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benmurphy66
349 posts

Ultimate Geek

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  #938344 21-Nov-2013 09:33
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SQLGeek: Watching this topic with interest, many thanks for all the interesting data.

I am going through a rebuild in Chch and will be installing PV panels thanks to a 15K sustainability payment from the insurance company. My old house had 3-phase power so is being replaced with 3-phase power. My electrician has told me that having just 1 phase might not be enough as the house is 310sqm and we are a high user of power with a spa, 3 heat-pumps, induction hob, lots of gadgets and wife & kids at home during the day. We have gas hot water.

I would like to get as much capacity as I can for the 15K and don’t want to waste money extra inverters, so do I really need 3 inverters? Could I get away with 1 inverter and have all the day-time stuff on that phase? Or could I just connect 2 phases and have 2 inverters?

Have been getting conflicting answers from the various retailers here in Chch.


I have spent a lot of time investigating the options of PV and how it relates to 3-phase power. Given you are doing a fresh build you might be able to get enough load on one phase otherwise SMA do a 3-phase inverter but the smallest is 5kw. Also note that how I understand it the generated power is evenly spread across the 3 phases. So unless your power is evenly distributed you might export more than you intended / costed.

I have just purchased a Owl Intuition-LC and waiting for it to arrive. This will give me the ability to graph my power use for each phase. So I can basically see what my average loading is. This will then help me to understand do I get

a. 3-phase system
b. 1-inverter on 1 phase
c. 2-inverter on 2 phases

If you wanted to ask me any specific questions let me know. I have spent a lot of time looking into it. Just message me

Parewanui
30 posts

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  #938368 21-Nov-2013 10:21
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@SQLGeek

$15K!
That's a useful budget.
I wonder if that would stretch to a solar-thermal system as well as a PV system?
Porboynz has both.
Would solar-thermal handle all your hot water during the summer?
Could you also use it to heat or top up your pool?

I looked at solar-thermal for hot water and to heat the house via radiators in the rooms when we built our house - which is a year old now - 210 m2.
So no need for heat pumps.
We have very cold winters here in the far south.
But the radiators and hot-water-reticulation was going to be expensive (for others this is a common option for new homes where I live - using a oil/diesel burner to heat the water instead of solar-thermal though).

But here's the kicker - the cheapest option was not to heat the house but to insulate it!?!?!
The house walls are extra thick timber framing with 2 layers of bats.
The same in the roof and polystyrene in the floor.
Thermal-break double grazing windows.
Wood window framing is best insulation - but was too expensive for us - but popular here in the south.
Large windows and north facing.
And this has worked - we have lived in the house over 1 winter now.
In July at the end of the day it is 3 degrees outside and the frost is still there in the shade.
We get home from school and work and in the house it is warm (16+ degrees)
I light the wood-burner to take the inside temp up to 22+ degrees.
It gets even more interesting as I have 2 neighbours who also have new houses.
Also built the same time as my house.
They visit my home at days end and cannot believe it is cosy!
They know we have no heat pumps and can see the wood-burner has not been lit yet.
I'm off-topic again, but since @SQLGeek is building new, I thought I mention my new build.

  #938380 21-Nov-2013 10:37
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+1 for insulation!! I built a house two years ago and I am so please I up speced the insulation as much as I did. It keeps the heat in during winter, and almost as importantly, keeps the house cool in winter. It is a very stable temp all year round and so comfortable to live in. I too went with thermally broken windows, 140mm framing, ultra batts with two layers of 90mm + 50mm, and ultra high spec Kingspan insulation in my roof (as I had a thin skillion roof so couldn't fit enough batts). Definitely worth spending the money on this stuff if you are able!!

k1wi
484 posts

Ultimate Geek


  #938389 21-Nov-2013 10:47
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+1 @ investigating a three-phase inverter and solar thermal (if it's covered by the insurance monies)

In the states most houses have 2x 110v phases to the house (to allow 220v to appliances such as stoves etc), so multi-phase residential connections can't be uncommon, but I'm not sure whether all 110v circuits are loaded onto the single phase first...

Tbh I suspect all your intermittent high drain appliances would probably well exceed your solar capacity, particularly at the time of day/year they are likely to be run (i.e. in winter, mornings and evenings, when the sun is either low in the sky or over the horizon). It would make sense to have the high drain appliances (apart from the spa, perhaps, as you may be able to demand shape it to solar generation) on a separate phase.

Porboynz

110 posts

Master Geek


  #939203 22-Nov-2013 18:20
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Today was a super solar Friday.  I have 310 litres of hot water at 65 degrees C in the HWC from my solar water panels and check out the solar PV results below.



Above is a screenshot of the Inverter and below is a screenshot  of the Owl monitor, from about 2pm, we are Exporting!



Not a perfect blue sky day, fairly hazy but no serious cloud.

Here is a screenshot from 6pm tonite , still generating!


Parewanui
30 posts

Geek


  #940370 25-Nov-2013 14:47
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The following are questions from above in this forum by Porboynz.
Answered by a lines-co project-manager electrical-engineer.
Of interest is that this person recently attended a conference on home-PV-generation.
I was asking him about batteries and off-grid systems which I found really interesting, but back to PV….
The key thing he said to me was:
- Electricity-networks are designed to cascade down.
- The voltage drops from network-entry down to the final consumer’s premises.

Anyway, read on for his answers….

Porboynz:
What do lines companies call an area fed by a large street transformer?
Is its a sector or a zone or some industry specific name?

Answer:
We label areas by what feeder they are on. The feeder is the line that comes from the substation at high voltage and all the distribution transformers tap of it

Porboynz:
I have one outside my property, its green, about 2.5 metres by 1.5
metre and 1.5 metres high with cooling etc.
I presume its an 11kV to 230V transformer?

Answer:
Depends on the network and what they run at. Likely either 11kV or 22kV. I don’t think Vector distribute at 22kV yet

Porboynz:
I understand that my inverter exports to the grid by lifting the
voltage slightly above that of the power lead-in cable so the current
reverses direction. It seems to me if all my neighbours had panels then the voltage would
rise exponentially as we all tried to export power to each other.
I suspect this is why I had to get a permit from Vector the lines
company first.

Answer:
The voltage rise is an issue that Vector would be concerned about. The voltage rise makes designed networks difficult as they are designed for a declining voltage The other thing that they would be concerned about is the disconnector being installed (usually part of the inverter in a packaged product). They want to make sure that the disconnector will stop exporting power to the grid when there is an outage on the network. This is to prevent back feeding an isolated line being worked on

Porboynz:
Can this exported power be transmitted backwards through a standard distribution transformer such as the one outside my house or must all my exported energy be used by my neighbours?

Answer:
When power is exported to the network it is shared. Power not used by neighbours on the same transformer will go through the transformer and be available for the network to distribute. Put it this way, if the house load on the transformer was 100kVA and 50kVA was generated by everyone using solar then the net load on the transformer would be 50kVA. If the generation was 150kVA the power flow would reverse and 50kVA would be exported the network to use

Porboynz:
How many houses are typically fed by one of these street transformers?

Answer:
Depends on the size, I’m not sure from those measurements of the size but it does sound large. If you find out the size (written in units of kVA) and divide it by 4kVA per house then that will give you an approximation.

richms
28176 posts

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  #940645 25-Nov-2013 20:43
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4kVA per house? That cant be enough really? I guess they have enough thermal mass they can tollerate a degree of overloading for a while, but surely come winter when every house has a couple of heaters on and their hot water heating etc it would be way over 4kVA per house.




Richard rich.ms

Parewanui
30 posts

Geek


  #940837 26-Nov-2013 09:21
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richms: 4kVA per house? That cant be enough really? I guess they have enough thermal mass they can tollerate a degree of overloading for a while, but surely come winter when every house has a couple of heaters on and their hot water heating etc it would be way over 4kVA per house.


4 kVA is not a typo.
Besides this PM, another has quoted that amount to me in the past.

Also, discussing getting grid-connected PV systems, certified.
There have been quite few home-made-electronics PV systems not shutting off in a power-cut and back-feeding.
Hence the whole safety-thing around certification.


Another post at /. …
USA-right-wing arguing amongst themselves while there rest of the country just wants to get on with solar.
    http://classic.slashdot.org/story/13/11/22/1716216

Meanwhile, over the last 8 years Germany has already taken PV mainstream and now they are moving on to storage…
    http://hardware.slashdot.org/story/13/11/09/1440242/germany-finances-major-push-into-home-battery-storage-for-solar
…and…
    http://www.greentechmedia.com/articles/read/germany-finances-major-push-into-home-battery-storage-for-solar


There are too many examples on the Internet discussing how wind and solar can handle base-load and peak demand, but this one backs my previous examples above that Germany is doing the right thing…
    http://www.greentechmedia.com/articles/read/Germany-Hits-59-Renewable-Peak-Grid-Does-Not-Explode

The next 2 links discuss why it is economic to do PV today in so many countries around the world…
    http://www.pv-tech.org/news/pv_module_costs_to_fall_to_36c_per_watt_by_2017_gtm_research

http://www.treehugger.com/slideshows/renewable-energy/important-graph-cost-solar-headed-parity-coal-and-gas/

So…
Germany has already taken PV mainstream.
USA already have massive commercial projects (some backed my Google actually).
It looks to me it will be mainstream in the USA-residential market in the next 2 years (new sub-divisions the size of Manukau getting built with every house having PV built into the roof?) .
Where USA goes, Australia follows (actually Australia already has some large factories making PV gear).
Since NZ, gets a bit of what ever Australia does, I expect to see home-PV gear at a 2-year-payback some time soon.
This does not mean wait a year or 2 - I believe there's many advantages to doing PV and solar-thermal today. 



Porboynz

110 posts

Master Geek


  #944291 2-Dec-2013 18:41
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I checked the transformer outside my house, its a 300kVA monster so according to Parewanui calcs that's about 75 houses at 4kVA per house. I doubt any of my neighbours have a solar PV array, I have not seen one anyway.

6 weeks in and I have my first full month power bill to share. (The actual payment amount is $92.59 once you apply the prompt payment discount, a power bill under $100 per month is very nice, plus we have had 8 people in the household for the last 3 weeks with relatives visiting from overseas) 



I exported 208kWh so that's 150kWh at $0.25 and 58kWh at $0.10.  This illustrates how important it is to size a PV array to your actual usage because with Meridian excess exported kWh are worth zip.  Meridian paid me $43.30 for my exported power, Contact would have paid me $37.44 so there is not much in it (I must check if the Contact rate is inclusive or exclusive of GST)

So in summary I am happy overall with my 3kW array, its probably got a 10 to 12 year payback compared with my optimistic 8 year payback, but that's not the whole point of the exercise for me.  Its been a lot more fun than my Mighty River Power and Meridian shares frankly.  Check out my usage graph on the bill above, I'll try to remember to post another bill in 12 months time so we can see a month on month outcome.

E3xtc
773 posts

Ultimate Geek


  #944835 3-Dec-2013 16:15
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We are experiencing the same sentiment - we installed our system about 6 months ago with the aim to just reduce our monthly outgoings (not with the aim to have a stunning ROI)...last months power bill was $20 (which was pretty awesome)....am looking forward to the rest of summer!
You do start to become more aware of just how you are using power and start to use timer delays etc (for eg on dishwashers) so that they use as much of the 'free' power being generated (rather than running them overnight like we used to)

k1wi
484 posts

Ultimate Geek


  #944997 3-Dec-2013 22:02
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Thanks for the update Porboynz!

Please don't leave us hanging for 12 months though, it would be really informative to see winter usage.

About the 4kVA average per connection for a distribution transformer - I'm also dubious of this (at least on the smaller transformers). I won't go into the specifics as to why, we could be here a while and its superfluous to the debate.

I do know the distribution extent of the transformer around the corner of me (a subdivision of 91 residences), but they weren't as kind as to post its rating in an accessible location. 0 solar cells.

Btw, Wgtn pad transformers are 100-1500kVA, while pole mounted ones are 10-200kVA.

k1wi
484 posts

Ultimate Geek


  #945082 4-Dec-2013 07:58
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Actually, there are two pad transformers for those 91 residences, just remembered where the second one was located on the subdivision. Hiding behind trees!

Parewanui
30 posts

Geek


  #954417 18-Dec-2013 16:27
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Kudos to you Porboynz.
Not only did you implement PV, you documented it too.
That's a doubly impressive effort.
I hope to emulate you, once I've saved $$.

Buy doing it and then sharing the information it adds to the discussion…
Why do micro-generators get a pittance for electricity production?
Why is PV gear expensive in NZ (not the actual suppliers fault as I see it)?
Real-life data is so important to force the point.

So dreaming about what could be…
The scene is the Auckland suburb of Avondale with its residential neighbourhood and near-by industrial area of Rosebank Rd.
Energy-broker-biz talks to the Rosebank-road-factories and determines power needs and 3 factories sign letters-of-intent.
Local-savings-bank agrees to finance the whole project and hire-purchase deals for PV for those that want it.
300 homes in Avondale agree to supply day-time electricity to the 3 factories - homes are generally empty during the day and dumping power.
Energy-broker-biz bulk-buys in PV gear for 300 Avondale homes and it is installed.
Local-council-biz and Local-lines-co move around transformers, sort out deals on lines-charges, and get rebates on national-lines-charges too.
Residential-micro-generators get 22c/kWh and the factories pay 28c/kWh (instead of the usual 34c/Kwh).

Regarding this 4 kVA discussion…
It does look weird when you consider that a home-oven draws 3.5 kW (assuming kW is equal to kVA).
But it is not about the sum of total demand.
If you are planning to install a transformer with 50 homes down-stream, maybe 65% of them have their ovens on at 1 time.
I talked to other lines-co's…
1 uses 4 kVA, another 5 kVA, another said 15 kW, another said 20 kW.
Also, transformers are moved around, so if 50 homes become 60 homes with swimming-pools gear is swapped.

Seasons Greetings.

Parewanui
30 posts

Geek


  #954419 18-Dec-2013 16:31
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I'm a dreamer but I'd like to see NZ suburbs setup like the one in this photo....

http://www.businessweek.com/articles/2013-12-06/teslas-solar-power-storage-unit

Porboynz

110 posts

Master Geek


  #954517 18-Dec-2013 21:33
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I have read a few articles online covering various methods of PV storage from flywheels to compressed air to batteries of all types.  Batteries still have the best space to storage to complexity ratio but darn they cost a lot a do not have the promised longevity of the PV panels.  I went to a friends house Saturday where he has taken up the Vector offer with a battery cabinet, its a big unit but he has it nicely positioned under a 1st floor deck.  What I can not get my head around is the $70 per month rental, because that's near what I am saving each month with my 3kW array.  Financials aside, it is a nice package that looked to be well installed and the web app easy to understand (but maybe a bit basic for a true Geekzone denizen) It looks to me that the Vector system first tries to provide all the household base load during sunshine generating hours, using any excess to charge the battery.  Any surplus once the battery is charged is then exported. Afterhours the battery starts providing output minimising the import.  I would have liked to have started turning on some big loads to watch how the kit reacted but it was not possible, we were there for a xmas get together.  I think the battery had about a 9kWh capacity fully charged.

That leaves me with the thought that if batteries are expensive and short lived,  grid tied has its place as long as there are not too many installations causing voltage issues as reported in Australia. There is also the question of the buyback rates offered by the retailers.   I am now considering a hybrid system with a charger inverter battery arrangement powering my household water pump, charging the battery only when there is power being exported, we will see.

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