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Solar PV savings estimation, have I gone wrong?

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  • Registered Users Posts: 1,732 ✭✭✭poker--addict


    What sort of self consumption percentage are people assuming or realising without batteries?

    In my own case, array will be larger circa 7kw, with household above average usage.

    😎



  • Registered Users Posts: 11,395 ✭✭✭✭the_amazing_raisin


    You're correct that I'm planning to charge the battery at night. I did rejig the calculations to account for the losses of charging and discharging the battery. Didn't seem to make a massive difference to the payback, maybe added a year worst case

    "The internet never fails to misremember" - Sebastian Ruiz, aka Frost



  • Registered Users Posts: 12,120 ✭✭✭✭KCross


    You're correct that I'm planning to charge the battery at night.

    your battery won’t cover all your usage though. You will be importing.



  • Registered Users Posts: 1,454 ✭✭✭DC999


    I'd be keen to see that too.

    I'm only live 5 weeks but only self consuming 40% average and that's with an ev on driveway a lot. Have backwards spinning meter so not in a panic to get it higher.

    Assume I have to go down the automation route if I don't buy a battery. But again that's a rabbit hole for me and will suck time. As is a DIY battery if I went there. So solar moves to being a hobby at thay point or at least taking the time of a hobby..

    Have a look at the monthly stats thread. Some include their self consumption but most there would have a battery I expect



  • Registered Users Posts: 301 ✭✭spose


    Coming up on 3 years with 4.7 e/w and no battery. High enough users. Have used 50% in the house, put 30% in the hot water and 20% exported



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  • Registered Users Posts: 12,120 ✭✭✭✭KCross


    That’s very good. Battery unlikely to pay for itself with your 20% excess, particularly since you’ll get paid for that 20% now as well.



  • Moderators, Sports Moderators Posts: 19,029 Mod ✭✭✭✭slave1


    20 months, 10.7MWh generated, 43% to Water, 28% to Home, 16% to EV, 13% Exported.

    Of imported electricity, 84% night, 16% day

    My stuff for sale on Adverts inc. EDDI, hot water cylinder, roof rails...

    Public Profile active ads for slave1 (adverts.ie)



  • Registered Users Posts: 2,735 ✭✭✭yankinlk



    Small array tho - so what are the import numbers? especially going in to winter. And if they have a day night meter than FIT wll be an estimate anyway. SO i get to fill battery and get paid for export same time! ;)



  • Registered Users Posts: 2,735 ✭✭✭yankinlk


    84% night! thats amazing? done with a battery or are u just a night owl?



  • Moderators, Sports Moderators Posts: 19,029 Mod ✭✭✭✭slave1


    No battery (yet), if you think about it I have little need for electricity during the day with PV in place so that will lower day time import, also from a maths perspective we have two EVs so a lot of Winter night rate usage (along with moving washing machine/dishwasher etc to night time, immersion too obviously)..when I get the battery up and going that 13% export should drop considerably and eat into the day/night basic house load usage.

    PV is a long game, start, observe/learn from usage and expand through more generation or battery/FIT

    My stuff for sale on Adverts inc. EDDI, hot water cylinder, roof rails...

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  • Registered Users Posts: 1,732 ✭✭✭poker--addict


    13% export with no battery, on a large system, that is impressive, if one is an average or above average user of hot water an EDDI may be the simple middle ground while waiting to consider battery options? 2 small kids in our house so bath requiring hot water almost daily. Are you actually using that amount of hot water?I suspect some people are heating water with EDDI's because they can without considering the value of doing so.

    😎



  • Registered Users Posts: 11,395 ✭✭✭✭the_amazing_raisin


    I'd like to get an Eddi as well but my heat pump has the controller built into the cylinder, so I'm not sure I'd be able to hook up to the immersion

    "The internet never fails to misremember" - Sebastian Ruiz, aka Frost



  • Registered Users Posts: 12,120 ✭✭✭✭KCross


    Some heat pumps have the ability to fire up their immersions via an external signal on their AUX lines which you could then control. Might be worth pulling out the manual and see if you can directly control the immersion. If it can, it would be alot cheaper than an Eddi which is €500 I think to buy. Worth looking into anyway.

    What you dont want to do anyway is start cycling your compressor. That's a bad idea for HP longevity.



  • Moderators, Sports Moderators Posts: 19,029 Mod ✭✭✭✭slave1


    4/5 of us, multiple showers so 100% yes to using the water, after house load it's the first I divert to. Maybe in a few years the battery will get more but that's us for the foreseeable...

    My stuff for sale on Adverts inc. EDDI, hot water cylinder, roof rails...

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  • Registered Users Posts: 301 ✭✭spose


    If I was staying with existing system I wouldn’t bother with a battery but adding another 3kw of panels so that should help feed the new battery



  • Registered Users Posts: 12,120 ✭✭✭✭KCross


    It will of course help feed it but will it be worth it relative to just pocketing the FiT payment?

    Have you got quotes for the battery?



  • Registered Users Posts: 301 ✭✭spose


    Everything is DIY so overall price won’t be too bad. Higher than it could be since I’ll have 3 inverters in the end but like a good few here it’s turned in to a bit of a hobby I’ve enjoyed messing around with.



  • Moderators, Sports Moderators Posts: 19,029 Mod ✭✭✭✭slave1


    3 inverters FTW, hobby is one word for it

    My stuff for sale on Adverts inc. EDDI, hot water cylinder, roof rails...

    Public Profile active ads for slave1 (adverts.ie)



  • Registered Users Posts: 301 ✭✭spose




  • Registered Users Posts: 228 ✭✭curioustony


    @the_amazing_raisin this is the same journey that I am on (retrospectively in my case). I did ballpark figures before installation, and reckoned I would save money. I did.

    Then I started to get real data (from the inverter) and the time of use stuff threw me for a loop. So I wrote a python app to help me out. I stuck it on github (You can read more here https://www.boards.ie/discussion/2058252242/calculating-the-best-time-of-use-tariff).

    You are the exact audience I was thinking of so quite curious if it matches your own figures...

    🌞4.55 kWp, azimuth 136°, slope 24°, 5kW, 🛢️10.9kWh, Roscommon



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  • Registered Users Posts: 65,410 ✭✭✭✭unkel
    Chauffe, Marcel, chauffe!


    You won't be self using anywhere near 100% of your production, not even with twice the size of battery you are planning, EVs at home and immersion diversion and a lot of self discipline. Couple of good days in a row, your cars will be full, your water hot, battery full and you will feed over 5kW directly to the grid for the whole day. Also your production estimate is way too high. If you had a 7.2kW inverter, you would make your 7MWh per year if the array is pure south facing in one of the better parts of Ireland for PV (like Dublin area, or the south east). But you are not getting a 7.2kW inverter presumably just a 6kW one. Also why buy Victron? They are overpriced for what they are and do not have Irish certification afaik


    As @KCross said, do the sums again and also without battery. With the generous FIT recently proposed, your pay back period is going to be shorter without one, unless you buy very well and DIY. Also with feeding in, by definition you will financially use every single kWh of your production



  • Moderators, Sports Moderators Posts: 19,029 Mod ✭✭✭✭slave1


    That’s exactly what I have, the ME is an inverter too. On a clear sunny day 15kW is possible, 2x6kW from PV inverters and 3kW from battery inverter. Enjoy an electric shower and plenty of headroom to charge an EV, work the oven etc

    My stuff for sale on Adverts inc. EDDI, hot water cylinder, roof rails...

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