What Size Solar System Do I Need?

what size solar system should I get?

When you decide to start looking at solar, one of the first questions you ask yourself is “what size solar system do I need?“. Most advertising revolves around 6kW systems but this isn’t always the right size for you. Some homes do fine with 3kW. Other’s need 9kW. 

This post will clear the haze and shed some light on what size solar system you need.

The Perfect Solar System

The ideal solar system is one that fits on your roof and gives you enough power during the day. If it’s too small, you buy extra power during the day and more at night. 

If it’s too big, you’re selling power back to the grid for 8-9 cents then buying it back later for 28 cents.

The problem with attempting to size a system to power your home with only daytime usage in mind is there are so many variables. 

For example, in Winter you receive less sunlight than in Summer. But you may work out that you cover this amount with a 3kW system. It’s not too big or too small. 

Let’s take a look at the 3kW system.

  • 3kW Solar System
  • Fronius Primo 3kW inverter 
  • 9 x 325W Jinko Panels
  • $4500  

If that looks expensive, it sort of. Sure it’s perfect if you have a small unit and don’t use much power. But, the cost of setting it up isn’t much different from a 6.6kW system. Hence why we sell more 6.6kW systems. 

Now let’s look at a 6.6kW solar system…

  • 6.6kW system
  • 5kW Fronius inverter
  • 22 300w Jinko Panels
  • $6700

While a 3kW will cost you $2200 less, it may not be your best option. 

Why Is A 3kW Solar System So Expensive?

Technically it isn’t. Compared to the trash you can buy for less than $3000 it may seem expensive. But quality costs money. It’s like buying a pair of Nikes from Nike or a pair of “Nikes” from the market. You can run in both shoes but one is going to perform better and not hurt you.

The same goes for solar systems.

We wanted to compare the same brands so you can get an idea of what the cost is.

Now you’re probably wondering why the 3kW isn’t half the price of a 6.6kW system.

The inverter is the big cost in the system. Whether the inverter is 3kW or 5kW doesn’t matter. The cost is pretty much the same. It’s the same size. The same amount of wire. The same amount of labour. Just a few tweaks to change the kW.

The panels are where you save money.

When you hear about rebates, this applies to panels. These rebates are already calculated into the sale price. Depending on where you live and the year you install affects the rebate you get (STC’s). An average 6.6kW will give you a rebate of around $4000 with a 3kW system giving you $1600.

When installing a system, the hours required doesn’t change much. A 3kW system will take our guys 6 hours and a 6.6kW system will take them 8 hours. 

The reason is they have to do the same work regardless of the wattage. They need to run the cables between the inverter and panels and work on the switchboard.

The major cost comes from the extra panels which have a big rebate on them, the extra few hours to install, extra mounts, and a couple of hundred dollars for the inverter.

Do You Benefit From A 6.6kW System?

The answer is it depends.

If you live in an area where the feed-in tarif is only 8 cents and you don’t need more than a 3kW system, then maybe not. But with electricity prices rising, the feed-in tariff is likely to rise. So, this may work in your favour to have a larger system.

But, in the cities where there is competition within the electrical company space then the benefits could work in your favour. 

Whilst some energy providers will give 8 cents, others can give you 18-20 cents. 

Let’s do some math:

  • If you only use 3kW then you have an extra 3.6kW going back to the grid.
  • If on most days you send 3.6kW back to the grid, that equals 7000kWh.
  • 7000kWh @ 8 cent (feed-in tariff) = $560/yr
  • 7000kWh @ 14 cent = $980/yr
  • 7000kWh @ 18 cent = $1260/yr

As you can see, the extra $2200 you spend can easily be offset by the money you’ll save each year. 

In the end, it’s all about your usage and whether the feed-in tariff is worth it for you.

When we install a 3kW system, we often recommend you get a 5kW inverter instead of a 3. The reason for this is if you choose to add more panels later, the only cost will be the extra mounts, labour, etc. The inverter cost is almost the same anyway. 

This means we don’t need to buy a brand new inverter and install it. 

Unless you live in a small unit and use minimal electricity and have a small feed-in tariff, a 6.6kw system is often the better system.

To view our systems, click here

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