Claire B

New solar & battery/ Tesla advice please.

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I've been in my new build home 3 yrs now and the amount of electric used is pretty high... 30,000kw p/a. It's just me and my son. Most of this I guess will be down to the space heating, ceilings are 6m high throughout  and possibly the AGA doesn't help. The house is 5,000sq ft single storey and electric is our only power source. I had a ground source heat pump system installed in the build and underfloor heating throughout. I thought this would mean low electric bills!

 

Now the world is falling to pieces I'd like some protection in the event of power outages and food shortages (want to know my fridges & freezers will be powered). I've had a quote for solar panels & Tesla storage battery. The solar installer recommended I have 20 Longi  370watt panels (they'll be ground mounted) giving me a 7.4kWp system for £7,700 plus Tesla battery storage at £8,500 incl vat. In the event of a power cut the battery will power one of the three fuse boards in the house, powering my 'kitchen end' of the house, fridge / freezer, lighting & plug sockets. I would likely have to turn off the AGA as this would use all the power so would have no cooking facilities (I'll buy a plug in electric hob). It would also leave me without heating and hot water. 

 

I would have thought it a good idea to power the heat pump as you get back 3-4 times the power it needs to run (thats my very basic understanding, I might be wrong)?

A local electrician told me he has a basic solar system that heats his hot water, again something to heat the hot water tank would be good, though if I power the heat pump I think that heats the hot water as well as the underfloor heating. 

 

Is there a better way of going about this? It would be pretty miserable without heat or hot water. I do have a wood burner but the room it's in is so big you have to sit next to it to feel any heat. 

 

Thank you. 

 

 

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WOW  30,000kWh of electricity per year.  If you pay the same as me (14.3p per kWh) that is £4290 pa.

 

That is FOUR times what our family of 3 spend in an all electric house.

 

Did the builders forget the insulation?  Something is not right somewhere?  our 4.5kW stove heats the whole house and you don't have to sit next to it to benefit.  Can you give some more details of the build?

 

Your (roughly 8kW) of panels will likely produce about 6000kWh of electricity per year, so even if your batteries let you self use all of that, it will only reduce your bills by about £850  That is going to take a seriously long time to pay for the panels and batteries, about 20 years, so does not make economic sense

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10 minutes ago, Claire B said:

30,000kw p/a

That is almost 3.5 kW of power on permanent (assuming your kw is really kWh).

 

Do a meter reading tonight at 8 PM, and another at 8AM, then another one at 8PM.

Post up the numbers as something does not seem right.

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22 minutes ago, ProDave said:

WOW  30,000kWh of electricity per year.  If you pay the same as me (14.3p per kWh) that is £4290 pa.

 

That is FOUR times what our family of 3 spend in an all electric house.

 

Did the builders forget the insulation?  Something is not right somewhere?  our 4.5kW stove heats the whole house and you don't have to sit next to it to benefit.  Can you give some more details of the build?

 

Your (roughly 8kW) of panels will likely produce about 6000kWh of electricity per year, so even if your batteries let you self use all of that, it will only reduce your bills by about £850  That is going to take a seriously long time to pay for the panels and batteries, about 20 years, so does not make economic sense

I pay more than that (Good Energy... I know, I need to switch)!

 

Builders / architects certainly didn't do something right! The house is very long so there's trace heating pipe along the hot water pipes so you don't have to run the hot water for ages on cold. i think this uses a lot of electric. I turned them off but its takes about 5 minutes of running cold water before any hot comes through so they have to stay on. Not very well designed. 

 

It's a converted nissen hut (steel frame, zinc clad) in a very windy exposed area so it cools down quickly. You can see it at www.saintsgreenplace.com 

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22 minutes ago, SteamyTea said:

That is almost 3.5 kW of power on permanent (assuming your kw is really kWh).

 

Do a meter reading tonight at 8 PM, and another at 8AM, then another one at 8PM.

Post up the numbers as something does not seem right.

I did this a few weeks back to see how low I could get it once my son was away on holiday. The day before he went (a couple of washing machine loads)  it used 64kw that day, next day 48kw then when I turned off the trace heating and AGA got it down to 32kw. Bear in mind this was summer so no heating on! 

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Posted (edited)
2 hours ago, Claire B said:

it used 64kw that day, next day 48kw then when I turned off the trace heating and AGA got it down to 32kw

kw, is really kW (1000 watts) and is power, or an instantaneous reading.

kWh (1000 watts, for 1 hour), is the energy.

 

32 kWh a day is still a lot.  Do you have a hot water cylinder, with an immersion heater, that is constantly on?

Even then, you would have to be using a lot of hot water every day.

 

Is there any chance that there is a wiring problem and you are supplying a neighbour.  The easy way to check this is to isolate your house at your consumer unit/'fuse box', and see if there is any movement on your meter.  If there is, then you are supplying something else.

 

2 hours ago, Claire B said:

I turned off the trace heating

What do these heat?

 

Where does the power for your sauna come from?

Edited by SteamyTea

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9 minutes ago, SteamyTea said:

kw, is really kW (1000 watts) and is power, or an instantaneous reading.

kWh (1000 watts, for 1 hour), is the energy.

 

32 kWh a day is still a lot.  Do you have a hot water cylinder, with an immersion heater, that is constantly on?

Even then, you would have to be using a lot of hot water every day.

 

Is there any chance that there is a wiring problem and you are supplying a neighbour.  The easy way to check this is to isolate your house at your consumer unit/'fuse box', and see if there is any movement on your meter.  If there is, then you are supplying something else.

 

What do these heat?

Trace heating wires run along the hot water pipes in the house to keep the water in the pipes hot so when I turn a tap on the water comes out hot instead of having to run it cold for 5 mins first. The house is 60m long so I do need these and they cost a bit to run (though I'm sure there could have been a better way of designing the system at design stage). 

 

I'll check that possibility this eve. (feeding neighbours house), I built three properties and sold 2. Coincidentally one neighbour was telling the other how low her electric bills were! 

I would consider myself a low electric user, I hang washing out to dry, and don't have a TV! The AGA is my only vice. 

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1 minute ago, Claire B said:

Trace heating wires run along the hot water pipes in the house to keep the water in the pipes hot so when I turn a tap on the water comes out hot instead of having to run it cold for 5 mins first. The house is 60m long so I do need these and they cost a bit to run (though I'm sure there could have been a better way of designing the system at design stage).

Decent insulation and a timed re-circulation pump would have done it.  All hot pipes need to be well insulated.

 

2 minutes ago, Claire B said:

Coincidentally one neighbour was telling the other how low her electric bills were! 

That should have been a warning.

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Posted (edited)

Given the size of the property, what's the size of the heat pump? a 20kW heat pump will be using 5kW of electricity on full steam and if you run it with all the doors open (as per pics), it could easily be doing that. A HP is more efficient than chucking direct electric at the problem, but not if just left on.

 

I'm tracking my consumption and our 5 bed farmhouse is currently averaging around 30kWh a day without any heating on! But we do charge an electric vehicle most nights which accounts for a decent chunk of that.  Immersion for water and electric cooking account for most of the rest.

 

The instantaneous and daily readings (particularly when it peaks and troughs) would be really helpful to understand where you're using the energy.

 

Edit- sorry I meant to ask- does the business/ retreat form a separate meter from the house or is it all one property?

Edited by Wil

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You need a serious think and investigation about lots of aspects of this house.

 

Do you have any details of how much insulation was put in when it was converted?  Is the neighbour with a low bill in another converted Nissen hut?

 

No 1 is ditch the trace heating system.  If it takes 5 minutes for the hot water to arrive, then the whole hot water system needs a re think.  Can you post a floor layout?  I suspect there may be e.g kitchens and bathrooms a long way apart, and you would probably be better with two hot water tanks close to the points of use to avoid the long runs.

 

The Aga.  Is that all electric and the sort that is always on?  they are a huge consumer of electricity. Seriously consider swapping that for a conventional cooker, even a range style cooker that just uses heat it needs when it heats it.

 

We are in still in summer (average 12 degrees here for the last 24 hours so you might not think it) so you should not be using much electricity now.  So what is your weekly summer usage?  

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Assuming you're not on a smart meter, get a clamp on current meter like this and put over the tails coming out of the main meter. Then you can turn off all the trips in the fuse board one by one, and see how much the consumption drops by for each, to determine exactly where the biggest consumers are. That will determine the low hanging fruit for making some savings.

Some other questions: Does the whole thing overheat in summer? Or do you have aircon too? Or use the Ground heat pump to provide cooling? I'm wondering if the trace heating causes other items to work hard to maintain comfortable temps.

 

 

 

 

 

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4 minutes ago, joth said:

Assuming you're not on a smart meter, get a clamp on current meter like this and put over the tails coming out of the main meter. Then you can turn off all the trips in the fuse board one by one, and see how much the consumption drops by for each, to determine exactly where the biggest consumers are. That will determine the low hanging fruit for making some savings.

Some other questions: Does the whole thing overheat in summer? Or do you have aircon too? Or use the Ground heat pump to provide cooling? I'm wondering if the trace heating causes other items to work hard to maintain comfortable temps.

 

 

 

 

 

No smart meter.

I turn the heating off in the summer but the house does get very hot. I've just this year installed air con in the yoga studio which has only been used for a couple of hours (students preferring to be outside when the weather is nice). I figured I could set the floor temperature in there to be a bit cooler in the winter then just use the air con system when a class is on to bring the room up to temperature. I might be wrong but I though that might be more cost effective given how slow the underfloor heating is to respond. 

 

 

 

 

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34 minutes ago, SteamyTea said:

Decent insulation and a timed re-circulation pump would have done it.  All hot pipes need to be well insulated.

 

That should have been a warning.

Of the two other houses I converted and then sold I finished one to completion and their electric is only slightly lower than mine (they have an upstairs which helps). The other I sold as an empty shell for completion so they have done things differently inside and got the feedback tariff for their ground source heat pump (which my builders didn't think to do!). I really doubt I'll be feeding them electric but will double check. They only moved in a year ago so I'd already had my first 2 years electric bills by then. 

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36 minutes ago, Wil said:

Given the size of the property, what's the size of the heat pump? a 20kW heat pump will be using 5kW of electricity on full steam and if you run it with all the doors open (as per pics), it could easily be doing that. A HP is more efficient than chucking direct electric at the problem, but not if just left on.

 

I'm tracking my consumption and our 5 bed farmhouse is currently averaging around 30kWh a day without any heating on! But we do charge an electric vehicle most nights which accounts for a decent chunk of that.  Immersion for water and electric cooking account for most of the rest.

 

The instantaneous and daily readings (particularly when it peaks and troughs) would be really helpful to understand where you're using the energy.

 

Edit- sorry I meant to ask- does the business/ retreat form a separate meter from the house or is it all one property?

Thanks for your reply. 

 

Yes its a 20kw heat pump. I don't run it with doors open! Heating is switched off in the summer, it will only be heating water.

 

I am aware of possible issues with the design and configuration of the UFH system and have had 2 people round to look at it as it doesn't get the house up to temperature in the winter "the system appears to be consuming approx 3 times the amount of energy it should whilst failing to deliver the required space heating". Maybe I'll do a separate thread about  this issue as time is running out if I'm going to sue, which I have been advised to do but I've had enough after years of battling to get to the end product. 

 

I don't have an immersion heater. I have been turning AGA off and then on daily to see if that helps but I'm not sure its more cost effective as it has to heat back up to temperature rather than just maintaining one constant temp. In the winter it will stay on all the time anyway and it helps heat the room (once the room is up to temperature the thermostat will stop calling for heat). 

 

Yoga studio is all part of the same property, only a couple of classes a day so really doesn't add much to electric cost and by renting the space out to teachers I'm getting a bit of income to help towards the bills. 

 

I'll start tracking daily usage again and see where we're at. 

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5 minutes ago, Claire B said:

I am aware of possible issues with the design and configuration of the UFH system and have had 2 people round to look at it as it doesn't get the house up to temperature in the winter "the system appears to be consuming approx 3 times the amount of energy it should whilst failing to deliver the required space heating". Maybe I'll do a separate thread about  this issue as time is running out if I'm going to sue, which I have been advised to do but I've had enough after years of battling to get to the end product. 

 

Who did the conversion?  How much insulation did they put under the floor?  It sounds awfully like not very much and you are heating the earth under the house?

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41 minutes ago, ProDave said:

You need a serious think and investigation about lots of aspects of this house.

 

Do you have any details of how much insulation was put in when it was converted?  Is the neighbour with a low bill in another converted Nissen hut?

 

No 1 is ditch the trace heating system.  If it takes 5 minutes for the hot water to arrive, then the whole hot water system needs a re think.  Can you post a floor layout?  I suspect there may be e.g kitchens and bathrooms a long way apart, and you would probably be better with two hot water tanks close to the points of use to avoid the long runs.

 

The Aga.  Is that all electric and the sort that is always on?  they are a huge consumer of electricity. Seriously consider swapping that for a conventional cooker, even a range style cooker that just uses heat it needs when it heats it.

 

We are in still in summer (average 12 degrees here for the last 24 hours so you might not think it) so you should not be using much electricity now.  So what is your weekly summer usage?  

Thanks for your reply. I had the nissen huts converted, they were finished approx 3.5 years ago. Insulation would have been to building regs (though probably nothing more than absolutely necessary knowing my builders), I'll dig out the specification and have a look. I'd imagine it's too late to go back in to the fabric of the building and change this now though. I'm having at least one partition wall in the long hallway that runs the length of the property, perhaps another one too will help stop the draughts.

 

Floorpans attached, you'll have to join the two images together ('hobby room' to the northern end and open plan living area to the south). 

 

Aga is electric and has always been on but Ive been turning it off more the past month and need to investigate whether its worth turning off and on or just leaving it on. I can't see me swapping it, Ive had one for 20 years,  I'm prepared to pay the cost of this. 

 

I'm going to track usage this next week before its time to turn the heating on again. 

 

 

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19 minutes ago, Claire B said:

Is the neighbour with a low bill in another converted Nissen hut?

yes, sorry, forgot that bit... however I sold that one as an empty shell for completion so she did things differently, I don't know the details but she had the feedback tariff for her GSHP which my builders didn't bother with! The third nissen hut I sold completed has similar electric usage to me, a bit less as they have an upstairs so I think that extra layer internally helps with heating. 

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Posted (edited)
23 minutes ago, Claire B said:

Insulation would have been to building regs (though probably nothing more than absolutely necessary knowing my builders)

Right, that's probably a lot of the issue. Builders will never spend more on anything unless they are very explicitly asked to do so, and this is doubly true for "invisible" items like insulation and airtightness.

 

If that entire area is done with UFH but merely at 2016 building regs insulation, it's going to cost a lot and indeed be extremely slow responding.

As an approximation, assuming the UFH flow temperature is 30ºC, you're going to be losing 0.25 * 60 * 9 * 20 = 2.7kW continuously down through the floor just heating up the ground under it. That's perhaps 10,000kWh going through the floor, depending on the heat pump that could be 3,000 kWh of primary energy. 

 

 

Edited by joth

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22 minutes ago, Claire B said:

Do you have any details of how much insulation was put in when it was converted?

 

IMG_3760.jpg

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IMG_3762.jpg

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53 minutes ago, ProDave said:

Who did the conversion?  How much insulation did they put under the floor?  It sounds awfully like not very much and you are heating the earth under the house?

RE Butler, local longstanding builder but this was they biggest project to date. MLM structural engineers and building regs (big company I believe) and FBB architects - awful people, we fell out very early on. It was a nightmare, husband became terminally ill and died half way through project, architects took advantage of the fact that we weren't 100% focused on what was going on with every pair of the build. Now just trying to make the best of a bad (but not so bad, I love living here) job. 

 

Probably not much under the floor as we had to keep the existing floor slab (so it was a conversion and not a new build). I imagine it would have been whatever building regs stipulated and no more. 

IMG_3760.jpg

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5 hours ago, Claire B said:

I had a ground source heat pump system installed in the build and underfloor heating throughout.

Do you know how big the ground connection for the heat pump is? A 20kW heat pump should need roughly 200m of trenches (slinky, dependent on soil conditions) or multiple boreholes. If undersized the efficiency can fall off a cliff.

 

58 minutes ago, Claire B said:

... perhaps another one too will help stop the draughts.

How bad are the draughts? Is the building uncomfortably cold on a windy day in winter?

They're potentially a huge heat loss for a building that large - assuming that the building is 60 x 6 x 3m and the temperatures are 5°C outside and 20°C inside with 1 air change per hour then you're going to be needing 5.5 kW of heating just to counteract the drafts. Making some assumptions about heat pump efficiency and the like, that's potentially 40 kWh of electricity consumption per day even before allowing for any heat going through the walls or floor directly.

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26 minutes ago, Claire B said:

Probably not much under the floor as we had to keep the existing floor slab (so it was a conversion and not a new build). I imagine it would have been whatever building regs stipulated and no more. 

IMG_3760.jpg

 

Working out the heat loss isn't too difficult: the 0.35 W/m2K is the critical number. Multiply this by the area of the floor slab in square metres and the temperature difference between the slab and ground underneath. For example:

(0.35) x (60 x 8 m2) x (35°C-15°C) = 0.35 x 480 x 20 = 3400W (3.4 kW)

 

For what it's worth the insulation levels don't look all that bad - Roof is probably ~0.17 W/m2K and wall is probably similar. They aren't great but significant improvements would be hard work so I'd be more interested in other loads:

  • The Aga and trace heating are ~16 kWh/day by themselves (6000 kWh/year: 20% of your total consumption), and the Aga could easily hit 10kWh/day without breaking a sweat. My suspicion is that this is a very large chunk of your consumption.

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  • The usual way of dealing with long dead legs is to fit a circulating pump and a return line, so hot water gets pumped around a loop on a regular basis, and the draw-off line is quite short. Depending on how accessible your pipes are this may not actually be that hard a fix, it won't reduce the heat consumption of the pipes (insulation is needed for that, which you could do at the same time) but it should reduce the bill substantially as the heat comes from a heat pump rather than electric resistance heating.
  • The additional 16kWh the day before your son left suggests something is going on more than just "a couple of washing machine loads" since most washing machines would use less than 1kWh per load. Large amounts of hot water use, electronics, cooking, something like that - that's another 6,000 kWh/year.

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5 hours ago, Claire B said:

It's a converted nissen hut (steel frame, zinc clad) in a very windy exposed area so it cools down quickly. You can see it at www.saintsgreenplace.com 

its obvious from what you have said that the insulation is your main problem --on floor and the main frame of the building 

dig out your plans and all spec of things you can  and post them up 

so we can see what and how much insulation and maybe one of the guru,s will do a heat loss calculation 

then get an independant engineer to look at the building and plans --

then you will know for sure the root of your problem 

 this has to be your next step before spending money on solar pv etc 

 

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Pretty sure a non trivial chunk of this is the Aga.

 

I used to turn ours right down overnight and back up in the morning. It meant you couldn't have the apparently-legendary Aga breakfasts and Aga porridge. I think it saved a bit (please ignore the "more efficient to keep it running" argument - it's the oldest myth in the energy efficiency book).

 

My conclusion was it was either the Aga or treading lightly on the world. So now I have the world's most expensive cupboard housing our roasting tins.

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It may be that the heat pump is not set up to well and the inbuilt resistance heater is on a lot (I am assuming it has one for the legionella cycle).

This may be able to be improved with a bit of tinkering.

 

How hot is your hot water?  Many on here with heat pumps only run up to 42° to 45°C.

Though with only one of you in the house it should not be the major energy usage.

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