How many solar panels do I need to power my house?

How do you work out the number of solar panels you’ll need for your home?  This is probably the #1 question we get asked by prospective customers every day!

Look around your neighbourhood and you’ll see houses with 8 or 10 panels, others with 30 or 40. How on earth you do decide the number of panels that’s right for you?

At SolarRun, we’ve got a nifty solar calculator that will answer the question: How much solar do I need? And we’re always happy to help by phone or email, so get in touch!

Alternatively, keep reading for a handy overview on how to work out the number of solar panels for your home.

In this post, we cover:

• Why panel quantity isn’t everything
• Your solar objectives
• Sizing your system: what to consider
  • Current electricity usage: how much and when?
  • Calculating the size of your solar panels system
  • Future electricity usage: EVs, batteries on your radar?
  • Roof space: a limiting factor?
  • Your network distributor: what limits are they imposing?
  • Ways of overcoming network distribution limits

Why panel quantity isn’t everything

Before going any further, let’s clear up one common misconception. And that is, the number of solar panels isn’t the most important decision to make when sizing a solar power system.  (The only situation when panel quantity may be an issue is when your roof space is limited. More on this later.)

What is important is the size, or capacity, of the solar system. This is expressed in kilowatts (or kW).  Check out any solar advertising and you’ll see systems promoted as 6.6kW or 9.9kW.  This tells you the maximum amount of electricity that the solar panels system can output at any point in time.

It may take 22 panels to make a 9.9kW solar panels system. There again, it may take 27 panels. Either way, you’re getting 9.9kW of solar electricity generating capacity installed on your roof.

But why the difference?

It all depends on the number of watts per panel.  These days you can buy panels sized from 350 watts per panel, right up to the latest 450-watt panels from Tier 1 manufacturer Risen.  That means each panel has the capacity to generate 450 watts of power at any point in time. It’s amazing how the wattage per panel has increased compared to 10 years ago, when a 250-watt panel was considered a technical triumph!

Here’s a table that provides two examples of the number of panels you could use to create a 9.9kW solar panels system. This is the most common size system we are currently installing for our residential customers at SolarRun.

Number of solar panels needed for a 9.9kW solar panels system

Your solar objectives

There are lots of reasons why you may want solar energy for your home.  The most common are:

• Cut your electricity bill
• Become more energy independent
• Charge your EV
• Reduce your household’s carbon footprint

A solar panels system can achieve all these goals for you.  Adding battery storage can also help. It’s all a question of how far you want to go.

For example, do you want to:

• Get your electricity bill to near-zero?
• Gain full protection from power outages?
• Go all-electric, with everything running off solar?
• Charge your EV both day and night. What about 2 EVs?
• Make your home 100% carbon neutral, or even carbon positive?

Of course, each of these goals has cost implications and budget is always a factor.

Whilst funds may restrict you from achieving everything at once, it’s good to have clear goals in mind. That way, you’re much more likely to get the right system installed now – and have the confidence it will meet your needs in years to come. We can provide you with advice on the costs and benefits of these different objectives, so get in touch!

Sizing your system: what to consider

System sizing is generally carried out by a solar expert when you call for a quote. At SolarRun, we have qualified solar consultants ready to talk to you about the best size solar system for your home.

Having said that, it’s useful to have a go working it out for yourself before you chat to a solar consultant. With that experience under your belt, you’ll know what questions to ask and be well-placed to get the best result for your home.

There are six main points to consider when sizing a solar panels system.

1. Current electricity usage: how much and when?

The first step is to work out how much electricity you are using in your home. You can find this information on your electricity bills where it will state the daily usage (in kilowatt hours), or monthly or quarterly.

Gather your usage data from 12 months of electricity bills to work out the daily average electricity usage in kilowatt hours over a year.

This will give you an insight into how your electricity usage varies from season to season.  It might be that your winter bills are the highest if, for example, you have underfloor heating. But maybe your summer bills are the biggest ones because you’re running aircon and a pool pump.

The average Aussie home uses around 18-20 kilowatt hours of electricity a day.  However, this varies widely between households. A four-person home with pool pump and aircon may use 30 or 40 kilowatt hours of electricity a day.  Whereas a single person working away from home may only use 8 to 10 kilowatt hours of electricity every day.

Another important piece of data to gather is: what time of day do you use most electricity? Are you normally out of the house during daylight hours?  If so, solar can worthwhile but you may want to consider use of timers on your appliances [link to self-consumption post] and investing in Wi-Fi enabled systems for your air conditioning [link to Haier aircon post] for example. Adding a battery could be a good option, as it allows your solar electricity to be stored and used in the evening when you get home.

For those spending more time at home during the day, solar panels are a great way to power your home. You can run all your energy-intensive appliances for free during the day – like your dishwasher, washing machine. This gives you the quickest payback on your solar system and it’s great for the environment too!

If you really want to delve deep into the detail of when you use electricity, you may be able to get this data from your network distributor.  It’s called ‘interval data’ and shows your electricity usage in 30-minute intervals for any time-period you choose.  Check out your network distributor’s website or give them a call to see if they can provide you with this information. Alternatively, talk to us and we can do it for you.

2. Calculating the size of your solar panels system

So, you’ve done step 1 and you’ve got the key statistic – the daily average kilowatt hours of electricity used in your home.  Plus, you know how this varies throughout the year.

Let’s use an example to demonstrate how solar systems are sized.  Let’s say your home uses an average 24-kilowatt hours of electricity every day, but in summer it’s up to 36 kilowatt hours because you’ve got an expensive old-style electric pool pump and lots of aircon.  Winter, on the other hand, is lower at 16 kilowatt hours a day because your heating is gas ducted.

The rough rule of thumb in sizing a solar system is to divide your average daily kilowatt hour usage by 4 to work out the size solar panels system.  Using this method, you get a 6kW solar system.  But there are a few other issues at play.

• Firstly, why not size up your system to 8kW or even 10kW to provide enough solar electricity to offset your aircon and pool pump summer usage?
• Secondly, what about your heating? Gas ducted is one of the most expensive ways to heat your home.  Switching to a more energy-efficient heating system, such as a reverse cycle air conditioning unit, means you can run it off solar during the day for nothing.

Taking these factors into account, 6kW may not be big enough. An 8kW or even 10kW gives you much greater scope to reduce other household running costs.  And the cost of adding another 4kW will not be huge thanks to government STCs (a form of solar rebate) – and because biggest solar systems are always cheaper than small solar systems if you compare on a cost per watt basis.

3. Future electricity usage: EVs, batteries on your radar?

Battery-electric and plug-in hybrid electric vehicles are estimated to comprise at least 30 per cent of new car sales by 2030. Chances are your next car, or the one after that, will be an EV!  With petrol prices going through the roof, the idea of powering your car for free with solar is very appealing.

Battery storage and EVs are a perfect match.  You’re out during the day, your solar system charges your battery. You get home in the evening, plug in your EV – or your two EVs – to charge overnight with free solar power. Think of the savings!

But of course, you’d need at least 10kW of solar panels, possibly even 15kW if you’ve got two EVs as well as most of your household appliance on electric.  It might even be worth upgrading from single-phase to three-phase power to get the infrastructure in place to guarantee low-cost driving and low ongoing electricity bills.  Get in touch if you’d like a quote for upgrading to 3-phase power or if you’re interested in setting your home up with battery storage and EV charging.

4. Roof space: a limiting factor?

OK, you’re up for a decent size solar system – at least 6.6kW, possibly even 10kW or 15kW.  But can you fit all the panels on your roof?  This is the point when the number of panels is important!

The table below shows how much roof space a 6.6kW and a 9.9kW solar system requires, depending on your choice of panel.  For example, you can see that the new Risen 450-watt panels take up 48.6m2 for a 9.9kW system, whereas the Sunpower panels need 52.9m2.

If you’ve got heaps of roof space, this isn’t going to matter.  But if you’ve got a roof that’s quite small, or with an unusual pitch, you may look for a panel brand that maximises the power output per square metre of roof.  Get in touch if this is a consideration for your property and we’ll be happy to undertake a full assessment.

5. Your network distributor: what limits are they imposing?

Distributed Network Service Providers, or DNSPs, are in charge of the poles and wires that bring electricity to your home.  They make the rules about connecting solar and battery systems to the grid.  Each DNSP has their own set of rules, but generally the default position is to allow 5 kilowatts of inverter capacity per phase.

Given that most homes have a single-phase power supply, this means your DNSP may approve you for a 5kW solar system (based on the inverter size), with up to 6.6kW of solar panels (as they let you oversize the panels by 33 per cent).

When you request a quote, we’ll check out the connection rules for your property with your DNSP and advice you on their response.  It can be a limiting factor in solar system sizing, but there are ways around it.

6. Ways of overcoming network distribution limits

Here are two ways of handling limits on the size solar system set by your network distributor:

• Export limit your system to 5kW (inverter capacity) and install 10kW (note: not all distributors allow this)
• Export limit your system to zero (if your DNSP says you can’t export any power to the grid) and install at least 5kW of inverter capacity and 6.6kW of solar panels. Go even bigger if you like and consider adding a battery so none of your surplus power goes to waste.
  Upgrade your property to 3-phase; that way you should be able to get 10kW or even 15kW approved, as well as exports.

Every network distributor has different rules on what’s possible, and what’s not.  Because we install systems throughout Australia, we know how every network distributor works and what they’ll allow.

Summing up

Having worked through the points above, you’ll have a strong understanding of your current electricity usage, future usage, and any possible limitations.  Thinking about the ways your household may use electricity in the future is important as it will help you decide on how to handle any possible limitations imposed by either roof space or your network distributor.

There’s no doubt that getting the right size solar system to cover you for the next 10-25 years is a wise move. No-one we know has ever complained about buying a solar system that’s too big, but lots of people have told us that they wish their previous installer had put on more panels!

Keen to talk solar?

If you’re thinking solar panels or a battery for your home, get in touch.  We’ve got a team of solar experts ready to discuss your requirements and design the right solar power system for your home and budget.