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## Talkiet

3882 posts

Uber Geek

Trusted
Spark NZ

Whoops! You're right! (That's the good thing about showing your working - others can check for errors :-)

For some reason I multiplied by a wrong number in estimating my use... Here's the actual data...

And here's the updated EECA calculation

Much much better but still nothing like good enough to make it worthwhile for me. Should I have to replace an inverter in the 25 years that would wipe out my savings...

In any case I am more interested in a functional differentiator (being able to charge and use power during an outage is a salient but hopefully infrequent benefit) and I won't get that for anything like \$4000...

Cheers - N

## TwoSeven

1313 posts

Uber Geek

Talkiet:

Running the EECA calculator I get this...

I'm presuming those values and savings are based on me being able to consume 100% of the generated power? It's not clear to me how they do that. In any case I think their analysis is very simplistic and ignores quite a few external variables that are going to affect the financial viability of a solar install.

Cheers - N

Under electricity use per year, you have 2.5kw (about 200/month) that seems awfully low. Is that both day and night units?

Scratch that - just saw most recent post

Software Engineer

## Hammerer

1891 posts

Uber Geek

My solar system is economic

I've had a retrofit solar water heating for ten years. I've been saving an average of about \$800 a year for that time (interesting that tdgeek is saving the same): I calculated a theoretical minimum of \$450 and maximum \$1,200. Our cost for the system was buried in a quote of \$13,000 for a large new cylinder, an internal partition, electrical work, new toilet installation, etc. It probably cost us \$8,000 so payback is 10 years and there is a positive ROI. But we have had zero maintenance costs so far. At some point they will kick in and probably reduce the ROI.

I would probably prefer PV now because there are more options to use excess electricity than excess hot water. At the time we installed solar hot water, PV was uneconomic because there was no option for us to sell back into the grid.

Look at a broad range of technology and opinions

I would always look at solutions more widely than just renewable energy sources like solar PV or water heating, wind and hydro generators. There is a lot of good technology out there, e.g. heat pumps, which might give as good a return while more closely meeting your needs. There are many possible solutions for improving your economic benefit and lowering environmental impact.  I'd also read through a lot of the threads here as there is a lot of good information buried in many different threads as in the examples below. Anyway, I've always found Aredwood has very useful opinions and technical expertise.

Solar should work better on a new build than a retrofit

I consider solar to be more attractive financially on a new build than a retrofit because you have the option to more economically integrate panels as the roofing material, e.g. I want this: "Solar Roof". The option also exists to install inside the roof space rather than on top of the roof. This gives lower heat losses, lower maintenance, doesn't break the roofline appearance (Our roof has 15 degree pitch and my wife wanted the solar collectors flat against it rather than at the ~42 degree pitch that would be optimum), is easier to clean and paint the roof, etc.

I've quoted and linked several topics here. I was actually searching for my original post on how my system was going but I didn't find it and maybe I didn't post it on Geekzone.

Hammerer:

If you're going with solar water heating in a new build then consider building the collectors into a roof cavity behind low-emissivity glass rather than placing it on top of the roof. It looks better for a start and the reduction in heat losses will be significant particularly where the weather is wet or windy. It will also be easier to maintain the solar system undercover and the part of the roof where you would otherwise be hindered by the attached system. There will be an additional cost for a tray to catch any fluid release that would normally spill onto the roof.

Consider a tracking solar system. This NIWA two page document is one of several useful resources on their website including the Solarview calculator [which calculates solar values by month and hour of day for any address in NZ. It is free to register as a public user.]  You'll see that you can get about a third more energy by having a solar system tracking the sun instead of at optimal tilt which gives 50% more than laying it flat. With a bigger spend the tracking cost becomes a smaller proportion so it is more likely to be an option for you.

Hammerer:

The economics of solar efficiency (both PV and thermal) point to getting a large water tank so you can use all the energy you generate. If you can get a bigger tank than 250l then you can use more of the output from the sunniest days. In Summer if you don't use much hot water then once you've fully heated the tank you won't be able to maximise the benefit of the electricity you generate.

I was interested to see that Energywise now has a calculator that estimates costs for replacing your water heating system and compares the different technologies. The results suggest, as you've already said, that some of the technology can cost too much up front to give a good economic return https://www.energywise.govt.nz/tools/water-heating/

Hot water cylinder and PV diverter/router

Hammerer:
Aredwood:

...  solar hot water is always a tradeoff. To get max savings you need to actively manage it. And there will be a few times you will have no hot water or low temps as a result.

As a solar user I agree that Solar water heating is usually a trade-off and does require some management to maximise savings. This is mainly because high solar efficiency and high water temperature don't naturally go together.

The water we use needs to be hot whereas the water we heat by solar is more easily heated the colder it is. This is because heat transfer is more efficient when the water is at a lower temperature.

The most effective means to make sure that you won't have to monitor solar water heating is to separate the solar heated water and the hot water you use. That's why some installers recommend a two tank system, solar water heating pre-heats the cold water so it can feed the main tank where the hot water is stored. As a retrofit to an existing hot water heating system the pre-heat tank works well provided you have a suitable space for it.

Time to give electricity the flick?

Hammerer:
You can check the solar energy available 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

3kW Grid Tied Solar PV: Watts and Warts

## Stan

929 posts

Ultimate Geek
Inactive user

Talkiet:

Whoops! You're right! (That's the good thing about showing your working - others can check for errors :-)

For some reason I multiplied by a wrong number in estimating my use... Here's the actual data...

And here's the updated EECA calculation

Much much better but still nothing like good enough to make it worthwhile for me. Should I have to replace an inverter in the 25 years that would wipe out my savings...

In any case I am more interested in a functional differentiator (being able to charge and use power during an outage is a salient but hopefully infrequent benefit) and I won't get that for anything like \$4000...

Cheers - N

In your case its harder as you are still a very low user but I will add some more maths to the equation and see what we come up with.

Lets assume you have no finance card and the only thing you are going to use it for will be this cost would be \$75

So you pay with the prompt payment discount 25.3c per KWH so with ecca formula above and 17 months interest free no payment you are looking at producing in the 17 months \$487 worth of power used + \$62 credit for power exported.

So \$487+\$62-\$75=\$474 off the purchase price of the unit a total of \$3525

Now looking at borrowing against your mortgage you are looking at an interest rate of 4.9% or less currently

Now I don't know what the calculator ie rising cost of electricity etc

Thoughts?

## Hammerer

1891 posts

Uber Geek

I'd seriously question rising electricity costs. What happens if Tiwai Point closes? The current agreement could end as early as 2018 and would be expected to drop average retail prices.

I've also realised that my drive to get electricity costs down has made my current solar water heating much less economic. On a minimum of 3,000 kWh saved each year I would have reduced the benefit from \$678 to \$573. Next year it will be \$474. So my ten-year payback will be out by quite a long way now.

My actual average cost per kWh peaked at 25.0 cents in my worst month with PowerShop in 2012. My next highest price is 22.6 cents per kWh for 2014 using 15,000kWh. The price is dropping due to offers and negotiations with my supplier. I can't be the only one getting good deals.

2010 20.0 c/kWh

2011 21.0

2012 22.2

2013 22.4

2014 22.6

2015 20.6

2016 19.1 (YTD+est. usage)

2017 15.7 (est. usage)

2018 16.5 (est. usage)

## TwoSeven

1313 posts

Uber Geek

You know that if you save up and pay cash you can reduce the cost by 6% per annum

And by the time you have saved up the technology for the same spend will have improved.

Software Engineer

## mattwnz

14549 posts

Uber Geek

I have been accessing the costs on a new house, and just can't see the numbers working for going solar in my case. It maybe slightly cheaper, but then you also have the ugly panels on the roof and issues around that. I certainly wouldn't look at borrowing to buy it either. I was also looking at heatpump water heaters, vs conventional, and also used the energy website calculators, it also didn't really work out much cheaper. It is a pity the systems capital cost and install price are so expensive still in NZ.

## Talkiet

3882 posts

Uber Geek

Trusted
Spark NZ

One person supports this post

mattwnz:

I have been accessing the costs on a new house, and just can't see the numbers working for going solar in my case. It maybe slightly cheaper, but then you also have the ugly panels on the roof and issues around that. I certainly wouldn't look at borrowing to buy it either. I was also looking at heatpump water heaters, vs conventional, and also used the energy website calculators, it also didn't really work out much cheaper. It is a pity the systems capital cost and install price are so expensive still in NZ.

[provocative statement]

It's the way it should be. individual solar power shouldn't be significantly cheaper than power delivered from an efficiently run and maintained grid, especially when you factor in the maintenance costs for your solar installation.

The fact that the economic case for putting in solar is so marginal makes me feel pretty happy about the price we pay for power from the grid.

I'd like solar for the cool value, and for the value of having redundancy in my electrical supply. (I do have a 2.5kW generator at the moment) Saving money though? Nah.

Maybe we're being charged artificially high solar install prices because of the grid cost, and all the places selling COULD sell the installations a lot cheaper if they wanted?

Cheers  - N

## Stan

929 posts

Ultimate Geek
Inactive user

Talkiet:

mattwnz:

I have been accessing the costs on a new house, and just can't see the numbers working for going solar in my case. It maybe slightly cheaper, but then you also have the ugly panels on the roof and issues around that. I certainly wouldn't look at borrowing to buy it either. I was also looking at heatpump water heaters, vs conventional, and also used the energy website calculators, it also didn't really work out much cheaper. It is a pity the systems capital cost and install price are so expensive still in NZ.

[provocative statement]

It's the way it should be. individual solar power shouldn't be significantly cheaper than power delivered from an efficiently run and maintained grid, especially when you factor in the maintenance costs for your solar installation.

The fact that the economic case for putting in solar is so marginal makes me feel pretty happy about the price we pay for power from the grid.

I'd like solar for the cool value, and for the value of having redundancy in my electrical supply. (I do have a 2.5kW generator at the moment) Saving money though? Nah.

Maybe we're being charged artificially high solar install prices because of the grid cost, and all the places selling COULD sell the installations a lot cheaper if they wanted?

Cheers  - N

Would you find it interesting to see a breakdown of all the costs?

## Talkiet

3882 posts

Uber Geek

Trusted
Spark NZ

Stan:

Talkiet:

mattwnz:

I have been accessing the costs on a new house, and just can't see the numbers working for going solar in my case. It maybe slightly cheaper, but then you also have the ugly panels on the roof and issues around that. I certainly wouldn't look at borrowing to buy it either. I was also looking at heatpump water heaters, vs conventional, and also used the energy website calculators, it also didn't really work out much cheaper. It is a pity the systems capital cost and install price are so expensive still in NZ.

[provocative statement]

It's the way it should be. individual solar power shouldn't be significantly cheaper than power delivered from an efficiently run and maintained grid, especially when you factor in the maintenance costs for your solar installation.

The fact that the economic case for putting in solar is so marginal makes me feel pretty happy about the price we pay for power from the grid.

I'd like solar for the cool value, and for the value of having redundancy in my electrical supply. (I do have a 2.5kW generator at the moment) Saving money though? Nah.

Maybe we're being charged artificially high solar install prices because of the grid cost, and all the places selling COULD sell the installations a lot cheaper if they wanted?

Cheers  - N

Would you find it interesting to see a breakdown of all the costs?

Not really - I'm largely behind my first point really, that small solar, being delivered efficiently is about the same price as we can get power from the grid. To me that makes the decision to go solar based on non price factors. In NZ it's hard to use the renewable energy argument, so for me at least it would be around having power redundancy and not much else.

Cheers  N

## Hammerer

1891 posts

Uber Geek

Talkiet:

mattwnz:

I have been accessing the costs on a new house, and just can't see the numbers working for going solar in my case. It maybe slightly cheaper, but then you also have the ugly panels on the roof and issues around that. I certainly wouldn't look at borrowing to buy it either. I was also looking at heatpump water heaters, vs conventional, and also used the energy website calculators, it also didn't really work out much cheaper. It is a pity the systems capital cost and install price are so expensive still in NZ.

...

Maybe we're being charged artificially high solar install prices because of the grid cost, and all the places selling COULD sell the installations a lot cheaper if they wanted?

How would we know if install prices are high? I also have the impression that component costs are high - is that anyone else's view?

In a similar field, solar water heating installs were receiving state subsidies for a while through the Solar Industries Assocation (SIA, now the Solar Assocation). AFAIK, the SEANZ (Sustainable Electricity Association of New Zealand) has never got any direct subsidies from the state. For a while the industry benefited from the high feed in tariffs but that is now gone, thankfully. So if install prices are high it's not because of state support for the industry association.

With solar water heating, a lot of people wouldn't buy solar water heating unless they got a state subsidy. One the one hand, that was a barrier to getting cheaper installs. But if an installer wanted to be an accredited member of the SA/SIA then they had to succesfully complete ten non-subsidised installs first. To match the subsidised pricing they would have had to drop their prices. This might well mean that there was a lot of fat in the install prices once you become accredited.

The SA/SIA say a lot about how they enforce quality standards and this probably ensures better quality installs and better trained installers. But SIA inspection of my install didn't prevent it having a significant defect that should have been picked up. Maybe it is much the same with the SEANZ.

## Talkiet

3882 posts

Uber Geek

Trusted
Spark NZ

I wrote imprecisely... I meant the price of a solar install (including labour, components, documentation, inspections etc) may be artificially high, not just the labour cost.

Cheers- N

## TwoSeven

1313 posts

Uber Geek

Talkiet:

I wrote imprecisely... I meant the price of a solar install (including labour, components, documentation, inspections etc) may be artificially high, not just the labour cost.

Cheers- N

I havnt looked into it too much, but I think in france for example, one gets a tax credit on solar collector (water) installations and the price of panels is around half a euro per Wp for the bigger panels.

I am not sure how popular solar farming is though.

Software Engineer

## blakamin

Murray River
4435 posts

Uber Geek
Inactive user

Anyone looked into the Tesla Powerwall 2? NZ have a distributor?
http://www.gizmodo.com.au/2016/11/teslas-solar-roof-and-powerwall-2-are-perfect-for-australia/

I'm actually looking at a 4-5kw system and this. We currently average 15kWh a day so a 14kWh powerwall would take some stress off us.

## Aredwood

3419 posts

Uber Geek

Subscriber

2 people support this post

Be careful when looking at baseload figures. As there are 2 types of baseload - Continuous and cyclic. Continuous is things like appliance standby usage and the server that runs 24/7. Cyclic is things like the fridge, chest freezer, hot water cylinder, underfloor heating ect. That constantly switch on and off by themselves. This means that a house that has a calculated base load of say 1kw/hr per hour. Will in reality have a varying load from as little as 10w (appliance standby loads) to say 3500W (3000W hot water cylinder, 250Wx2 for fridge and freezer). Put a 1kW solar system on this house and it will both export and import power throughout the day.  If you want zero daytime import you could easily need a 4kW system. And if you want zero daytime export you will need a stupidly small system. Or diversion to battery / hot water cylinder / swimming pool ect. This is why I think that 3kW+ systems are so commonly sold. To try and avoid daytime import.

Not complex enough yet - In areas that have separate meters for the hot water cylinder. You might be exporting power on your general use meter. And importing power at the same time on the hot water meter. And if you have 2 phase or 3 phase power, you might be exporting on one of the phases, and importing at the same time on a different phase. And then there are power factors. Lots of electronic equipment has a harmonic power factor (only draws power at the peaks of the mains waveform) Yet a solar inverter outputs a unity power factor (perfect power factor - same as what a resistor would draw) So depending on how a smart meter might interpret such a situation. You might be switching between exporting and importing power 100 times per second. (not 50 times as there are 2 peaks per mains cycle)

Also the electrical rules in NZ regard grid connect solar electrical work as high risk work. This means your electrician has to organise an electrical inspector to inspect and sign off his work. So an extra cost added to the install cost. Im not going to take sides as to whether this is a good thing or if the risk classification of solar work should be changed to remove the inspection costs.

Diversion to a hot water cylinder is far more economic than using batteries. Unless you want to have backup electricity available during a blackout, and you are willing to pay extra to get that feature. As the dirverted power offsets power that would otherwise have been drawn from the grid.

But if capacity based charging gets introduced - Then the cheapest way to reduce your bills will then be - switching to gas cooking. And putting a timer on the hot water cylinder to move it's power usage to off peak times. Note also that in Auckland at least - if you have an electrical connection rated at more than 69KVA (3 phase at approx 120A per phase) then you have to go onto a capacity based charging plan. (typical house is 15KVA) But get it setup right and your per unit lines fees are almost nothing. So you pay hardly anything over the wholesale price per unit. This is why hardly any large business customers have solar installed. As they make bigger savings on their power bills by reducing the amount of capacity and KVAR they need to buy. (small customers don't have to pay for KVAR)

This also means that an average residential customer pays more in lines fees than they do for the actual cost of the electrical energy. (I have been with flick electric for just over a year, Every single bill from them I have paid more in lines charges than wholesale electricity.) Would be the same for other power companies, they just bundle the charges together. So residential solar massively reduces the revenue of lines companies. Which is why we got the so called solar tax in Hawkes bay. As they realised that non solar customers were subsidising solar customers. - this is why directly charging for capacity is the fairest way of doing things. As your total unit usage often doesn't bare any resemblance to your capacity usage.

It is only a matter of time until a major urban lines company introduces capacity based charging. There will be protests at first, then people will figure out how to structure their usage to take advantage of the new charges. And people in other areas will start to wish that they also had capacity based charging. Note that the benefits in "The Lines Company" area are more subdued, as they have to cover a large alpine area, that has a low permanent population and a large seasonal population.

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