Talk to us: +64 21 942985

Solar Power – The Assumptions and the Payback

Photo: Andreas Gucklhorn - Unplash

Photo: Andreas Gucklhorn - Unplash

Being a “greeny” we plan to install Solar Photo voltaic panels on our soon-to-be-completed Passive House. The reasons:

  1. To do the right thing for the planet, 
  2. To save us some $$
  3. To learn more about renewables, to better inform our Clients. 

This has led to us researching the best options ...which has shown that many of my assumptions around using Solar PV power are not necessarily true. This is information I want to share. If anyone has a contradictory view, or information I don’t know, I would be pleased to hear.

Note: much of this information has come direct from SunZ a solar energy specialist.

Assumption No. 1
Solar PV (Photo Voltaic panels) in NZ is the right environmental choice.

Assumption No. 2
Solar PV with Batteries will ultimately save you $$

Assumption No.3
If you have PV and are grid tied, you will have power in a power cut

Assumption No.1
Solar PV (Photo Voltaic panels) in NZ is the right environmental choice.
Source – Electricity Authority report: Energy in New Zealand report 2018         

  • Approximately 85% of electricity generation in New Zealand is from renewable sources(water, wind, solar and geothermal heat).
  • Being renewable does not mean zero carbon (CO2). Solar has approximately double the lifecycle CO2 of hydro power (which accounts for over 50% of electricity produced in New Zealand).
  • Note 1: The European PV panels are typically ½ the carbon footprint of the Chinese made versions.
  • Note 2: Hydro power comes with other environmental concerns - as it changes a rivers ecosystem which will affect both people and wildlife.  

Assumption No. 2
Solar PV with Batteries will ultimately save you $$
Source: a house in Hawea Flat December 2017

  • The cheapest battery storage system costs 23.00 c/kW
  • Power costs 22.06c/kW from the grid
  • Payback from the grid 7.52c/kW
  • Saving per kW of installing batteries – 14.54c/kW
  • This means you are paying 8.46c/kW to have the battery system, which you think is saving you money…

Note:this is based on costs based on a certain house at a point in time. Not to be treated as gospel for all situations. This will change – see summary!

Assumption No.3
If you have PV and are grid tied, you will have power in a power cut
If you are generating power from PV, and there is power cut, your PV system is automatically switched off.
The reason: if it wasn’t, you would be electrocuting the man from the power supply company who came to sort out the power cut on the line.

So, the question comes – why do it?

Smart Meters
Touted by the power companies as “a way to improve our service to our customers”, this is really a way for the companies to charge you more when you are using the power at an expensive time for them to purchase the power. If you are operating under a smart meter system this is what it actually means you could be paying: 

Peak times: 7am – 9.30am & 5.30pm – 8pm
Cost: 60.39c

Shoulder times: 9.30am – 5.30pm & 8pm-11pm
Cost: 24.46c

Off Peak: 11pm – 7am
Cost: 16.76c

Electric Vehicles (EV’s)
They are coming, the power companies know it, and they will place a HUGE load on the network.
Smart meters could also be used to alter the feed in tariffs you get for your solar energy, so in the middle of the day when power on the whole sale market is cheap, you will get less for it. 

Source: 2018 Vector Report

  • “electricity networks had traditionally been sized based on the number of houses on the street. A customer with a big-battery EV would add the equivalent of 1 to 20 houses' power needs”
  • “Manufacturers expect cars with longer range and larger batteries to be available in the market within the next few years. If current uptake trends continue, 1 in 15 Auckland households is expected to have an EV by 2021. Even if uptake was not widespread, Vector said there could be problems if all the EV owners chose to charge during peak time or use faster charging options.”
  • “It was likely that people would choose to put their cars on to charge when they got home in the evening, just as other households were turning on appliances or cooking.”
  • “more cost-effective time-of-use pricing model would be needed to encourage EV owners not to charge their cars until after 9pm”


  1. Whilst solar is the environmental choice in many countries, due to our heavy reliance on renewable power in New Zealand, solar PV power is arguably not the best choice for the environment (at present) for New Zealand households.
  2. In the next few years, the electricity market will change dramatically (smart metering is the start of this). We will be paying higher line charges, and higher rates for the power we use. This will affect everyone, even if you don’t become an early adopter of the EV. This completely changes the payback of the battery system, from the current situation of a negative payback (i.e. it is impossible for it to pay you back) to payback in just a few years. Therefore, ensuring that your house is ready for solar now, and the system will be battery capable will have a real financial incentive in just a few years.
  3. If you have a battery system, with the correct inverter, you can also have power when the grid goes off.

I realise this blog could be seen as polarising, and possibly confronting to many traditional views on sustainability and what this means. This exercise has certainly been an interesting one for me to confront my own assumptions and has somewhat changed my viewpoint. Despite this, we are still planning on using PV panels and preparing for the time when batteries will become a much better option.

I still believe the ultimate way you can affect carbon usage is to reduce your energy requirements, and the best way to do this is to create an energy efficient home. Solar is then something you can chose to adopt when the time is right for you