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Should I add solar to a BER A3 house with ASHP due to high electricity costs

  • 01-11-2021 8:22am
    Registered Users Posts: 16

    Morning folks,

    We've been lucky to be able to move into a new 4-bed home (built in 2020). It's a modern design (BER A3 or A2 - I can't remember). It has good insulation, underfloor heating downstairs using an ASHP (Grant), and upstairs we have low pressure rads. All with mechanical ventilation. It sounded great on paper .... with us having come from drafty old houses in the past!

    The reality is that we're stunned by our electricity costs. Through the colder months of the year we're paying around 400 - 500 euro every two months. We've the target temperatures set downstairs to 19 degrees, with upstairs only varying that figure by a couple of degrees over the day. The water tank is set to 45 degrees C. I'm switching energy supplier each year, and currently on a dual fuel deal with Energia. Example bills received in Dec last year were 2266 units consumed, and in Feb of this year 2762 units consumed.

    Is this just the reality of air source heat pumps? Should I be expecting those sorts of bills - reading other threads here, possibly so. We have been thinking about investing into Solar PV Panels, or Solar Tubes to off-set our electricity costs. We're not planning on leaving this home, but we don't qualify for any grants - meaning this would be a massive investment for us. But maybe it's the right thing to do, we're not sure. 50% of the roof does face south, so it's in a good position.

    If I ask suppliers, they'll want to sell me on the idea. I'm hoping folks here might give me a more balanced opinion?!



  • Registered Users Posts: 33,058 ✭✭✭✭Penn

    You electricity bills may be high, but that's because you're not also paying for another fuel. ASHPs count as renewable energies because they create at least 2.5x more energy than they use.

    You could install solar panels, but it could be up to 10 years before you start to see any profit/payback from it to offset the installation costs. If you're sure you'll be in the house long-term, it's definitely worth considering. I'd go with Solar PV panels for electricity supply rather than tubes for water heating, it'll work better with your existing setup.

    But like I said, the initial costs and payback period, coupled with the minor effect it'll have on your house's BER and house value, means it's only really worth it if you'll be in the house for at least the next 15-20 years to really find any benefit.

  • Registered Users Posts: 36 D.flynn

    not sure if my input is worth anything, but here goes.

    Disclaimer, I don't have either of these technologies, but as an electrician, my 2 cents may be worth something. (please correct me if I'm wrong as I'd like to learn also)

    I've wired what I consider 2 types of ASHP, 1 that heats up an external hot water cylinder and one's that have the hot water storage integrated and from what I've been told, both types always prioritise maintaining hot water.

    my concern with ASHP's is that they are normally 6Kw + and that this needs to run in order to heat the hot water storage. During the night, this isn't so bad as you're on a reduced rate, but during the day it can be quite expensive.

    If the HP supplies an external cylinder, then having a 3kw immersion installed in that cylinder would seem more cost-effective to run than the HP.

    can anyone tell me whether I'm right or wrong on this ?

  • Posts: 0 [Deleted User]

    Sounds like a similar set up but in since early 2019 and never had a bill over 350. We keep thermostat around 22 in winter months. Rarely vary temperature. With EI from the start. Ours is 4 bed semi D <130sqm.

  • Registered Users Posts: 3,205 ✭✭✭cruizer101

    How does it compare to your normal usage? How much extra are you spending over the winter? Electricity bills do go up over winter anyway even if heating isn't part of it.

  • Registered Users Posts: 18,776 ✭✭✭✭Del2005

    Keeping your hot tank at 45C might be good for the pocket but it's not a good idea to store water at that temp, it should be >60C

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  • Registered Users Posts: 2,344 ✭✭✭bullit_dodger

    I'd echo what cruizer mentioned. You need to definitively find out what your usage is. The "best" way in doing that is investing in an energy meter , something like

    Efergy E-Max Kit (1 CT Sensor 12mm) : DIY & Tools

    Where you can turn things on/off and look at the usage to determine what is using what. But even going old school, you can simply look at number on your meter and then looking again in 24 hrs and you get your rough amount used per hour. Then turn off (and leave off) the heat pump for 24 hrs and perform the same experiment. You need to do it for a few hours as turning it off for a few hours at night would be a different load than a few hours at daytime (where the ambient temp is warmer - it may have less work to do)

    Your hunch is probably correct though that it is the Heat pump, but what you may find though is that there are many appliances eating leccie parasitically that you aren't aware of. It will at least give you a percentage of consumption which is the HP.

  • Moderators, Home & Garden Moderators Posts: 5,520 Mod ✭✭✭✭graememk

    Solar won't offset much of the cost of the heat pump. As when you need the heat pump it's usually winter!.

    Solar is generally a good investment, as long as you don't over pay! Have a look at the Pv quotes thread for an indication of how much a system would cost.

    Also look into getting a energy monitor

    for the house, it will give you a profile of when your power is being used. It might be beneficial for you to be on a day/night tariff.

    As for the hot water tank, that's fine. Heat pumps normally boost the tank to 60+ once a week to prevent legionella.

    I was running napkin math on another thread comparing heat pumps to oil. And the "average" oil usage is about 2500L/ year. Current price is 85c which is just over 2k a year.

    How come you have a dual fuel bill? Do you have gas just for a hob?

    The ratings of heat pumps are the heat output of them not the actual power consumed (I'm sure there's ones where the input is 6+kw too)

    But with heat pumps they have a COP (coefficient of performance) from 2.5-4 (depending on how hot your looking to heat) - that means for every kwh of electricity you put in, you get 2.5-4kwh of heat out. An immersion is just a straight 1-1 conversion.

  • Registered Users Posts: 16 chrisjcbt

    wow - thank you so much for the feedback!

    We do plan on being in the house for the next 20+ years (and beyond all being well). So solar (even without grant support) could make sense. cruizer101 you raised a point - in the summer I see roughly half those costs. For example our August bill, covering the 2 months prior had 1394 units consumed.

    Graememk - you're spot on, we are on a dual fuel contract because we have a gas hob and one gas fire in the house.

    We'll obviously have less solar in the winter, so it's not like the PV Panels will replace the need to use the ASHP right? We'll still need to run it for heating the home in Winter. I guess I'm never going to see the electricity rates drop to say 100 euro a month - even with PV panels?

    I have been clamping a number of the bigger circuits, and it's definitely the ASHP using the majority of the power draw. We've had Grant out many times to inspect it, and they say nothing is wrong.

    There is one point that caught my attention, should I be setting the water tank to around 60 degrees? The thermostat on the tank is set to 45. I was worried that if I set it to higher then it is going to keep calling for heat from the ASHP, increasing my costs even more. But as D.Flynn says maybe it is better to have the immersion inside the tank bring that temp up. I'll have to check what the thermostat controls - ASHP or Immersion.

  • Registered Users Posts: 2,126 ✭✭✭SD_DRACULA

    For winter unless you have a massive system of over 10kw, expect generation to be around 100-200kwh (if even) from November until March

    Can still be worth it long term for hot water in summer, also if you have an EV.

    I suggest to go to: put in your address, house orientation and system size and it will give you a graph with the estimate production expected.

  • Registered Users Posts: 2,344 ✭✭✭bullit_dodger

    Some rough math though. You mention your bill in Aug had 1394 for 2 months. So dividing that 60 (days) you get 23.23 units/day. Let's call it 24 units? So your "base load" is 1kw/hr?! That's pretty high for August when your Heat pump would be off, right? Or are you still using it for hot water?

    Something doesn't seem right there from the math. You have some heavy use going on there which considering it was summer time it's probably not the HP, like your doing a lot of baking, or washing with tumble dryer.....or something.

    That said, many of us have systems here which would regularly generate 20-30 Kw /day in the summer months (May-Aug), so you should be able to cover most of that 23units/day with solar in the summer and be left with a small import .... and of course the "standing charges"

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  • Moderators, Home & Garden Moderators Posts: 5,520 Mod ✭✭✭✭graememk

    In the summer, the panels will run most of your daytime electric, The payback of a battery system then is getting better, (without a grant). The grant helps things a bit.

    The Monthly solar performance thread, (Now that is November,) is a hot topic, and I try and work out what im actually saving with solar as the months go on. - I do have quite a large array, with a decent battery. I am running the house and a farmyard off it.

    I dont doubt that the Heatpump is the biggest energy user. The energy meter is to tell you the actual profile of your use, eg, would a day night meter be more beneficial to you. - Remember you dont have a big gas bill (or oil). <I done some rough napkin math comparing a high temp heat pump vs an oil burner. Gas is billed in kWh, so no conversion necessary. maybe the efficiency would be in the 80-90% mark too.

    You have the low temp rads and underfloor heating, your dealing with a low temperature heat pump and they have COP of 4+, so for every kwh of electricity you put in, you get at least 4 kwh of heat.

    Dont worry about the Hot water, The grant heatpumps have the weekly boost to 60C to prevent legionella.

  • Registered Users Posts: 10,415 ✭✭✭✭the_amazing_raisin

    Do you have the heating or hot water on a timer? If so then I'd recommend switching them to on all the time and control the heat with the thermostats

    The issue with using the heat pumps on a timer is that they take some time to heat everything up. If they take too long they might start using their backup heater to boost the temperature, which will cost you lots of €€€€

    FWIW, were in a similar type of house and our electricity bill is in the order of €2k per year. But that's with 2 electric vehicles in the mix as well, so I'd say you're definitely seeing too much consumption

    As for the question of whether you should put solar panels on your roof, I'll refer to this handy flowchart

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

  • Registered Users Posts: 16 chrisjcbt

    The downstairs thermostats are basically set to the same temperature, 24x7. Upstairs is basically the same, but we up the temp by a couple of degrees close to the kids bedtime. So I wouldn't say things are on a timer, in that there is no time where the heating would not be able to come on if it didn't need to call for heat.

  • Registered Users Posts: 3,428 ✭✭✭John.G

    You averaged 46.8 kwh/day, 2 month period Jan/Feb. and 22.5kwh/day 2 month period July/Aug, difference 24.3 kwh/day which, IF you generated your HW from the HP in both cases can be allocated to heating. If the HP water temp is/was kept to 45C then a COP of 2.5 should be reasonably achievable so your heating requirements were 23.4*2.5. 58.5 kwh/day or 2.44 kwh/hour running 24/7 or 4.88 kwh/hour running 12 hrs/day.

    DHY heating, the cheapest way to heat the water is to run the HP at 45C which will give water at 40C and just boost the whole cylinder from 40C to 60C once/week for legionella protection with a electric immersion.

    If your HP has a poor COP of 1.5 or so (at 45C) then one the main culprits can be defrosting which if not controlled properly can destroy the COP, some simply used a timer. others measure the deltaT across the evaoprator and carry out the necessary defrosting based on this. I would make enquiries about your HP defrosting methods if you still think that your consumption is excessive or post make/model of your unit here.

  • Registered Users Posts: 5,368 ✭✭✭JimmyVik

    OP, try doing this and see what happens.

    Friend of mine moved into an a rated house with ashp around 4 years ago. His electricity bills were similar to OPs.

    A couple of years ago he decided to turn off the heat pump.

    Got instant shower and instant hot water system for taps.

    Then he put electric panel heaters in the rooms with programmable thermostats.

    His electricity bill went from average over €200pm to less than €100pm.

    BEcause its so well insulated the heaters hardly ever have to be on long in the rooms. When they reach the desired temp they switch off and then back on when the temp goes lower. He can set each room for a different temp at different times of the day. eg bedrooms 16C day time, 19C all night. Kitchen and living room 21C when daytime and off at night. I always found his house nice and toasty.

  • Registered Users Posts: 3,205 ✭✭✭cruizer101

    That doesn't really make sense.

    Electric heaters put 1 unit in get 1 unit out, heat pump put 1 unit in and get 3 units out.

    If it is so well insulated the heat pump should have worked fine, when rooms get to temp and return to pump reaches a threshold it would turn off. Even if it was heating a full tank compared to just what was being used I can't see it making that much of a difference.

    I suspect there was some other issue there if the bill dropped that much, even if heat pump was undersized and was struggling you should still get better than 1:1 ratio.

  • Registered Users Posts: 10,415 ✭✭✭✭the_amazing_raisin

    Do you mind sharing what model heat pump you have, maybe we can get more info?

    From the bills you're posting, it sounds a lot like the auxiliary heater is being used, which could be indicative of a configuration issue

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

  • Registered Users Posts: 36 D.flynn

    whilst reviewing one of the solar threads, I found this entry from user stiofan

    he basically says that having an a3 rated house will exempt you from solar grant. might have some impact on your decision.

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,039 Mod ✭✭✭✭Jonathan

    Grant is based on year of construction. i.e. built and occupied before 2011. No reason why someone who built a house to A3 standards prior to 2011 can't apply, but they would be very rare, and someone of that persuasion would likely have already added solar PV.

  • Registered Users Posts: 16 chrisjcbt

    The ASHP we have is a Grant Aerona3, I believe it is the 10kW version (but I would need to check). The sq/ft on the house is 2,380. Does that help?

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  • Registered Users Posts: 3,428 ✭✭✭John.G

    Your house has a BER of A2/A3 say 50kwh/M2/annum = 50*220=11000kwh/annum= 30kwh/day but this time of year maybe allow 50kwh/day for heating. If you allow ~ 15kwh for normal usage then HP output (C.heating) = ~ 35kwh, with a COP of 2.5 = 14kwh so your daily consumption ~ 29kwh.

    Suggest monitoring your daily elect consumption for a few days, this might give you a better handle on whats going on.

  • Registered Users Posts: 2,344 ✭✭✭bullit_dodger

    +1 John.

    Also, I mentioned it earlier, but an average consumption of 1Kw/hr in the middle of summer (where your HP would be switched off?) sounds off to me. Unless you got some bitcoin rig or two chuggin' away? Not saying that your HP isn't a huge drain, but I also think that you have some other utilization that you may want to account for.

  • Registered Users Posts: 3,428 ✭✭✭John.G

    I also see that a house should have a HLI (heat loss indicator) of 2 (W/Kdeg.M2 floor area) or less to make it suitable for a HP. By my calcs, with a ambient of 5C and house temp of 20C (deltaT of 15C) then a house with floor area of 200M2 will require 2*15*200, 6000watts or 6KW, does this sound correct?. I read somewhere that this equates roughly to a BER C1 rating of 150kwh/M2/annum or 30,000kwh for a 200M2 house, These numbers seem extraordinarily high, have you any comment on this??.

    The attached Spreadsheet might be of some aid to navigation. Posted twice but can't remove, values in yellow may be changed.

    Post edited by John.G on

  • Registered Users Posts: 1,470 ✭✭✭MAULBROOK

    Yes the grant helps but the grant also costs. The SEAI requires certain equipment and paperwork that is just not required and cost money.

    Get a quote and run the math's

  • Registered Users Posts: 107 ✭✭Coltrane

    Your bills look much too high. Mine (period house, partly but by no means fully insulated, air-source HP) are much lower (if I disregard generation from our solar PV).

    Possible sources include a settings issue with your HP that means its immersion is on unnecessarily, an issue with its thermostats (these are often very cheap and unreliable accessories) or an issue with your insulation/air tightness.

    On our HP we can see the number of hours/kWh that the immersion has been activated.

    Cross-check the temperature according to your HP's stats against another stat/weather forecast.

    A thermal camera or even cheap heat gun from Amazon could help you find the issue with your insulation/air tightness.

    Solar PV is a great investment from the point of view of climate change, but obviously won't help all that much during the darkest months.

    Good luck!

  • Registered Users Posts: 16 gidxl03

    I had a 2012 C3 BER and I just installed 6kWhp + large battery. Annoyed me greatly that I had to get a new BER even though the old BER was still valid(10 year lifespan). Today (12 Jan 2022) was a sunny day, and am pleased that it generated 9.3kWh, so my house was effectively off grid from 10am to 4pm and the 6kWh from the battery will power the house from 4pm to 11pm. My 6kw HP has a COP of 3.4 (easy enough to calculate) so gets about 19kWh out, ran for 4 hours last night (half price electricity) so used 24kWh. If you account for the half price rate, the solar generates about the same value of electricity that the HP uses. On the usual overcast days, since Christmas it only generaets about 5kWh but still impressive considering that you can't see the sun behind the clouds at it is still generating 1kW.

    Anyhow, main point is that my BER assessor advised that there is a discussion between the gov and the SEAI bureaucrats about doing away with the need to have a C3 BER before getting the solar grant. A kWh of renewable energy from a G BER is as good as an A BER when fed into the grid. SEAI is resisting all logic as usual so we will see who wins out in the next few weeks. I know of several houses that will or will not get solar depending on the outcome, alas too late for me. One house would have installed solar even if there was no grant, but when they learned that they didn't qualify for the grant are just waiting until SEAI finally understand that there is a climate crises.


    • My battery will only output 4.2kW of power so if the 6kWh HP is running during an overcast day in winter, some power is still pulled in from the grid.
    • Am considering installing a second array of solar and will then need to dump power in the summer (limit for export to the grid is 6kW). I know that home wind turbines dump power using a simple heater but none of the solar suppliers that I spoke to had any experience of this. I have one EV, considering a second so have plenty of use for the kWh's. Am thinking that over-specing will become more common as the price of PV continues to drop.

  • Moderators, Home & Garden Moderators Posts: 5,520 Mod ✭✭✭✭graememk

    It's already announced that the BER is going, and it's been extended to houses before 2021.

    When it actually comes in, we don't know yet.

    Solar doesn't need to dump power. The inverter just "generates" less from them it's not like wind where the power has to go somewhere.

  • Registered Users Posts: 12,006 ✭✭✭✭KCross

    My 6kw HP has a COP of 3.4 (easy enough to calculate) so gets about 19kWh out,

    Does it really use 6kW when running?

    Are you sure it’s not 6kW output, instead of input?

    6kW input is a large HP!

  • Registered Users Posts: 1,697 ✭✭✭poker--addict

    How do you know pump COP?

    What figure dictates expected KW/ day for a pump?


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  • Registered Users Posts: 7,276 ✭✭✭kenmc

    It should be quoted for the make and model in the documentation. Usually reduces as temp drops,and they quote COP at a couple of temperatures


    specifications section