Can Solar do it all

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.

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

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.

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🤣

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.

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

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! 😛

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.

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.

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.

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.