While we usually try to make our blog posts understandable to almost everyone, this post gets technical as I use the numbers to show why the new 1000 volt limit for residential solar is improving life for installers and homeowners alike .
Australian solar installers are now celebrating that the latest version of the Australian standard for solar inverters – AS4777 – has enabled home systems to be increased to 1000 volts DC.
My first inverter was and is a Latronics PVE 2500. Made in Queensland, it’s a simple box. With a high current MPPT input, the specifications were very inflexible.
You could have up to four strings in parallel, but maximum only 206 volts meant that four 45 volt solar panels in series (4 panels x 45V = 180V) was the only string configuration; take it or leave it. This complicated matters when salespeople mistakenly ordered six panels and installers had to explain to customers that they would have to spend $1,800 for two more panels.
Australian brutalist icons.
The Europeans also had inflexible inverters
If the sticker on the side of an SMA SunnyBoy 2500 says “180 – 500 VDC input”, your measuring device measures 200 V, but it still doesn’t start, you have to curse. Nominal 45-volt modules can be a bit doughy on a hot summer morning with only six modules in series and two strings in parallel.
SMA Sunny Boy labels. Old transformer units at the top, transformerless at the bottom, with the maximum voltages increasing as the modeling progresses.
We soon learned that a single 12-string was the only option for these devices, even though they were outside the 500 VDC maximum, and SMA came to the same conclusion, even though they had a reputation for being conservative when it came to blowing up inverters be. Because cold solar panels are more efficient, SMA had to deal with sub-zero temperatures in Alpine Germany with overly powerful solar panels, but the Australian heat made the panels less efficient, allowing SMA to supply Australian units with a 600V DC limit.
Now we have amazing breadth
NowadaysInverters have large operating windows. From 40VDC you can use a 2 panel array (!) or 13 panels for 600VDC – unless it’s a Sungrow 8 or 10kW hybrid series. Your 4 MPPT inputs have some strange little problems as they require a relatively balanced voltage, no more than 150VDC distributed between them. I haven’t heard a good explanation for this problem.
The Sungrow specs on the flyer are impressive, but it’s difficult to make the thin text readable on a mobile screen.
The Sungrow flyer contains asterisks** to refer to installation instructions. These indicate that the starting voltage is low, but the power rating requires an average of 6 or 7 panels for everything to work.
Harmonization sings from the same book
When the last AS4777 was written, an incorrect clause was restricted network connected converting inverter systems to 600V, which created a ridiculous situation where 1000V household systems were permitted under AS5033, but only if they were off-grid. With the demarcation between the standards, they are now harmonized as they relate to, but do not overlap, other related solar standards.
However, New Zealand still uses 20-year-old standards. They publish them, but the government fails to mention them in legislation. With more than 300 updates required, you’re more likely to see a Tasmanian tiger there before citing AS/NZ4777.2024.
600 volts DC, suitable for single phase power supply
Electrically speaking, it’s not hard to fully load a 5 or 6 kW inverter with a few strings under 600 volts. The Fronius Primo 8.2 is the only device I can remember well single phase and 1000 volts Entrance.
It’s actually a question of inverter topology. Anything is possible, but inside the box it is easier to convert less than 600VDC to 230VAC, whereas 1000VDC is more efficient if you want a 400VAC output for three phases.
Despite The clamor from Enphase and its supporters about the inherent safety of low voltage direct current 1The vast majority of solar power systems use string inverters.
The real advantage is the ability to significantly oversize the solar system while remaining below the standard inverter limit of 10 kW set by the grids.
For those playing at home, multiplying 15 panels by 38 volts and getting to 570 volts sounds easy, but once you increase the power for low temperatures in your location, 13 or 14 panels becomes the practical limit.
This graphic shows the effects of sunshine and temperature. Cold panels are more efficient.
Manufacturers have programs that simplify the calculations, but when adding additional Australian rules, the use of software is essential to cover all variables
Let’s consider a LONGi Hi-MO 5m 54c 420W:
- Maximum power (Pmax): 420W
- Open Circuit Voltage (Voc): 37.3V
- Short Circuit Current (Isc): 14.12A
- Maximum Power Point Voltage (Vmp): 31.0V
- Maximum Power Point Current (Imp): 13.55A
1000 volts brings more current into the same circuit
In round numbers, using 38V panels will create a series of 14 532 volt open circuit (Voc) circuits connected in series.
Under ideal conditions, the array develops 5.86 kW, which corresponds to a maximum output of 434 volts (Vmp) multiplied by 13.5 amps. (imp)
Now if we are allowed to go up to 1000 VDC then 24 panels will develop 912 VAC.
This means that 24 panels develop 744 volts (Vmp) multiplied by 13.5 amps (Imp), giving you 10 kW from the same circuit.
Using a higher voltage on the same cable also results in lower losses.
Industrial is already 1000 VDC
Higher voltage systems have been permitted in commercial buildings for years as long as the switchgear is secured or the inverters are in cages.
However, “limited access” has now been turned on its head, “immediately available” is now the key term in AS4777, allowing school children to play around with the switches.
3-phase requires 1000 VDC
As solar energy became cheaper and large systems became more feasible, we encountered problems.
Inverters rated for 1000V input voltage could not be “topped up” without exceeding 600VDC.
Parallel strings help, but the current values of the modules increase faster than those of the inverters, so parallel arrays with cheaper devices are not possible. In addition, anything other than the simplest roof can cause spatial design problems.
The result? Filling your roof with solar energy was more expensive because you had to buy more inverters to work under the artificial ceiling.
This design brings a 15 kW Fronius inverter to full capacity in accordance with the new AS4777 rules.
If we use the old rules from 2016:
In the complex example above, the strings would be limited to 13 panels at a temperature corrected 570 Voc. A Sungrow inverter would be stuck at 4 strings of 13 each, for a disappointing total of 52 panels and 16.38 kW
The inimitable Fronius Symo manages 3 strings in parallel for channel 1, then 2 strings in parallel for channel 2, so that the total number could be increased again to 3 x 13 + 2 x 12 = a total of 63 panels…
While using an additional parallel string solves the electrical design problem, it also adds another panel. This is great news, except that the physical layout on the roof would no longer work since there are 17 panels facing west in the example.
It’s like Tetris with a third dimension. Removing or adding a single panel can ruin such a layout and cause a lot of teeth-gnashing for installers, designers and customers.
The future is brighter with 1000 V
These AS4777 updates have finally aligned Australian standards with global ones, allowing residential solar energy to reach its full potential. By increasing the permissible voltage to 1000 V, the new regulations will make solar systems more efficient, cost-effective and flexible.
For installers, this means less frustration and more design options. For homeowners, this means more power, lower costs and a faster payback on solar investments.
The future of solar energy in Australia is now much brighter – and much more powerful.
Footnotes
- I hope Finn loves being teased ↩
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