Can I Install a 10kW Solar System on Single Phase?
The maximum residential solar system size allowed here in Brisbane used to be 5kW of inverter capacity per phase. Since the majority of households are single or three phase, that meant the largest you could install was 5kW solar systems, and 15kW solar systems respectively. It does appear single phase households get the short straw, as currently due to high feed-in tariffs and the reducing cost of solar, larger solar systems actually save you more money in both the short and long term. However, the rules have changed. Now, according to Energex, we can install a 10kW solar system on a single phase premises:
5.4 Inverter Phase Limits: Single phase inverters, are acceptable up to and including 10kVA of installed capacity on a customer’s installation, however total export shall be limited to 5kVA or less via partial or minimal export operation, as per Section 5.9.1. Proponents with a single phase service wishing to export greater than 5kVA will need to make application with their retailer to upgrade their service to two or three phases.
So, post over. You can install a 10kW solar system on single phase, and this should now be the norm for single phase, right?
Well, not exactly. The line, “Export Shall be limited to 5kVA or less,” puts a spanner in the works.
What is “Export Limiting?”
The concept is simple. Energex will approve your solar connection, as long as you ensure no more than a set amount of power is sent back to the grid at any one time. Before these connection standard changes, if you wanted an inverter larger than 5kW, you needed to upgrade to 3 phase. This can be quite an expensive upgrade and could be comprised of trenching, traffic control, Energex fees, electrician fees, etc. In some circumstances, it just isn’t financially viable. You were better off installing a 5kW solar system, just having it cover what it could. So now, for high usage single phase households, there is an alternative option – keeping your connection as single phase, but installing up to a 10kW solar system with export limitation. The far more financially viable option. If you read into Mark’s previous blog that debunked Goldilocks solar and showed the benefits of going as big as possible, you may also be thinking 10kW inverter capacity should be the norm for single phase. However, because we’re required to export limit the site, we have to ensure the household benefits from it.
How Does it Look?
I always like a visual explanation, and I will find any excuse to post an image of a graph. Below is the solar production of a household limited to 5kW exportation, with a Fronius 8.2kW inverter and 10.2kW worth of panels. The green filled-in portion is what is being sent back to the grid, while the grey filled-in section is what’s being consumed by the household. In this export limited scenario, the green portion can never exceed 5kW.
As you can see I’ve also filled in the potential missed production in a darker green colour. This is an estimate as to what the system could have produced, and therefore sent back to the grid, but was unable to do so due to the 5kW exportation limit.
However, if the base load was increased, the system would be able to reach its full potential, and nothing would be “wasted.” Below is an example of what the production graph might look like with a higher base load.
You can see that by increasing the base load of the house, there is no “wasted” production as export limitation doesn’t need to occur. This is good practice for installing a larger than 5kW solar system on single phase.
Have I missed the boat if I already have a 5kW Solar System Installed?
If you already have an existing solar system in place, and more roof space available, we can simply install an additional Fronius Inverter alongside it. As long as the new total inverter capacity does not exceed 10kW, it also doesn’t matter what type of inverter you currently have. However, we would need to install a Fronius Smart Meter to control the Export Limitation, and the consumption data would unfortunately not report properly. But, if your existing inverter is a Fronius Primo, we can simply link both data loggers, enabling you to also have full consumption data of both inverters on the one monitoring portal. You can also utilise your existing smart meter if you had one on your original install. So, if you’re finding you have large daytime usage and more roof space to play with, it may be worth giving us a call to discuss your options to see if and how you can achieve a 10kW solar system.
10kW Solar System Size Restrictions with Batteries
If you wanted to install larger than 5kW of inverter capacity on single phase to help cover your high base load, you could not install a Tesla Powerwall, or any other AC battery that pushes your total inverter capacity above 10kW. This is because AC batteries use an inverter to convert the AC power they receive from solar inverters to DC power for storage. Although this has no effect on the grid, Energex has deemed this storage inverter as inverter capacity. Since the Powerwalls’ AC to DC inverter has a 5kW output, anything larger than a 5kW Solar inverter pushes us above the 10kW Energex limitation. You could install DC batteries just fine, and there may be other alternative options out there in the future. Furthermore, if you require a system larger than 5kW to meet your household requirements, you’re not going to find enough excess generation to charge an AC battery anyway, so the point is somewhat moot.
Reviving the Fronius Relay
If you want to take advantage of a bigger system on single phase, but don’t have the base load to justify it, and have an off-peak electric hot water system, then it’s a good case to revive my previously declared dead, Fronius Relay. The general concept of the post was; exporting power is a more valuable solution than heating a hot water unit, due to increased feed-in tariffs. But since the anticipated base load is not high enough, you may run into this “wasted” generation. This means the production diverted to the hot water unit via the use of a Fronius relay would have been unable to be exported anyway, so the calculation changes. This is a prime revival case for the Fronius hot water relay, but as the discussion is a bit more in depth it’s best to read the blog first to understand it better. However, hot water timers are still well and truly dead.
Conclusion
Through the use of export limiting, single phase households can now install a 10kW solar system. However, it’s important to understand the effects of export limitation, and whether it’s a good solution for your particular circumstances. Having additional intelligently timed loads, or excessive daytime usage will minimise, or even eliminate the “wasted” power export limitation incurs. If you have an electric hot water system, it’s also a good revival case for the Fronius Hot Water Relay. If done correctly, larger single phase systems through the use of Export Limitation can be a great, cost-effective alternative compared to upgrading to three phase.
Notes
- You may have noticed my examples were using 8.2kW primos, even though the approved amount is 10kW. This is mostly due to price, flexibility, and the diminishing returns of 10kW. The only current way to achieve 10kW solar systems on single phase is to install 2 x Single phase inverters. This is far more expensive than a single 8.2kW inverter, and you’ve now got an extra 5kW of potential export limited power that you’ll need to utilise to see the benefits. If you truly do expect a consistent base load of around 5kW, then it may be worth upgrading to 3 phase. If that’s not an option, then investigating 2 x 5kW Primo’s may be the go. However, for the majority of our installations, the 8.2kW Primo provides sufficient power, is flexible in its design, and cost-efficient.
Ben Neville
Sales Manager
MC Electrical
