Insulated Solar Electric Cooking

Hey y'all,

Thinking of a simple way of cooking direct with PV in the summer - ie, DC, no batteries or inverters. This concept seems simple and scalable, has anyone tried anything similar?



It would be great to incoporate a hotplate into something like this, with insulated covers like an AGA or Rayburn...

Ah, something a bit like this perhaps -



- http://heatkit.com/html/bakeov11.htm

Here's a smaller example of the same idea...

The electric cooking I do with solar is NOT direct DC but standard AC skillet and/or slow cooker(s). I do find that on cloudy days I can cook this way whereas using the solar oven on cloudy days is pretty much an exercise in futility. Interesting concept though of going direct DC. The cloudy day thing would apply for DC cooking as well I would think although it requires sufficient (excess?) solar panel wattage. In other words if I had only a single 300 watt panel it would not likely be much use on a cloudy day, but having 9 of the same wattage panels would likely work fine. On a sunny day with only one 300 watt panel one could likely be fine with a cooker that uses 300 or fewer watts. On darker cloudy days with my setup, I may only be able to use the slow cooker.

Robert Yaklin wrote:The electric cooking I do with solar is NOT direct DC but standard AC skillet and/or slow cooker(s). I do find that on cloudy days I can cook this way whereas using the solar oven on cloudy days is pretty much an exercise in futility. Interesting concept though of going direct DC. The cloudy day thing would apply for DC cooking as well I would think although it requires sufficient (excess?) solar panel wattage. In other words if I had only a single 300 watt panel it would not likely be much use on a cloudy day, but having 9 of the same wattage panels would likely work fine. On a sunny day with only one 300 watt panel one could likely be fine with a cooker that uses 300 or fewer watts. On darker cloudy days with my setup, I may only be able to use the slow cooker.

Great to hear your experience Robert!

I was envisioning something pretty scaled up - using around 3kW of PV. There are MPPT controllers designed for direct connection to heating elements which would further help with efficiency.

It was this little cooker that got me thinking - according the manufacturer it uses around 85kWh/week which I can match in Summer with PV.

It does cause me to wonder how much a vacuum thermos could be scaled up?  If the glass was say 1/4" thick.  Eliminate most of conduction and convection and if the outer layer is mirrored on the inside most of radiation too.  Put that in a heavily insulated conventional shell and 100 watts would probably be enough.  Put a large slab of some heat storage material in the over over the element.(slab of granite counter top maybe?)  If you needed excess heat simply taking that or another slab to trade out to an optical concentrator would let you take the heat inside.  

Or if the goal was a simmer pot a bit of piping and a evacuated tube solar collector would let you simmer clear to boiling with a completely passive, active collector.


That said if you can afford enough solar panels and good enough insulation it will certainly work.  Probably ideally you would like a lot of mass and one oven you could get really hot and another oven that had a damper to the first oven so you can run a cooler oven to better utilize and store heat.  One thing to remember is an oven will need a vent or otherwise you will end up with things like steamed bread.  

One other thing to think about is pollution created making the solar cells vs pollution created doing some other form of cooker.

I have wondered on 2 answers in my thinking.  1.  A heavily insulated oven tapping heat from a stratified water storage tank so it was always 140 degrees.  Add a second insulating door that is in place most of the warm months.  That way slow cooking in the oven is always there.  When it is needed as an oven the added heat would be much smaller by 70 degrees.  The dream over should be wood fired, gas and electric.  Still dreaming there.  2.  Thinking of an built in crock pot or set of crock pots running off the same hot water tank.  There again slow cook.  Easier to insulate.  And a built in heater would let it get hotter at need.  If it was heavily insulated with a heavily insulated lid it would use very little extra power.

There are vacuum insulated pots with 12 VDC heating coils built in.
They are designed to keep foot hot over many hours.
I looked into them as an alternative to fast food ,cold meals or hunting for a microwave while on the road.
I think you could actually cook in them over the course of 6 or more hours.
Constant heat added to an insulated environment over time really adds up.
When I was an electrician you would sometimes  see a hot box in use on big jobs.
Just a box lined with foil with a light bulb in it,  it allowed  20 guys to heat up their meals,  something a single  microwave couldn't do when you only had 1/2 hour lunch.
Sure,  they had to put the food in in the morning,  but it worked, and took very little energy.

I just acquired a scrap  electric water heater use as a "rainbarrel".
After stripping the insulation and filling it,  I'm pretty sure there wasn't anything wrong with it.
I wonder if it could be used as the shell of a photovoltaic solar oven.

C. Letellier wrote:It does cause me to wonder how much a vacuum thermos could be scaled up?  If the glass was say 1/4" thick.  Eliminate most of conduction and convection and if the outer layer is mirrored on the inside most of radiation too.  Put that in a heavily insulated conventional shell and 100 watts would probably be enough.  Put a large slab of some heat storage material in the over over the element.(slab of granite counter top maybe?)  If you needed excess heat simply taking that or another slab to trade out to an optical concentrator would let you take the heat inside.  

Or if the goal was a simmer pot a bit of piping and a evacuated tube solar collector would let you simmer clear to boiling with a completely passive, active collector.


That said if you can afford enough solar panels and good enough insulation it will certainly work.  Probably ideally you would like a lot of mass and one oven you could get really hot and another oven that had a damper to the first oven so you can run a cooler oven to better utilize and store heat.  One thing to remember is an oven will need a vent or otherwise you will end up with things like steamed bread.  

One other thing to think about is pollution created making the solar cells vs pollution created doing some other form of cooker.

I have wondered on 2 answers in my thinking.  1.  A heavily insulated oven tapping heat from a stratified water storage tank so it was always 140 degrees.  Add a second insulating door that is in place most of the warm months.  That way slow cooking in the oven is always there.  When it is needed as an oven the added heat would be much smaller by 70 degrees.  The dream over should be wood fired, gas and electric.  Still dreaming there.  2.  Thinking of an built in crock pot or set of crock pots running off the same hot water tank.  There again slow cook.  Easier to insulate.  And a built in heater would let it get hotter at need.  If it was heavily insulated with a heavily insulated lid it would use very little extra power.

William Bronson wrote:There are vacuum insulated pots with 12 VDC heating coils built in.
They are designed to keep foot hot over many hours.
I looked into them as an alternative to fast food ,cold meals or hunting for a microwave while on the road.
I think you could actually cook in them over the course of 6 or more hours.
Constant heat added to an insulated environment over time really adds up.
When I was an electrician you would sometimes  see a hot box in use on big jobs.
Just a box lined with foil with a light bulb in it,  it allowed  20 guys to heat up their meals,  something a single  microwave couldn't do when you only had 1/2 hour lunch.
Sure,  they had to put the food in in the morning,  but it worked, and took very little energy.

I just acquired a scrap  electric water heater use as a "rainbarrel".
After stripping the insulation and filling it,  I'm pretty sure there wasn't anything wrong with it.
I wonder if it could be used as the shell of a photovoltaic solar oven.

Great ideas! Lots of food for thought, I never get notifications so just noticed these replies. Really like the idea of tacking a slow cooker onto a hot water storage tank...

I'm playing about with some heat storage bricks just now, seeing how much insulation they need and how practical it is to use them for cooking.

Something really cool I've discovered from the researchers in the original post - Hot diodes!: Dirt cheap cooking and electricity for the global poor?

"Direct DC Solar (DDS) electricity can inexpensively cook food and charge appliances. Insulating the cooking chamber allows the food to cook with a lower-power (less expensive) solar panel over a longer cooking time. We explain how using a chain of diodes instead of a resistive heater extracts more energy from a solar panel over a variety of solar intensities and also acts as a rough, inexpensive voltage regulator to charge batteries and power appliances. We show how a diode heater produces more heat from a solar panel than either a DDS resistive heater or a PWM/battery-connected resistive heater, averaged over a wide variety of solar intensities."

I've ordered a bunch of diodes and will have a further play around...

I've just learned of the now discontinued 30 amp "night storage" AGA - see here.

"Built around a core of bricks, it’s heart retains a heat of   750˚c , gradually releasing heat during the day, giving a constant and continuous room heat beyond that of any other model and a consistent cooking temperature."

I have a whole heap of storage heater bricks and elements that I'm playing about with just now - this kind:



I'm thinking I could bastardise the AGA concept and create a "day storage" cooker, using the core of bricks to dump excess summer PV into. I'd be sticking juice in from around a 6kW PV array...

Mock up below to illustrate the concept. Thinking I could create a bit of a convection current with the holes in the dividing wall - but maybe in a setup like this it wouldn't function if the entire mass of the oven reaches a thermal equilibrium of sorts...

Here's a PDF of how the night storage AGA fits together.

A few fans to move heat around, but I reckon we could do without these. Someone here stuck a storage heater inside a redundant AGA and found he could even use the hobs - https://community.screwfix.com/threads/convert-aga-to-electric-using-storage-heater.215650/

Quick after thought - it would be wise to isolate the ovens from the storage heater bricks and elements - moisture would not play well!

I came across some "cook and hold"ovens on an auction site and had to look them up.
They are 120v AC appliances that cook food low and slow, then hold it at safe tempatures.
Essentially the oven version of a crock pot, built for comercial cooking.

Food cooked in them retains more moisture, and meats in particular are tenderized.
They are not cheap, but they can be bought for pennies on the dollar at auction, they have relatively low power requirements,  so the inverter loss hurts less, and they have smarts built in.
The possibilities for proofing, sprouting and fermentation are intriguing.

Cook and Hold Ovens

Another thing that reminded me of this thread was pressure cookers.
I was reading about them and realized the pressures they are built for are pretty low compared to a commercial boiler or even a waterheater.
Turns out , you can make a water heater over into a pressure cooker.
The dangers of such a device should be obvious to anyone with sense enough to make one, but in case they are not: BoOM! Shrapnel to your face 8s what you are risking.

A standard electric pressure cooker could be worth running off of a solar system, even after the  inverter loss.
They have a lot of built in options.
An electric pressure canner might make even more sense.