[chbot] 60 min of free power per day

Sun Jun 25 10:34:34 BST 2017

Mark,

Same problem as solar power in Chch. You get it when you don't need it and don't get it when you do. If you could reliably and economically store the energy then all may be well, but batteries fail the second test today. Under floor heating and cooling with high thermal mass seems to be the way to go for solar, and a free hour of power just adds to the fun. Not much use unless you build from scratch to cope with it.
Water heating is typically limited to 3kW or so for a short period, and what to do with the rest??
I did contemplate using a swimming pool as a heat sink/source for heat pumps but that also fails the economics test. Free just isn't what it used to be . . .

Colin

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________________________________
From: chchrobotics-bounces at lists.linuxnut.co.nz <chchrobotics-bounces at lists.linuxnut.co.nz> on behalf of Henri Shustak <henri.shustak at gmail.com>
Sent: Sunday, June 25, 2017 9:00:07 PM
To: Christchurch Robotics
Subject: Re: [chbot] 60 min of free power per day

I love this comment!

> On 25/06/2017, at 8:28 PM, Mark Atherton <markaren1 at xtra.co.nz> wrote:
>
> Thank you Helmut,
>
> No immediate plans to charge the platoon of Nissan Leafs from the one dangling light socket in the house, for 60mins !
>
> Given the obviously available methods of energy storage within a house (hot water cylinder, electric storage heater), and the availability of low cost nighttime electricity, it became quite quickly obvious to me that the whole marketing ploy of electric-kiwi was rather clever. At first brush, it seems a brilliant deal; upon investigation it seems almost useless. Isn't that almost the definition of brilliant marketing ?
>
> Regards, Mark
>
> On 25/06/2017 8:01 PM, Helmut Walle wrote:
>> 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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>
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