markharro

New passivehaus plus project

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We are in the early stages of planning to build a new house to the PH + standard. At the moment I am researching various incidental technical matters.

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Good morning and welcome,

Looks like we are in pretty much the same situation, do you have the plot already? what area? hopefully i will have a plot in the not too distant future and design can start properly

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Thanks. Yes we have the plot (and existing house) in Edinburgh. How much research have you done so far? I am still trying to get my head around the issues surrounding the massive PV installation needed and how you confer with your local grid company to a) check they can deal with the export and b) find out how costly any upgrade to the infrastructure might be - which presumably the house-owner would have to deal with? 

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Posted (edited)
1 hour ago, markharro said:

I am still trying to get my head around the issues surrounding the massive PV installation needed

 

IIRC Passivhaus Plus uses footprint (not floor area) to calculate energy generation requirement. So a 100m2 footprint would require 6000kWh/annum. Even in sunny Edinburgh that is only 7-8kWp. You would probably only fit an inverter of 6kW anyway. The greater part load efficiency more than makes up for the slight loss on rare perfect days. Inverters which limit export are now available. If you could arrange for the panels to have two orientations this would further limit peak output. If your requirement is considerably larger then 3-phase, when 11.04kW can be exported without concern might be an option.

 

You might find this discussion informative - https://www.navitron.org.uk/forum/index.php?topic=29370.0

Edited by A_L
minor typos

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8kWp would be ample, and as said you can limit the export with something like a SolarEdge inverter ( 12 year warranty as it uses dry capacitors instead of the weaker wet ones ). 
You’d probably be a good candidate for a domestic battery at that size array, even if you have an EV, as the house can fully utilise the PV + batts, and you can use the car off Octopus overnight / off peak selectively. 
Thinking a domestic system will charge a car has been what I’ve discussed mostly with clients lately, eg as in I t’s simply not viable ( 10kwh domestic battery vs 70kWh EV battery = no chance ever ) but they still believe!!

 

In summer use the car battery for absorbing any excess in the really sunny ( few days ) we get and otherwise load shift off octopus / other for the known ridiculously high loads like EV’s. 
You can even load shift DHW off an off peak tariff if you size the DHW capacity to do that. 
Lots of ways to skin a cat. 
NB: try to use D/C batteries as A/C losses will fly in the face of PH+. 
Out of curiosity, why PH+? It gives you a lot of hoops to jump through that will require some additional spending to comply with. 

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2 hours ago, Nickfromwales said:

NB: try to use D/C batteries as A/C losses will fly in the face of PH+. 

PH+ hasn't got anything to say about batteries, having no batteries at all is by far the simplest way to achieve the certification. They just look at (predicted) generation output vs (predicted) energy consumption. Doesn't matter where the generated energy is used.

 

Personally (as someone half way through an EnerPHit PH+ retrofit) I'm deferring installing batteries  [and on upgrading to an EV for that matter] as they also require some additional spending, don't aid the core goals of the project, they are still rapidly dropping in price, and after a year or two in the house I'll have far better idea what I can actually benefit from.

 

FWIW though - if you really want DC coupled batteries that tends to rule out SolarEdge PV inverter. The Luxpower stuff looks a good integrated/hybrid option.

 

 

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14 minutes ago, joth said:

FWIW though - if you really want DC coupled batteries that tends to rule out SolarEdge PV inverter. The Luxpower stuff looks a good integrated/hybrid option.

Yes, typically Fronius if DC batteries ( Solarwatt for eg ). Plus they don't charge off the grid at all, and are designed to mothball themselves at the lower discharged rate until the PV starts producing excess again. The downside with the Lux / A/C systems is you have to include them in your DNO application. So, if you can get ~4kWp per phase, for eg, adding 7.2kWh or 9.6kWh of A/C batteries may well get your connection refused. If you install D/C batteries then they are on the consumer side, not the grid side, and you can have as much as you like without declaring them on your PV > DNO application.

 

14 minutes ago, joth said:

as they also require some additional spending, don't aid the core goals of the project

PV costs money to install, yes, but I can't exactly see that these systems don't aid the core goals myself :/ .

I've just been involved in an NZEB build, which smashed PH, and NZEB, and finally attained ZEB recognition, with an RER of 37% and negative 2.3T carbon p/a...( in a massive 6 bedroom / 6 bathroom all electric dwelling), and that would not have been possible without the PV or the battery system ( plus one of the best and most anal site managers I've ever met !! ).

36 minutes ago, joth said:

They just look at (predicted) generation output vs (predicted) energy consumption. Doesn't matter where the generated energy is used.

Do they not look at the RER? I'm not sure what is actually in the PH / PH+ to do / not to do list.

 

28 minutes ago, joth said:

PH+ hasn't got anything to say about batteries

Not directly conflicting / associated with PH / PH+, but my point is the loss of at least 13-15% from an A/C system, if installing batteries, is easily preventable and more in line with that 'core ethos'.

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It's projected footprint of rooms within thermal envelope.  This means an integral garage with no room above is excluded, but any first floor overhangs have to be included.  The exact amount of PV you need is based on PER.  If your PER is less than 45 kWh/(m²a) you don't actually need a full 60 kWh/m²AProjected*a.

 

We are also targeting PH+ and these are our numbers:

Heating Demand:        11kW

Treated Floor Area:     305m2

Projected footprint:     208m2
PER:                               30 kWh/(m²a)

PV required:                 38 kWh/m²AProjected*a.)  =    7904kWh/yr

 

In our case (south-east england) and ignoring shading (which is minimal anyway) this requires 27 x 360W panels split over east/south/west roofs.  

 

Regarding DNO and export, this really comes down to what you grid is like locally.  For 10kW in our area we have the option to use single phase or three phase, but we've decided to go with a three-phase inverter because the bungalow we knocked down already had a three phase supply.  You can apply for what you'd ideally want to do and then work backwards from there with most DNO's. Also some DNO's have a online map which will give you a rough idea. e.g. https://www.ssen.co.uk/generationavailability/

 

 

 

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1 hour ago, Nickfromwales said:

Not directly conflicting / associated with PH / PH+, but my point is the loss of at least 13-15% from an A/C system, if installing batteries, is easily preventable and more in line with that 'core ethos'.

 

Right, my point is the OP said they wanted to achieve PH+ and didn't mention a requirement for batteries at all, so rather than trying to design a DC vs AC system I'd recommend starting with no batteries, check if you can meet the project goals  with that, and go from there :)

 

 

1 hour ago, Nickfromwales said:

. The downside with the Lux / A/C systems is you have to include them in your DNO application. So, if you can get ~4kWp per phase, for eg, adding 7.2kWh or 9.6kWh of A/C batteries may well get your connection refused. If you install D/C batteries then they are on the consumer side, not the grid side, and you can have as much as you like without declaring them on your PV > DNO application.

 

OK think I see what you're saying --  DC batteries that directly feed DC equipment without any AC stage? (I was thinking more of AC vs DC tie from batteries to PV). Certainly more efficient, but this means a DC distro around the house as well as AC so I didn't even consider it (might have done for a few select items like the lighting controller rack / LED drivers - but there's no way I'd make enough usage to be worth it, given I don't care much about off-grid backup). 

 

But still I'd go back to my first point that if the goal is PH+, put all the $ into fabric and reducing consumption and installing microgeneration (e.g. PV), and leave battery design (if any) driven as a separate decision point.

 

 

46 minutes ago, Dan F said:

If your PER is less than 45 kWh/(m²a) you don't actually need a full 60 kWh/m²AProjected*a.

 

This was true for us too (although being EnerPHit+ the thresholds are a bit different) detailed over here: (gosh a whole year ago)

 

 

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34 minutes ago, joth said:

OK think I see what you're saying --  DC batteries that directly feed DC equipment without any AC stage? (I was thinking more of AC vs DC tie from batteries to PV). Certainly more efficient, but this means a DC distro around the house as well as AC so I didn't even consider it (might have done for a few select items like the lighting controller rack / LED drivers - but there's no way I'd make enough usage to be worth it, given I don't care much about off-grid backup). 

No.

DC direct from panels to batteries, then that parallel grouping to an AC inverter. AC only house with zero conversion losses.

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37 minutes ago, joth said:

Right, my point is the OP said they wanted to achieve PH+ and didn't mention a requirement for batteries at all

correct.

8 hours ago, markharro said:

am still trying to get my head around the issues surrounding the massive PV installation needed and how you confer with your local grid company to a) check they can deal with the export and b) find out how costly any upgrade to the infrastructure might be - which presumably the house-owner would have to deal with?

So, the info I supplied will help jump the DNO hoops if the size / export is an issue ( bearing in mind it ( the house ) should be designed to self-consume what it produces ). An ac system / hybrid will all have to be added together and the sum presented to the DNO for approval as the grid tied capacity. Massive PV + AC batteries = high likelihood of getting a no-no from the DNO, albeit you CAN be lucky IF the infrastructure is good / very good.

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Wow first of all thanks for all the contributions to my post. I had no idea this forum would be so active or knowledgeable. My problem is that I can see that my own knowledge is totally rudimentary reading through some of the replies. I need much simpler explanations.

 

If it helps our internal floor area is planned to be around 180 m2. PH+ was my idea rather than our architect's and I have modelled my thinking on this built project in England - https://www.bere.co.uk/architecture/lark-rise/?acceptCookies=5f40eb7ebbf92

 

There is lots of data on this on the architect's website. Its further south than us but from memory about the same sort of size we hope to build; it has a 12.4 kWp PV array and a Tesla Powerwall battery. Given our more northern latitude I assumed that we may need a bigger array eg 14kw or so? I have to say that I am now a bit puzzled by Dan F's comments that he is planning on 27 x 360W panels ie around 10kW for a substantially bigger house!

 

Can anyone comment in simple terms on how my logic might be out? 

 

On a separate point, my thinking was that to make things affordable sourcing used or budget panels might be the only way we could afford the 50/60 that would be needed for an array totalling around 14kW. Has anyone experience of using this (German) site to source used panels - https://www.secondsol.com/en/index.htm - as it seems possible to buy very cheap panels by the palletload from them!

 

thanks

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44 minutes ago, markharro said:

Can anyone comment in simple terms on how my logic might be out? 

 

1) PH uses external dimensions, so if your house is a regular detached house with 90m2  of internal floor area per floor it is likely to have a footprint of around 105m2  which implies a maximum generation of 6300kWh per year which is easily achievable with 7.5kW of PV.

 

2) This for a PH+ house with the maximum energy use allowed (PER of 45kWh/m/yr). IIRC if it has a lower value the energy generated can be proportionately reduced.

 

3) There are panels in the U.K. for 30p per Watt e.g. https://midsummerwholesale.co.uk/

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2 hours ago, markharro said:

might be the only way we could afford the 50/60 that would be needed

340w panels;

12,000 / 340 = 35 panels. 
Don’t forget the consumables / trays etc. GSE don’t cover every panel size, so check compatibility and consider EasyRoof if you need bigger. 
If you’re on true split elevations you’ll need a dual string inverter, and if you use micro inverters you’ll need to factor in the cost of a controller. 
Make sure you get the required parts list right when ascertaining costs ;)  

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Posted (edited)
On 22/08/2020 at 11:05, markharro said:

have to say that I am now a bit puzzled by Dan F's comments that he is planning on 27 x 360W panels ie around 10kW for a substantially bigger house!

 

Can anyone comment in simple terms on how my logic might be out? 

 

How much generation you need to meet PH+ depends on your PER, and isn't fixed.  Lark Rise has a PER of 37kWh/m2.yr so needs 48 Wh/m2.yr in generation (see below).  That said, they installed 79kWh/m2.yr, so around 60% more than they needed for certification.

image.png.09352d9aac6db16a702b2e64636ee160.png

 

How the PH+ requirement translates into a PV array size will depend on area of country, orientation of roof, pitch and any shading though.  So you know what you projected area will be, your roof area/type or any of this yet?  Also, you should think about array size based on expected usage and not just certification if possible.

 

 

Edited by Dan F

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On 17/08/2020 at 19:19, Nickfromwales said:

So, the info I supplied will help jump the DNO hoops if the size / export is an issue ( bearing in mind it ( the house ) should be designed to self-consume what it produces ).

Is that still true? In a world with fixed tariff rates which don't change with demand then it makes economic sense, but from an environmental point of view it doesn't and smart meter tariffs mean it makes economic sense to shift demand too. They're also quite a bit easier to deal with than self-consumption as they've got a far larger applicable market at the moment.

 

To give an example, you need 10kWh for water heating at some point over 24 hours and are on Octopus Agile/Outgoing:

image.thumb.png.10620282dd21a3b966855948b3ad2707.png

 

Using this between 2am and 4am will cost 50p. If you have a PV array producing the same amount of power between 11am and 1pm you could export it for about the same price. However, if you've say got a west-facing array which still produces after 4pm today you're much better off exporting than self-consuming: you'll be paid about 12p/kWh to export compared to the ~5p/kWh you would pay for the same electricity overnight. It's also significantly cheaper and easier to use a smart time clock to shift the demand rather than batteries - and price is a pretty good proxy for environmental impact since the low emission forms of generation all have essentially zero fuel costs and so will want to generate whenever they can. It's not perfect, but with increasing amounts of wind on the grid the odds are that this will work out best over the course of a year.

 

Certainly the cost difference isn't big enough to justify spending very much on load shifting - at most you could justify something which uses weather forecasts to predict daily PV generation and load shift based on expected exports and export/import prices.

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2 hours ago, pdf27 said:

you'll be paid about 12p/kWh to export compared to the ~5p/kWh you would pay for the same electricity overnight.

Who’s paying 12p/kWh for export ?

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Posted (edited)
20 hours ago, Nickfromwales said:

Who’s paying 12p/kWh for export ?

https://octopus.energy/blog/outgoing/ - the wholesale price is multiplied by the M_tariff figure, plus the B_tariff fixed rate all the time and the C_tariff number between 4 and 7pm. Back calculating from the tariff graph above to work out the wholesale rates, exports after 4pm yesterday would have been paid about 12p/kWh. Before then it would have been about 4-5p/kWh: a bit lower than the import rate, but virtually identical to the overnight cheap rate. Essentially that means there is no benefit to using PV when produced as opposed to exporting it outside the 4-7pm window and using overnight cheap rate electricity. Within the 4-7pm window, there is a positive incentive to export as much as you can.

Values are based on the South Eastern region where I am - the logic is probably quite a bit different in Scotland for instance.

Agile pricing regional coefficients

Edited by pdf27
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23 hours ago, pdf27 said:

However, if you've say got a west-facing array which still produces after 4pm today you're much better off exporting than self-consuming: you'll be paid about 12p/kWh to export compared to the ~5p/kWh you would pay for the same electricity overnight.

 

Wow. I've passively thought about this balance  (Indeed last week I just moved to Agile for import; and I'm not planning any battery storage as mentioned before), but now you call this out, our 8kW PV array will be entirely SW facing so I really should think closely about export maximization during this time window. The fact I'm on agile for import is already incentivizing behaviours & designs to allow this, even before the PV goes on.

 

(Right now, the only power is that used by our contractor, they knock off by 4.30pm hence why getting on Agile import during the build seemed to make sense.  Aside: it took less than a week for them to switch out SMETSv1 meter over from ovo to Octopus, so far better than the 'median' expectation I'd set for it)

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On 22/08/2020 at 13:44, Nickfromwales said:

340w panels;

12,000 / 340 = 35 panels. 
Don’t forget the consumables / trays etc. GSE don’t cover every panel size, so check compatibility and consider EasyRoof if you need bigger. 
If you’re on true split elevations you’ll need a dual string inverter, and if you use micro inverters you’ll need to factor in the cost of a controller. 
Make sure you get the required parts list right when ascertaining costs ;)  

I see micro-inverters cost about £100 a piece. That's a lot for a 40+ panel array ie it basically doubles the cost of the panel! Or does it come to about the same as the big inverter you would otherwise need?

 

Oh and another thing what is the difference between a microinverter and these SolarEdge Inverter Review - Power Optimisers ?

thanks 

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2 hours ago, markharro said:

I see micro-inverters cost about £100 a piece. That's a lot for a 40+ panel array ie it basically doubles the cost of the panel! Or does it come to about the same as the big inverter you would otherwise need?

 

Oh and another thing what is the difference between a microinverter and these SolarEdge Inverter Review - Power Optimisers ?

thanks 

 

With solaredge optimizers you'll be looking at about £45 for each optimizer + £1,500 for a 10kW inverter, so £3,300.  

 

That said, unless you have shading, strings split across mutiple roofs or specifically want per-panel monitoring you don't have to use either.  The difference with the micro-inverters (e.g. enphase) is that they convert to AC on the roof.

 

 

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One additional thought not mentioned yet - are you in an urban or rural setting, and do you already have services to the plot? If you're in an urban area and don't already have a connection, it's worth trying to get a 3-phase one which should let you export 12kW without problems, and makes other things like a future electric car connection easier.

Lark Rise used a battery because they are in a rural area with a pretty terrible grid connection - a large PV connection therefore needs to be badly throttled, wasting huge amounts of energy and making them a good candidate for a battery. By comparison I'm only about 10 miles away from them, but have 3-phase going right past my door and would need to move the connection anyway - the incremental cost of going for 3 phase (basically a slightly more expensive bit of cable) is trivial and well worth while.

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7 hours ago, Dan F said:

 

With solaredge optimizers you'll be looking at about £45 for each optimizer + £1,500 for a 10kW inverter, so £3,300.  

 

That said, unless you have shading, strings split across mutiple roofs or specifically want per-panel monitoring you don't have to use either.  The difference with the micro-inverters (e.g. enphase) is that they convert to AC on the roof.

 

 

In addition to those you list, the other slight benefit of the solaredge optimizers is they limit the panel output to 1V until connected to their inverter, reducing the risk of death by 1000V DC in certain situations.

 

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I am reading this thread with interest, but I am puzzled by what seem to me like high energy use figures for a passive house +, i.e mention of 6000kWh per year?

 

My own house that is built to a good standard but never attempted any passive house calculations uses a total, real world measured figure of 1706kWh pa for heating and at about 150 square metres that's 11.37kWh per square metre per year.

 

I do have solar PV which generates more per year than the house uses in space heating, but not quite as much as the house uses for space heating and DHW.

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