Thread: Grid can go 75% renewable

Originally Posted by Graeme

My system includes a smart meter in the meter box on the pole which has 16mm2 cable from the 10 KVA transformer. My inverter's voltage limits include an allowance for the voltage difference between the smart meter and the inverter at peak export, with the agreement of the local Essential Energy inspector. The inspector was prepared to allow a slightly higher peak grid voltage but that wasn't necessary as derating is minimal with the current settings.

EE have a policy of not allowing private service upgrades to transformer poles which has been interpreted by the local EE inspector to include wiring upgrades rather than the addition of more services. He won't allow our pole to inverter 20m private overheads to be upgraded from 6mm2 to the necessary 16mm2, instead requiring a separate pole and then underground to the inverter plus upgrading the overhead to the house to bring the house connection up to current allowable voltage drop standards. I had a quote of approx $15K a few years ago to put all power underground from where the inverter is located so now would be well over $20K excluding a new pole and its associated costs. The PV savings don't justify an additional $20K investment. Furthermore our feed-in tariff is set to drop from 21 cents to 12 cents mid October adding $400+ to our annual power bill which increases the existing PV system's pay-back period significantly.

Yes, that is a lot of money.
We are spending about $7k for our new underground connection from pole to house, but that includes a new box on the house and a second connection from pole to the new garages, including a 40A circuit to cope with welding. There are also some internal upgrades in the house.
Our old system is 30 years old and pretty dodgy, so we are getting it up to a modern standard. For example, there is already a second phase from pole to house, but it was for the hot water heater we no longer have, is disconnected and our electrician thinks it is too light and is not keen to use it. Better to start again with 25mm, he thinks.
The whole electricity system is being revolutionised as it moves away from a small number of centralised coal power stations towards a decentralised system with lots of solar, wind and batteries, so the transmission companies have to adapt or lose customers. Consumers have been burned by overcharging by power companies and see household solar as the way to cut their bills.

Originally Posted by DiscoMick

Consumers have been burned by overcharging by power companies and see household solar as the way to cut their bills.

the govt over the years and their lack of control is also to blame.

Originally Posted by DiscoMick

Your point about undersize wiring from street to house is not mentioned much, but is important. We are currently having ours upgraded from 6mm to 26mm to overcome voltage drop when our solar is exporting to the grid. This is on the advice of our solar installer and electricians.

Our inverter often reads the grid voltage at around 251 volts in the middle of the day in our rural residential area, so I think there is still a margin to export some more solar.

Here's the difference between the 6mm original wire to the street and the 25mm new connection, so that should slash the voltage drop.

Originally Posted by DiscoMick

Here's the difference between the 6mm original wire to the street and the 25mm new connection, so that should slash the voltage drop.

Assuming a 50 metre cable run and say full load being fed back into the grid from a 5KW system (around 20 amps), then around 2.5% better (Remembering voltage drop has to stay within 5%) so yes a worthwhile upgrade - for a variety of reasons. That old cable would have limited your usage to around 30 amps give or take so that on it's own is a good result in my book. The 25mm cable would allow over 100 amps if you needed it (again, assuming the 50 metre length - could be lot longer, but just for rough calcs).

Originally Posted by Homestar

Assuming a 50 metre cable run and say full load being fed back into the grid from a 5KW system (around 20 amps), then around 2.5% better (Remembering voltage drop has to stay within 5%) so yes a worthwhile upgrade - for a variety of reasons. That old cable would have limited your usage to around 30 amps give or take so that on it's own is a good result in my book. The 25mm cable would allow over 100 amps if you needed it (again, assuming the 50 metre length - could be lot longer, but just for rough calcs).

Volt drop for solar is less. 2% from the street to the inverter basically.

Originally Posted by Vern

Volt drop for solar is less. 2% from the street to the inverter basically.

Ah - thanks. I've not done any Solar installations. Then he was already toast with the 6mm then.

We are spending about $7k for our new underground connection from pole to house,

Don't forget that the allowed current capacity for a cable buried underground is a lot less than a cable strung in the open air. Just another reason to upgrade it.

Originally Posted by Homestar

Ah - thanks. I've not done any Solar installations. Then he was already toast with the 6mm then.

Yeah its a pain really. I just quoted a job yesterday to get power to a shed 250m away for solar. 630mm2 cable is required, or conductors in parallel.
Could use 95mm2 if we went to 5% volt drop.