puntloos Posted May 30 Share Posted May 30 (edited) So, on good sunny days, I have a good amount of extra power left in my PassivHaus. I have a few options: 1/ Send it to the grid. Not the best value for my money but perhaps worth it 2/ Cool (or heat, I suppose, rare..) my 2 concrete floors with UFH Perhaps beyond normal parameters? 3/ Cool the warmer-than-average loft. This is the one I'm curious about - I have aircon in the loft, but we don't tend to go there a lot, it's storage. Does it make sense to aircon warm air that we don't care a lot about? The heat, or cold (passivhaus) wouldn't really escape that much, but would it also make the lower floors more pleasant? Or am I running a device (wear and tear) for no real benefit? 4/ Heat the warm water cylinder to (say) 65C? Free de-legionella I suppose Will a cylinder retain heat long enough for it to matter? ... others? And also, what to prioritize? Edited May 30 by puntloos Link to comment Share on other sites More sharing options...
SteamyTea Posted May 31 Share Posted May 31 4 hours ago, puntloos said: 1/ Send it to the grid. Not the best value for my money but perhaps worth it This one has the greatest utility value as your home is quite energy efficiency already. You don't mention charging and EV? 2 Link to comment Share on other sites More sharing options...
MortarThePoint Posted May 31 Share Posted May 31 I really like the idea of hydrogen generation (hydrolysing water) and storing that for winter heating. I looked into it a few years ago but the tech just isn't there yet. 1 Link to comment Share on other sites More sharing options...
ProDave Posted May 31 Share Posted May 31 Heat your domestic hot water is the easy and obvious one. It will reduce your HW bills to close to £nil for much of the summer. The next obvious one is use all your big domestic appliances like washing machine, dishwasher etc one at a time at around mid day. 2 Link to comment Share on other sites More sharing options...
Crofter Posted May 31 Share Posted May 31 28 minutes ago, MortarThePoint said: I really like the idea of hydrogen generation (hydrolysing water) and storing that for winter heating. I looked into it a few years ago but the tech just isn't there yet. How does the round trip efficiency of H2 compare to pumped storage? Link to comment Share on other sites More sharing options...
JohnMo Posted May 31 Share Posted May 31 8 hours ago, puntloos said: 1/ Send it to the grid We try not to don't get paid for it. 8 hours ago, puntloos said: 2/ Cool (or heat, I suppose, rare..) my 2 concrete floors with UFH We do cool as required in summer, if it's sunnier the house is generally warm enough it needs to be cooled - free cooling. 8 hours ago, puntloos said: 3/ Cool the warmer-than-average loft. Not sure about 8 hours ago, puntloos said: 4/ Heat the warm water cylinder to (say) 65C? We don't do legionella cycle, as we consume enough hot water not to require it. But we do heat the cylinder to 70 via diverter. Reduces or stops any requirements to heat via heat pump. Our primary excess goes to battery first. Link to comment Share on other sites More sharing options...
Crofter Posted May 31 Share Posted May 31 5 minutes ago, Crofter said: How does the round trip efficiency of H2 compare to pumped storage? To answer my own question, a quick Google suggests that pumped storage or compressed air offer around twice the round trip efficiency of hydrogen. And with much simpler technology. Obviously pumped storage is location dependent. I can feel a Heath Robinson project coming on... I've got land 50m above my house... 2 Link to comment Share on other sites More sharing options...
JohnMo Posted May 31 Share Posted May 31 16 minutes ago, Crofter said: pumped storage or compressed air offer around twice the round trip efficiency of hydrogen But does either work on a small scale? Link to comment Share on other sites More sharing options...
Crofter Posted May 31 Share Posted May 31 1 hour ago, JohnMo said: But does either work on a small scale? Probably not. I doubt anything involving hydrogen does either. Link to comment Share on other sites More sharing options...
JamesPa Posted May 31 Share Posted May 31 (edited) 11 hours ago, puntloos said: So, on good sunny days, I have a good amount of extra power left in my PassivHaus. I have a few options: Get an electric car and use the excess to charge it? I have had both 'free' (or almost free) motoring since mid May and 'free' DHW since mid April. Edited May 31 by JamesPa 1 Link to comment Share on other sites More sharing options...
Iceverge Posted May 31 Share Posted May 31 Take up some kind high electricity hobbies. Maybe smelt some steel or do some evaporative desalination. 1 Link to comment Share on other sites More sharing options...
Dan F Posted May 31 Share Posted May 31 (edited) Mine bitcoin? Seriously though, don't you get 15p export? It's no a huge amount but if house is already at good temp, hot water tank full and car and batteries both charged, exporting at 15p is as good as anything isn't it? Edited May 31 by Dan F Link to comment Share on other sites More sharing options...
Nick Thomas Posted May 31 Share Posted May 31 I export the excess at ~15 or 25p/kWh (octopus flux). That builds up credit that pays for a good chunk of what I import in winter. Totally worth it. Link to comment Share on other sites More sharing options...
JohnMo Posted June 1 Share Posted June 1 9 hours ago, Dan F said: Seriously though, don't you get 15p export? A fuller answer Only with a smart meter or 4.5p without (or with a smart meter that doesn't communicate). And you do an MCS install or are accepted on to the octopus trial and have also paid a big chunk of money over to them and possibly a structural engineer for the privilege. I just chuck the excess into my battery, when that's full hot water. If the sun's out the ASHP is cooling for free also. Link to comment Share on other sites More sharing options...
puntloos Posted June 1 Author Share Posted June 1 Absolutely, I have octopus flux and in many cases I get 15p or even I think 30p during the peak (4pm-7pm). But my gut feeling is that my house "energy loss" (aka U value, really), not to mention the ASHP (AC and water/ufh) efficiency is 300% at very least so anything I can heat or cool is very likely going to yield me more value-for-energy. @SteamyTea Ah I completely forgot, yes I have an EV but don't use it a ton so often that's full too. In fact I'm actively considering building my own V2H system so my car battery can power my home. Nobody have any idea if I should cool my hot loft (even though I don't care it's hot?) Link to comment Share on other sites More sharing options...
Marvin Posted June 1 Share Posted June 1 (edited) 41 minutes ago, puntloos said: Absolutely, I have octopus flux and in many cases I get 15p or even I think 30p during the peak (4pm-7pm). But my gut feeling is that my house "energy loss" (aka U value, really), not to mention the ASHP (AC and water/ufh) efficiency is 300% at very least so anything I can heat or cool is very likely going to yield me more value-for-energy. @SteamyTea Ah I completely forgot, yes I have an EV but don't use it a ton so often that's full too. In fact I'm actively considering building my own V2H system so my car battery can power my home. Nobody have any idea if I should cool my hot loft (even though I don't care it's hot?) Being paid 15p to 30p is by far the best choice for energy you do not use productively. We have PV, EV and ASHP. When our PV is on our generation goes directly to the background demand from the house. Then if there is more it goes to the solar diverter and heats our 205litre hot water tank to 75C (meaning that it will be useably hot for about 3 days or mains charged if the ASHP is not on). Our tank has extra insulation just for this purpose. Then if there is a lot more the EV charger (3kW) will come on and charge the car. Then if there is anything left, it will go into batteries. This will power small things when the PV is not working but the batteries are charged enough. All the time the ASHP will use power when there is demand. When we have "generally excess PV generation" heavy loads are used. Also during sunny days with excess generation, we charge the household small rechargeable batteries and ride on equipment. We give the rest away. Edited June 1 by Marvin further thought Link to comment Share on other sites More sharing options...
SteamyTea Posted June 1 Share Posted June 1 56 minutes ago, puntloos said: Nobody have any idea if I should cool my hot loft (even though I don't care it's hot?) Would need some data about it. Size, U-value, temperature ranges and frequencies. Link to comment Share on other sites More sharing options...
puntloos Posted June 1 Author Share Posted June 1 (edited) 3 hours ago, SteamyTea said: Would need some data about it. Size, U-value, temperature ranges and frequencies. 54sqm usable floorspace, 2.25m ceiling height. 74m2 full space (we have a large hall 'gap' thats unusable but does contain hot air) - so perhaps 74*2.25 = 166.25 m3 air to heat/cool. Temperature on the hottest day in May went to 25.3C, normal days 24.0 cold day 23.0 U-Value of the roof: 0.094 (according to PHPP, perhaps use slightly worse value (0.1) instead.. Edited June 1 by puntloos Link to comment Share on other sites More sharing options...
JohnMo Posted June 1 Share Posted June 1 3 minutes ago, puntloos said: Temperature on the hottest day in May went to 25.3C, Our living room gets to those temps! That isn't even that hot Link to comment Share on other sites More sharing options...
SteamyTea Posted June 1 Share Posted June 1 5 minutes ago, puntloos said: Temperature on the hottest day in May went to 25.3C, normal days 24.0 cold day 23.0 1 minute ago, JohnMo said: That isn't even that hot Not worth the effort, open a shaded window. Link to comment Share on other sites More sharing options...
MikeSharp01 Posted June 1 Share Posted June 1 3 hours ago, Marvin said: ride on equipment Can we know more about what this comprises - bikes, scooters, rodeo simulators...... 1 Link to comment Share on other sites More sharing options...
puntloos Posted June 1 Author Share Posted June 1 1 hour ago, SteamyTea said: Not worth the effort, open a shaded window. Ah but the point is, I already have AC in those rooms, my question is if it's "thermally helpful" to cool it. As in, is any cooling I put into that room (at 300% efficiency) more value for my kwh than seling it to octopus? I can imagine two scenarios: A/ Cooling those rooms means the cold air will "by osmosis" trickle down into the other rooms downstairs (where cooling would be welcomed), or would somehow "cool the whole house" to some degree, which I care about if it's a hot set of days. B/ Cooling those rooms will only cool the actual rooms, and we don't care if they are a bit toasty so it's wasted effort. No meaningful "spreading around" effect. Link to comment Share on other sites More sharing options...
puntloos Posted June 1 Author Share Posted June 1 2 hours ago, JohnMo said: Our living room gets to those temps! That isn't even that hot Ah but if you're a finnicky posh human then of course 0.3C above 25C is an _outrage_ Link to comment Share on other sites More sharing options...
Andehh Posted June 1 Share Posted June 1 Hot paddling pools! On weekends when we have lots of sun, PV and an ASHP we turn the hot water on and use the DHW to fill large paddling pools and water slides with the hot water for the kids! Bath time outdoors. Two weekends we ago managed 1200L of hot water for less then £3 daily usage. Fun all day. 1 Link to comment Share on other sites More sharing options...
joe90 Posted June 1 Share Posted June 1 I remember years ago regarding solar thermal there were discussions about excess hot water in summer and I suggested plumbing it into a hot tub. Link to comment Share on other sites More sharing options...
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