Guide to understanding on-farm solar quotes

Most quotes will state a headline system size, usually in kilowatt peak (kWp). This is the rated capacity of the solar panel array and is the standard unit used for pricing and benchmarking. It may also be referred to as the DC capacity, as the solar panels produce direct current electricity.

System capacity is calculated using the number of panels multiplied by the rating of each panel.  

For example — 120 panels × 415 W = 49.8 kWp 

This figure drives most of the equipment cost. Typically, PV systems generate an output less than their peak performance as real-world conditions rarely recreate the conditions they are tested in. 

Quotes will list the panel model, the number of panels, and the rated output per panel in watts (W). Sometimes they also include panel efficiency, degradation, product warranty length, and performance warranty terms.

Higher-watt panels reduce the number of panels needed for a given system size. It is important that the panel choice suits the site (wind, corrosion, mounting), and that warranty terms are clearly stated. 

The inverter rating sets the maximum power the system can deliver at any moment. Quotes will specify inverter model(s) and output (kW). It may also be referred to as the AC capacity, as the inverter is used to convert the DC electricity produced by solar panels into alternating current. 

On farms, inverter capacity is often lower than panel capacity by design. For example, 50 kWp of panels paired with a 40 kW inverter means output is capped at 40 kW at any moment in time. 

This configuration will usually optimise the value of the system (and therefore produce better returns) as the solar panels only produce full output some of the time. This should be clearly explained on a quote so that you can compare different options. 

If a battery is included, quotes should state both battery capacity (kWh) and battery power (kW). Capacity determines how much energy can be stored; power determines how fast it can charge/discharge. 

 
For example — A 100 kWh / 50 kW battery can deliver 50 kW for 2 hours. 

For farms, the power rating is often critical for backup and for supporting high-load equipment. 

Quotes should also include: 

• Usable capacity — Batteries are not normally operated at 100% of their rated capacity to protect battery life. For example, a 90 kWh battery may have 72 kWh usable. This may also be expressed as ‘depth of discharge’ (DoD). 
• Warranty — Warranties may express the number of charge-discharge cycles the battery is designed to deliver at a certain depth of discharge. Alternatively, it may express a cumulative ‘throughput’ in MWh (which represents the total quantity of energy which the battery has supplied). Many modern batteries are rated for 6,000+ cycles, or an equivalent throughput, which supports long-term use. 

Quotes usually show where panels will be installed and how they are oriented, either in text or farm photos/diagrams. Orientation and tilt may be expressed as ‘north-facing at 20° tilt’. Orientation and tilt affect when electricity is generated and how well solar matches your farm’s demand.  

Mounting type matters too. Roof-mounted systems should factor in any access requirements for maintenance, and whether panels are mounted parallel to the roof plane or tilted up (parallel is most common, but tilt mounts may be justified for low-pitch roofs). Ground-mounted systems add considerations like fencing, trenching, access for maintenance, stock/machinery interaction, terrain, and wind loading. 

A good quote clearly states the total cost, whether it is inclusive or exclusive of GST, and an itemised list of what is included. This could include:  

• Panels  
• Mounting systems 
• Cabling  
• Inverters 
• Batteries 
• Modifications to existing electrical systems 
• Civil works such as trenching/backfill or fencing (if required) 
• Scaffolding or safety systems 
• Testing, inspection, and compliance 
• Metering 
• Network costs and approvals  
• Installation labour (hours and rate per hour) 
• Council consenting costs (when applicable). 

Any exclusions or items marked ‘subject to confirmation’ should be clearly identified. 

Payback is usually calculated as total installed cost divided by annual net savings.

Example — Installed cost $120,000 ÷ annual savings $16,000 = 7.5 years. 

Payback is very sensitive to assumptions about self-consumption, export limits, export price, and electricity tariffs. 

Return on investment (ROI) expresses similar information to payback but as a percentage return. A rough relationship is that a 5-year payback equates to about a 20% return, while a 10-year payback equates to about a 10% return. 

Some quotes include charts showing cumulative savings over 20-30 years, or a calculated cost per kilowatt-hour of solar over the system’s lifetime. 

These figures depend heavily on assumptions about electricity price changes, system degradation, and replacement costs. They are best treated as scenario illustrations rather than concrete predictions.

Some quotes include avoided emissions calculations. These are typically based on New Zealand’s average grid emissions factor. 

Examples you might see on a quote include: 

• Consumption offset — percentage of your electricity use covered by solar 
• Tons of CO ₂ avoided per year 
• Equivalent car distance avoided 
• Equivalent number of trees planted. 

Because New Zealand’s electricity grid is already highly renewable, the avoided emissions number is often modest compared with countries with coal-heavy grids. This can still be useful for reporting, but it should not be relied on as the primary decision driver unless you have a specific emissions reporting need. 

Quotes can include an estimate of how much electricity the system is expected to produce over a year, expressed in kilowatt-hours (kWh). 

This estimate is modelled using system size, panel orientation and tilt, shading assumptions, location, and historical weather data. For example, a 50 kWp system might be modelled to generate between 60,000 and 70,000 kWh per year depending on site conditions. 

This figure drives the savings model, so it should be clear what assumptions were used. 

Quotes may reference export limits imposed by your local lines company. These limits cap how much power you are allowed to export at any moment and act as a design constraint. 

For example, a system may be designed assuming a 45 kW export limit. At midday, any generation above on-site use plus that export limit is curtailed unless a battery is installed. Export limits should be clearly reflected in system sizing and configuration. 

Financial modelling relies on assumptions about your current electricity prices. Quotes may list peak and off-peak rates, fixed daily charges, and export prices. 

Electricity used on-site is valued at your retail electricity price, at the appropriate time of day. Exported electricity is valued at the export rate, which is usually much lower. This difference has a large impact on savings and payback. 

You should also consider whether your current electricity plan (and retailer) will be the most cost-effective after the installation of solar. 

Learn about selling excess power 

Some quotes subtract ongoing costs such as inverter replacement, battery degradation, maintenance, or finance costs, while others do not. If these are excluded, savings might look better than reality. 

If the quote assumes you can shift loads into the day or assumes a daytime-heavy profile that doesn’t match your operation, the system may be mis-sized and returns overstated. You should discuss this with potential installers.  

Quotes should state whether any consenting or approvals are required and who is responsible for obtaining them. 

Farm systems may need additional steps depending on site and design, including engineering design for wind loading, building consent for some structures, or resource consent for ground-mounted arrays in certain zones. Network approvals should also be clearly included in scope. 

The quote should clearly state what is included and excluded (scope of work), and how payments are staged (deposit, progress payments, final payment on commissioning).  

You may need to pay a deposit upfront, typically about 10-30% the total cost. The remaining balance may be due shortly after the installation has passed inspection. Other installers require 100% payment within a week of invoice. 

Quotes should clearly list product warranties for panels, inverters and batteries, and whether performance warranties apply (for example, panel output guarantees over time). 

 
Minimum warranties for their workmanship and equipment should be at least: 

• 2 years for workmanship 
• 10 years for batteries (lithium-ion) 
• 5 years for inverters 
• 10 years for the product warranty on panels. Some will also include a performance warranty. 

Workmanship warranties should be stated clearly. Look for a warranty on their workmanship of at least 2 years.

As important as the number of years is clarity on who is responsible if the system is not installed correctly, fails early due to installation issues, or does not perform as designed. 

Quotes should identify who will do the electrical work and confirm appropriate registration (for example, EWRB-registered electricians). For farm installs, it’s also useful to know whether the provider has experience with farm switchboards, network approvals, and rural installations.