kWh/kWp, whilst N gives 468kWh/kWp. 45d gives 988 & 444 respectively.

[Oliver90owner]

If I were even to consider that, I would likely use polycrystalline panels - so much cheaper, and likely better than monocrystalline out of direct sunlight.

[Tinbum]

My 8Kw of North east facing panels are doing this at the moment. It's a really cloudy sky but fairly bright. SW photo sensor is saying 173w/m2, so NE is not much less.

[Tinbum]

My North East panels are doing about 750w on a very overcast day, though I missed 700w of that as the Growatt decided to play up this morning. I don't know why it does it, but a reboot of a battery pack normally sorts it.