How Many Solar Panels Do I Need?

A Complete Guide For New Zealand Homes

Here’s the short answer:
Solar panel system sizes suitable for New Zealand homes normally range between 3 kW (9 solar panels) and 8kW (20 solar panels).  

A 3kW solar power system is roughly 10 solar panels - suitable for a 3 bedroom house, with standard appliances: heat pump, washing machine, dishwasher, led lights, etc. The larger 8kW, which is roughly 20 solar panels, is more suitable for a power-hungry home - with 5 bedrooms, a spa pool, battery storage, EV charger, etc.

However, the statement above is very generalised, and a one-size-fits-all approach usually doesn’t work well when it comes to solar power. Every household is different, and I wouldn’t recommend picking a solar power system off the shelf.  In fact, there’s a lot to consider when picking a system size and therefore the right amount of solar panels. 

If you want to take the easy route and get a specialist to make a recommendation for you, click here to get 3 free quotes.  Otherwise, read on…  

First, A brief clarification between solar panel size vs. the number of solar panels.  

Although “how many solar panels do I need?” is the common question, the more precise question is what system size is best for your home.  

Solar panel sizes vary in the amount of power they produce in optimal conditions, for example, the power rating of solar panels sold in New Zealand typically varies between 300W and 440W. Ten 440 W solar panels will create a lot more power than ten 300 W panels.  

On the other hand, the system size is the total number of panels in terms of watts/kilowatts.  A system with ten 300 W solar panels is called a 3 kW system, whereas one with ten 440 W panels is a 4.4 kW system.

A 3kW Solar Power System in Tauranga NZ

Here’s a table that shows roughly how many panels each system size is equal to.  Depending on what size solar panels your installer uses, this may vary.

The advice on how many panels (or system size) to install varies from country to country due to various government incentives such as rebates and tariffs.  There are no government incentives for solar power here in Aotearoa, which makes sizing advice unique. This is a guide specifically for New Zealanders.  Let’s crack into it…

There are several main factors to consider when choosing a system size.  

1. The system size that gets the best return on investment
2. The roof space available
3. Budget
4. Future-proofing

The Best Return On Investment

Generally, the more panels installed / the bigger the system size, the better the bang for your buck (from economies of scale). But there is a tipping point where a larger system will bring a lower return on investment. If you install too many solar panels, generating more power than you need, you will be selling your excess solar power to the energy retailers who generally don’t pay much for your power.

If you install a system size that will offset your grid power usage, your system will be generating power in place of what you would normally pay the electricity retailer at around 33 cents.  Whereas any power you don’t use will be sold to your energy retailer at a rate between 7 and 16 cents.

Why Solar Self-Consumption Is Important

Simply put, solar self-consumption is how much solar power is used up by the appliances in the home. The more solar power you can self-consume, the higher the return on investment will be.

Solar power is generated during the day when the sun is out, and normally peaks during the middle of the day, and for many homes, a lot of power isn’t normally used at this time. Therefore the key is to change your energy consumption pattern to use as much of the solar power as possible within the home first as a priority and then only export excess solar power.

A household can easily have a self-consumption rate of 60%, i.e using up 60% of the solar power generated.  But there will need to be a few adjustments around the home, like timing the use of the washing machine and dishwasher sometime around the middle of the day.  Also, making sure the hot water cylinder only turns on during the day by using a timer or an appliance controller helps.

Below is an example of a home in Christchurch and the likely return on investment for installing different system sizes from 3 kW to 9 kW, and our best guess of the self-consumption rates likely to be achieved with different system sizes. 

In this particular example the customer will get the most bang for their buck with a 4 kW system with an estimated self-consumption rate of 60%.

How To Calculate Your Solar Savings Estimates

My Solar Quotes has a useful online tool which estimates the return on investment for any New Zealand home and what the expected annual savings will be.  Just move the self-consumption and system size sliders on the results page and you’ll see how your savings and ROI change. Get a glimpse of our smart solar calculator results page in action below.

Have a go of My Solar Quotes's solar calculator now!

How To Guess Your Self-Consumption Rate

You can either take a good guess at what your solar self-consumption rate might be or you could do a little math:

If you have the average New Zealand home, for example, and you use around 8000 kWh of electricity each year - if you look at a 3 kW system above, that generates 4260 kWh a year, you could probably say that you are likely to use most of that solar power, you just need to make sure half of your total electricity requirements is used during the day when the sun is out.  

If you are looking at say a 6kW generating twice the amount, you would assume that you wouldn’t be able to use as high of a percentage of the solar power generated, you could possibly self-consume about half.

Solar self-consumption at this stage requires a bit of guesswork.  If your actual self-consumption rate is higher than the initial guess, then great - more savings for you.  If your self-consumption rate is lower than what you thought, then there are always ways to improve this rate.

Tip: Annual power usage can normally be found on a recent power bill or from your energy retailer’s app.

Solar Power System Sizes To Suit A Budget

Although a 5 kW system might provide the best return on investment, a 3 kW system size might be right for your wallet size.  The option is open to specify to the solar installation company what your budget is, and go for the maximum system size your budget will allow you to go.

Here is a list of rough solar power system prices, to give you an idea.  

View more solar power system price examples here.

*Please only use these prices as a guide.  The solar power system prices assume straightforward installation on a metal roof. Actual prices can vary based on several factors.

Go Larger To Future-Proof The Solar Power System

Electric Vehicles

It’s fair to say that within the next 10 years most of us will be driving an electric vehicle (EV), whether it’s a second-hand Nissan Leaf used for short commutes or the latest long-range Tesla or Rivian, EV’s are the only option in the future.

This needs to be factored into sizing a solar panel system - if you’d rather power the car with solar than grid electricity.  For most people, you’d probably want an extra 1 to 2 kW on solar panels on your roof to charge an EV.  Therefore, if the above information helped you land on a 4 kW solar power system being right for your home, take it up to a 6 kW system.

Yes, you can upscale the system in the future, but it’s a lot more cost-effective and easier to get the lot done now if you have the means.  

Solar batteries

Solar batteries are a big expense, and not for everyone.  Their price may come down in the future, but there are no guarantees.  But if you are thinking you might like to install a solar battery within the next 10 years then it may be worthwhile installing a larger system now for efficiency, so once the battery is installed then there will be plenty of solar power left over to store in the batteries to use at night or during a power outage.

To start the journey to figuring out what’s best for you check out My Solar Quote’s calculator.

Ready for the next step?  Get 3 Free Solar Quotes through our online form to compare the best solar companies in your area.