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Porboynz

110 posts

Master Geek


#133819 3-Nov-2013 22:11
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I think there is some value in starting a discussion about installation of a Grid Tied Solar PV to compare with the Vector Solar Panel trial thread started by Dav4122

In 2005 I installed a single flat plate solar hot water system, connected to an ancient Rheem 180litre HWC. That single panel easily provided too much heat for the glass lined Rheem HWC (max 65oC) during the summer months. The fortuitous acquisition of a 310 litre stainless HWC from a friend allowed the fitting of a second solar flat plate panel, and it’s been providing 95% of our hot water for the 5 months between December and April each year ever since, plus providing a very useful preheat during the autumn and winter months when electricity top-up is necessary. The payback was a very satisfactory 5 years because the cost of a kWh of power has increased considerably but mainly because I installed it myself with guidance from the helpful folk at Energy Conscious Design (Thanks Ian) What has been interesting is the number of folk who do not understand this is a simple flat plate collector system, water pumped through tubes bonded to a flat plate collector under solar rated glass heated by the sun. Many thought the panels created electricity which then heated the water.

Back in 2005 solar Photovoltaic (PV) panels were prohibitively expensive. In 2013 the situation is different, there is a PV panel oversupply and manufacturers are discounting panels aggressively. We also have a local supplier Enasolar in Christchurch who build state of the art grid tied inverters, complete with WiFi web access. It was clearly time to recheck the financials, but it’s not all about ROI, there is also the FG and HWDWTMTW factors to be considered, not to mention environmental empathy.

I fitted an energy monitor which showed the household 24 x 7 background consumption was around 0.5kW to run 2 x Mysky boxes, 1 x Tivo, 1 x fridge, 1 x freezer, 1 x home ventilation fan, 3 x WiFi AP’s and a VDSL modem plus the usual collection of wall plugs and standby devices like TV’s and PC’s. We have a 7kW heat pump, electric oven, gas hobs (LPG bottle) and electric HWC (solar assisted as above)  This all combines for an annual consumption of 9600kWh. Those MySky boxes and Tivo use a lot of power, they pump out a lot of wasted heat, no energy star ratings just wanton consumerism, guilty as charged.

Careful analysis of the last 12 months power usage and the houses daytime usage suggested a 3kW system would be more appropriate than my initial ‘bigger is always better, it does not matter what the question is....’ 5kW system. I was able to get a 3kW 12 x 250W panel installation for under $12k complete with warranty and an internet connected monitoring system (essential geek functionality) Checking the daytime usage was an important decision factor, because with a grid tied system what you do not use gets exported and the price paid for exported power is at the whim of the energy retailers.  

   

It’s been 2 weeks now since switch on and I have my very first power bill, but first to discuss how I got to the point of being able to turn it on and turn photons into electrons. Feedback welcomed if anyone thinks this is a subject worth continuing, or not.

FG = Feel Good
HWDWTMTW = He who dies with the most toys wins

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Crysoganus
23 posts

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  #926943 4-Nov-2013 12:33
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I for one am interested in the journey!

dontpanic42
1574 posts

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  #926975 4-Nov-2013 13:24
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Indeed, also interested in your adventures.

langi27
576 posts

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  #927009 4-Nov-2013 14:00
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Count me in
I'm about to build and need to decide how far I want to go with Solar.

I'm almost cetainly going to install Solar Hot Water but need to weigh up the pro's and cons of PV Solar and a grid tied system. 

Dratsab
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  #927019 4-Nov-2013 14:19
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Most definitely interested in hearing more about this!

nutbugs
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  #927031 4-Nov-2013 14:41
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Yep - definitely of interest to me! :) Thanks!

Fo0L
54 posts

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  #927089 4-Nov-2013 16:21
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+1 - I'm keen to learn more about whats involved and what to expect, I'd like to look at a system for my home sometime in the next few years so the experiences of others in the real world are definitely relevant.

Porboynz

110 posts

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  #927296 4-Nov-2013 22:30
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We have critical mass, I'll type up some posts over the next few days. In no particular order I'll try to cover off the selection of a power retailer, installation of an import export meter, online web access, panel selection, inverters and of course all the little stumbling blocks along the way plus share a few misconceptions I started out with. I think the most amazing thing so far has been the way the panels start generating power with the barest amount of indirect sunlight early in the morning when they are still covered in dew, and how they keep generating some power even when its cloudy and raining. (We do get a bit of rain here on the North Shore) I had not expected that sort of efficiency.

Porboynz

110 posts

Master Geek


  #927828 5-Nov-2013 19:34
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Part Two:
Once I had convinced myself it was a good idea to fit the panels I needed to settle on the best size for my situation. I had some facts to deal with:

- 9600kW per annum average usage
- 33kWh daily usage in winter months (lower panel output)
- 20kWh daily usage in summer months (higher panel output)
- 0.55kWh average background usage during daytime hours 365 days of the year
- 3kW of 250 Watt panels would fit all 12 panels on the garage roof facing North
- 5kW of 250 Watt panels would require a larger 2 string inverter, 12 panels on the garage roof and 8 panels on the main house roof.

I used a spread sheet to model both a 5kW and a 3kW system. A larger 5kW inverter can have 2 x panel arrays (called strings) and I did consider starting with a single 2.5kW string. I could then add a second 2.5kW string when the ROI was better understood with real data from 12 months use plus there was the potential of buying the extra panels cheaper if prices continued to decline.

Well all I really did was confuse myself with various predictions of anticipated generated kWh in winter and summer less the 0.55kWh daytime usage, the buyback rates of Contact and Meridian, global warming, the angry wife factor if the panels looked really ugly, etc. In the end it was simpler to go with the 3kW array which covers the garage roof only as in the photo below and has a single string 3kW inverter (cheaper).



After just 2 weeks I can see from the results gathered already 3kW was probably the right choice for me. With all the uncertainty around what rate the power retailer will pay you for exported power investing in excessive capacity seems risky to me. The ideal balance is a nebulous point where you consume as much of the power produced during the day as you can by delay running washing machines and dishwashers, with the excess exported to balance your non sunshine hours usage.

wongtop
545 posts

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  #927901 5-Nov-2013 22:02
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Thanks for sharing. I note that the panels to the left (east) will get a bit of shading from the higher roof (and a partially shaded panel has pretty much the same output as a fully shaded panel). Could you not have installed the array so it was slightly further away from the house to avoid this shading (or is there something to the west of the garage that would have shaded the panels if you moved them in that direction?

Porboynz

110 posts

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  #927968 6-Nov-2013 07:21
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wongtop: Thanks for sharing. I note that the panels to the left (east) will get a bit of shading from the higher roof (and a partially shaded panel has pretty much the same output as a fully shaded panel). Could you not have installed the array so it was slightly further away from the house to avoid this shading (or is there something to the west of the garage that would have shaded the panels if you moved them in that direction?


Excellent observation.  This is a concrete tile roof and the brackets need to pass under the lower edge where they are screwed to the support purlins.  One of the jobs I had to do prior to installation was to get the roof repointed and repainted, after 30 years the Monier tile glaze was all but gone and the roof had a grey concrete patchy appearance, porous and ugly and needed a chemical clean every 12 months to keep the moss at bay.  Anyway, to fit the stainless mounting brackets you must remove the tile and grind a small relief for the bracket.  Having just had the roof re-pointed and resprayed I discovered it was very difficult to remove tiles from the western end of the garage roof as it would have disturbed the pointing of the edge tiles. We mounted the last bracket as far to the west as practical and overhung the mounting rails as much as possible, hence the position of the array.  In practice the end panels are not shaded by the early morning sun, but I think it will be a factor in winter when the sun is lower.  It was a compromise I had to make at the time, but with a lot of addn work I could change it in the future if it does prove to be a significant problem in the winter months.

nutbugs
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  #927981 6-Nov-2013 08:16
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Thanks for this. What are the dimensions of the panels/array? ie what was the actual area of roof space you needed for this size array?



Porboynz

110 posts

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  #928341 6-Nov-2013 18:35
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nutbugs: Thanks for this. What are the dimensions of the panels/array? ie what was the actual area of roof space you needed for this size array?



Hi there nutbugs, these 250W panels measure 1640x990 each and with about 15mm between panels the 6 x 2 12 panel array measures 3330x6040.

Here is a closeup of the end bracket that secures the panel to the horizontal rails and attaches to the bracket that is mounted to the joist.



Here is a view of the bracket screwed to the joist from inside the roof space, nice and solid, stainless fittings.



Here is a view of the joining bracket between panels that connects to the horizontal alloy rails



Underneath the panels you can see the rails and the connecting wiring



Last of all, here is a photo of the older technology, the 2 x solar water flat plate collectors, 5 years old and going well.


jpoc
1034 posts

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  #928399 6-Nov-2013 21:28
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Awesome, thanks.

nutbugs
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  #928518 7-Nov-2013 09:09
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Awesome - thanks Porboynz. Great pics :) Great to get an idea of space required also. Now to work out what part of my roof a similar setup might fit on! :)

langi27
576 posts

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  #928600 7-Nov-2013 11:07
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What are the current buy back rates and who offeres them?

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