So you’ve got solar panels on your roof and you want more so you can get your bills even lower?
(Note: If you are on a premium Feed In Tariff then you need to understand how solar upgrades can affect your eligibility.
If you are on the NSW solar bonus scheme, then your FiT is ending on 31 December 2016 – and you should time your upgrade to happen as close to this date as possible)
You are probably weighing up 3 alternative approaches to your solar upgrade:
1) Add more panels to your existing system – using your original inverter.
2) Get a new, bigger inverter and add more panels too.
3) Get a whole new separate solar system installed next to the original.
Let’s go through each option in detail so you can weigh up the best approach for you.
Option #1 Adding more panels to existing system using your original inverter.
The first thing to be aware of (and not a lot of people know this) is that you are allowed to have a panel array with a peak power up to 133% of your inverter’s rated peak power.
If you have a 1.5kW inverter, you can have up to 2kW of panels attached.
If you have a 3kW inverter you can have up to 4kW of panels attached.
If you have a 5kW inverter you can have up to 6.65kW of panels attached.
And if you don’t go over the 133%, you can claim the solar rebate (STCs) on those extra panels which will cover a big chunk of their of their cost (excluding installation costs and installer margin).
So if your inverter is big enough, adding panels is a cost-effective option to get more energy. You may be wondering how on earth this can be the case if the inverter limits the power output. Let’s use a 3kW inverter as an example.
3kW of panels will generally only produce 80% (2.4kW) of their rated peak power due to losses.
4kW of panels, after losses will produce a peak power of 3.2kW. A 3kW inverter will safely clip this down to 3kW. So you are only losing 0.2kW of power. And that is only for a couple of hours each side of midday on a summer’s day. In the mornings, evenings and winter the peak power will be way less than the rated 3kW of thew inverter.
So oversizing your inverter by 133% is a good way to squeeze more energy from it.
Two big caveats here are that:
1)Unless your original solar installer does the upgrade you will void your existing system warranty.
2)It depends on your installer finding the same or very similar panels to your existing ones.
If you want more panels than your inverter can handle (using the 133% rule), or you can’t find compatible panels, then your next option is:
Option #2 Replace your small inverter with a bigger inverter and add panels.
It seems like a waste of money and resources to remove a perfectly good inverter. However the sad truth is that over the last 7 years a lot of the installed inverters that have been cheap and nasty and are probably on their last legs. If your inverter is a Sunny Roo, KLNE, JFY, JSI, Aerosharp, Sharp, or other inverter with a penchant for going bang after a few years, then this is a great opportunity to replace the thing with a genuine premium inverter, such as SMA.
Another reason to bite the bullet and swap your old inverter for a new bigger one is that one inverter is much easier to add batteries and backup to than two separate ones. So if a battery ready system with backup is a priority, having a single, large inverter is the way to go. (This post explains what a battery ready system with backup is and how that differs from a battery ready system without backup)
If you do decide that up-sizing your inverter is the way to go then watch out for these gotchas:
a) With panel technology changing so quickly, you may struggle to find extra panels that match your existing array. In this case get an inverter with 2 or more inputs so you can install new, different panels without affecting the old array.
b) If possible get the original company to do the work, then they keep the responsibility for the system warranty.
c) I recommend getting an inverter with SUNSPEC/MODBUS. This is a communications protocol that will make it easier to add batteries in the future. All the SMA models on sale now in Australia have this baked in. I would say that SMA are the safest bet here.
Note: ABB inverters can also talk MODBUS with a $500 interface box. And although the Fronius data sheets seem to claim all their inverters talk MODBUS, the word on the street is that in practice it is only usable in their expensive ‘hybrid’ models. Perhaps some one from Fronius would like to comment?
d) You can’t claim any rebate on the inverter, but you can claim the solar rebate on the panels. So put as many panels as you can on that inverter (133% of inverter rated power) because the rebate (STCs) covers a large chunk of their cost.
If you don’t want to replace your existing inverter, then your third option is:
Option #3 Get a whole new separate solar system installed next to the original.
This option can make a lot of sense – if batteries with backup are not on your radar. You get a new system, with a separate warranty. And because installers are so efficient at installing whole systems, and don’t have to fiddle around integrating into existing solar wiring, it can often work out cheaper than upgrading your existing system. And yes – you can claim the solar rebate (STCs) again on your second system – it will already be included in any quoted prices.
So to summarise:
Be aware that you can legally oversize most inverters by 133%. This may give you all the energy you need with your existing inverter.
If 133% of your inverter rating is not enough, then you can replace your inverter to allow you to add more panels. Just be aware that this can be surprisingly expensive as it is not as straightforward as a fresh installation. If you are getting a new inverter ask for one with MODBUS/SUNSPEC communications as it will be easier to add batteries to in the future. And if the original company does the work then your warranty should stay intact. You do waste your old inverter though.
It is often cheaper to add a whole new solar system using either a conventional string inverter or micro inverters . In grid connect mode these 2 systems side by side will work great, but it can make adding batteries+backup more complicated down the track.
And I’d be remiss if I didn’t mention that you can get quotes for a solar system upgrade using my free service here.