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The Whole Problem with Solar PV

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The Whole Problem with Solar PV

Posted 28 Jul '17 11:24 AM

For years i've been trying to get around this problem with going solar PV. This past month living in Christchurch i'm convinced the power companies are raking it in. After recent dumps of rain, the spot prices of power have not gone down much as it should, pushing me to re-think about solar PV installs.

How do you specify solar PV size when the conundrum is, when you need electricity the most (in winter time), the sun is out the least amount of hours. The sun also is at a low angle so it seems best the solar PV should be mounted at the most direct angle (excess of 45 deg). In the summer time there's plenty of sun and the house uses least amount of electricity. At the same time the power companies (for grid tied) pay you peanuts for any electricity put back in the grid.

$15K for battery storage is a killer price and how sustainable? After 15 years or so you're forking out $$ for another Tesla Powerwall Pack. Where is the logic and where are people's senses in terms of cost savings ??

My current power retailer is Flick Electric and while in the summer months they were fantastic with real low pricing, they are really creaming me now at winter prices x 5 times on average than summer rates. A spot rate of say 30cents/kW/hr is like 60cents retail. I've seen peak demand as high as $1.50/kW/hr.

I suppose things could be worse, like living further south.

RE: The Whole Problem with Solar PV

Posted 31 Jul '17 04:12 PM

Focus on a more energy efficient house first, people rush into PV before fixing their house, our neighbor bragged their system has their power bill down to $90 a month, our house is larger and only has a $45 power bill a month (in summer), winter $125.

RE: The Whole Problem with Solar PV

Posted 07 Aug '17 09:52 AM

The most energy efficient house won't matter when it comes to cooking meals. If you have a wife and elderly that enjoys heating up the bathroom 1st before having a shower (and i'm speaking where 22C room temperature is not enough as they're accustomed to 25C room temp when coming out of the shower), no amount of effort in home insulation and passive heating will change luxury habits. Those that pro-eco minded don't mind their homes in winter months dropping down to an indoor temperature of 10C overnight. Their comfort level of 18C does indeed save, put on an extra sweater.

Perhaps the architect designer I spoke at Peter Ray Homes pre-2010 told me, "In NZ, Kiwis just put up with rising power prices and don't care about extras such as solar PV or solar hot water.

RE: The Whole Problem with Solar PV

Posted 07 Aug '17 11:54 AM


if the house is built to right spec, it takes bugger all energy to heat the bathroom to 25 C.
I also like to have the house warm when I get up and I don't want the temperature to drop down to 10 C over night.
This is achiveable with a continously insulated thermal envelope and low energy consumption.
A nice and warm house with low energy consumption is my motivation to do what I do and the choice of materials.
No, even if my house is not a passive house it is a highly energy efficient house and that's all I need.

RE: The Whole Problem with Solar PV

Posted 26 Aug '17 02:22 PM

As an update for the past week i've been in contact with many local solar PV installers and it's interesting to hear all the different ways of setting up a roof top solar PV array. Everything from string inverters, micro inverters, and hybrid inverters. However I would like to share a very critical issue that none of these installers have yet got back to me on or care to give me a very detail explanation. The problem arises that our house is on 3-phase power and if you read the following article, I am concerned for those that intend to be grid tied:

While the article is Australian based, (NZ does indeed follow a similar safety standard as Australian in terms of electrical code). my brief Google search didn't show NZ power retailers do 'net-metering'. Please correct me if i'm wrong and I would most certainly be grateful if I can find a clear answer to this potential problem.

RE: The Whole Problem with Solar PV

Posted 21 Sep '17 07:39 AM

Interesting question, looks like iy's easier to find real professional in this sphere and ask for some help than to do it on your own :(

RE: The Whole Problem with Solar PV

Posted 21 Sep '17 10:12 AM

Hello Dave. There was no intention of doing the installation on my own and it was good that I kept prodding along quotes from different installers around Chch.

The conclusion became clear. While all the installers didn't want to risk losing a sale, none didn't want to say dwellings with mains power connected to 3 phase were at a disadvantage to those on single phase. Instead the solutions they provided were:

1) Use 1 of the 3 phases where a single phase inverter would be connected and that this 1 phase be the one that had the most 'day time' use load in the house. This meant a re-wiring of the switch board to get the maximum use of day time solar. The problem with this setup is that the other 2 phases would draw power from the grid, despite it may be of little load. High demand loads such as heat pumps, ovens, etc. would be re-wired to the solar power generated phase. However with all this effort, it seems we're trying to change a 3 phase connected house back to a single phase. We can't mutually exclude 1 device for daytime use - such as heat pumps, where we often use in the winter months at night. I mean there's only so much power used in the daytime.

2) Use a 3 phase power inverter which equally splits power from the solar array to each of the 3 phases. The problem with this setup is each phase would only have 1/3rd of the maximum solar power generated. So if we have a 6kW array, each phase would see 2kW. But many appliances such as heat pumps, ovens, and kettles, draw well over 2kW of power so the net difference will come off the grid. WHILE the other 2 phases that may not have much load, gets exported to the grid (goes UNUSED for self consumption).

So the whole issue is that in NZ, the retailers don't do a "net metering" which is the sum generated minus the power drawn off the grid, regardless on which phase. Without net metering, I can't see how solar PV are economical unless you have the ability to go with a massive 10kW array, a capacity that far exceeds the maximum use on each phase. Battery storage is a possibility but then we're going towards an off the grid situation.


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