Understand what needs to be installed and connected at your place for a solar system to generate electricity.
Key parts of a solar installation
You need to have solar panels and an inverter, but a battery is optional.
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Solar panels
Photovoltaic (PV) solar panels convert sunlight into electricity.
They are usually installed on a roof but can also be placed on facades, conservatory roofs, garages, or stands on the ground.
The panels are normally fixed at the angle of the roof, but can be mounted at a different angle if necessary to get them working effectively. -
An inverter
The inverter converts the electricity so you can use it.
It changes direct current (DC) electricity generated from solar panels into alternating current (AC), which is used in your home. -
A battery — optional
With a battery installed, you can store electricity for use after dark or in emergencies. You’ll also have less need to buy electricity from the grid outside of daylight hours.
Most people in New Zealand choose to install solar without a battery, as battery storage makes the overall cost a lot higher.
However, including a battery may stack up financially if your household typically uses lots of power at night.
Add-ons for optimising solar usage
You can enhance your home solar system with various add-ons.
- Hot water timer or solar diverter — If you have an electric hot water cylinder, including a timer or diverter in your install is highly recommended as it can turn your cylinder into a cheap form of energy storage. These devices will pre-heat your hot water while the sun is shining so you can make use of it later.
- Home energy management system (HEMS) — This type of system automates the operation of connected appliances, tracks solar generation, maximises consumption within the home, and manages exports to the grid.
- EV charger — You can set the timing of your EV charging to use solar rather than grid electricity.
How long solar tech lasts
- Panels — If they’re well maintained, you can expect solar panels to last 25 to 30 years, with only a small decrease in output of around 0.5% per year.
- Inverter — You’ll likely need to replace the inverter after about 10–15 years, depending on its quality and maintenance.
- Battery — The lifespan can be highly variable, but a solar battery should last 10 years or more. The exact duration depends on the battery type (such as lead-acid or lithium-iron-phosphate), quality, and how intensively it’s used.
Sizing a solar system for your needs
To get your solar system set up and sized correctly, you need to know:
- your current annual power usage, including how this varies between summer and winter
- the power plans available to you, particularly ‘buyback rates’ for solar energy exported back to the grid
- your roof’s size, orientation, tilt and level of shading.
System size
It’s best to base the size of your home solar system on the amount of electricity you normally use.
It’s not cost-effective to get a larger system than your home needs, while a smaller one may mean you miss out on potential savings.
Here are some key things to consider with system sizing:
- Future needs — Are you likely to add any high energy users like an EV or spa pool? If so, that would increase the ideal system capacity for your home.
- Your roof — The larger the system, the more solar panels you’ll need, so the amount of suitable roof or ground space may limit what’s possible. High-end, efficient panels can be used to generate more power per square meter if space is limited, but they can also cost more.
- Storage — If you plan to include a battery from the start or add one later, you’ll need a system size that generates excess energy to charge it. If you have an electric hot water cylinder, remember to consider using a timer or solar diverter as a cheap form of storage.
Inverter size
An inverter is essential for turning the energy harnessed from solar panels into electricity you can use in your home.
Having around 20% more solar panel capacity (kW) than inverter capacity tends to produce the best value for most New Zealand homes. This is known as 'overpaneling'.
You’ll lose a small amount of potential power output when the inverter reaches its maximum (on sunny days in summer), but your solar system will generate much more output over the course of the year with only a minor additional cost.
As there are different kinds of inverters, a range of sizes and varying prices, it’s wise to ask a solar expert for guidance.
Battery size
Having a battery allows you to store the solar energy your system produces, so you can use it later. This can reduce or even eliminate your power bills.
Typical capacities are roughly 5 to 10 kWh, 10 to 15 kWh, or 20+ kWh.
A small solar system won’t fully utilise a large battery, so avoid getting a bigger one than you need.
Good to know:
- With a modular solar system, you can start without a battery and add one later. This will keep your initial installation costs down while giving you time to see the impact of solar on your power bills without a battery.
- At current prices, including a battery is only likely to be the right choice if your home consumes a larger than average amount of electricity, and you use most or all of that power at night.
Selling back to the grid
When your home generates more solar electricity than you can use, it’s sold to your power company, generating credit on your power bill. This is also known as 'exporting back to the grid'.
The buy-back rate will be lower than what you pay for grid electricity, so it’s better to use the power you produce yourself whenever you can.
Tips
- You may be able to build up credit with your power company during the summer and use it to offset your winter power bills.
- Buy-back rates can vary a lot, so check what plans and rates are being offered by different power companies. This is especially important for larger solar systems with high exports back to the grid.