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Photovoltaic and mortgage calculator


How much money can I save by installing solar photovoltaic (electricity) panels on my roof?

This question does come up a lot, and rightfully so. It is something we researched before we put panels onto our campervan. To make the process much easier for you, we have created below two calculators: the first one is specific to NZ with average costs, gains and electricity prices that we took from official sources (Energywise, NIWA, Stats NZ). The second calculator is changeable to any national and international, specific requirements. 


We really want to thank our partners for New Zealand from Solarcorp, that have helped ensure we include inflation as well as the efficiency losses of the solar panels over time. Please do check out their site to find out if they are the right partner for you.


There are two simple steps to getting the most out of solar photovoltaic panels:

  1. Install your system on the roof side receiving the midday sun: in the southern hemisphere on the north and in the northern hemisphere on the south side of the roof

  2. Program all your high-power usage electronics to work during the hours of solar gain. The less energy you feed into the electricity grid, the higher your savings. Your cost per kWh to purchase electricity is usually higher than what you get from the electricity company to supply a kWh to them. Please be aware that there might be countries offering high subsidies for providing electricity to the grid. In those places, feed all electricity from your solar photovoltaic panels into the grid system


We have assumed within the calculator a loss of 25% on the controller, inverter and mounting orientation/ angle. 


If you want to find out the pros and cons of solar photovoltaic, please click here. For any inquiries to price or more information, please do get in touch for a free consultation.

You can find the number for sunshine hours in your city here. Just add all months together and divide the result by 365.



  1. We included a 0.6% annual efficiency loss in solar PV panels.

  2. We included 25% loss due to controller, shading and orientation.

  3. We have assumed that you would stick with the same electricity contract. 

  4. Choose kWh solar system based on your actual usage and ensure to utilise as much of the created electricity as possible.

  5. We have assumed all components to last the full 25 years.

  6. We have assumed a 8 Cents constant payback for every kWh of electricity fed into the grid for 25 years.

  7. We have assumed mounting of the panels facing the midday sun.

  8. We have assumed the electricity prices as per average numbers including GST.

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