Why connecting your solar system to the grid is harder in NSW

What are the rules for connecting to the grid in NSW?

Australians love their rooftop solar and believe it or not, despite our relatively small population we have collectively installed more household solar systems than almost any other country in the world.

For consumers, it’s a no brainer but the electricity companies seem to be making things more difficult as time goes by. Is this justified and are their technical issues we need to understand as solar owners, or are they just profiteering?

The grid is a complex beast and the electricity industry is even more complicated, so the answer is ‘a bit of both’. In fairness to the utilities, and because I’ve had a heap of emails from frustrated NSW folks, I thought I would highlight the New South Wales Service Rules as one example of how technical issues need to be considered.

The basics of grid energy flow, voltage drops and voltage rises.

The poles and wires around your neighbourhood were designed to transport energy from huge generators (typically hundreds of kilometres away) to your home. The further the energy travels the more losses . To compensate, the voltage starts high and by the time it gets to your house it will be lower, theoretically at 230V AC.

However, there’s a lot of stuff going on that can change the losses (and as a result, the voltage). Big factories switching on or off, high or low temperatures or the worst case, a heat wave where millions of Australians simultaneously flick on their air conditioners at 4pm when they get home on a searing hot day.

Generally speaking massive loads cause the voltage to “droop”. Network operators can tweak things to some degree and have to keep the voltage within certain limits.  But as a rule we live with and barely notice the ups and downs of our supply voltage. It’s the network operators job to control and manage these issues.

When we connect to the network, there is a cable from the power pole on the street that runs to your house, which is called your ‘point of supply’ and obviously there can also be losses between the pole and the point of supply too, depending on cable size and demand.

From the point of supply, there is yet more cable, the ‘consumer mains’ to your switchboard and of course, more potential losses. From the main switchboard into your household power points and lights the are more potential losses, although as a general rule these are lower because the loads are spread across different circuits.

Chatting with some New South Wales installers, they highlighted that historically the cable between the power pole and the point of supply was pretty thin, especially in rural areas or in older houses. Over time the rules around losses have got tougher so cable sizes have got thicker.  The thicker the cable the lower the resistance of the cable and the lower the voltage drop.  If you find that counter intuitive then think of the electric current like water flowing through a  pipe. The thicker the pipe the easier the water flows.

Enter, the solar dragon.

Now as you might have already realised, adding a solar system to the network actually has the reverse effect to a load. Instead of the voltage dropping under load, networks with lots of solar systems can experience voltage rise.

“That’s surely a good thing !?” I hear you say. In essence that’s true because more solar equals less demand, which equals less losses. However, to a network operator solar’s impact can be a variable; much more on sunny days, much less on cloudy days and on sunny days with passing clouds, the voltage can rise and fall dramatically in areas with lots of solar. If the network voltage gets too high or too low, solar inverters can switch on and off regularly which is not what you want.

So in fairness, it adds a whole new complexity and its one they have virtually no control over.

Much of the focus of the rules in NSW is around older and rural properties described above. In these properties the network operator typically increases the network voltage by adjusting transformer settings so that (for example) the voltage might start at 253V. Under load and with losses from the old skinny cables, by the time it gets to the house it will be down to perhaps 240V and by the time it gets to the power points, it’s down to 235V.

Now, if there is minimal load (like when you are out during the day) the voltage at your power point won’t be subject to as many losses and could actually be much closer to 253V. If we then add some solar, it will logically push the voltage even higher and could exceed 260V or more. This is bad for your appliances, bad for the network and bad for your inverter; in many cases if voltages are in this range the inverter will simply switch off. That’s bad too!

As a result of these issues New South Wales revised its NSW Service Rules to include specific rules about acceptable voltage rise for solar installations. If you connect a solar system in NSW your installer MUST do a voltage rise calculation in accordance with these rules and prove that they have worked out what will happen to voltage under various scenarios.

The diagram below shows what the voltage rise requirements are:

In NSW the voltage drops in these cables must be less than 1%

Now we do know that some parts of the Australian network can cope with better than others. Alice Springs and Southern Queensland have had case studies done on this very issue and a great summary report by the APVI is here for the data geeks. Generalising a little, their networks are more modern and or beefier; so the variations can be absorbed more easily without as much voltage rise. Another recent study done as part of a CSIRO pilot study into Smart Grids highlighted the variables around Port Stephens, which you can see in this map. In this one small area you can see some parts of the network are suffering low voltage from large loads and yet only a few kilometres away the voltage is quite high, most likely due to high concentration of solar systems.

The strength of the grid around Port Stephens, NSW. Blue is weak, red is strong.

What does it mean if you want to buy solar?

The New South Wales examples have several implications for potential solar owners.

Firstly, in NSW your installer must do the calculations to allow you to be connected, so make sure you confirm that they will before agreeing to buy off them.

If you have a voltage rise issue there are several potential solutions. The network company may be able to adjust the transformer voltage down depending on a variety of issues. If they can’t, then you may be required to increase part or all of your cabling so that losses are reduced; a cost but not such a bad thing in terms of efficiency, as many of your appliances will run more efficiently with a more stable voltage closer to the ideal 240V.

A good installer will be right across these options.

If none of the solutions above are practical then another solution is to limit the size of your solar system to one that does not increase the voltage by more than 1%. Alternatively you can keep your big-ass solar system, but use a special inverter that limits the amount of solar energy exported to the grid.

If you go for the ‘limited export’ option, then to avoid wasting precious solar energy, it can also make sense to install a device that dumps as much excess power as possible into your hot water system (think of it as thermal storage). The best option I’ve seen in Australia is the Immersun from ENA Solar which is approx $500 + installation.

A properly sized, well designed  solar system with a hot water controller and an export limiter is a very elegant solution that will allow you to get a solar system big enough to keep your bills down, even if your local grid is a bit puny.

Technical bit for geeks:

If you are curious about why reducing system size (or export limiting) is a solution to the voltage drop rules, then have a look at this equation:

Voltage drop = Length x Current x 0.017
                                                  Area

Volts= Voltage drop.
Length= Total Length of cable in metres
Current= Current (amps) through cable.
Area= Cross sectional area of cable copper

If changing the cable length or area is not possible, then the only thing left to change is the maximum current going through the cable. The smaller your solar system (or export limiter), the smaller the max current through the wires. The smaller the current, the lower the voltage drop.

Thanks to Nigel Morris From Solar Business Services for help with this post.