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What size solar system do I need?

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Understanding Solar System Sizing

Before we dive in, it’s important to understand how the size of a solar system is measured.

When we talk about the size of a solar system, we’re referring to its solar PV ‘Peak Output’ which we measure in kilowatts. A Watt is the basic measure of electrical power and the kilo means we’re talking in 1000s. i.e 1 kilowatt (kW) = 1000 Watts. 

A system is made up of multiple panels, each with an individual ‘Peak Output’ measured in Watts (at standard test conditions). By adding more panels we increase the size of the overall system. For example, a system with 16 panels, each generating 410W, would result in a 6.56kW ‘Peak Output’ system.

The Power of a Kilowatt

For context, one kilowatt can:

  • Operate four desktop computers (250W each)
  • Run 10 x 100 Watt light bulbs
  • NOT run your microwave as it is 1.2kW.


So, what do you need to consider when determining solar system size?


1. Why are you getting solar?

Your motive guides your system design. It might be to reduce your energy bill, shrink your carbon footprint or protect yourself from grid outages. Or all of the above. Your system size and design should align accordingly.

For example, if you’d like to have protection from grid outages, your system will include a battery, whereas if your motivations are purely financial it might not.

Starting with the why helps you and the person designing your system make the right decisions throughout the process.

2. How much electricity does your home use?

Your electricity bill shows your energy use over time and the total kWh you have used. This gives us a good idea of your home’s demand peaks throughout the day and the year.

Typically, a well-designed grid-tied system will produce enough energy during spring and autumn to meet the demand of the home. This means in summer you’ll likely produce more than you need and export some energy to the grid. And in winter you’ll need to import some energy from the grid. This usually provides the best return on investment, rather than designing a system to match winter consumption, which would be much larger than needed for the rest of the year (and cost significantly more).


3. How many solar panels can fit on your home?

Ideally, we’re looking for a north-facing roof or elevation, free from shading and at a pitch of between 10 and 40 degrees. If your pitch is lower than this, don’t worry, we can use tilt frames to increase the angle.

A standard panel measures 1.8m x 1m. Most houses will require between 10 and 30 panels. Using specialist software we can model a property to asses how many solar panels will fit. Taking into account orientation, the pitch of the roof, local weather data, shading from nearby trees, buildings and topography. This provides realistic generation predictions that we can match to your demand discussed above, to come up with the ideal system size.

If you don’t have appropriate roof space for panels, a ground mount array might be an option.


How to get a ballpark estimate of system size

You can use a straightforward calculation to get a general idea of how many solar panels you need.

Begin by dividing your average daily energy consumption by the average kWh produced by a single panel in a day.

To find out your average daily energy consumption for the year, look at your power bill to get an average winter and summer day’s consumption. Add these values together and divide this by two.

Next divide the average daily consumption by the average Kwh you get per panel, per day. A 410W panel in Wanaka produces about 1.5 kWh per day (2 kWh in Summer and 1 kWh in winter).

If your average daily consumption is 30 kWh, you would require 20 panels to meet this demand. This would result in an 8.2 kWh system.

Average daily consumption / Average panel production = Number of panels

30 / 1.5 = 20

=20 x Panels

While this provides a general estimate, it relies on averages and does not factor in the dimensions and orientation of your roof, nor does it account for your underlying motivations.


The Right Solar System for You

The best answer is to get good advice from a qualified solar expert who can design a personalised system size with you, to suit your needs.

It’s worth putting in this groundwork to get a personalised system design that’s right for you and will perform as needed. We provide this design as part of our free proposal process. 

Want to find out what size solar system is right for you? Contact us for a free proposal.

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