Running a freezer intermittantly musings...

[Adam Funk]

Yes, this is why I do the laundry overnight on a timer (for example).

[Adam Funk]

Whenever I freeze excess milk, I open it & pour a little out first to allow for expansion.

[Adam Funk]

I think you've re-invented the freezer pack. ;-)

[Theo]

It's not a fixed peak on Agile AIUI, it's that electricity pricing is always most expensive 4-7pm (when people cook their tea). Agile reflects that demand. Because it's market priced, the website just indicates some common scenarios, but you are taking the market risk. Adapting to changes in the market is up to you (hence the OP's enquiry).

gives the pricing for today and historical pricing.

Theo

[Max Demian]

Welcome to the 21st century, when you eat when the electricity company says you can.

[Jeff Layman]

I thought you were being sarcastic. But with the comments not too long ago about getting rid of gas (as it generates CO2), and everyone having to use electricity - from renewables of course - what you said is not outside the realms of possibility, especially with remote Smart Meter control. :-(

[Spike]

It's more a case of explaining the benefits of using the latent heat of the unfreezing process, and having a way of controlling where in the temperature range that takes place, rather than rely on the much lower energy transfer of water ice as suggested by a PP, and the unknown transition point of some freezer blocks...this is DIY, of course...;-)

A back of the envelope calculation suggests that 4 x 500ml bottles of NaCl solution as described will demand enough heat during the melting process roughly equivalent to running the freezer for about 30 minutes, so should cope well with the OP's 3-hour stipulation. Put the bottles against the sides of the freezer.

Some points to note: - Don't use ethylene glycol for this application - Water in ice form has a specific heat capacity of 2.1 kJ/kgK and not as stated. - Allow some ullage for the expansion on freezing

[The Natural Philosopher]

In south Africa, where they are pissing around with renewables despite sitting on more coal than Arthur Scargill, they have scheduled load shedding, and yes, literally, you have to plan your day around when you will have electricity.

[Paul]

Electricity generation works from the "basket" principle. You use a mix of technologies, solving the temporal and load characteristics.

No one source gets to provide all the power. Even before windmills and solar panels existed, they were wheeling and dealing.

Some technologies, like the "Musk" battery bank in Australia, they exist not because of overall load engineering (providing a battery with 24 hours of power in it). A relatively modest battery can provide swing power that prevents "gaming" of spot power pricing from your neighbors. And that's exactly what the Australians are using theirs for. So if you need 1GW from 8AM to 9AM, and your neighbor asks 100x the going rate for that spot power, you tell him to piss off and you draw down that power from your "Musk" battery.

We were gouged here, years ago, on spot power, in exactly the same way. Somewhere around 100X the going rate, at 8AM. The impact was high enough, to affect the rate to ratepayers. And all so some weasel can afford nice Italian suits. Either a Musk battery, or a natural gas powered generator, can do that job, of forcing the weasel to wear off-the-rack suits.

Time of day pricing is here to stay, because it does such a nice job of smoothing the peak demand at 2PM. (Industrial demand can be just as impactful, as a tea time. We have an aluminium smelter running off that grid.) Before time of day pricing, there'd be announcements on the radio to "turn off your AC for a while, as we're short of power". They don't have to do that now. Whacking the ratepayers with a hammer, is much more effective than a radio announcement.

Paul

[ARW]

Inverter from the car battery.....

[Spike]

The real bonus of the ice-water bottles comes when the internal temperature of the freezer reaches 0 degC, at which point the comparatively massive Latent Heat of Melting cuts in at 334kJ/kg, essentially holding the freezer contents at that temperature until all the ice has melted. Water in ice form has a specific heat capacity of only 2.1 kJ/kgK

Use this huge the Latent Heat of Melting by employing a liquid that is frozen at the normal freezer internal temperature, say -18degC, but which melts at perhaps -15 degC, using that Latent Heat of Melting to keep the freezer contents at that temperature.

A NaCl salt solution of 220g/litre freezes at -15degC, and a mixture of propylene glycol and water in a ratio of 30/70 glycol/water freezes at

-16.6 degC. Both of these would use that lovely ice-to-water transition to keep the freezer at that temperature until it has all liquefied.

Two litres of this salt or glycol solution would take 668kJ to fully melt. There are 3600 kJ in a kWh, If one's freezer uses 1kWh/day, 668kJ would be equivalent to running it for 4.4 hours.

[Jimk]

If it's already "close to 0" in there, how much extra time at "slightly less or the same as close to 0" does that buy your frozens?