North facing solar PV - bad idea?

Dublin is 53°21′N + your roof pitch @ 35°

It's pretty bad for Minneapolis @ 45°N and Dublin is even further north:

unkel wrote: »

If you cycle once per 24h on night rate and on average once per 24h on solar, payback is just 5 years.

Linky

I see in the PylonTech battery spec it is rated for >4500 cycles.
If you manage to cycle the battery twice a day, like you say above, thats only 6yrs which is just around the same as your payback period.

As discussed before I think it would be very very difficult to cycle the battery twice a day unless you were really managing the system. I think very few people would be able to do it. Maybe your hobby will allow you to do it but the warranty and the state of the battery after 6yrs is going to be an issue, imo.

You can say that its a 10yr warranty and its their problem but if you are cycling more than they have in their spec they can throw that back to you! I'd be reading the fine print before writing the cheque.

EDIT: I see this in the warranty: "... be used on a daily cycle basis and only for energy storage system,"
My reading of that is one cycle per day.

unkel wrote: »

Some good points there, KCross, but I would be confident that I would not draw the short straw should it come to an argument over a dead battery after 6 years.

How would you be confident of that though?
The system will clearly show/log that you are outside the warranty?

Their warranty isnt great either.... 60%. That's pretty poor tbh. So, the system could be only providing you 1.3kWh usable by the time it has broken even. The figures dont look too promising then to actually "make" money off it.

unkel wrote: »

Also modern Li-ion batteries seem to last longer than most people estimated. And one of my assumptions is that I can add on more batteries myself for very little money in a few years time (shortening the overall payback time of the system)

How much to add on another 2.4kWh module? Another £1200?

unkel wrote: »

Hell, I could even decide to sell the battery immediately after the install for say €800 (new €1200), so I have a battery ready AC coupled system installed and certified for just €200 and then wait until batteries get cheaper / better

Now thats more like it! That makes financial sense!

unkel wrote: »

Warranties are pretty meaningless. You are quite well protected in this country by the sale of goods act

Sale of Goods wont protect you if you use it outside its design guidelines (one cycle per day).

Usually sale of goods helps you when a manufacturer gives you a 1yr warranty and it stops working after 2yrs. You can then apply sales of goods act and say it should still be working after 2yrs or 3yrs etc.

However, if you use the product in a way that is contrary to its design sale of goods wont cover you. For instance, telling a car manufacturer that the clutch shouldnt be gone after 2yrs of a 1.0L petrol car pulling a horsebox.... do you think a judge would rule in your favour!?

The same principle applies here. You are planning on cycling it twice a day and it tells you how many cycles it is warratied for.... no judge or manufacturer will rule in your favour on that.

Now, you could be lucky and the battery will last longer than their design.... and maybe it will.... but it will be degraded so you need to factor that into your payback. This isnt a 30kWh EV pack, its a 2.4kWh pack... one bad cell and you lose a much bigger % than in a large EV pack.

unkel wrote: »

I'd say not much more than €500 in 2-3 years time

You think the batteries are going to be less than half the price in 3yrs time? :eek:

In that case why not just wait a year or two and get a cheaper battery? The savings in capital cost will nearly be as much as the grant plus you'll still get the grant.

€500 is wishful thinking though, imo.



Sorry for derailing your thread...

unkel wrote: »

If you get a bad cell in a 3 cell mobile phone battery, for sure it has an impact. Two bad cells and the phone's for the bin. Could be wrong here but a quick Google shows that the Pylontech has 15 cells, so losing one or two will not have a big impact.

On the contrary, 2 out of 15 is quite a high percentage on top of normal degradation.

unkel wrote: »

I have no doubt the judge would find in my favour.

I admire your confidence!

Dont lose sight of the degradation anyway in your calculations. The battery is unlikly to hit 60% to trigger a warranty or small claims court case but if you are using it twice as much as its stated design you can expect accelerated degradation. 4500 cycles is alot and you've only broken even at that point.

Somehow, I dont think you are for changing your mind anyway. You are hell bent on drawing that grant!

To bring it back on topic, have you calculated the differences in production (winter and summer) by using North facing vs south? Will it still allow you to do 2 cycles, which seems key to your ROI?

Also, any chance the solar thermal could move to the north roof and blanket the south with PV? Or would that be ridiculous money to move?

unkel wrote: »

Nah the efficiency figures from beazee's post are pretty brutal. And that's much further south than we are in Ireland. North facing here is a non runner, unless your roof is almost flat. Mods can close this thread. My question is answered.

Would it make sense to get rid of the solar thermal in place.of the solar pv ? Using an eddi the solar could heat your water with the excess,.but prob low enough during the winter ?

On the battery thing, been an interesting thread, and good timing, my batteries went in a week or so ago, and had a crowd in yesterday doing some firmware upgrade on them.Maker is Soltaro, and warranty.covers 10,000 cycles, not limited to one cycle per day either.

Isn't this a planning permission issue never mind the poor performance of not facing fully into the sun

unkel wrote: »

Horse, cart? There is no point applying for PP if it makes no economic sense to go ahead with the (north facing) PV installation

But maybe your question is do you need PP for solar PV / solar thermal? If so the answer is yes if the total used by these exceeeds 12m2 on your roof (whatever direction and whether it is visible from the public road or not)

No I mean does planning not negate the fact you could get pv. As in you can't put it on the front of the house ?

wexfordman2 wrote: »

On the battery thing, been an interesting thread, and good timing, my batteries went in a week or so ago, and had a crowd in yesterday doing some firmware upgrade on them.Maker is Soltaro, and warranty.covers 10,000 cycles, not limited to one cycle per day either.

Those batteries look much more robust alright. Warranty of 10k cycles or 10 yrs. I wonder does the price reflect that? A case of you get what you pay for.

Cheap batteries might not necessarily be a good long term investment.

Are you happy to share the cost of the Soltaro batteries or do you only have a full Solar+battery cost and no breakdown?

In relation to battery cyclying guys. Does the battery only start discharging when it has reached full power? Haven't been home much with my panels but on these dark days I notice the panels are feeding all the house needs plus dumping onto the grid for a couple of hours, So that excess could be going into a battery. If a thick cloud comes overhead could it take from a battery or does it have to wait until it's full?

Also in a power cut I will be able to get some power from the battery. During the day in a power cut would it just keeping charging the battery and feeding the house (on a good sunny day etc.)