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Advice on which is better - Roof N/E <-> S/W or Ground Array

  • 16-04-2022 11:05pm
    Registered Users Posts: 660 ✭✭✭

    Hey folks,

    Looking at solar PV options for the near future. I have an off set East/West roof orientation on bungelow. Pretty large roof with more space on the back (N/E) than the front (S/W). 1/2 Acre of field with east, south and south west unrestricted view of the sky. Insulated 20ft shipping container 20 meters away behind the house.

    40 tube solar install will happen first as we have a triple coil cylinder (boiler stove and Oil) so not interested in EDDI.

    House built in 1976 so it has the old disc meter. We use about 16Kw every 24hrs on average. Day/evening times - Dishwasher, cooking, washing machine etc. Base load during day is usually ~500w per hour. One of us is working from home every day of the week. Plan on getting EV in a few years when it will be time to change the diesel so looking at home charging also.

    I'm wondering if I should aim for filling the roof as much as I can or go for ground mount which has as much space I want and the better solar orientation. Going the ground mount means that I can use the shipping container as the base for inverter etc as it will be closer than going to the house. Either way, I will go the DIY battery (Aliexpress 10Kw) route and storing it in the container, so there will be a cable going from shipping container to house distribution board anyway

    Roof Mounted Option (Maxed out potential) - panels being 1m wide and 2m in length and keeping .5m away from edges. I've left space for 40 tubes.

    Ground Mounted which would be 25m away from the shipping container. As as mentioned, the container is 20m from the house. ~30m if you add linear length to distribution board. The red lines is just showing North/South - East/West. Yellow lines would be the ground mounts. Orange line is the ESB buried cable supplying the house outside meter. Ground around container cleared since google image was taken.

    If you were in my position, which option would you do? Either system wouldnt need to be large at the get-go. I'd happily add to it over time if cost effective.

    Look forward to suggestions and thanks in advance.



  • Registered Users Posts: 528 ✭✭✭mike_2009

    How old is the roof & roof tiles? Are they likely to need replacing in the next 5 years? Once you lay down Solar PV, it'll be more costly to do repairs / replacement although they do protect the roof somewhat from direct sunlight / weathering. That would be one of my first considerations....

  • Registered Users Posts: 660 ✭✭✭bunderoon

    Thanks for the reply. Roof (Slated) is 10 years old. Full house renovation done in 2012, new roof & structure, new wiring and plumbing. Standard insulated cavity walls.

  • Moderators, Sports Moderators Posts: 18,659 Mod ✭✭✭✭slave1

    Fill the roof first, see how you get on and then you can S ground mount, why create the expense of a ground mount when you have a free roof. Wherever you are putting your inverter leave room for a second one beside it and ensure your cable from inverter #1 to consumer unit can take the power from inverter #2 if you go that route. I put in a larger than required cable from Inverter #1 which will make my life considerably easier now I'm putting in inverter #2

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  • Registered Users Posts: 660 ✭✭✭bunderoon

    Thanks for that.

    My thinking was that DIY has the better option for orientation.

    Reading the Solar 2020 Quotes thread, I see that a few people went with SaaS last year. And some in the 2022 thread are doing the same. I'm thinking about this route now for the roof and then next year, buy them out and expand the system; replace inverter with a hybrid or go with the second inverter as you described.

    Thanks again for your input.

  • Registered Users Posts: 2,424 ✭✭✭bullit_dodger

    If your ultimate goal is to have a large system, going via SaaS isn't the way to go I fear.

    Don't worry too much about orientation. Sure, we all want an exactly south facing arrary, but an east/west split isn't the end of the world as it produces about 80% of what the same panels do facing south. So you add on 2-3 more panels (€600-700) and you're now generating the same as a south facing ground array.....without the expense of having to buy/build a ground mount and run long cables.

    In fact there are some inherent advantages of east/west splits. With a south array, you get this one big peak during the day at noon. Great. It's the orientation which produces the most for the year, but many batteries have a max charge rate. That could be (say) 3kw, so while you might be producing 6kw, and your house using 1Kw, you can't fire more than 3kw into the battery the rest goes exported to the grid. With a east/west split you get 2x minor peaks, one in the morning and one in the afternoon. Lower max output, but for longer.

    By the way, I'm not suggesting that east/west is "better"......what I'm saying is that there are things with an east/west which are advantageous, so I wouldn't discount it as not workable.

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  • Registered Users Posts: 660 ✭✭✭bunderoon

    That's for that.

    Very valid points on orientation. ^^^ This is why Boards members are invaluable!

    For now, I would like a system that takes the base load of the house (500-600wph) and also the light appliances where it can. So I'm leaning towards a 3-3.6kw system. SaaS and buy two extra panels. But I would like to have a battery sooner in the journey, which made me consider a ground array, shipping container for battery and achieve the best orientation possible.

    My thinking was that the DIY ground route would save me a fair bit over an installer and roof and I could go large as I wanted.

    But as I dont have the budget for the large arrays yet, SaaS will be ideal for the first few years. Then add to the roof or venture out the back. I'm sure my mind will change several times before then anyway.