We have PVs generating electricity. If we invest in a Watson, we can use an optiplug which will turn on gadgets that are unaffected when turned off because insufficient electricity is being generated eg a dehydrator or washing machine.

Do you know if we could use it to run an additional freezer? The freezer would be turning off whenever there was no electricity generated. But if we didn't open the freezer when it was off, eg in the evenings and at night, would the food inside be OK until the freezer turned on in the next generating cycle. It's likely to be the excess fruit and veg from the garden.

Many thanks for your experience / knowledge.

Frig it via the thermostat? Force it to run when the PV is doing it's thing rather than preventing it from running when the PV isn't.

The problem you'll run into is complexity. A piece of shit G to A rated old freezer that's better off scrapped than running is easy to frig. (mechanical thermostat) Modern A+++ equipment that's worth having is hard to frig. (inverter driven digital thermostat and so forth)

You might get lucky and find an A+ or A++ that still has on/off contacts to decide when to run. Wattson runs a contactor to bypass the OE thermostat and force the freezer to run; fit a second thermostat to stop it by -30C* or so?

*ask a refrigeration guy for a sensible number.

Exporting the electricity and making jam from the fruit also works.

Posted By: tonysome kind of bypass switch that would switch on at -16 would solve it and then use the one you are planning to use to run it at -20 that would save a reasonable amount of money.

Seems a good plan to me. Less temperature margin for power cuts, though.

Not overly convinced by A++++++ fridges. Seems to me that the extra PV to run a more moderate one (A+ or so) can be cheaper than the extra cost of the fridge, bearing in mind that the fridge usefully acts as a heating element throughout the heating season. In the summer your extra PV runs it anyway, though you lose the COâ‚‚ benefit of exporting the electricity.

Sorry for a tangential question, but why don't fridges have drawers the way freezers do (or just doors for each shelf)? Seems like an easy and cheap way to reduce the amount of cold air falling out when you open the door, but I've never seen it.

Posted By: SteamyTea: “There is very little air in a fridge, which has a low SHC when compared to a few cans of beer.”

Indeed, the effect of air getting into the fridge is not large but to the very limited extent it does matter the effect of condensation of water vapour (and freezing it in a freezer) is nearly as important as simple cooling.

Number sources can be found in this blog post: http://edavies.me.uk/2013/12/dehumifiers/ , particularly the table in the other place linked from there.

Room air at 20 °C, 60% RH would contain 9 g/kg of water vapour. Cooled to 5 °C, 100% RH it would contain 5 g/kg so 4 g/kg would need to be condensed out. At around room temperature water has a latent heat of vaporization of about 2.4 MJ/kg so 2.4 kJ/g or with 4 g/kg of water vapour 9.6 kJ/kg of air.

For comparison, the SHC of air is around 1 kJ/kg so cooling it from 20 °C to 5 °C needs 15 kJ/kg so a total of 24.6 kJ/kg. A litre of air has a mass of just under 1.3 g so it'd be about 30 J/l.

A heat pump with a cooling COP of 2 (equivalent to a heating COP of 3) consuming 150 watts would extract 300 W (or 300 J/s) so get rid of that in a tenth of a second.

Thank you all for your comments. Lots to absorb before we make a decision.

Just the sides. Luckily for me the gap I had allowed for nearly 4 inches of insulation.

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