[chbot] 60 min of free power per day

[Helmut Walle]

Safety warning...

A word of caution regarding this line of thought - and I am sure you are 
more than aware of this, Mark, but it may warrant stating explicitly: 
time is obviously limited. You have one hour to "download" all the 
energy you can get, which appears tempting. But there clearly is an 
incentive to draw a high current in this tariff.
Now while the service fuse may be rated 60 A, surely many of the 
downstream parts of the installation are not. This lies in the nature of 
residential wiring work, which is there to provide electricity to many 
places in the house, but the power available per socket is quite 
limited. The current rating on any individual circuit will typically be 
10-20 A. All circuits should have appropriate over-current protection. 
But there are some potential issues with this: any electrical 
installation is subject to ageing. One thing that happens is that 
connection points of any kind show a higher resistance over time, which 
can be due to corrosion or loosening. The increased resistance can lead 
to excessive heating under high load (high current). One of the possible 
outcomes is a fire. But even moderate heating that doesn't cause an 
outright fire can damage and degrade insulation, which can in the long 
run again lead to a fire.

Older houses in particular may be fraught with various issues affecting 
the safety of their electrical wiring, which can be a serious safety 
risk under very "normal" operating conditions that do not even go 
anywhere near maxing out the current ratings.

So this is something to keep in mind: when connecting higher loads or 
drawing higher currents than before from the same installation, be 
particularly careful and alert regarding these safety concerns.

Kind regards,

Helmut.

On 25/06/2017 11:50 a.m., Mark Atherton wrote:
> Hello All,
>
> Only just found about this energy company, and their offer of 60 min of
> free off-peak electricity per day -
> https://www.electrickiwi.co.nz/hour-of-power
>
> Haven't run-the-numbers yet to see if there are real savings to be had,
> but figure this might make an interesting chocolate-fish-challenge for
> the group.
>
> So the question is: how maximize the benefit of this kind of offer.
>
> So for a 60A service to a house, this is almost 14kW, and at $0.35 per
> (daytime) unit, this could amount to just under $5 per day, if the
> entire 60A could be consumed. This amounts to around $150 per month
> possible savings.
>
> Obvious thing to turn on is the heater on the hot tank (3.5kW), which
> would normally be heated at the night rate ($0.15 per unit), so only
> $0.52 savings here.
>
> So, the problem looks like it converges on a need for daytime power, if
> the higher saving is to be leveraged.
>
> Anyway, just a daft thought experiment.
>
> Comments welcome.
>
> -Mark
>
>
>
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