Plan your on-farm solar system

Solar systems are sized in kilowatts (kW). This refers to the peak amount of DC (direct current) power the system can produce at any moment, not how much energy it produces over a year. This is sometimes referred to as kWp (kilowatt peak). 

While typical residential systems range from 3-10 kW, farm installations are often much bigger, ranging from around 20-50 kW up to more than 300 kW, depending on electricity use, load profile, and scale of operation.¹

The best system size is one that will give you the greatest return on investment. 

A detailed system design should be based on your annual, seasonal, and daily electricity needs. Part of the optimisation will also include the fact that larger systems are generally cheaper on a per kW basis. 

A solar installer or consultant can help you determine the best system size by analysing your energy use. They should be able to explain why a particular size makes sense for your specific operation - including the pros and cons of going bigger or smaller, and how you could improve daytime use if you’re not installing a battery. 

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Modern PV panels can generate around 220 watts or more per square meter of panel (m2), with each panel ranging in size from 1.6-2.2 m2. However, depending on the layout, particularly for large arrays, you usually need space between panels to stop them shading each other, so the total area the system takes up is often much bigger than just the panels themselves.

Panels facing north, northeast, or northwest generate the most electricity over the year. East- or west-facing arrays can still work, particularly if electricity demand is higher in the morning or late afternoon, but total annual generation will be lower. South-facing panels generally perform poorly.

A panel tilt of roughly 30-45 degrees produces the highest annual output across most of New Zealand. Shallower tilts still work, but with reduced generation. Flat or very steep angles generate less electricity unless additional racking is used, which adds cost.

It’s cheaper and simpler to install solar when panels are close to your main switchboard, as longer cable runs and trenching can add to the cost.

Open or exposed sites may require stronger mounting for ground-mounted systems, which can affect cost and placement. In some areas, this may also trigger additional consenting or engineering requirements.

Panels should be installed on structures that are in good condition. If a roof is likely to need replacement or major work within the next 10 years, this should be addressed before installing solar.

Shade reduces output. Even partial shading during the middle of the day can noticeably affect performance.

On average, your panels will produce considerably more electricity in the height of summer than they do in depths of winter. This is due to longer daylight hours and the higher angle of the sun.

Most simple roof- or ground-mounted solar systems don’t need consent, but there are exceptions. 

• Building consent - may be required in some cases, particularly for ground-mounted systems in windy or exposed areas, or for larger structures.  
• Resource consent - rules vary by council and depend on factors like zoning, location, and visual or environmental effects. There’s no single national rule. 

Before moving ahead with an installation, it’s worth you or your installer checking with your local council to confirm whether any consents apply to your site.

If they’re well maintained, you can expect solar panels to last 25-30 years, with only a small drop in output of around 0.5% per year.

The size of a solar system refers to the total power-generating capacity of the panels, measured in kilowatts (kW). 

System size depends on: 

• The number of panels installed, and 
• The rated capacity of each panel  

For example, a farm system might use 100 panels rated at 450 watts each, giving a total maximum output of 45 kWp (kilowatt peak).

As there are different kinds of inverters, a range of sizes, plus varying quality and pricing, it’s helpful to ask a solar expert for guidance.  

String inverter — the most common, the cheapest, and best when your panels will get full sun.  
 
Microinverters — are installed behind individual panels. They cost more but a good option if panels experience partial shading or are spread across multiple roof areas. 

If you’re installing panels now but might add a battery later, choose an inverter that can work with a battery in future. These are usually called hybrid inverters.

You’ll likely need to replace the inverter after about 10-15 years, depending on its quality. Replacement during the life of the solar system is normal.

Having slightly more panel capacity than inverter capacity often provides the best value. This is known as 'overpaneling’ and works because inverters are a relatively expensive item, and the value of the inverter is maximised by having it operating at full capacity for more of the time. 
 
You may lose a small amount of potential power output when the inverter reaches its maximum (on sunny days in summer), but this is a small trade off.  

As there are different kinds of inverters, a range of sizes and varying prices, it’s helpful to ask a solar expert for guidance.

A solar battery should last 10 years or more, depending on the battery type and quality, plus how intensively it’s used.  

A battery should still be operating near its full capacity after 10 years, and only needs replacing if it no longer meets operational needs.

Batteries are sized in kilowatt-hours (kWh), which tells you how much energy they can store. 

Many battery systems are modular, so they can be added to over time as your needs change.  

A small solar system won’t fully charge or make good use of a large battery, so avoid getting a bigger one than you need.

To use solar and battery power when the grid is down, the system needs to be set up to safely isolate from the grid and stop exporting electricity. This usually requires a small design change and adds a modest cost compared with the overall system.

Solar panels on their own won’t power your farm during an outage, because the inverter needs AC electricity to run.

A smaller battery may be enough to cover essentials like lighting, internet, and some systems. Powering larger loads - such as pumps, refrigeration, or a milking shed - requires a lot more battery capacity and higher power output. 

Being clear about what matters most during an outage helps ensure the battery is sized to meet your needs.

Yes. Many farms add batteries after the solar system is installed. It’s best to make the system battery-ready from the start, which may involve a hybrid inverter and pre-installed cabling to simplify future upgrades.