Are solar panels right for your home?

Before you can enjoy a sun-powered home, you’ll want to find out if solar panels stack up for you.

Solar panels on roof of house against blue sky.

Photovoltaic (PV) solar panels can seem an attractive option – who doesn’t want lower electricity bills and clean, green energy? However, before you can enjoy a sun-powered home, you’ll want to find out if solar panels stack up for you.

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In August 2018, we arranged for four solar installers to assess homes in Auckland, Christchurch and Hawke’s Bay, and provide a quote for an appropriately sized grid-tied system.

Are you solar-suitable?

A PV system for an average-sized house can be installed for under 10 grand. However, how long it’ll take to pay itself off depends on several factors, including:

  • how much power the panels generate, how much of that you use, and how much is sold back to the retailer
  • the earnings you forgo by not investing the money spent on solar elsewhere or, if you are borrowing, the interest payments you make
  • how much power prices and buy-back rates rise or fall over the lifetime of your panels, and
  • the lifetime cost of the system, including any repair.

Assessing your property for PV suitability essentially comes down to two factors: the power a system can generate and how much of that power you can use.

How to assess your home

There are online tools you can use to assess the viability of your home for solar:

In both you can input details about your home, current energy usage, and behaviours to find out if solar is right for you – we recommend trying both tools and comparing the results you get, as each uses different assumptions.

When making any assessment, it’s important to note solar PV is a long-term investment, which brings added risk and uncertainty. Over the 20+ year life of the system, there are likely to be changes to interest rates, electricity prices and buy-back rates, and household electricity use that could reduce or increase the actual return provided.

What can you generate?

In the southern hemisphere your panels need to face north to get the best power production. Your roof will ideally be north-east- to north-west-facing, with a 15 to 45° pitch. Falling outside this range cuts down how much power panels can generate.

Look for shading on the roof – think nearby hills, trees or buildings. As soon as panels are in shade, their generation levels plummet. Small patches, such as the shadow cast by a chimney, can be overcome using micro inverters or power optimisers, but these cost. Think long-term as well. How big will the neighbours’ trees be in 20 years? Is there the possibility of taller buildings being put up in your area?

What can you use?

Getting PV panels installed on your roof is only part of the equation. You also need to make best use of the power produced. Selling it back isn’t financially attractive (the buy-back rate from power retailers is 7 to 8¢ per kWh). A better option is using the power produced on your roof during the day.

Power usage peaks in the morning and evening for most households. We use more electricity in the winter, and the peaks are higher too, as we turn on heaters and use more hot water on chilly mornings and evenings.

Solar PV isn’t much help with winter power peaks. The bulk of solar generation is between 11am and 3pm. Solar panels also generate considerably more power in the summer, when the days are longer and the sun is higher in the sky.

To get the best payback from solar PV, you need to use as much of the solar power as possible as it is generated. Some of the power used in morning and evening peaks can be shifted. Using timers to delay and stagger appliances could be one part of the puzzle. Another is switching electric water heating to come on during the day.

However, solar PV becomes most viable if you consume power all day, especially in the summer. That could be because your home is occupied all day, you heat a spa pool, run a swimming pool pump, or have an electric car charging.

Ultimately, getting the best bang for your solar buck requires a home with large daytime power use, plus a behavioural change for your household to bring consumption into line with production.

Typical household consumption & PV generation

line graph showing exported vs imported power

Solid line = Power generation
Dotted line = Power consumption

Getting the right size

The ideal solar PV system for your home is sized so you can use most of the power it generates, selling as little as possible back to the grid. You will pay more than three times as much to buy power from the grid as you’ll get for the power you sell. So a large system may be cheaper per watt generated, but it could take a long time to pay off the extra investment.

Installer assessments

The installers all did a good job of assessing our three households. They all checked the latest power bill, asked questions about our household size and behaviour, and noted any major power uses (such as a pool or home office). All installers highlighted that to realise any financial benefits, the household would need to adjust how it used its power.

There was variation in recommended panel array sizes across the board. However, many recommended pairing the panels with a larger-than-required inverter. We think this is a good idea, as it allows the addition of generation capacity in the future (for example, if batteries were to be installed).

Two Auckland installers recommended including a battery now. However, we think the payback time for the battery is far longer than its lifespan. The other installers in Auckland and all of the installers in Hawke’s Bay and Christchurch told us batteries weren’t economical, and didn’t recommend we install one.

18aug solar body image
All quotes were inclusive of equipment, installation, and any consents or paperwork needed to switch the home to “distributed generation”.

Installers at our Hawke’s Bay property all quoted scalable systems. The inverters quoted were either larger 5kW models or micro-inverters. This factored in the pool that was being installed and would allow for more panels to power the pool pump and potential water heating.

One company incorrectly identified our Christchurch property as having too much shading and quickly left after the sales pitch. This particular roof was in full sunlight during the 1pm visit and it’s difficult to ascertain the shading from such a quick look. While it was overly cautious on the installer’s part, it did show care and consideration for our homeowner.

Each company offers several brands of panels and inverters. However, there isn’t a marked difference in their ability to generate power (they range from 270W to 300W per panel). For inverters, the smart choice is a system with monitoring software so you can see in real-time the amount of power you generate and use. This enables you to adapt behaviour to use as much self-generated power as possible.

It’s important to check your warranty. For panels, you want a guarantee of minimum power production levels for at least 20 years. Panels and inverters should also be covered for physical and electrical issues.

All quotes were inclusive of equipment, installation, and any consents or paperwork needed to switch the home to “distributed generation”. The only extra we were warned about by all installers was a charge of a few hundred dollars for an import/export meter, paid to our electricity retailer.

Tier one?

You might see or hear the term “tier one” in solar panel sales pitches. Don’t mistake it for anything regarding panel performance. Rather, it’s a measure of the size and financial vitality of the manufacturer. The only use to you is it indicates the company is more likely to hang around.

The ideal solar PV system for your home is sized so you can use most of the power it generates, selling as little as possible back to the grid.

Solar tech 101

Panels

Panels are roughly 1.6m by 1m with outputs of about 270 to 300W. A 3kW system needs a minimum of 10 panels – for reference, 3kW is about how much power you’d use to run a clothes dryer and an electric cooktop simultaneously.

On a summer day, you’ll get peak production for a few hours either side of midday. Over time, panels lose some of their generation capacity (they’ll usually experience a 15 to 20 percent drop over 20 years). However, you can expect a maintenance-free run over this period. You may need to clean them annually, which may involve a cost for someone to do this.

Inverters

An inverter converts the direct current (DC) electricity produced by the panels to the alternating current (AC) used in your home. For grid-tied systems you’ll need a grid-tie inverter to synchronise your system with mains power and sell electricity back into the grid when you’re producing a surplus. There are different types of inverters:

  • A string inverter is a large centralised inverter that’s usually mounted to a wall in your garage or housed outside. String inverters only work as well as the worst-performing panel – if one panel is shaded, it brings down the power generation of the whole array. Power optimisers can improve shaded performance, but they add extra cost to the system.
  • Micro-inverters sit on the back of each panel. They make it easy to add more panels because you don’t need to buy a new, higher-capacity string inverter. They can also better optimise each panel’s power production – each panel is independent, so if one gets shaded the others keep churning out at full power. Micro-inverters tend to cost more than string inverters.

Inverters are unlikely to last as long as the panels, and over 20 years you’ll need to replace them at least once.

Import/export meter

Export meters measure how much power you’re selling back into the grid. This is an upgrade over your standard meter.

Could you be saving on power?

Enter your household details to find out how much you could be saving on electricity and gas.


Member comments

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Paul S.
12 Aug 2020
Harrison's specials on their website misleading

We got a quote for 10 panels from Harrisons about 5 months ago at around $10,000. We then saw some specials on their website for 12 panels at $7990 fully installed, but when we contacted them for a revised quote, they quoted even more. When I challenged the price, they said that the price on the website is for single story, corrugated roofing. This information isn't on the website, and I was pretty disappointed to find out that they couldn't do the full install for the price on their website

Paul S.
13 Jan 2020
Scaffolding almost doubles the cost of solar installations

The main issue we have, and many other home owners in New Zealand have, is that scaffolding is now required for all solar installs. The cost of scaffolding isn't cheap either, and can almost double the cost of the solar installation, meaning solar isn't a viable solution for a lot of kiwis.

Stephen E.
22 Jun 2019
Asphalt Shingle Roofs

We would be keen to invest in solar power, but have been turned down by prospective providers because we have an asphalt shingle roof. We don't know the details but is there an expert out there would could suggest how to overcome this (apart from having our roof re-done with another type)

Ron P.
22 Jun 2019
Decomastic, Asphalt tiles roof.

If you are talking about old decromastic tiled roof then most have asbestos in the asphalt that bonds the stone to the sheet metal as I understand it. We have this type of roof and Hazmat came and did a test which proved positive. They, (HazMAt) have a service to replace specific tiles or secure appropriate mountings in a secure and safe way, It cost a modest amount and nothing like taking the rood away. I have not had solar fitted yet but that is what we are going to do. probably about 800-900 extra depending on the number of tiles to be replaced

Consumer staff
25 Jun 2019
Re: Asphalt Shingle Roofs

Hi Stephen,

We’d suggest contacting a solar installer and a roofer. They will be able provide an assessment and advise you on the technicalities of installing panels on that type of roof.

Kind regards,

Natalie – Consumer NZ staff

Ray S.
18 Mar 2019
PV Roof Power Systems - Roof Maintenance

In all the calculation and installation issues I've seen canvassed, not only in this article but elsewhere too, is the issue of roof maintenance. At several points during the life cycle of the panels the roof will need to be painted and/or replaced - depending on its age and condition at time of installation, roof materials, corrosion factors (e.g. sea air, geothermal air) and so forth.
It would seem this could have a substantial impact on costings - roofs will continue to corrode and the panel fixings may also corrode, and depending on material compatibility may even speed up the corrosion process. To do such work the panels may need to be removed and refitted. Damage may occur to the panels and/or fixtures.
This this could have a significant impact on the economics, in addition to any other considerations.
Therefore, I would recommend roof maintenance be added to the factors to be considered.

Linzi D.
13 Jul 2019
Roof maintenance - be proactive

We painted our tin roof before our panel install. Given that the roof is still in excellent condition at over 60 years old, I think it should outlast the 20-25 year panel lifespan. As for the fixings, everything that went through the roof was stainless steel, had rubber grommets or watertight seals - so should be no issues there either. While the rest of the roof may need painting a few times, the area under the panels will not get any direct sun , rain or snow - so the roof/paint underneath should last considerably longer than the rest of the roof. The panel mountings give a generous air gap between panels and roof, so the edges of the area under the panels is also able to be painted.

So if you are proactive and do all your roof maintenance before you install panels, then there should be no issues with any of this for a tin roof.

Colin F.
09 Mar 2019
Do The Job Properly Consumer

In all the examples water heating was by gas. very convenient for you. do the job properly. There is no comments about diverters, alternate energy storage, timing use of energy etc,
This report is not worth the paper it is written on. You will inference people incorrectly, be responsible.

Colin F.
09 Mar 2019
Solar and hot water

While you talk about batteries you don't talk about the energy storage system in all houses. If the water heating is timed during the day it will reduce the power being exported for a rip off price. If the water is heated with a inverter heat pump even better. Maybe under floor heating is in the house which of course means a even bigger energy storage system in the house. So many variables...

Gillian B.
11 Nov 2018
Where's Wellington?

Gah! Was so looking forward to reading about this solution for Wellington but ..nope Dissapointing.

Steven P.
19 Sep 2018
Payback - Low user tarrif and therefore low daily charge

I brought an electric car (love it). I used to use about 7000 units per year before solar and thus was in the low daily charge of $0.33 in auckland.
Now with the electric car I should be using over 10,000 units per year and thus should be paying the much higher daily charge of $1.84 per day.
Because of solar, I’m able to stay on the low user tarrif and therefore save $550 annually.
That’s a great saving that the solar calculators don’t allow for.
Reducing your daily connection charge is awesome.

Laydan M.
20 Oct 2018
Enjoy it while it lasts

The low fixed charge for homes is currently under review, and is likely to be abolished in the near future. People with solar eligible for the LFC rate aren't contributing their fair share to the cost of maintaining the lines which were never designed to cope with reverse power flows, and the cost is ultimately footed by the people less able to buy electricity let alone pay to install solar.

shar t.
15 Sep 2018
ESTA USA overcharging

WARNING. Take care when travelling to USA, you need to complete an entry ESTÀ. When doing a google search to get the online form it is very easy to inadvertantly go thru an agent, and pay US$89 instead of US$14 for the same form. What can be done to rectify this? We want to WARN OTHERS

Bryan P
02 Sep 2018
Why isn't the comments option a regular feature of your articles?

For example, months ago, I looked at an article on e-bikes and was disappointed that it didn't feature any of the Avanti models. I ride an Avanti Inc E that I find to be a great bike (and would have thought it just as worthy of evaluating as any of the 14 on your list); if the option had been there, I would have commented then.

Consumer staff
03 Sep 2018
Re: Why isn't the comments option a regular feature of your articles?

Hi Bryan,

Thanks for the feedback. As we can’t practically test all e-bikes on the market, we chose which e-bikes to test based on whether they were popular and available. This included an Avanti model: https://www.consumer.org.nz/products/electric-bikes/avanti-discovery-low-e

Kind regards,
Frank – Consumer NZ staff

Lindsey B.
01 Sep 2018
Smart Usage

I think the energy saving can be much larger. We have our major electricity consuming devices time clocked. Hot water (large heat pump), freezer, dishwasher, washing machine and dryer all only operate during the day when we are generating the most. We don’t run out of hot water and the freezer doesn’t defrost over night. Savings are much more significant and payback period is less if you are smart about usage.

Jean W.
01 Sep 2018
It's not about the payback time for me

It's about reducing my carbon use. I put in grid-connected solar about three years ago and calculated an 18 year payback time. But I wanted to increase the renewable % of NZ power generation. I was influenced by the Auckland Council eco adviser who told me that although NZ as a whole has 80%-odd renewable electricity, it is a much smaller % in Auckland (where we live) and we still depend heavily on Huntly fossil electricity at peak times. But we get all our hot water off peak because our installer offered a $700 gizmo called a power reducer, which senses when we are importing from the grid, and only puts power (from the panels) to the hot water when we are not importing. We have to boost the hot water with power from the grid about 6-8 times per year. Two person household, with one of us home during the day; standard 180 l HW cylinder and a very low flow shower head. I looked at battery storage and concluded that storage should be left to the big companies to solve. But if I was starting again, I might look at a battery without any solar, as the battery stores off-peak power and reduces peak demand, and hence reduces fossil fuel use. Vector took this approach in north Auckland, putting in 1000 batteries on houses in new developments.

K L & Judith A H.
01 Sep 2018
Solar Power

I had a grid tied system installed 3185 days ago (8.7 years -(these are real stats). 1.8kwh capacity (that was big then). Cost then (installed) was $18154.78. In that time it has generated 19664kwh value $5033.12. Average daily output 6.17kwh (about 1/3 of its capacity). It has operated for 35953 hours (daily average 11.29 hours). If I had put the money in a renewable 12month term deposit with SBSbank I would have earned $4945.32. So I am $87.80 better off? We generate somewhere between 20 - 40% of our power usage (approximate). A system today is bigger, would generate more, but would not operate any longer. Our roof is optimal for solar, 35 degrees pitch, north facing, no shading. We live in Christchurch. The economics of our installment changed when Meridian reduced its buy back price from equivalent to daytime buy in value (approximately 30 cents now). I currently get 8 cents a unit from Contact. Christchurch location. The reality with solar is that we live in the land of the long white cloud (remember!), solar generates its maximum power at a time when the energy companies demand is weakest; during the day, and peak demand is late afternoon/early evening; in summer and peak demand is in winter. Reality: power companies don't want/need our power. The stats speak for themselves. Check out any solar retailers claims very carefully! Make up your own mind!

Trevor B
01 Sep 2018
Solar Panels

Your solar panel review was very interesting. I am contemplating replacing my 1950's concrete tile roof and have considered solar panels, including with battery storage. As a retired person living alone it doesn't seem financially viable. However living in Upper Hutt a battery system would give considerable resilience in the event of long term power loss such as an earthquake. Turn everything off at the wall except the refrigerator/freezer.

K L & Judith A H.
01 Sep 2018
Check it out!

Check this out - if your system is tied into a grid then if the grid goes off, then your system stops generating

Frank D.
20 Apr 2019
Check this out! is incorrect with Tesla Battery

The Tesla battery will continue to supply the home in the event of the grid going down for a tied-grid system...assuming of course it isn't empty. Additionally it has various configurations for backup settings.

Wal Marshall
01 Sep 2018
Batteries are important

I have built my own grid tied solar system and its been up 2 years on the Kapiti Coast. 7kW of panels 5KW inverter, and 36kW hrs of lead acid battery storage. The batteries give me 18kW hrs of useable storage (50% DOD) and are miles cheaper than overpriced Testa Power walls) ) . Total system cost $36K. My unit cost is 30c import and 10c export . 100% electric home with full home ducted heat pump space heating and heat pump hot water. Payback time is tracking to be less than 10 Years, mainly due to the battery storage displacing costly evening imports. Annual power bill about $400 total, incl connection fees. We mostly net import in winter, and bulk export all summer. After 10 years the batteries will probably need replacing, but the entire system will be paid for. Often overlooked is that our system probably adds $20-30K of capital value to our home and so this another tangable recoverable. Overall a great investment.

Valerie B.
30 Oct 2018
Provider?

Hi who was the provider/ installer of your solar? Cheers

Linzi D.
13 Jul 2019
Increased capital value - more/cheaper battery options

I agree Wal, its not all about payback, the install has added value to your home and also as electricity prices continue to rise, you are protected more from these increases than others.

By the time your batteries need replacing there will be many alternatives available, including Lithium at much cheaper prices than today. There are many people now using recycled Nissan Leaf (see Williamgerr on YouTube) and other EV batteries in a home Solar set up. As more EVs arrive in NZ there will be more and more of these available, as when they reach only 70% capacity they are generally replaced in a car, but still viable for Solar storage.

In the UK there are people who have a small battery set up from Powervault which they charge up on cheap night rates then sell back to the grid at peak times. The system has recycled Renault EV batteries in it and software to price monitor - so the technology is already there for people with a PV system to tap into this type of market. Check out Powervault episode Oct 2018 from Fullychargedshow on Youtube - we could do with this type of set up here for when we run short of power.

Lynette Z.
25 Aug 2018
Solar energy payback

I take issue with your payback calculations. We paid cash for our system. That was money we had set aside to buy another car. We are now saving to buy that car. After that we will be saving for holidays. For us there can be no calculation for investment over the life of the unit.

Robert H.
11 Aug 2018
PV vs Direct Hot water solar

I am not try to change to subject but heating water directly with the sun is much more efficient than using electricity collected from the PV to then run the element

Steven P.
02 Sep 2018
PV is best to heat hot water because

It can do 2 things, General Electric work to drive anything and heat hot water.
The problem with old style solar hot water heating is it can only do one thing. Once the water is hot, the energy is wasted.
To maximise PV hot water you do need a small hot water controller like paladin (no I’m not affiliated in any way, but yes I do have installed). This whereby your hot water cylinder is controller by paladin and it maximises your own solar consumption pushing excess power that you would have sent to the grid to your hwc.
I’ve gone to grid 3 times since oct 2017 to heat hot water, the rest of the time my 3.6 kW solar array has run the house and heated the hwc.

Graham
11 Aug 2018
SolarZero a no show

I had Solar City booked to do a SolarZero install on my roof in Wellington on the same day that the capital took a hit with a widespread power outage. Unfortunately Solar City had cancelled the install earlier as they had not yet standardized on vertical seam roofs! Totally not understanding the reasoning, and that they can break an installation contract like that.

As for carbon, we might feel a warm fuzzy if we are reducing our carbon footprint, but in the scheme of things it makes 0 difference when we have countries signed to the Kyoto agreement that are allowed unlimited carbon emissions.

The only thing that is really going to help is to sequester carbon by planting millions of trees. And I do pay my air new zealand carbon tax when I fly to help with this.

David C.
19 Apr 2018
Storage methods

Was wondering if you have any information on low-pressure hydrogen storage for solar installations - Hylink have one installed in Soames Island in Wellington. At the moment the Hydrogen is used directly for heating, but given the rapid advances in fuel cells for automotive use, any thoughts on when it might turn in to a viable system for residential power storage? H2 storage and a fuel cell are a vastly cheaper and cleaner option than batteries.

Consumer staff
20 Apr 2018
Re: Storage methods

Hi David,

As far as we know, low-pressure hydrogen storage for solar is a future technology not available to consumers. Same for hydrogen fuel cells in cars. It’s something some companies are working on (Toyota for example) and see as the ultimate future away from combustion engines. But it’s a long way off being consumer-ready.

Cheers,
Paul Smith - Consumer NZ head of testing

David C.
15 Sep 2018
Hydrogen...

Hyundai are running a fleet of fuel cell SUVs in California and are soon to offer them generally - https://www.stuff.co.nz/motoring/news/106213537/hyundai-serious-about-hydrogen-in-new-zealand - and fuel cells vehicles are coming from a brace of other makers - https://en.wikipedia.org/wiki/List_of_fuel_cell_vehicles.

The fuel cells themselves are still developing apace but offer a solution superior to batteries, as they are vastly less energy dense and cleaner to make and recycle, quick to refuel for mobile applications and the use by-product is water. There is also the prospect of using a vehicle fuel cell to power a house when the vehicle is there.

Just think NZ needs to wait a bit before charging off down the route of a heavy investment in battery technology, as the products are evolving so fast we may end up in a technological cul-de-sac.

Shirley J.
05 Mar 2018
Do you have to be grid tied

Given that the pay back price is minimal, do you actually have to be grid tied. Can your system be set up so that you only measure the amount you use when your system is not producing enough to run the household?

Previous member
09 Mar 2018
Re: Do you have to be grid tied

Hi Shirley,

If you want to feed PV into your house to use as and where needed, you either need to be grid-tied (maintaining a connection to the grid for times when your PV system doesn’t provide the power you need), or go totally off grid. With the latter, you’ll be totally dependent on your own PV feed for all electricity. You can fit a PV system that isn’t grid-tied, but it needs to be connected to specific circuits with no direct link to the grid, rather than the entire house.

Cheers,
Paul Smith - Consumer NZ head of testing

Linda C.
14 Jan 2018
Wrong Calculations on solar

Ditch the economists and their irrelevant theories. Pay back time Is not the right measure for solar. We have had it for three years and the return on our investment in electricity bill savings here in North Canterbury has been 11% non taxed. If we had had the same money in the bank it would have got 3% taxed. Smaller monthly bills are really important to people on fixed incomes like pensioners. Don’t be put off by theory the practical reality is different.

Grant R.
21 Feb 2018
I agree with you Linda . . .

As you rightly said, it's not "all" about payback. I totally agree that reducing the cost of living when you are on a fixed income / pension is very important. If you install a solar system - when you can afford to, makes sense to me.

Candice P.
27 Sep 2016
SPPA supplement

What happened to this supplement you mentioned in November last year?

We’re putting together a supplement to this article covering SPPAs. You can expect to see this online by next week.

Previous member
28 Sep 2016
re: SPPA supplement

Hi Candice,

You can find more information on SPPAs at the bottom of this page — see the section “No money down”: https://www.consumer.org.nz/articles/grid-tied-pv-systems#no-money-down

Kind regards,
Fonda - Consumer NZ staff

Donald P.
09 Aug 2016
buy back rates aren't time dependant: they are taken over the month by Meridian

I had a supplier of solar panels over last week trying to sell me a system. He said that Meridian totals the number of kwh you use in a month and subtracts that supplied from your system over the period.

If this is true that the time shifting referred to in this article is irrelevant until the power companies start to do this.

Did the solar guy tell me a little white lie?

Tom P.
01 Sep 2018
That sounds like the bar graph on our Meridian bill, but not the bottom line

We're with Meridian and have solar. The invoice includes a bar graph of monthly consumption over the last 2 years. That's nett consumption (imported kWh minus exported kWh), but the price calculation treats them separately. For example, our latest bill included:
390kWh imported @ 29.75c/kWh = $116.02
34kWh exported @ 8c/kWh = $2.72 credit
...for a total energy price of $113.30. Meanwhile, the bar graph just showed a single figure of 356kWh for the month, which I suspect is what your solar guy was referring to.

The bill doesn't show our self-consumption, of course, because that's where we use the energy straight off the PV system, without its passing through the meter.

Load shifting matters, because the energy purchase price is different from the feed-in price (like my 29.75c/kWh versus 8c/kWh).

Linzi D.
13 Jul 2019
Meridian Solar buy back

I think your solar guy over simplified things - or is very out of date with his info. I installed solar on my previous house, now my rental property. When it was first installed we had a net bill - as they were paying the same rate for each unit we sold back to the grid as the units we consumed/used/bought from the rid - but that ended several years ago - maybe in 2014 or 15. The buy back rates changed then to summer 8c and winter 11c rates - but it has since changed toa flat rate all year about 2 years ago.
The bill from Meridian shows you used/bought units at xx cents and sold units at x cents and the bill is worked out using these figures. There is a bit on your bill that states the Net Units consumed (used/sold) - but this isn't how they calculate your bill.

John E.
03 Aug 2016
Night Rate more important than Buy Back rates

We use all the energy our PV generates. We designed it that way.

Remember that a PV system will only generate the rated output in the middle of the day - most of the time it generates much less, and in winter it will generate less - see the NIWA site at http://solarview.niwa.co.nz/ to calculate what you will actually generate.

A well designed system is unlikely to export much energy - to be economic the system needs to be sized so you use most of the energy generated - for this reason buy back rates do not matter much.

What does matter is the cost of electricity at night - because clearly with a grid connected system you will need to buy energy at night.

Most suppliers will not supply a PV installation at night rates if you also export - if they do the night rate discount is trivial.

So if you use energy at night, and install a PV system, your cost of electricity can go up because you loose your night rate discount.

Buy back rates are a distraction - it is more important that night rates are offered to all customers with similar loads, including PV.

John I.
13 Jul 2016
Investment Value of PV Solar Panels

I used a BNZ Term Deposit earning 3% interest to pay about $8500 for a 2.5kW solar array that I have estimated after two years production will pay for itself in about 5 years. I use a fair part of the PV production to charge the battery of my PHEV Mitsubishi SUV. At the time I also paid for an internal paint job costing about $8500. In another 13 years, if I haven't already sold the house (for an increased capital gain of at least $17000 to recoup the costs of both investments), I will have to repaint the inside of the house again. In the meantime the PV array will simply have kept paying for itself several times over. There is no way my Term Deposit could compare with that return on investment.

Roger & Jodie W.
14 May 2016
Here's some additional costs

1. Grid tied PV requires an Import/Export meter to be installed. Cheapest I think is Mercury who charge $99 for installing it (and take < 5 days instead of weeks)

2. If you have an older house (like us) the installer may arrive and go "Your board is made of asbestos, I can't install on it" thanks to the new health and safety regulations this year. At which point you will be required to replace your meter board in order to continue. I don't know the actual cost of that yet, but one electrician in Australia says "800 to 2,000"

Robert D.
13 May 2016
Greeness of Solar Panels

This is commenting on the statements both in the article and in the consumer booklet on heating that, because much of our electricity production is from renewals, Solar Panels don't have much effect on our carbon emissions. This is just plain wrong. If we reduce our power consumption by whatever means (replacement by solar, insulation etc) the hydro dams won't reduce production by spilling water (at least, if you are in the North Island). Rather, the gas and coal fired stations will run at a lower capacity, so have have to think of the solar panels replacing electricity generated 100% by fossil fuels. You can see how the electricity is being produced at http://www.em6live.co.nz. The gas plants are always running during the day and the coal plants usually running, especially on those still sunny days when there is no wind generation and lots of solar. The trouble with solar panels is that they don't reduce local infrastructure costs and it is hard to get the electricity generated to where is it needed if you can't use it yourself. And the discussion on lifetime use of carbon during production etc still applies.

Roger & Jodie W.
14 May 2016
Except that

If you are generating solar and not storing any of it, that 100% coal fired power is still used because it's primarily at peak load in the morning and evening when solar production is at a minimum.

Sue H.
09 May 2016
home economics of solar panels

Our outlay was 12 panels and the cost was around $12 000 for the panels and another $1000 for incidental expenses including a new meter and electricians and inspections. Total outlay $13 000. Over the previous 12 months our household usage averaged 31 Kwh per day (from the power bills), In the 8 months since installation we are averaging 20 Kwh/day. The maths I use shows saving 11 Kwh/day x 365 = 4 015 Kwh/ year x 36 cents unit (yes thats Northland for you) = $1 445.40 year or 11% return on our investment and it is tax free, We have also added capital value to our house. I cant think of a safer place to invest our money. How long it takes me to pay it off is very speculative and does not interest me.

Peter A.
12 Jun 2016
Hello

Hi There
May I ask which company you used as I live in Northland and had enough of being taken to the cleaners by energy supply companies?
Did you use the Mono cells?
Regards Peter

hops
14 Feb 2016
SEANZ on this article

For some balance:

SEANZ did a response to some consumer questions regarding this article

http://www.seanz.org.nz/News-Events/News/SEANZ-response-to-Consumer-Magazine-Helping-the-public-understand-Solar-PV

Much of the damn-with-no-praise of this consumer piece are similar to the points made in the EAP discussion paper "Implications+of+Evolving+Technology+for+Pricing+of+Distribution+Services"

Some of the SEANZ submissions to this may be even more illuminating

http://www.seanz.org.nz/files/file/55/SEANZ+Submission+-+Implications+of+Evolving+Technology+for+Pricing+of+Distribution+Services.pdf

Previous member
16 Feb 2016
re: SEANZ on this article

Hi hops,

Thanks for your comments. To clarify – the SEANZ response was in reference to a 2013 article of ours on grid-tied PV systems (superseded by this article) which was more negative on the economics and environmental benefits of PV. Since this article was published, SEANZ has indicated they support our findings, acknowledging PV only “makes sense in the right environment” - see http://www.seanz.org.nz/News-Events/News/Consumer-NZ-Supports-Solar-PV

Kind regards,
George – Consumer NZ staff

Roger & Jodie W.
09 May 2016
Links no longer work

Neither for this or for consumers reply.
Try: http://www.seanz.org.nz/files/file/505/Consumer+Solar+PV+SEANZ+Report+Website+FINAL.pdf

Jean W.
27 Jan 2016
Long payback but still happy to have done it

My 3.75kW grid-connected solar array cost $16,000 in Sept 2015, somewhat more than the $10k for 3.5kW that Consumer found. I have the most expensive type of panel from the most expensive supplier, on the grounds that if you have a 20 year warranty, you want to pick a company that is likely to still be around.
I also have a Power Router on the hot water circuit, that only puts power to the hot water cylinder when we are not importing power. This cost $700. (It blew a fuse when we turned it on the first time, but our installer fixed it immediately.) We have to boost the hot water from the grid maybe once a month. We have a meter that shows how much we are producing.
My reasoning for putting up lots of panels was that we do all need to switch to electric cars, and NZ does not yet have 100% renewable electricity, so still needs more renewables for the cars. My payback time for the panels is at least 20 years.
The panels have changed our behaviour. My partner is at home during the day. We always do our washing on sunny days anyway, and we have become very focused on checking our production before we turn things on. We know how much every appliance in the house uses. I have acquired a second slow cooker so that I can cook and do things like the annual jam-making while the sun is out.
My main reason for putting up the panels was guilt at my past carbon use (I have flown a lot), extreme anxiety about climate change and despairing of the NZ govt ever having the balls to give unpopular messages. I notice that even Consumer can't bring itself to advise people not to fly. Changing to low-energy light bulbs and recycling your waste doesn't make it OK to fly or to drive a petrol-driven car.

Previous member
28 Jan 2016
Re: Long payback but still happy to have done it

Hi Jean,

Thanks for your interesting comment. We’ve heard the same from a number of other members who’ve installed PV and ended up changing their consumption patterns to increase the amount of power they draw from the panels, and to improve their energy efficiency in general.

The aim of our report was to show that solar PV is only economic for certain household consumption patterns, and that there are cheaper ways of improving energy efficiency and reducing your carbon footprint. But as you’ve shown, if people are willing to change their consumption patterns and combine PV with LED lights etc., it can be a good option.

Consumers concerned about carbon emissions from their air travel may wish to consider low-carbon transport options where possible. For example, travelling by rail instead of short-haul domestic flights is considerably more carbon efficient, and can be almost as quick where high speed rail is available (e.g. Western Europe, Japan, and increasingly China). But it’s not all bad news on the air travel front, as there are a number of ongoing projects seeking to develop low carbon aviation fuels from captured CO2 and waste biomass.

Regards,
George – Consumer NZ staff

JMH
03 Jan 2016
PV Panels vs Calder Stewart Solar-rib

We're designing a new house in Chch and are keen to know if anyone has done any comparisons between the cost of purchase of and installation of PV panels onto ordinary long run corrugated iron compared with the cost of purchase of and installation of Calder Stewart's Solar-rib (http://www.roofer.co.nz/index.php?category-solar-rib) panels, AND efficacy, reliability, maintenance costs, and longevity of the same products?

Previous member
28 Jan 2016
Re: PV Panels vs Calder Stewart Solar-rib

Hi JMH,

We are unaware of any comparisons between PV panels and Calder Stewart’s Solar Rib. If you’re keen on solar rib roofing, our advice is to ask the installer for a detailed analysis of the long run economics of the technology (ideally an NPV analysis), which shows how it compares to standard PV panels. You can then get this checked by an independent energy expert or professional engineer.

Regards,
George – Consumer NZ staff

Gerald D D.
07 Dec 2015
We need electric cars - and we don't have enough renewables to run them

To reduce our transport emissions we need electric cars - and we don't have enough renewables to run them. Even if Tiwai Point closes, electricity prices will increase. PVs will be part of the mix.

Roger & Jodie W.
14 May 2016
Except Genesis

Who had so much renewable supply the other day they had to pay people to take it. Maybe they should look at being able to use it to pump water back into the dams?

Lindsey B.
05 Dec 2015
Combining solar with energy efficiency

Hi.
We installed an 8kw solar grid tie system in Waipukurau. This system generates between approx 15kWh (winter) and peaking at 50kWh (summer). The system cost us $23k to install.

We have also changed our energy habits. LED lighting, heat pump heating and heat pump hot water system. We have time clocked our hot water cylinder (240l) and our fridges and freezer so that they only come on during the day when the system is generating. The freezer doesn't defrost and we still have hot water for a shower in the morning. We only run our dishwasher and washing machine off solar unless it's an emergency. Our house is fairly solar efficient having been built to optimise the sun ( esp in winter). We run our heat pumps in the summer to stay cool from the solar energy. We still need the heat pumps in the evening to stay warm, but it's not difficult to wrap up.

We've had our solar system fo 15 months now and are pleased with it. The first full year has resulted in a net saving of approximately $2800. This equates to 12% return. Better than money in a bank! This has been calculated from savings on power bills plus income from power sold.

I agree with your article than solar panels alone are a dubious investment, but when used intelligently with other strategies are worth while. If you are thinking of solar then a change of mindset is also needed.

The added bonus is that it also makes you feel good.

Cheers
Lindsey Bishop.

Glenn B.
20 Nov 2015
Wellington more sun the Kapiti?

that Branz PV generation calculator seems to give Wellington more annual sunshine hours than Paraparaumu. Using the same parameters for both regions, the calculator always has Wellington coming out with higher estimation generation.

It's well-known (?) that the Kapiti coast is sunnier and warmer than Wellington, or has that been an invalid assumption for most of us?

Previous member
20 Nov 2015
re: Wellington more sun the Kapiti?

Hi Glenn,

Generally Paraparaumu Aerodrome weather station receives more annual sunshine hours than Wellington’s Kelburn station, so it’s odd that the BRANZ calculator is giving more kWh per year for Wellington. For example, last year Paraparaumu Aero received 2112 sunshine hours, compared with 2057 at Kelburn. We’ll raise this issue with BRANZ.

NIWA’s Solarview tool is a great way to get solar irradiance information specific to your location. It also takes into account shading: http://solarview.niwa.co.nz/

You may also be interested in NIWA’s historical (1981-2000) mean annual sunshine hours for various locations around the country:
https://www.niwa.co.nz/education-and-training/schools/resources/climate/sunshine

Kind regards,

George
Consumer NZ staff

Graeme L.
15 Nov 2015
A Fair Price for Buy-Back Rates

Particularly relevant with nations hopefully making real commitment to greenhouse gas emissions, our government should be legislating to establish minimum buy-back rates to support PV for residential situations. Consumer could be more helpful here. The need to acknowledge the big picture and report accordingly, in support of this not just weighing up the costs and drawing simplistic conclusions.

Previous member
16 Nov 2015
re: A Fair Price for Buy-Back Rates

Hi Graeme,

We had some concerns about the bill to set a minimum buyback rate, which was voted down at its first reading last week.

Currently, residential power bills in NZ include a fixed component which represents the cost of electricity distribution. If you install solar power, then you reduce the amount you pay for the lines that bring electricity from the grid to your home. But many solar users still use the peak capacity of the network (for example on cold winter nights when solar power’s not generating and they need to run their heaters or stoves). So, they often use just as much power as before they installed PV, while paying less for the network.

As a result there are concerns that an increasing number of PV users may shift the cost of building and maintaining electricity distribution infrastructure onto non PV-owning households, who are usually not as well off as PV-owning households. The Electricity Authority recently released a consultation paper on the ‘implications of evolving technologies for pricing of distributions services’ if you’d like to learn more: https://www.ea.govt.nz/development/work-programme/transmission-distribution/distribution-pricing-review/consultations/#c15642

In addition, we don’t think residential solar PV, at this point in time, represents the best way to reduce New Zealand’s greenhouse gas emissions. Other renewable energy options, such as hydro, wind and geothermal, are considerably more cost effective and a better fit for New Zealand’s electricity demand profile. And the dominant solar PV technologies currently have some harmful environmental effects related to their production and end-of-life disposal. That said, I’d be very happy to be proved wrong if panel efficiencies rapidly improve or the cost of battery storage falls dramatically.

Kind regards,

George
Consumer NZ staff

hops
14 Feb 2016
Re fair price for export rates

(Its not buy back since retailers never owned it in the first place)

"Currently, residential power bills in NZ include a fixed component which represents the cost of electricity distribution. If you install solar power, then you reduce the amount you pay for the lines that bring electricity from the grid to your home. But many solar users still use the peak capacity of the network"

For a start its 2 fixed components, one part of the daily charge, the other part of the per unit rate ( the greater part actually). The daily fixed charge is unchanged grid-tie solar or not,
the per unit distribution portion is tied (fairly) to the amount of power used.

This argument is utterly fallacious ( but commonly propagated by the existing gentailer industry in multiple countries)
If you install solar power you are using less grid power and therefore using a lesser portion (bandwidth) of the distribution network. What amount you are using (importing) you are paying the same proportion of grid costs that a non-solar connected user does for the same amount of energy.

If you are actually sucking more at peak times/dates it's the same again as a non solar installed site and you are paying the same rate (and proportion of distribution) costs that you are using.

Your above argument (re using less power implies being subsidised by other users) applies equally to installers ofany power saving devices or appliances ( eco -efficient washers and LED light bulbs) or anyone who finds other ways to decrease their power usage.

You might have a better argument if power generators paid grid distribution costs but they dont - its all consumers.

You argument points out a market failure not a subsidy/fairness situation - to address that you would need price signals for consumption at peak use ( i.e Time of Use pricing) and/or Tiered pricing penalising consumers of increasingly larger amounts of power.
As it is with the current pricing methodology the smaller power quantity consumers (domestic) are subsidising the larger consumers who have negotiated cheaper pricing ( e.g Tiwai point).

Barry M.
15 Nov 2015
Solar zero option

Has Consumer caught up with the SolarCity scheme, 'SolarZero' and does it have any comment on that scheme?

Previous member
16 Nov 2015
re: Solar zero option

Hi Barry,

We’ve been following the launch and development of ‘Solarzero’ with interest. These schemes are known as solar power purchasing agreements (SPPAs) and have proved very popular overseas, with almost 70% of the residential solar market in the US now based on this model. They’re basically rental-and-servicing arrangements, where the solar provider retains ownership of the panels and is responsible for maintenance.

The idea is that at the time of installation, your combined solar fee and your grid electricity bill will match, or be slightly lower than, the amount you currently pay for power. Installers then say your savings will increase every year as electricity prices rise. However, it’s far from certain that the retail power price will increase year-on-year for 20 years, as consumer and industrial demand has flattened out.

The projected annual and lifetime savings advertised for SPPAs rely on 100% in-home consumption, and you’ll only get close to this if you have someone home all day every day, or have a high level of baseline demand like a heated swimming pool. We think these schemes are only worth considering if you’re confident you can use most of the power generated by panels during the day, and if you have the long term financial wherewithal to keep up with 240 monthly payments over the 20 year period.

As for what happens if you move house before the term is up, you’ll have to either:
• Convince the new buyer to take over the remaining payments.
• Move the system to your new house (incurring an additional fee).
• Prepay the remaining fees using the profits from the sale and have the owner take over the panels, and any other payments associated with the system.

We’re putting together a supplement to this article covering SPPAs. You can expect to see this online by next week.

Kind regards,

George
Consumer NZ staff

hops
14 Feb 2016
re power price increases

Consumer staff apologist reply:
"However, it’s far from certain that the retail power price will increase year-on-year for 20 years, as consumer and industrial demand has flattened out. "

Though since 'deregulation' that (price increases) has been the only way to bet.
Note that while demand has allegedly flattened you couldnt prove that by the year on year retail power price increases ( as your own powerswitch price graphs show)...

Clark M.
14 Nov 2015
PV & Full electric car...

Having a full electric car will probably a "driver" for PV also, ideally one would have a PV setup at work too.

Powerwall/storage + PV + electric car is an interesting combination in that the Powerwall/storage can in theory fast-charge/top-up your car as well as offer some storage for the house too. Any leftovers can be fed into the grid.

Roger & Jodie W.
10 Nov 2015
Having WON a Solar Array with PowerWall from Vector

And THANK YOU Vector. We just had the opportunity to upgrade it from 3kWh to 4 of 5 kWh for $3000 and $5000 respectively.

Now, this means a majority of the install costs (inverter, scaffolding, etc) are covered by the array we won (I'm quoting). and here are how the costings worked out:

http://www.branz.co.nz/PVcalculator

Says 2kWp array in AKL at 20 degree incline and 20 degree from North will generate ~2300 – 2400 kWh / year
Our roof is a 16 degree pitch, and I think they said west side, so more than 20% off north.

I’m paying $0.182 / kWh

Assuming I put $5,000 on a 20 year mortgage at 7%
And power prices increase at 7% per annum, which is possibly way too high.

And I used ALL the power myself (unlikely)

https://www.solarquotes.com.au/calc5/
says 15 years to pay back ( “payback” under graph on the right).

Even if I use all the power, pay only 6% interest, and power prices increase at 20%

The payback is still 10 years

Conclusion: Parity it ain't. The array and battery are warrantied for 10 years, and the inverter should be replaced at 15 years.

By my estimate, the array cost would have to about 1/2 to be acceptable, and storage, well my "off grid" estimate a few years ago (3 days power) was about $250,000 for batteries. or about $85,000 for one day. With the power wall? It drops to about $90,000 for 3 days power, and $30,000 for 1 day. That's $3,000 / year for the 10 years it's warrantied for, or more than my average monthly power bill.

So batteries need to be about 1/4 or less the price before they are cost effective.

Previous member
16 Nov 2015
re: Having WON a Solar Array with PowerWall from Vector

Hi Roger & Jodie,

Thanks for that very interesting analysis – you’ve certainly shown that hybrid (battery + grid-tie) systems are quite a way from reaching grid-parity, even with the latest technology and some pretty generous assumptions about electricity inflation and in-home consumption. We think a 7% p.a. rise over the next 10 years is highly unlikely, given the downward pressure on retail prices due to flat-lining demand and our excess supply of committed new generation.

Kind regards,

George
Consumer NZ staff