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Can Solar do it all

  • 23-02-2022 1:43pm
    #1
    Registered Users Posts: 5,672 ✭✭✭ seannash


    Hi,

    We will soon be starting a complete renovation of an old Georgian house and it got me thinking about a Solar set up.

    From what I understand I can have the panels potentially generate electricity for the house, fill up a battery and charge a car. All sounds great but I cant figure out how/if it could potentially heat a home.

    What heating setups are available using solar. I've thought electrical underfloor heating with supplementary electric heaters but my concern is that if I cant generate enough electricity to power this then heating a home with mains electricity will be very expensive in comparison to gas.

    Heat pumps might be a solution but I've heard mixed reports about them so unsure if it would do the job also.

    Has anyone got solar doing everything for them currently?



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Comments

  • Registered Users Posts: 3,725 ✭✭✭ Dakota Dan


    Heat pumps cost 15-20k and old houses need to be retrofitted to use them so the cost rises considerably. The average cost of heating a house in Ireland is €800/year a heat pump will only save €300/year so there’s a huge payback timeframe. Also the heat pump only lasts7-9 years when it needs replacing something that the people touting them won’t tell you.



  • Registered Users Posts: 2,124 ✭✭✭ bullit_dodger


    It's a nice idea. I'd a similar thought myself before I got my installation in, that the solar panels could do everything. Power all my computers, do the washing, heat the house and eventually fuel the car once I get an EV.

    The good news is that the reality is that is can..... but only for about 6-7 months of the year. Panels as you can imagine work best with direct bright sunshine. A bit like we have today in Dublin. Sadly in winter we get multiple overcast days where the panels (even if you have a shed load of them) are just not capable of absorbing enough power to keep everything running.

    It's the dark cold days in December/January where you use the most power for lights/heating etc, and this is the times of course when your panels operate the lowest. To give you some context, I use about 30 units/day. Average solar output for my installation in Dec = 1.88 Units/day, Janurary = 3.19 units/day

    that said, once March comes about, you can get very high % of your power from solar and that will run through until oct.



  • Registered Users Posts: 5,672 ✭✭✭ seannash


    Thanks for the reply. I can wrap my head around how I would use solar for powering the house and even in winter I'm happy to run it off a battery thats charged on the overnight rate but its the heating thats really not clicking for me. I guess though as it would be the colder darker months where I'd need the heat electric heat isn't a good idea as it would solely rely on the grid.

    Anyone thought about a windturbine for the darker months?



  • Registered Users Posts: 3,930 ✭✭✭ graememk


    You may be eligible for a deep retrofit grant!

    Now is the time to get stuff done, Insulate, Under floor heating no matter the heat source (So you can have more efficient oil/gas/heatpump due to lower flow temperatures)

    As for running it from solar. the gotcha there is when you need heat, its winter, the weather is poor, sun is low in the sky and the days are short.

    Its not impossible but you would need a lot of solar.



  • Registered Users Posts: 5,672 ✭✭✭ seannash


    I think that cost is for the ground source heat pumps right?

    I'm not sure we can use the old averages for heating a home as more and more people will be working from home now all year round and as a result the heating will be on more but I have heard they are simply not worth the upfront costs to do it.



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  • Registered Users Posts: 5,672 ✭✭✭ seannash


    I think they've have stopped that grant right?

    I think even the battery storage system might help with running it on electric in winter but its probably still a lot more expensive than gas. Might have to be a mixed system which I really didn't want



  • Registered Users Posts: 1,261 ✭✭✭ Gant21


    I have heat pumps 15 years in service and still working correctly. Where are you basing your facts on? Googling the interweb is unreliable.



  • Moderators, Education Moderators, Home & Garden Moderators Posts: 7,711 Mod ✭✭✭✭ Jonathan


    @ELCAT2009 might be able to here as someone with a HP + PV.



  • Registered Users Posts: 8,699 ✭✭✭ the_amazing_raisin


    So we're an all electric house (heat pump, electric cooking, 2 EVs) insulated to A3 standard. We're currently consuming about 12,000kWh from the grid per year, of which about 4,000kWh is the 2 cars. Hopefully that'll give you a starting point regarding consumption.

    Even with all of that I calculated that I'm saving quite a bit versus oil or gas heating and an ICE car

    I don't have solar yet but I'm very interested, especially given the current lunacy in the energy markets


    I did the calculations on solar PV and found that I can't meet the demand all year around, it's just too much and there's too many overcast days in winter


    However, I reckon I can reduce my bill by around two thirds with enough PV and batteries. Even more if there's a decent FIT

    If you do go ahead with the solar installation, here's some tips:

    Don't factor in the EVs when calculating battery size, it just doesn't make sense to charge an EV from the house battery

    Install as many panels as you can, easier to add batteries than panels later


    Look into diverters, devices which use excess solar energy instead of sending it to the grid. One example is that you can get EV chargers which will divert power to charge the EV instead of losing it to the grid

    Remember you can charge your house battery from the grid during the night rate. So if you can size it correctly you can move any grid consumption to cheaper rates. Factor this into your savings



  • Registered Users Posts: 5,727 ✭✭✭ Ubbquittious


    I think the general consensus is that small wind turbines are pure cat. If you can put one up thats 15m or so high and generates a good few kw it might be worth it



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  • Registered Users Posts: 3,725 ✭✭✭ Dakota Dan


    A local business had to replace theirs after 9 years the installer said they usually go around 7 years. If you were using Google they’d tell you they’ll last 50 years but time will tell either way it’s a big cost to replace them for the energy they save.



  • Registered Users Posts: 1,261 ✭✭✭ Gant21


    Ironically google does say that, the life span of a heat pump depends on various factors.



  • Moderators, Education Moderators, Home & Garden Moderators Posts: 7,711 Mod ✭✭✭✭ Jonathan


    I don't want this thread to descend into a pro and anti heat pump thread. @seannash has come looking for advice on this situation so let's contribute on that basis.



  • Registered Users Posts: 1,261 ✭✭✭ Gant21


    To be 100% accurate to the op are they hoping pv roof panels will do their electrical requirements.

    If that is their query then the answer is no.



  • Registered Users Posts: 186 ✭✭ ELCAT2009


    Yes I have heat pump now for almost 12 years but Pv just since Nov 2021 so early days yet on the pv side! Also got an EV in Jan 2022 so lots of changes in my Power usage for the year ahead that i plan to monitor monthly for year ahead. So this time next year ill know more! Very happy with my heat pump for last 12 years. 2900 sqft house and average annual esb cost has been €1400 approx using around 9-9500kwh. For anyone considering a heat pump my advice would be house will need to be A3 rated ideally with great insulation and good airtightness. Underfloor heating works best with heat pump and heat recovery ventilation. Back to the original question can solar do it all, in my opinion you won't be able to provide all the power you need without oversizing dramatically but then you will be exporting significantly in summer. I have gone with 6.2kw system with 4.8kw battery which I think will be around the sweet spot of balancing my usage and pv production and storage. Time will tell 😀. Right now I'm running heat pump primarily at night on night rate. In few weeks time I expect I'll be changing the times to run during the day to heat my hot water to use up some of the solar pv. Hoping in the really good days my EV will soak up the excess...hopefully will be days I work from home🤣



  • Registered Users Posts: 11,697 ✭✭✭✭ KCross


    From what I understand I can have the panels potentially generate electricity for the house, fill up a battery and charge a car.

    Yes, you can do that. The panels generate electricity and it is fed to your house and you can use that electricity any which way you like. How much it generates is dependent on the number of panels and whether the sun is shining.


    All sounds great but I cant figure out how/if it could potentially heat a home.

    As others have said, in reality it wont do that. You need heat most when the panels are generating the least (i.e. night and in winter).

    Therefore, you will still need a primary heating system of some kind, whether thats a stove, oil, heat pump etc. Even A-rated houses need a boost of heat and if the sun isnt shining you need a plan B.


    Has anyone got solar doing everything for them currently?

    If you have a heat pump the planels can/will provide some of the energy required to run it, but it wont come anywhere close to "doing everything". Its technically possible but you'd need a large number of panels and a massive battery system to take you through the multiple days that you will have no sun shining. Its just not practical in terms of "doing everything". You'll still need a primary heat source.


    Heat pumps might be a solution but I've heard mixed reports about them so unsure if it would do the job also.

    There were lots of cowboys installing HP's and a badly installed HP will cost you money in the long run. Get a reputable installer with years of experience and verifiable references and a HP will serve you well. There will be negative stories about high energy bills and units needing to be replaced in the same way you will always have people saying a particular car "broke their hearts" while thousands of others have no issues with the same car.

    A good quality HP with a properly designed/sized install will work for decades. HP's are not new tech. They've been around for decades in countries much colder than ours. Reputable installer is the key!

    Of course, they can go wrong and need some maintenance. There are circulation pumps etc that can/will fail but you should not need to throw the entire system out after 10yrs unless its a cowboy install.

    The key benefit of a HP (with underfloor heating) is that you get much more comfortable living conditions with steady temps 24/7/365. Its not just a money decision in my opinion. Its comfort too. And as stated, your Solar panels will marginally help on the running costs but I wouldnt factor that in, just think of it as a bonus on the few days where it is helping to run the system.


    We will soon be starting a complete renovation of an old Georgian house

    Have you employed any company to look at your insulation and heating needs and come up with a plan for you?

    e.g. uValues, windows, doors, insultation, air-tightness, heat demand figures, Solar, water etc etc. A few quid spent on that now by a professional will be money well spent as it will be what you are living with for decades to come.

    Insulation and decent doors and windows are a must-have, regardless of what you decide in terms of heating/Solar.


    Good luck with the renovation. Im sure a Georgian house will give you plenty surprises as you work through that!



  • Registered Users Posts: 11,697 ✭✭✭✭ KCross


    Right now I'm running heat pump primarily at night on night rate. In few weeks time I expect I'll be changing the times to run during the day to heat my hot water to use up some of the solar pv.

    Is that practical though? If its a crude timer based switch you are making you will be hoping that the sun shines at exactly that time everyday. That wont work in reality. You'll get free water some days and double priced water the next so overall you wont win.

    Unless you have some additional smarts like a Solar PV hot water diverter, in which case you wont really be switching the heat pump to day at all, you will simply be turning off the heat pump from hot water generation and letting the Solar excess do it via the diverter. If the sun doesnt shine you dont get hot water though so that could be an uncomfortable discussion with the wife that day! :)

    Its not as simple as it sounds so I'm interested to know how you think you will achieve that without looking at forecasts and the sky everyday and continuously adjusting things... which will get boring very quickly and not really a good use of your time.

    Also, the cost of heating hot water at night with a heat pump costs pennies.... its not really worth the effort of continuously trying to second guess things for a few measly cent.

    Much better to use the Solar excess for charging the car, imo, thats if the car is around by day.



  • Registered Users Posts: 186 ✭✭ ELCAT2009


    Yes that would be completly impractical if you had to be manually turning on and off every day depending on sun etc. So this is my logic and what im planning to do! So I have a 4.8kw battery. So by 12noon I'm expecting my battery will be at least 50% full or more even on days without blazing sunshine. Then I will have the heat pump set to heat the hot water for up to 2hrs even though I expect it will have heated the tank fully in 1.5hrs. Even if the sun isn't shining my battery will be enough to run the heat pump (possibly topped up with live solar pv). The heat pump will give me 3kws of hot water for every 1kwh of solar so 3 times more efficient than a diverter. The heat pump will also be a little more efficient running in day time with higher temps air temps than at night. The ev will just be 1kwh for 1kwh so doesn't matter if its charged day or night on that front so slightly more efficient to use heat pump 1st for excess solar followed by ev charging. It goes without saying charging the batteries in the house come before both of above! Hope above makes sense. Will see how it works in a few weeks time when I charge over my heat pump from night running to daytime.



  • Registered Users Posts: 8,699 ✭✭✭ the_amazing_raisin


    Just use a diverter instead which does it automatically, like this





  • Registered Users Posts: 8,036 ✭✭✭ Markcheese


    How does a Georgian house and a deep retrofit combine ?

    Because a heat pump will cost a fortune in a leaky old house - and you'll still be freezing - my sister has an old house , and a air to air heat pump , and a couple of stoves , and it's cold ..

    Slava ukraini 🇺🇦



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  • Registered Users Posts: 11,697 ✭✭✭✭ KCross


    So this is my logic and what im planning to do! So I have a 4.8kw battery. So by 12noon I'm expecting my battery will be at least 50% full or more even on days without blazing sunshine. Then I will have the heat pump set to heat the hot water for up to 2hrs even though I expect it will have heated the tank fully in 1.5hrs. Even if the sun isn't shining my battery will be enough to run the heat pump (possibly topped up with live solar pv).

    I’m still skeptical! Let me see if I can punch a few holes in your theory! 😀


    even if the battery is fully charged does it have the electrical spec to be able to deliver enough current to drive the HP?

    if it does, for how long? And is it long enough for a full water cycle?


    what if the battery isn’t charged, what will you do then? Are you going to rush over to the HP and reprogram it for that day?


    what if you need water in the morning for showers. Are you going to be looking at forecasts each day to decide how your HP is programmed for the day ahead?


    If you get it wrong even on a few days it will be costing twice as much as it should and any savings you made other days will be wiped out you need to get it right everyday. That’s a tall order without spending alot of your personal time watching the weather and programming your HP.


    I just think it’s not practical to be second guessing the solar excess. Our weather is just too varied, even in summer. You need a fully automated system that doesn’t leave your wife in a cold shower! 😛



  • Moderators, Education Moderators, Home & Garden Moderators Posts: 7,711 Mod ✭✭✭✭ Jonathan


    As @the_amazing_raisin has already pointed out, the Eddi can already do this. The relay board can be integrated with a heat pump to call for heat above certain surplus thresholds. See application examples 12, 13 and 14: https://myenergi.com/wiki/eddi/application-examples/



  • Registered Users Posts: 11,697 ✭✭✭✭ KCross


    I know a diverter can do it. I’m just saying doing it the way ELCAT suggests is rather difficult.


    the Eddi isn’t without its issues too due to its high price.



  • Registered Users Posts: 186 ✭✭ ELCAT2009


    I hope I don't jinx it but I reasonably confident my plan will work!

    I'm confident the battery will run the heat pump. Battery can output 2.5kw and the heat pump will pull about 2kw running during the day. It will heat my 300l tank in 2hrs or less. Most of the showers etc are at night in our house but I expect there will still be enough hot water in the morning. I expect this because currently I heat my water from 11pm to 1am and still have enough hot water for showers at 9pm ie 20 hrs after hot water has finished heating.

    This year will be a learning curve for me in terms of my power usage with new solar pv and the ev car so I will be monitoring it closely and making changes where I think they will be more cost effective. Once I get a handle on how im using my pv to maximise its use i dont expect to be making changes to heat pump times. Come back to me in 6 months and see how I get on🙂...wish me luck🤞😆



  • Registered Users Posts: 11,697 ✭✭✭✭ KCross


    one last point, you are only saving night rate, not full day rate, when you use your battery to heat the water.


    you will have a dead battery at the end of the hot water cycle and hoping the battery gets charged up again to get you to the start of night rate. That will work fine some days and not others. Again second guessing weather and when you get it wrong some days (and you will) it will negate savings you made other days .

    im not a battery fan but their strong point is that they allow you to displace expensive day rate, not night rate, so it’s questionable to move hot water to day, particularly with a HP


    I do wish you luck though. It’s a learning curve and different for everyone’s own circumstances.



  • Registered Users Posts: 2,124 ✭✭✭ bullit_dodger


    Question: Why do you heat your water from 11pm to 1am? Why not at (say) 6am-8am? It's still night rate of course and your heat losses would be less at 9pm that evening as the water would have had less hours for the heat to escape.



  • Registered Users Posts: 186 ✭✭ ELCAT2009


    Because I am using the heat pump to heat underfloor heating upto 8am to get the benefit of space heating during the day for as much of the day as possible.



  • Registered Users Posts: 2,652 ✭✭✭ yankinlk




    What is your base load? If the battery is chucking out 2kw for 2 hours to heat water... there is only 500w left for base... . .



  • Registered Users Posts: 186 ✭✭ ELCAT2009


    Around 400/500w. I think 2kw will be max heat pump needs, I actually think it will be more like 1.5kw. Also even on the dullest of days from late march i expect my solar will still be producing a minimum of 500w so between battery and solar pv I should have ability to pull 3kwh if needed and I only need 2 -2.5kwh.

    Just to clarify the whole point of me planning to move my heat pump run time to day time from night time will be use excess solar pv and prevent me dumping to grid for free. Charging of my battery will be first priority but I expect to have a full battery by middle of the day. I had thought i wouldn't making this change until late April but I've really noticed a pick up in solar pv yields in the last couple of weeks so I'm thinking now might be more like late March I could be in a position to make the change. As I said this year will be learning curve. Maybe it won't work as I think but I'm reasonably confident based on what I'm seeing so far in my pv yields and from what my heat pump uses energy wise.



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  • Registered Users Posts: 2,124 ✭✭✭ bullit_dodger


    Gotcha - and that sort of makes sense to me. However, to potentially improve your efficiency do you have control over the hot water aspect of things along with your Underfloor heating? As in can you set the hot water to only heat 6am-8am? Ultimately while people say ....

    "ohh but I get the hot water for free when I turn on the heating"

    in reality they don't. It still takes energy to heat water, and with losses for 6 hrs you have to pump a few 100 watts into that tank while your sleeping to keep it at temperature that you've set. Since your not using that water until 9pm the following night by all accounts, then you'd be better heating the water as late as you can on night rate.

    Overall, while what your proposing is a little odd, I don't see anything major wrong with your strategy. Well, my $0.02 anyway :-)



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