Quote:
Originally Posted by roKWiz
Why is there still such things as domestic overhead powerlines.
Didn't these go out when someone knew how to operate a ditchwitch, our little town doesn't have many.
|
It is really expensive to retro fit.
On a green field site (e.g. a new housing estate), the cost differential isn't so bad. Last time I saw actual costs (about +10 years ago), it was around $4k per lot for underground in a new housing estate and about $1.5 per lot for overhead in a new housing estate. Some local councils insist on undergrounding in new estates. Others, chasing population growth, don't.
Undergrounding an old overhead network can get very expensive. Rule of thumb is about six times the cost to completely redo overhead for the low voltage and 11/22kV distribution network.
But the costs don't stop there. A spot on the ground has to be found for the local distribution transformer. If there isn't enough space on the footpath, then it requires buying or compulsory acquiring about 15m2 off someone's front garden. This makes people very shirty. Next, all the houses with an overhead connection have to be converted to an underground connection. This means digging up lawns, cutting (or tunnel boring) driveways, etc. A certain (albeit small) percentage will have their water mains / sewerage / NBN / gas accidently cut in the process. Figure $5K for the average job.
When it gets to higher voltages (like 66kV and above), long underground transmission lines have other unwanted technical characterises. The short version is they are highly capacitive and cause unwanted voltage swings and transients on the network. (Even underground transmission cables around town can cause issues.) Cost of underground transmission can be up to 16 times that of overhead transmission. It is usually only cost effective to underground transmission in heavy urban areas where it would be impossible to run a new overhead transmission line.
Some other unexpected engineering issues can pop up as well. For example, underground cables don't like trees. Underground cables require some moisture in the soil, so that the soil wicks away heat loss in the cables. Obviously, trees require soil moisture to live, and during droughts, they will aggressively go chasing soil moisture. This dries out the soil near the underground cable, and dry sandy soil is more like a thermal blanket. The heat becomes trapped around the cable, which drives more moisture away. Cables run hotter and this shortens the cable asset life (under good conditions should be between 80-100 years).
There is also technology change on the horizon to consider as well. It costs considerable money per household to go from overhead to underground. Effectively, the asset owner gets a massive loan and pays it back over the next 40 years.
The cost of undergrounding is borne by everyone, regardless whether they can afford the cost or not, and regardless whether they want the extra reliability or not.
So, there is this ongoing discussion inside the electricity industry. Instead of forcing customers, should we leave it to the customer to make their own decision on reliability? Or even should we go as far as disconnecting the grid at the fringes of the network and leave it to the customer to install their own power supply.
Consider the cost of, say, a 5kW solar PV system, a 13kWh Tesla Powerwall, and a Tesla gateway is around $25k installed. The Tesla Powerwall and Gateway effectively gives the customer 13kWh UPS level resilience. And the 5kW solar PV gives them a chance to recharge the next day.
Or an alternative solution, about $7K installed, one can get a 6kW standby generator with auto-start and auto-changeover.
One final point, there are a lot of Australian based technical papers on the web that discuss the pros and cons of undergrounding, and the cost to the community. Worth having a read through them.