How to build a solar powered electric oven • Hacker News Board

Re: How to build a solar powered electric oven

#51

Post by kragen » Mon, Nov 03, 2025, 5:25 AM UTC

jacknews wrote: post #50

Lio wrote: post #20

I wonder, how hard would it be to make a vacuum insulated oven like a big thermos flask? I know this is “low-tech” but still think it might be possible to fabricate something even if it means spending some of your power budget maintaining the vacuum with a pump.

maybe vacuum insulated panels. A big thermos would be much more challenging, though there are already long vacuum bottles/tubes used as solar cookers.

I have in fact cooked eggs at night by running water over them that was heated in such vacuum-insulated-tube collectors, then held in an insulated tank. This used to be an economical way to get hot water when PV was more expensive.

Re: How to build a solar powered electric oven

#52

Post by conductr » Mon, Nov 03, 2025, 2:44 PM UTC

kragen wrote: post #48

conductr wrote: post #47

Earlier quoted context omitted.

Yes this is exactly my point, I don’t cook ~12 hours a day every day. Usually less than 1 and even use the oven less often, most days not at all

Right. Although actually cooling is less energy-intensive—removing 3000 watts of heat only costs about 1000 watts of electricity.

Hrm. You probably know better than me, but I always assumed that since my cooling cost in Summer is 5x the cost of my heating cost in winter (with similar differentials, eg. heat+30 degrees, cool-30 degrees) that it was a less efficient process.

The napkin math still doesn't make since if I have to increase the cooling of house ~half the day (would be more since summer has longer days.) Other considerations would be extra wear on the HVAC equipment and just the comfort impact of increased fluctuations.

Re: How to build a solar powered electric oven

#53

Post by eternityforest » Tue, Nov 04, 2025, 5:22 AM UTC

buckle8017 wrote: post #7

oritron wrote: post #2

I think some simple MPPT circuitry would be a smart investment for this, rather than a fixed resistance connected directly to a solar panel.

An MPPT would double the cost of this setup.

Can't you do it inductorlessly if the load is a heater, and you can freely choose the resistance, just by PWMing the element from a capacitor?

If so that's probably like a $3 board in quantity, which could also give you the option to use a USB-C solar panel, which is probably the most versatile and convenient for a lot of people, with LEDs to indicate power and help you aim.

It would go against the low tech concept, but if I was going to build something like this I would probably go for MPPT

Re: How to build a solar powered electric oven

#54

Post by airbreather » Wed, Nov 05, 2025, 11:16 AM UTC

kragen wrote: post #34

Some design alternatives: • Use lime cement rather than portland cement for the mortar. Portland will be damaged over time by the 120° temperature and may spall explosively, causing injury, particularly if you embed nichrome heating elements in it. • Similarly, don't use plaster of Paris inside the oven. It will also degrade over time at that temperature. Waterglass would work to fix tiles to wood but will foam up wh…

yes, perlite is the insulation of choice, as long as you keep it dry, very few things surpass it.

Re: How to build a solar powered electric oven

#55

Post by buckle8017 » Thu, Nov 06, 2025, 2:28 PM UTC

oritron wrote: post #40

buckle8017 wrote: post #7

Earlier quoted context omitted.

An MPPT would double the cost of this setup.

You've gotta count the cost of your time as negative for that to be true. The author built multiple ovens from scratch here, and every cooked meal could be done sooner if the temperature were higher.

The author does value his time at negative lol.

This entire endeavor is financially absurd.