How Many Solar Panels Do You Need

Determining how many solar panels you’ll need for your home or business means first knowing what your goals are. Do you want to minimize your carbon footprint? Maximize your return on your investment? Save as much money as possible? Most people want to save money while minimizing their environmental impact.

To calculate how many solar panels you need, you need to know the following: how much energy your household uses; your roof’s usable surface area; the climate and peak sunlight in your area; the wattage and relative efficiency of the photovoltaic (PV) panels you’re considering; and what Net metering is available (how much the power company will pay for the excess electricity generated by your solar system)

One simple way of answering the “How many solar panels do I need” question is to consult a Zerosolar Consultant, who will give you a Free Solar Evaluation. PH 0800 400 900 or email:

1. How much solar power will you need?

To determine your home’s average energy requirements look at past power bills. You can calculate how many solar panels you need by multiplying your household’s hourly energy requirement by the peak sunlight hours for your area and dividing that by a panel’s wattage. Use a low-wattage “older panel” (150W) and high-wattage (390W) example to establish a range (ex: 17-40 panels to generate 11,000 kWh/year). Note that how much sunlight your roof gets and factors such as roof size and battery storage will figure in as well.

If you work with ZeroSolar, our Solar experts will handle all these calculations for you. But to give you some idea of how many solar panels are needed for the average home (or for your home in particular), here is a sample set of questions that a solar professional might use to figure it out:

2. How many watts do you currently use?

Look at your electricity bill for average usage. Look for “Kilowatt Hours (or kWh) Used” or something similar, and then note the time period represented (usually 30 days). If your bill doesn’t show kilowatt hours used, look for beginning and ending meter readings and subtract the previous reading from the most recent one.

You want daily and hourly usage for our calculations, though, so if your bill doesn’t show a daily average, just divide the monthly or annual average by 30 or 365 days, respectively, and then divide again by 24 to determine your hourly average electricity usage. Your answer will be in kilowatt-hours (kWh). (And just in case you are wondering, a kilowatt-hour is how much power you are using at any given time multiplied by the total time the power is being used.)

A small home in a temperate climate might use something like 200 kwh per month, and a larger home in the south where air conditioners account for the largest portion of home energy usage might use 2,000 kWh or more. The average N.Z. family home may use about 550kWh per month. So that’s 18.33 kWh per day or 0.764 kWh per hour.

Your average daily energy usage is your target daily average for to calculate your solar needs. That’s the number of kilowatt-hours you need your solar system to produce if you want to cover 100 percent of your energy needs.

It’s important to note that solar panels don’t operate at maximum efficiency at all times. Weather conditions, for example, can temporarily reduce your system’s efficiency. Therefore, experts recommend adding a 25 percent “cushion” to your target daily average to ensure you can generate all the clean energy you need.

​3. How many hours of sunlight can you expect in your area?

The peak sunlight hours for your particular location will have a direct impact on the energy you can expect your home solar system to produce. For example, if you live in Hawkes Bay you can expect to have a greater number of peak sunlight hours than if you lived in Invercargill or Dunedin. That doesn’t mean an Invercargill homeowner can’t go solar; it just means the homeowner will need more panels.

The NIWA SolarView gives an estimate of the available solar energy available at any NZ Location, try the Solarview calculator.

Now multiply your hourly usage (see question No. 1) by 1,000 to convert your hourly power generation need to watts. Divide your average hourly wattage requirement by the number of daily peak sunlight hours for your area. This gives you the amount of energy your panels need to produce every hour.

So using the average New Zealand family home (550 kWh/month) in an area that gets five peak sunlight hours per day would need 3,667 watts ( therefore 10-12 Panels)

Calculation:  (550kWh x 1000=550,000 watt divide by 30 days= 18,333watts /day then divide by 5 hrs = 3,667 watts  divide by 370watts = 9.9 panels) ie  10 panels  x 1.25(25% cushion) = 12 panels

​4. What affects solar panel output efficiency?

Here’s where ZeroSolar Jinko Solar panel quality makes a difference. Not all solar panels are alike. Photovoltaic (PV) solar panels (most commonly used in residential installations) come in wattages ranging from about 150 watts to 390 watts per panel, depending on the panel size and efficiency (how well a panel is able to convert sunlight into energy), and on the cell technology ( ZeroSolar Jinko Panels convert a minimum of 22.8% of the sunlight it receives into energy)

For example, solar cells with no grid lines on the front (like Jinko solar panels) absorb more sunlight than conventional cells and do not suffer from issues such as delamination (peeling). The construction of our cells make them stronger and more resistant to cracking or corrosion.

Because of these wide variations in quality and efficiency, it’s difficult to make generalizations about which solar panels are right for you or how many you’ll need for your home. The main takeaway is that, the more efficient the panels are, the more wattage they can produce, and the fewer you will need on your roof to get the same energy output. Conventional solar panels usually produce about 250 watts per panel, with varying levels of efficiency. In contrast, ZeroSolar Jinko panels are known to be the most efficient solar panels on the market.

To figure out how many solar panels you need, divide your home’s hourly wattage requirement (see question No. 3 above) by the solar panels’ wattage to calculate the total number of panels you need.

So that average NZ. home in Invercargill, may need approximately 20 conventional (250W) solar panels or  12-14 ZeroSolar Jinko (370W) panels.

You should also consider Net Metering you’re considering figuring out your ROI for your solar system. Net metering is how your Power/utility company credits you for the excess solar energy that goes to the Grid ( when the sun is shining and they let you draw from those credits )when you’re using a conventional power grid at night, if you don’t have a solar battery storage system( which we strongly recommend you invest in, to Maximise your saving on Solar ) however you can obviously Add storage later when you have the funds !