3kW Grid Tied Solar PV: Watts and Warts.

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110 posts

Master Geek

#1153168 13-Oct-2014 21:44

SQLGeek: I have been quoted $17,000 for a 15 panel 4kW system using micro-inverters. Micro-inverters were a good choice as the house has 3-phase power and allows the PVs to be split over each phase. The 3-phase inverters are way too expensive, as was getting 3 x single-phase inverters.

This is a new build in Chch, with the panels going on a flat Butynol roof so the installer has allowed extra for the fittings.

A great thread, thanks to everyone for sharing.

Wow 4kW is a generous amount of generation. You have 3 phase power installed so the micro inverters make sense. Have you measured each usage phase and made a decision about which phase will get what solar generation yet? I'm interested in the grid tied aspect, you get a single meter that measures the import and export on all three phases presumably.

What is your daytime base load that you want/need a 4kW array? I understand that in CHCH you have access to very cheap night rate power which I do not have here in AKL. Make sure you have calculated what 4kW exported to the grid is worth to you compared with using cheap night rate power to heat water etc. Here in AKL I can export 5kWh per day and get paid $0.25/kWh then draw the same 5kWh back after dark and get charged $0.22/kWh so net gain, the grid acts like a battery. After 5kWh per day though Meridian pay me just $0.10/kWh. If you export the same 5kWh and get the same $0.25/kWh that's good but any surplus after that is just $0.10/kWh which is about the same as what you can buy Night rate power for to heat a large water cylinder. You need to make sure you size your PV to provide your daytime base load plus export the sweet spot 5kWh per day. (averaged over winter and summer) Investing any more in PV may reduce your ROI.

Porboynz

110 posts

Master Geek

#1153170 13-Oct-2014 21:48

Hammerer:
Jase2985: Ive been following this thread for a while now and when we eventually go to renovate we will be putting some solar panels on the roof.

My question is my "north" facing roof faces about 20deg to the east of north (020) and is only small about 7m wide at the guttering) (long narrow section) so you wouldn't be able to fit many pannels on there. but my "west" facing roof 70 degrees to the west of north (290) is huge about 15m wide at the guttering. How is this going to effect how many Kw/H i am able to generate? would a split array be better? ie some on the north facing side and some on the west facing one?

also is the angle of the panels critical? from what ive read its doesn't make a huge difference if they are 20 degrees or 37 degrees or 45degrees, is it worth having them tilted to the optimal angle or just throw in another panel?

Thanks for all the info thus far its been very informative

I'd guess that 20 degree NNE will give you 10-20% more energy than 290 degrees WNW. You can check this for your location using NIWA's Solarview which calculates cumulative available energy per m2 on several different days of the year. Simply input your address and if it find it you'll see what you get north facing then you can input the two scenarios you have and compare the results. You can also see the difference for different panel angles.

NIWA also has a short but useful background article https://www.niwa.co.nz/sites/niwa.co.nz/files/import/attachments/solar.pdf

That's a great reference site thanks for sharing. Now that I have 12 months real data I will compare it with the theoretical NIWA prediction.

bfginger

1229 posts

Uber Geek

#1153242 14-Oct-2014 06:59

Is $17,000 for a 4kWp system really value for money?

SQLGeek

129 posts

Master Geek

#1153276 14-Oct-2014 08:09

bfginger: Is $17,000 for a 4kWp system really value for money?

It is when you have a $15,000 subsidy :-) This is an earthquake rebuild, my insurance policy included 15K for green tech (there has got to be some wins for not having a house for over 4 years).
3 phase power is what makes it so expensive, it’s over 300 square meters, so a single phase is not enough.

Porboynz

110 posts

Master Geek

#1153310 14-Oct-2014 08:49

Absolutely fair enough and what a great idea a Green Initiative is. I would make sure you get a large stainless hot water cylinder installed with dual elements. I suspect you are going to want to divert some of that 4kW into heating water. Alternately some sort of night store or underfloor heating you can divert energy into while the sun shines and use effectively at night. We have the technology.

SumnerBoy

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#1153329 14-Oct-2014 09:07

The big problem (and it isn't really a problem as such) is that down here in ChCh we get such a good deal for night rates that diverting excess PV during the day gives very little benefit. My night rate is 13c/kWh (excl. GST and discounts). Once I export my 150kWh (on Meridian this is) the export rate drops to 10c/kWh, as it does for everyone. But that means up until that 150kWh threshold I am far better off exporting during the day and getting my 25c/kWh. Then after I hit that threshold I am only losing out on 3c/kWh by continuing to export rather than divert. So I would have to be diverting a LOT of kWh to make it worthwhile.

I realise for those who aren't lucky enough to get these night rates it is a different story.

A good problem to have, but a little disappointing as I was very keen to get one of these PV diverters up and running!

SQLGeek

129 posts

Master Geek

#1153350 14-Oct-2014 09:29

SumnerBoy: The big problem (and it isn't really a problem as such) is that down here in ChCh we get such a good deal for night rates that diverting excess PV during the day gives very little benefit. My night rate is 13c/kWh (excl. GST and discounts). Once I export my 150kWh (on Meridian this is) the export rate drops to 10c/kWh, as it does for everyone. But that means up until that 150kWh threshold I am far better off exporting during the day and getting my 25c/kWh. Then after I hit that threshold I am only losing out on 3c/kWh by continuing to export rather than divert. So I would have to be diverting a LOT of kWh to make it worthwhile.

I realise for those who aren't lucky enough to get these night rates it is a different story.

A good problem to have, but a little disappointing as I was very keen to get one of these PV diverters up and running!

Yeah the cheap night rate power is a good problem to have. Initially I was thinking of putting in a night store heater, but it's just not worth it.
I've got under tile heating in the bathrooms so I might look to use that. It would be great to automate this so that if the PVs are generating turn on the under tile heating. I've just started investigating home automation, I'm quite interested in the kit you have at smartthingsnz.co.nz so might get in touch.

SumnerBoy

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#1153357 14-Oct-2014 09:43

I am doing this with my washing machine - once I am exporting more than 750W then my automation system turns the WM on and in theory I get a free wash! Under tile heating would be a much better load, since it is purely resistive and would happily handle being switched on/off, I might have to look into this! This sort of thing is pretty simple to setup using a Fibaro 1x3kW relay (or even the 2x1.5kW relay) hooked up to either openHAB or the Fibaro HC Lite/HC2. You then just need a feed from your solar inverter to monitor your generation and add a rule to switch the relay accordingly.

If you are getting an Enasolar inverter then I have a script that will poll the device and spit out readings to an MQTT broker, if you are interested. Or you can go down the route of a proper energy monitoring system, I have just installed one of the EmonTX monitors from OpenEnergyMonitor (www.openenergymonitor.org). Their stuff is all open source with a very helpful community. If you want any further information let me know.

Once you have the data (via energy monitors) and the control (via Fibaro/switches) then it is just up to your imagination how you link them all together!

Porboynz

110 posts

Master Geek

#1153972 14-Oct-2014 21:58

Happy Birthday: One Year Old Today
At 10am on the 14th October 2013 my 3kWh solar PV array was commissioned. 12 months on I have real data to compare with my ROI calcs, I have had a lot of interesting interactions on Geekzone and built some gadgets to further exploit ol Sol.

Recap:

3kWh PV array consisting of 12 x 250 W Renesola panels
3kW Enasolar Inverter, Made in NZ and recommended
North facing concrete tile garage roof at 17 degrees pitch
Owl Intuition power monitoring web connected gateway
Kiwibank Renewable Energy loan for $12k, got my first $800 rebate last month
Existing 2 flat collector solar hot water panels and 310 litre HWC
Understanding wife

Real Data:
Import Export Meter readings: 6560kWh Imported 1984kWh Exported
3kW Inverter readings: 12kWh Average daily generation 4409kWh generated during 4124 hours of sunshine (11.3 hours per day average)

Calculations: 9600kWh per annum average before PV (but also before heat pump and LED lights and #2 son off to Uni in Wellington)
4409kWh generated - 1984kWh exported = 2425kWh used (approx. 6.6kWh per day)
6560kWh Imported + 2425kWh from solar = 8985kWh for the last 12 months

Power Bills Oct 2012 to Sept 2014 $2556.14
Power Bills Oct 2013 to Sept 2014 $1398.49

Enasolar snapshot 14/10/14

Enasolar Annual Bar Graph

SumnerBoy

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#1153976 14-Oct-2014 22:04

Awesome - pretty good results you got there - looking forward to seeing how mine compares in another 10 or so months!

freemark

103 posts

Master Geek

#1154104 15-Oct-2014 08:49

Excellent stuff!
Applying a very small percentage increase to the figure (17 degree tilt drops you to about 98.5% capture efficiency) gives 1492 kWh generated per installed kW. We had been using 1425 as our baseline figure for Auckland calcs (with Enasolar) and I have heard of some installers promising up to 1800. Can't wait to see the figures for next year - NIWA numbers are done on a long term average.
That is great performance.
How many meters of DC cabling between the end of your string and the Inverter? Have you washed the Modules at all during the year?
Cheers

gchiu

1206 posts

Uber Geek

Trusted

#1154163 15-Oct-2014 09:47

Power Bills Oct 2012 to Sept 2014 $2556.14
Power Bills Oct 2013 to Sept 2014 $1398.49

I take it that is two separate years?

How much was the final cost of the installation? Or did the 12k loan cover it all?
And what is your latitude?

Porboynz

110 posts

Master Geek

#1154205 15-Oct-2014 10:33

freemark: Excellent stuff!
Applying a very small percentage increase to the figure (17 degree tilt drops you to about 98.5% capture efficiency) gives 1492 kWh generated per installed kW. We had been using 1425 as our baseline figure for Auckland calcs (with Enasolar) and I have heard of some installers promising up to 1800. Can't wait to see the figures for next year - NIWA numbers are done on a long term average.
That is great performance.
How many meters of DC cabling between the end of your string and the Inverter? Have you washed the Modules at all during the year?
Cheers

I washed them down around April/May and they are due for another wash now. Mind you I still see the full 3kW output from time to time, usually on cooler days when the sun suddenly bursts out from a cloud. The DC cabling run is less than 5 metres. 1800kWh per installed kW is very ambitious, similar to the claims some solar water installers were making 5 years ago that it would half your power bill. My result of 1470kWh per installed kW is of course because I am on the North Shore, there is very little cloud or rain here during the day.

SumnerBoy

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#1154212 15-Oct-2014 10:40

In my estimates, when deciding whether to install solar or not, I was using a value of 13.65% for annual average production per kWh. This was given to me by one of the guys selling PV down here in ChCh. The other guys I talked to said around 14%. So for my 3.12kW of panels I estimated 1195kWh per year. Will be interesting to see how that pans out over 12 months - I would of course expect less that you blokes up on the sunny north shore, but we get our fair share of clear sunny days down here in Nicechurch so it will be interesting to compare.

Porboynz

110 posts

Master Geek

#1154237 15-Oct-2014 10:42

gchiu:

Power Bills Oct 2012 to Sept 2014 $2556.14
Power Bills Oct 2013 to Sept 2014 $1398.49

I take it that is two separate years?

How much was the final cost of the installation? Or did the 12k loan cover it all?
And what is your latitude?

You spotted an error, apologies:
Power Bills Oct 2012 to Sept 2013 $2556.14
Power Bills Oct 2013 to Sept 2014 $1398.49

Latitude huh? According to the Niwa site I'm at -36.722735 latitude and 174.72409630000004 longitude, Browns Bay.

The install for 3kW panels and inverter inc the Owl Intuition web monitor was just under $12k. The Monier concrete tile roof increased the installation cost. I was very happy with the install, all the DC and AC is in conduit, nicely clipped, labelled etc. If you are in the upper North Island I can recommend Tim at Solarcraft, mind you I think he has done installs as far away as some of the Pacific Islands, nice for some.

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