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Green Building and Design => Green Construction/DIY => Topic started by: dan_b on July 08, 2019, 08:18:44 AM



Title: New build eco-house solar pv and battery sizing
Post by: dan_b on July 08, 2019, 08:18:44 AM
Hi chaps
I have a friend who is in the process of designing a new build which he wants to be as eco as possible - they're going for passiv-haus levels of insulation and heating demand, but the bit they're now trying to work out is the size of the solar and battery they should look to install.

Roof size wise with modern 400W panels he could probably get 16kW of panels on a south-facing roof.  But there must come a point where there's really no value in putting extra panels on and spending more money on storage or other self-consumption devices, and of course there's no FiT payment anymore?

I have said to him to consider perhaps a smaller south-facing array but then to add some west-facing panels to extend the evening generation profile, but basically - for those of you here who are effectively zero-import on electricity, or actually fully off-grid,  what sort of sized PV and battery array are you looking at as a rough rule of thumb?

They'll get a decent sized battery system like a Tesla PowerWall, and they're looking at the SunAmp heat batteries for hot water storage plus occasional heating requirements.   But they're intending not to have a gas connection at all, so cooking would be electric.  They're looking at a  heat pump for occasional heating requirements in the winter.

Is it really as simple as "fit as much solar as you can", or is there a point where there's really no point adding any more, and indeed you'd be better off spending on extra batteries?

Any thoughts/ suggestions?


Title: Re: New build eco-house solar pv and battery sizing
Post by: Fintray on July 08, 2019, 10:26:57 AM
Dan

I've 14kWp of PV (3.87 which gets FIT's) and a Powerwall 2 battery and in the last 3 months have imported about 6kWh from the grid, A PV diverter has supplied all my hot water and extra power has been used to supply heating when required. There is also the option of going for the Outgoing Octopus tariff from Octopus Energy which gives a flat rate 5.5p/kWh or a variable rate if you go Agile.


So if your friends have passiv-haus levels of insulation their heating requirements should be pretty minimal and if they go for A++ rated appliances their electricity requirements could be very reasonable meaning more to export if they can get approval for that level of export, failing that they could install SolarEdge inverters and limit their export.


Title: Re: New build eco-house solar pv and battery sizing
Post by: A.L. on July 08, 2019, 04:26:01 PM
hello,

- I would limit it to an annual output 2x their current/likely annual appliance use. The summer excess can heat the hot water initially with an EV in short order to soak up the rest, maintain their eco-credentials. After all it will always be possible to add more later (although that will be subject to VAT). As for batteries, 4 usable days storage should be the max.


Title: Re: New build eco-house solar pv and battery sizing
Post by: brackwell on July 08, 2019, 07:12:56 PM
I think a lot of this depends on where you live,no.of people, no/mileage of EVs. and other large personal loads

I live on the south coast and if i was building paasivhaus standard i would not have a heating system relying on passiv solar, and a pellet stove and/or leccy storage heaters (on E7) for just in case.

Ken



Title: Re: New build eco-house solar pv and battery sizing
Post by: nowty on July 09, 2019, 04:56:47 PM
Solar PV is so cheap now that I would "fit as much solar as you can" as you will never have enough in winter, you will wish you had more in Spring / Autumn and you can always sell excess back to the grid in summer. This is especially so if your friend is going for a Powerwall as this will help soak up the excess generation.


Title: Re: New build eco-house solar pv and battery sizing
Post by: dan_b on July 09, 2019, 06:16:17 PM
Thanks thatís basically what I thought - I have suggested he might want to try and pop some West facing panels in to stretch the generation profile out a bit.
With panels now routinely in the 300+ watts rating does anyone care about panel efficiency anymore or is it really just down to get as much kWp as you can for the lowest acquisition cost?


Title: Re: New build eco-house solar pv and battery sizing
Post by: Iain on July 09, 2019, 06:26:57 PM
Hi

Quote
I have suggested he might want to try and pop some West facing panels in to stretch the generation profile out a bit.

Possibly less important with a battery as the battery will "Stretch the profile"

Iain


Title: Re: New build eco-house solar pv and battery sizing
Post by: billi on July 09, 2019, 06:43:53 PM
Exactly as Iain said , if the  array is on the south facing roof then  at that size it will still deliver   some   at  the morning and evening  ( when  the kettle is on  for coffee in morning or the pizza oven  in the evening )

Maybe me sentimental , it hurt me to   have the  el. oven on in the evening  and too much power came from the battery  .... but  i have  only 4 kW PV

the tesla  power wall  is far too small and far too expensive  , a 100 kWh   industrial fork lift battery similar price ,  will suit a 10 -15 kw PV much better  , for  beside electricity , for heating , hot water and electric driving

a 15 kW PV is doing about 20 kWh on average a day in November  in South UK  , so ....



Billi




Title: Re: New build eco-house solar pv and battery sizing
Post by: Scruff on July 09, 2019, 07:15:34 PM
What are the benefits of a battery for a grid connected installation?


Title: Re: New build eco-house solar pv and battery sizing
Post by: billi on July 09, 2019, 07:20:04 PM
well what are the benefits of  a big PV then in times of no FiT ?


Title: Re: New build eco-house solar pv and battery sizing
Post by: nowty on July 09, 2019, 07:23:58 PM
Hi

Quote
I have suggested he might want to try and pop some West facing panels in to stretch the generation profile out a bit.

Possibly less important with a battery as the battery will "Stretch the profile"

Iain

I agree that if you have a small PV array, then a battery will stretch the profile, thus better to have it all facing south, but I find that if you have a large array it helps reduce the peak power generation problem if you spread it around and its more efficient to use the power as its generated rarther than store it in batteries.

My last lot of PV has gone on my NE facing roof. Partly cos there is no more room elsewhere for it !, but also because it helps me run my heatpump from very early in the morning (Mar to Sep) without solely relying on the batteries.


Title: Re: New build eco-house solar pv and battery sizing
Post by: Scruff on July 10, 2019, 12:33:39 AM
well what are the benefits of  a big PV then in times of no FiT ?

Competitive cost-effective power.

A battery is an efficiency reduction device of arguable financial merit. Data to prove otherwise from existing installations is not something I've witnessed. I'd love to see some. 
Can it compete with cables and direct drive? Why does it compete with cables and direct drive?
Looks like an expensive endeavor in proprietary electron farming.

Genset offsetting is an entirely different fish of kettles.


Title: Re: New build eco-house solar pv and battery sizing
Post by: billi on July 10, 2019, 06:48:40 AM
Scruff , there is a other point too in my opinion

While there was a war in Irak   and the the german government decided at the time to send  soldiers there , there was a movement of  people  called "no blood for oil"   many business people of that movement refused  to pay their tax  at those years

If anyone   refuse to   connect to the grid  and tries not  to joining criminal politics , like it is happening in the the UK and Germany right now , with  minor or close to nil  incentives  towards a faster  conversion towards a fossil-fuel  free politics  , then   i am still convinced to  advice people to cut the line and do not  wait .

That was my decision  15 years back  to not connect to the Irish Grid

So being off grid is more viable and cost efficient nowadays  then ever ,  sure  it needs  a situation that suits   and some investment upfront ( that does not mean its more expensive then  a grid  connected idea )  , but with those factors of electricity ,  heat  and hot water ,  electric charging  one can  utilize  own sun power pretty   good  and  with a sunny smile

Billi


Title: Re: New build eco-house solar pv and battery sizing
Post by: dan_b on July 10, 2019, 09:15:22 AM
Right so to summarise the advice here is now
Big arrays are pointless
Storage is pointless
Going off grid is the only solution
But only if you have a big array and a big battery?


Title: Re: New build eco-house solar pv and battery sizing
Post by: knighty on July 10, 2019, 10:34:51 AM
I'd go for as much PV as possible... but as you said split some onto the other side of the roof... maybe keep most of it south facing?

do you know what his export limit is? - it could be an option to miss out the battery for now and cover both roovs in PV, probably more cost effective (with 5p/kwh for export)

then... if he wants batteries add them later when they're cheaper?  (prices are falling pretty quick?)


Title: Re: New build eco-house solar pv and battery sizing
Post by: biff on July 10, 2019, 01:14:16 PM
If you are not going off grid,
                                Then it is pointless getting a large array and massive storage battery bank. All you would need is a 4kw array, even less and enough storage to tide you over an outage of 48 hours.
  Getting a large array with no storage is just generating free lecky for the company.
  Yet if there is potential for an off grid installation situation, then it should be carefully calculated to see what figures will be required to run the dwelling comfortably. Off grid installations do not have to be a hardship Spend the money correctly at the beginning, invest in good technology, avoid complicated stuff and run with as high a voltage as possible in DC . Our Battery bank would be the single biggest expense, 60 forklift cells but they can take strings of pv at 140vdc+, and do not need any fancy Mmtp controllers. The juice just gallops across the lawn and into the 2 ton of lead acid.
  Our inverter is only 2kw but plenty to run all our appliances, including the washing machine.
  PV is so inexpensive and trouble free these days that it would be a sin not go go offgrid and run bill free for the 8 months alone, ;D, Our wind turbine is my first love and I admire it as it battles away through the winter and delivers the goods of as AG says, " Cuts the mustard".
  I have less love for the Irish ESB than Billi has and would not piddle on them to put their fire out. They have prevented Ireland from taking advantage of our potential to be leading lights in the renewable energy stakes. We never took that into consideration when we handed it over to the Troika.
   If not going off grid, you will only needs a few days at the most for storage and with proper management of freezers and circulations pumps, fossil fuel driven GSHP for the duration of the outage, then it is not a large installation at all. On grid or off grid it don,t really matter but you should always have a backup up plan in case of prolonged outage and investing in a small economic generator that can be stored properly is a must.
                           Biff


Title: Re: New build eco-house solar pv and battery sizing
Post by: Pile-o-stone on July 10, 2019, 02:27:09 PM
Solar PV is so cheap now that I would "fit as much solar as you can" as you will never have enough in winter, you will wish you had more in Spring / Autumn and you can always sell excess back to the grid in summer. This is especially so if your friend is going for a Powerwall as this will help soak up the excess generation.

I was about to post exactly this, but nowty saved me the effort. :)

In the UK you're looking to generate enough on dull summer and short winter days to cover as much of your usage as possible. The more panels, the more coverage. One of the costs in installing solar panels is renting the scaffold. If you pal is building a house, then he would have this cost anyway, plus if he fits roof integrated panels he'll not only benefit from enhanced aesthetics, he can save on roof tiles.


Title: Re: New build eco-house solar pv and battery sizing
Post by: biff on July 10, 2019, 03:32:52 PM
Definitely  not intergrated PC panels.
          Pv performs better with 100mm space between pv and roof.
                  Biff


Title: Re: New build eco-house solar pv and battery sizing
Post by: Sprinter on July 10, 2019, 04:51:18 PM
If he could i would actually go East and West facing rather than South, To me South only ever made sense if you are trying to maximise FITS payments or just happen to use peak energy at midday.

I am fully west facing and on a perfect day we peak at late afternoon around 17:00 just when we are cooking tea, things are a bit sparse in the mornings but we are getting enough to cover most of the houses background needs.

We have batteries and when they are working, its nice to have them topped off at the end of the day ready for the evening, however i also agree with more is better when it comes with solar, with our peak in the late afternoon i am considering putting some east facing ones up to catch the morning sun and top us up a bit faster, this would also give us a higher incoming baseling for longer, then of course i will add other things like a sunamp at some point in the future to make more use of it.

As for battery storage, whatever you go for its never enough, i should be increasing to 8 kWh next week (if the supplier ever gets their act together), we started with 4 and was impressed, then we increased to 6 and was more impressed, now we are going to 8 and i am already aware that for a lot of the year we will never fill them up unless we mains charge, hence i am now also considering east facing panels to help collect useful amounts for longer in the year.

but when it comes to "Need" if Need can be considered "N" then the equation for the correct amount of battery or solar will always be "N+1", which to be honest is the same formula i use to work out how many fishing rods, motorbikes, pushbikes Etc that i need, a very simple equasion and rarely wrong (unless the wife manages to count my fishing rods).


Title: Re: New build eco-house solar pv and battery sizing
Post by: jtp10000 on July 10, 2019, 04:54:36 PM
Definitely  not intergrated PC panels.
          Pv performs better with 100mm space between pv and roof.
                  Biff


Is this why my 4kw panels have never, according to the Enlighten gizmo, produced more than 3.5kw of power?


Title: Re: New build eco-house solar pv and battery sizing
Post by: biff on July 10, 2019, 05:27:32 PM
I cannot speak for your installation  jtp10,000,
                   No 1 is the fact that integrating with the roof like they do in France blocks the cool air from reaching the rear of the panels and if there is any kind of hot weather the Panels output drops some 10 to 15% of its potential. The pv light cells need to be able to dump the heat freely.
      No 2 is more of a structural maintenance problem. Flashing integrated  panels is both a headache and a nightmare. It is simply the worst way to do it. Its is foolishly more about looks than efficiency.
     Biff


Title: Re: New build eco-house solar pv and battery sizing
Post by: Scruff on July 11, 2019, 04:45:50 AM
PV is very useful.
Batteries without utility power are very useful.
Any clean power you make is great.
Battery lifecycle and supporting system costs do not make financial sense at a domestic civilian level I think it's just fashionable.
I have many many batteries, different flavours different breeds; doing all sorts of wonderful things. None of them offer me cheaper kWh cost than utility power.
Keeping the lights on in a power cut  8)

Batteries aren't green they're a catalyst to green. If used for soft gridding they and their supporting hardware are generating operational losses that could otherwise be offsetting a gas-fired utility turbine.


Title: Re: New build eco-house solar pv and battery sizing
Post by: dickster on July 11, 2019, 10:58:23 AM
If I had my time again and given the right circumstance, my new build would have a single plane roof completely covered in solar panels. In fact I'd be looking at ways to use the panels as large roofing tiles and forming the roof itself. So that is solar maximized and then battery storage can come along any time incrementally in the future.



Title: Re: New build eco-house solar pv and battery sizing
Post by: biff on July 11, 2019, 12:38:15 PM
  To Quote Scruff,    "Batteries aren,t green",
                That is true,  However in respect of some specific purpose not just life critical but other dedicated select purposes, then batteries are invaluable. They are the greenest answer when the mains are down, If these grid batteries can keep the freezers going and the circulation pups going and the ground sourced heat pumps going, then, they are indeed a valuable green asset in time of need. There are quite a few pounds worth of food locked away in these freezers during the summer when the power is really needed to keep them cool and fresh.
                                           Biff