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North facing solar PV - bad idea?

  • 18-12-2018 10:49am
    #1
    Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    My rear roof is 100% south facing, but it already has 3 velux windows (attic conversion) and a 40 tube solar thermal system, leaving very little space for PV panels

    My front roof is 100% north facing, but empty. The house is a typical Irish 3 bed semi detached built in 2000 in Dublin. As a rough guess the roof pitch is about 35 degrees?

    How much less efficient is a north facing array like this? If going ahead I would like a 4kwp array, taking full advantage of the new PV subsidy. I know I will need planning permission for an array this size

    This article shows that the loss of efficiency was a lot less bad than I thought:

    Linky

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



Comments

  • Registered Users Posts: 1,343 ✭✭✭ beazee


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

    It's pretty bad for Minneapolis @ 45°N and Dublin is even further north:
    img1-500x320.jpg


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    So about 50% less production at least. That's not good.

    The article I linked has figures for Charlotte (NC), which is @ 35°N. That would explain why the differences are relatively low.

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 9,775 ✭✭✭ Effects


    unkel wrote: »
    If going ahead I would like a 4kwp array, taking full advantage of the new PV subsidy.

    Battery system?


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    Effects wrote: »
    Battery system?

    Might as well. An AC coupled system like this shouldn't cost more than €2k installed, so just €1k net of grant. If you cycle once per 24h on night rate and on average once per 24h on solar, payback is just 5 years. Also easy to extend DIY when batteries get cheaper over the next few years

    Linky


    Looks like north facing is out though, might have to get a wooden loghouse in the back garden to install 4kwp PV on (south facing)

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 11,344 ✭✭✭✭ KCross


    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.


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  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    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.

    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)

    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 :D

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 11,344 ✭✭✭✭ KCross


    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 :D

    Now thats more like it! That makes financial sense! :)


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    KCross wrote: »
    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.

    Warranties are pretty meaningless. You are quite well protected in this country by the sale of goods act
    KCross wrote: »
    How much to add on another 2.4kWh module? Another £1200?

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

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 11,344 ✭✭✭✭ KCross


    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...


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    KCross wrote: »
    Sorry for derailing your thread...

    No probs. It wasn't you who brought up the battery :)
    KCross wrote: »
    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.

    Maybe it is, maybe it isn't. I've already seen them for sub £700 (plus VAT). I wouldn't be surprised if you could buy a 2.4kWh battery for €500 by early 2022. I would expect global battery production to be far, far higher than it is now. And prices to come down significantly.
    KCross wrote: »
    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.

    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.

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

    Spec sheet says cycles >4500 and design life >10 years. If the thing breaks down after 6 years and Pylontech or its reseller refuses to refund me or replace or repair the battery, I will take them to the small claims court. Do you think they'll contest it? Most unlikely. And even if they do, do you think the judge is going to be entertained by a story of that you can only cycle it once a day (while they claim a design life of over 10 years and 4500/365 which is over 12 years)? Do you think they'll present an engineers report saying I have cycled it twice a day, so it will only last 5 years instead of the >10 years they claim as design life? I have no doubt the judge would find in my favour.

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



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  • Registered Users Posts: 11,344 ✭✭✭✭ KCross


    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! :)


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    KCross wrote: »
    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.

    It's possible. It's also possible that even with cycling twice a day the battery is still at 75% after 10 years.

    Also break even is for the complete installation. Parts (including battery and storage inverter) and labour. Should the battery break after 6 years and I have no come back - worst case scenario - I can install a new battery myself and have a new break even period of no more than say 2 years (with the reasonable assumption that the other bits last at least 10 years)
    KCross wrote: »
    Somehow, I dont think you are for changing your mind anyway. You are hell bent on drawing that grant! :)

    Haven't made my mind up yet at all. But after paying a fortune in taxes in my time, it is nice to get a few grand back in grants here and there :D

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 11,344 ✭✭✭✭ KCross


    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?


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    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.

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 2,452 ✭✭✭ wexfordman2


    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.


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    Solar thermal makes many times more money per m2 installed on the roof than any solar PV!

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 30,666 ✭✭✭✭ listermint


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


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    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)

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 30,666 ✭✭✭✭ listermint


    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 ?


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    As I said, it doesn't matter where you want to put thermal or PV, front or back or side of the house or wherever. If you exceed 12m2 you need planning permission.

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



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  • Registered Users Posts: 11,344 ✭✭✭✭ KCross


    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?


  • Registered Users Posts: 626 ✭✭✭ conor_mc


    unkel wrote: »
    Solar thermal makes many times more money per m2 installed on the roof than any solar PV!

    Doesn’t that depend on the heat source it’s replacing, eg electric immersion vs gas boiler, no?

    Fair to say they’re more efficient (as in convert sun’s energy to power) for sure, something like 70% efficient vs 20% for solar pv, right?


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,702 CMod ✭✭✭✭ unkel


    conor_mc wrote: »
    Doesn’t that depend on the heat source it’s replacing, eg electric immersion vs gas boiler, no?

    Yes indeed. My source it partially replaced was a 98% efficient modern condensing gas boiler, which is the cheapest way to heat water in Ireland, so my savings are the lowest compared to anyone heating their water in another way

    Yet my savings are about €300 - €400 per year (we use a lot of hot water)

    A similar size PV array is about 3 panels. So about 900W, which will generate about 900kWh max per year, or theoretically about €150 if you use up every single kWh for stuff you could not have done on the cheaper night rate or with oil or gas, etc. In practice you'd do well if this array makes you about €70-€80 per year without a feed in tariff. And if you use a diverter with a small solar PV system, it actually costs you money

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 2,452 ✭✭✭ wexfordman2


    KCross wrote: »
    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?

    Don't know the actual cost of the batteries sorry, but it came as part of my overall solar install. The installer was to out in 5kw prime hybrid and 5kwh batteries, but as he was having a few technical isssues with the prime solution and my install was being delayed,he has put in 5kw Soltaro inverter and 6kwh battery for the same price. I think he is looking to deploy a.mix of the two vendors across his customer base rather than rely on one brand, but I think the Soltaro comes in quite competitive also


  • Registered Users Posts: 2,977 ✭✭✭ randombar


    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.)


  • Registered Users Posts: 2,452 ✭✭✭ wexfordman2


    GaryCocs wrote: »
    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.)

    So,.the way mine is working St the moment, is

    1) the battery will only discharege to 10%
    2) whenever there is excess solar it will charge the battery.
    3) when I am on night rate, the battery will charge from the mains.
    4) the battery will discharge when the load of the house exceeds what is being generated by the solar.


    In the event of a power cut

    1) the battery will not provide power to the main circuits.of the house.
    2) a small number of circuits can be selected at install stage to run off the battery.
    3) Solar generation will be disabled for the duration of the power cut.

    Item 3 is annoying but due to fire regs I beleive.


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