Deleted

Qyburn

Ectophile said:

A lot of the confustion in this thread is people mangling their electrical units.  What does "you can save 250 watts a day" even mean?  Is it that you can save 250 watts for a day, or 250 watt-hours per day, or 250 watt-days per day?  Who knows?

I was thinking the same,  too much "watts per hour" or "watts per day". Both are meaningless, and error prone when people try to work out what was actually meant. As seen in the first few posts trying to guess what a "24 hour running cost of 500W" was supposed to mean.

mmmmikey

Deleted_User said:

Freezer uses 500kwh a day so it'll need to run off the mains for this winter at least.

I think if your freezer is using 500kWh/day something is seriously amiss 

victor2

Deleted_User said:

...
If your panels generate 1kw per hour for 5 hours they have generated a total of 5kw of power.
...

No they haven't. They have generated 5kWh of energy.

At no point was 5kW of power generated, the most was 1kW. You could never have run, say, a 2kW kettle directly off the panels, as they didn't generate enough power. Storing the energy in a battery and subsequently releasing it from that at a faster rate than it was generated could provide enough power to run the kettle.

As the article you linked to says, "kWh is a measure of energy, whilst kW is a measure of power"

In the example of a fridge freezer, I had an old one which recorded a peak power consumption of 800W, and used 3kWh of energy per day, so an average of 124W power all day long, but at no point in the day was it drawing 124W. Fridge/freezers with a frost-free feature often have a heating element in them to support this - that is where my 800W came from (in addition to the regular compressor cycles). In that case the heating element came on about once every 24 hours for a fairly short period of time, certainly less than one hour. I have no idea how powering off such a fridge/freezer for a number of hours every day would affect that cycle or it's effect on the freezer.

Qyburn

Deleted_User said:

Qyburn said:

Ectophile said:

A lot of the confustion in this thread is people mangling their electrical units.  What does "you can save 250 watts a day" even mean?  Is it that you can save 250 watts for a day, or 250 watt-hours per day, or 250 watt-days per day?  Who knows?

I was thinking the same,  too much "watts per hour" or "watts per day". Both are meaningless, and error prone when people try to work out what was actually meant. As seen in the first few posts trying to guess what a "24 hour running cost of 500W" was supposed to mean.

Well I've answered the question, explained umpteen times why it's not appropriate to use KWh when making comparisons. I've even quoted from articles that explain it and provide links. If people won't read or can't understand there's not much I can do. Life will go on if people don't understand what I'm saying!! 

Getting back to the question of whether it's safe to turn the fridge off at night. I think I have another solution. My system has DC output capable of delivering 360 watts. It would be possible to get a fridge that can run off that - my big fridge is old anyway and I could manage just fine with a smaller one.

I have two options - I have a fridge in my campervan that runs on DC or Gas. I never use it. It's brand new - albeit installed 8 years ago!! I could whip that out and install it in the house. That would run off of my generator via DC. Alternatively, I can buy an undercounter fridge that is AC powered. There's enough wattage via my DC port, but I'm trying to figure out if there would be drawbacks to getting a DC to AC converter and running the fridge this way.

It's DC 12 A / 30 V output. 

Freezer uses 500kwh a day so it'll need to run off the mains for this winter at least.

Maybe an analogy would help.  Today I drove at 50mph.  Yesterday at 30mph.  Which day did I travel further?  Was either day better or worse than when I drove, to use your terminology, "40mph per day"?
I'll give you a clue, Watts are units of power, not energy.  Mph is a unit of speed, not distance.  

mmmmikey

Qyburn said:

Maybe an analogy would help.  Today I drove at 50mph.  Yesterday at 30mph.  Which day did I travel further?  Was either day better or worse than when I drove, to use your terminology, "40mph per day"?
I'll give you a clue, Watts are units of power, not energy.  Mph is a unit of speed, not distance.  

Surely that's a trick question - you haven't told us how many miles of petrol you used?

QrizB

It doesn't work like that.

Today I drove 270 miles ( that's a true statement). How far did I drive between 11am and 12 noon?

MalMonroe

To return to your question - "what are the implications of switching off fridge and freezer for say 12 hours out of every 24?"

The implications for me are defrosted (ergo - ruined) food in the freezer, coupled with a warm fridge. 

I've tried it. It was totally accidental, I have to say but I did it. 

As an accidental experiment, it was a total, expensive failure. Twelve hours is too long for a freezer to be switched off because food defrosts and then if you turn it on again after 12 hours, the food will refreeze and that's a health hazard.

Therefore the answer is - the implications are disastrous and unhealthy. It'd be better to get rid of a fridge and/or freezer altogether than to use them 50/50.

Apodemus

Deleted_User said:

QrizB said:

It doesn't work like that.

Today I drove 270 miles ( that's a true statement). How far did I drive between 11am and 12 noon?

if you understand what a KWh is then you would realize it DOES work like that!! LOL.

Why can I never find that face/palm emoji when I need it?!  

Qyburn

Deleted_User said:

How about another analogy. Today my solar array generated 1.7Kwh of energy. How much power was generated between 11 am and 12 am? You should be able to answer that - after all, KW = KWh / hours.

A solar power expert might be able to give you a rough estimate, if you provided the orientation and inclination of your panels, your exact location, and detailed weather conditions. But I suspect you think you can work it out by dividing energy (1.7kWh) by time (22.41 hours).  That would only be correct if your solar panels generate the same power at all times both day and night.

In the same way my freezer uses around 0.55kWh per day.  Do you think that means it could be run off a 35W inverter?

On-the-coast

I might have missed it as i scanned down this thread, but there appear to be several vital data points missing:
- what's the maximum instantaneous output of your inverter
- what's the maximum draw of your fridge and your freezer
For bonus points
- what happens when both fridge and freezer happen to be at maximum draw at same time,
- what's the power factor on both of them (which can make an inverter a lot less efficient than first appears...)
- how does the inverter handle short overloads...
- how do the compressors start (do they start) if peak power requirement can't be met
All relates to the discussion of average energy use v. power.  I personally wouldn't worry too much about the food hygience issues until I'd resolved the above.