3kW Grid Tied Solar PV: Watts and Warts.

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484 posts

Ultimate Geek

#928642 7-Nov-2013 11:37

Looking forward to following this.

A few questions re: how you decided on the tilt of the panels - it looks like you just used the slope of the roof? How close does this line up with the optimal pitch of ~35 degs? Given your .55Kw base load, did you look into a winter bias, in order to smooth out supply over the year? (I.e. sell a little less back to the grid in summer, but make a little more in winter).

Did you estimate a payback period?

I would love to move toward solar but I'm still on the fence with the technology here in NZ, in the mean time I'll happily follow your experiences :)

mclean

581 posts

Ultimate Geek

Subscriber

#928647 7-Nov-2013 11:43

Very interesting topic. Questions:

I assume your average background use is 0.55kW, not kWh?

When you say you delay running washing machines and dishwashers, do you mean that you delay them until you have solar generated power available?

No batteries?

Porboynz

110 posts

Master Geek

#928933 7-Nov-2013 17:00

k1wi: Looking forward to following this.

A few questions re: how you decided on the tilt of the panels - it looks like you just used the slope of the roof? How close does this line up with the optimal pitch of ~35 degs? Given your .55Kw base load, did you look into a winter bias, in order to smooth out supply over the year? (I.e. sell a little less back to the grid in summer, but make a little more in winter).

Did you estimate a payback period?

I would love to move toward solar but I'm still on the fence with the technology here in NZ, in the mean time I'll happily follow your experiences :)

The optimal pitch discussion is interesting, my main objective was to minimize the visual pollution and avoid the unhappy wife factor as much as possible. (Happy wife, happy life). Plus angling the panels requires some serious engineering. The roof pitch is approx 17 degrees, so its way less than optimal, but in practice I am generating energy for more than 12 hours a day and I wonder if its as big a problem as the theory indicates. My payback period is 8 years according to one particularly favorable spreadsheet iteration I did, but honestly I will be happy if it turns out to be a self funding experiment. What I am observing already is that during the summer I will be exporting >50% of whats generated. In winter with reduced generation capability and increased daytime load it may get nearer neutral. Its a real challenge to use power during the day when the home is empty of wet-ware. Both the dishwasher and washing machine can be set to operate on time delay during the day, but there is no assurance the sun will be shining when they are operating. Maybe I'll finally allow the kids to use the Heat Pump for cooling in the summer. Maybe.

Porboynz

110 posts

Master Geek

#928937 7-Nov-2013 17:14

mclean: Very interesting topic. Questions:

I assume your average background use is 0.55kW, not kWh?

When you say you delay running washing machines and dishwashers, do you mean that you delay them until you have solar generated power available?

No batteries?

Hi there mclean, yes you are right the background power use is approx 0.55kW or 550watts during the daytime hours when there is often no one home. This will change when school holidays start and then there will be PC's TV's and lights on and probably fridges left open. Both the dishwasher and washing machine do have delayed start functions but it actually requires process re-engineering the household routines. Even then you might schedule a delayed start but its cloudy for that hour of the day. Interesting problem, it means getting the best buyback deal from your power retailer so you can use the grid as a battery to time shift your generation capacity.

Porboynz

110 posts

Master Geek

#928938 7-Nov-2013 17:17

langi27: What are the current buy back rates and who offeres them?

Hi there langi27, you are clairvoyant as that was going to be my next discussion element. I'll try to post later tonight what I found with Contact and Meridian.

Porboynz

110 posts

Master Geek

#929071 7-Nov-2013 20:24

langi27: What are the current buy back rates and who offeres them?

Right, as promised here is the next instalment of my path to photonic phantastica.

Export Power rates:
It’s easy to misunderstand how this works when you read the power retailers website faq. Based on my installers recommendation I moved from Contact to Meridian some months before the installation. Interestingly the day after I submitted the change request my old analogue meter was changed out to a new smart meter by Contact. It seems they were upgrading all the meters in my area, just a coincidence but it seemed too much trouble to argue the point. An Import Export meter needs to be installed to measure the power you Import from the grid and the power you Export to the grid. Apparently there is some mysterious GST problem if they simply charge you the difference.

Contact offer $0.1988 per kWh buyback with no limit on how much you generate for any system less than 10kW peak. They bill you for whatever you use at whatever rate plan you are on. They will install the import export meter at no install charge, but they do require you to bill them each month for the exported power, this is your responsibility.

Meridian offer $0.25 per kWh buyback for up to 5kWh per day. They pay $0.10 per kWh after this 5 kWh and charge $85 to install the import export meter. At this stage they have no way of actually measuring how much power you export each day so its averaged out to 150kW per 30 day month.

Here is my first power bill from Meridian.

You can see Meter 13003032 Register 1 has 172 units Imported and Register 2 has 92 units Exported for the 13 days the solar panels were in operation. Based on 13 days at 5kW per day they then credited me with 65 units at $0.25 and the remaining 27 units at $0.10. Below that on the bill is my original Meter 212628512 with 508 units Imported before the new Import Export meter was installed.

I decided to go onto the Meridian low energy user plan 2 days before the bill was run thinking it would apply to the coming month. I was surprised when it was applied retrospectively. When they say “next bill”, they really mean next bill. The Low User plan has a higher $0.294 per unit charge and a lower supply charge of $0.3852 per day. Optimally I probably should have waited until after I got my first bill and stayed on the older Standard User plan of $0.2268 per unit and $1.86 per day, can’t win them all though.

This is important knowledge to retain if later I decide to change plans for winter. You can monitor your usage for most of the month and decide the best plan on the last day it seems.

nutbugs

269 posts

Ultimate Geek

Lifetime subscriber

#929251 8-Nov-2013 09:22

Great information thanks Porboynz.
Are these buyback rates contracted for any period of time? Or do they reserve the right to simply alter at any time it suits them?
And it seems that Meridian do all the paperwork for you? Seems much simpler than having to invoice them!

Thanks for sharing :)

k14

629 posts

Ultimate Geek

#929252 8-Nov-2013 09:31

Did you do any analysis on Contact vs Meridian in terms of your expected output? Doing a quick calculation I think the per monthly generation required before Contact becomes a better proposition than Meridian is approx 380kWhr, or around 12-13kWhr per day. At your current output you are easily exceeding this, although things skew the other way in winter. Although this doesn't take into account the other usage rates of the two retailers, which could skew it one way or the other.

If you have already said this I apologise but have you calculated what your expected annual generation will be and what this is per month? I live in Central Otago so think the short winter days may not make it the most lucrative project but maybe the longer summer days could help balance it out?

Porboynz

110 posts

Master Geek

#929272 8-Nov-2013 10:08

nutbugs: Great information thanks Porboynz.
Are these buyback rates contracted for any period of time? Or do they reserve the right to simply alter at any time it suits them?
And it seems that Meridian do all the paperwork for you? Seems much simpler than having to invoice them!

Thanks for sharing :)

There are no forward contracts and I am prepared for the worst and hoping for the best. It will be like many things, great for the early adopters then nec minute everybody is doing it and the clamps come on. Meridian had recently changed from a one for one swap Import less Export deal to the current arrangement, I do not expect they will make another change in the near future. Comparing the 2 retailers, the Contact website is the better in my opinion, the Meridian website looks good but its slow and full of dead ends and not at all intuitive, probably designed by a Bach of Fine Arts graduate who could not get a job at McDonalds.

I agree that the Meridian arrangement for billing is superior, sending off an invoice each month is not attractive, maybe you would have to declare it to the IRD as income and pay tax on it? Crikey!

mclean

581 posts

Ultimate Geek

Subscriber

#929273 8-Nov-2013 10:10

k14: Doing a quick calculation I think the per monthly generation required before Contact becomes a better proposition than Meridian is approx 380kWhr, or around 12-13kWhr per day.

I make the Contact buy-back better above 7.6 kWh/day, and the actual buy-back was 7.1 kWh/day. But as you say the choice is going to be affected by all sorts of other things, including the consumption profile in the house. It's better to use the solar power than to sell it back.

If you can generate a surplus it adds a whole level of complexity to choosing a retailer!

bazzer

3438 posts

Uber Geek

Trusted

#929274 8-Nov-2013 10:16

Porboynz: I agree that the Meridian arrangement for billing is superior, sending off an invoice each month is not attractive, maybe you would have to declare it to the IRD as income and pay tax on it? Crikey!

That's an interesting point. Why would you not have to pay tax on it. Isn't it income? On the other hand though, you should be able to deduct the expenses (panels, install etc).

LennonNZ

2459 posts

Uber Geek

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#929275 8-Nov-2013 10:18

Regarding the invoice.. as (I presume) you are not GST registered you have to send them a bill with no GST on it..

Is this is the issue you where talking about with the GST problem and if they just went with what you used - what you imported would not work.

SepticSceptic

2186 posts

Uber Geek

Trusted

#929276 8-Nov-2013 10:19

Porboynz:
I agree that the Meridian arrangement for billing is superior, sending off an invoice each month is not attractive, maybe you would have to declare it to the IRD as income and pay tax on it? Crikey!

A GST invoice ? You get charged with GST for normal usage, would you have to also have to produce a GST invoice ?

LennonNZ

2459 posts

Uber Geek

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#929277 8-Nov-2013 10:27

SepticSceptic:
Porboynz:
I agree that the Meridian arrangement for billing is superior, sending off an invoice each month is not attractive, maybe you would have to declare it to the IRD as income and pay tax on it? Crikey!

A GST invoice ? You get charged with GST for normal usage, would you have to also have to produce a GST invoice ?

I've had this before.. I was supplying a service to a NZ Company (as a normal person not company) but _I_ had to invoice the company to get my money..

I had to send them a Invoice for them to pay me. As I was not GST registered the invoice didn't include GST.

If you work out how much you save you have to take this into account as well.

say $100 export + GST - $50 import (+ GST) is quite a bit different than $100 export + GST - $50 import (no GST)

mclean

581 posts

Ultimate Geek

Subscriber

#929295 8-Nov-2013 10:53

Not only income but on the face of it generating and selling power seems to meet the definition of a business. If it is then the equipment has to be depreciated but can be claimed as a tax deductible (after taking some sort of share for personal use)!! Anyone from IRD reading?

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