How to successfully Cook in a Solar Oven - Northern Latitude

After 2 years of building and testing various solar oven arrangements, I finally have success! Most solar ovens are built and used in hot climates closer to the equator, but people in the north need off-grid solutions too!

I live in zone 4 - northern America.

The advice for warmer climates does not work here. I've built ovens out of boxes, clay pots, Fresnel lenses, and various cooking supplies - but I've finally worked out the details to succeeding in colder locations.

In order to succeed at solar cooking in a northern latitude - you must do the following:

1. Use a parabola shaped sun reflector - all others are inefficient
2. Take advantage of multiple layers of heat trapping
3. Do not attempt in the winter, cloudy days, windy days, or when the sun is low (before 9am or after 4pm)
4. Plan ahead - especially if you need to cook meat - and allow for a multi-hour cook time.

Take a look at our solar oven:

What is it made of? A parabola that covers all sides and the bottom of the "pan" with reflective material. You can build or buy this. Ours is made of sheet metal. You can make our own from sheet metal, aluminum foil on cardboard, mylar blankets, or in a worst case scenario - mylar packaging (like chip bags or juice pouches.)

The "pan" is a large pyrex bowl with a black ceramic bowl placed inside it (largest size pyrex bowl.) This is covered with a clear glass pyrex lid (from a baking casserole dish.) The clear lid and bowl allow sunlight to enter the cooking space, they also keep the heat in. The black bowl absorbs the heat.

You can cook directly in this set up, or you can place a smaller black pan (wrapped in a cooking bag) or lidded pyrex inside to provide an additional layer of heat trapping.

I placed an oven thermometer from a broken gas grill inside the "oven" to keep track of the temperature. Always wear gloves when touching any part of the oven as it will be very hot. Also - wear sunglasses when near the reflectors so you don't burn your eyes.

On June 22nd at 9am, 80F - we set the oven out to pre-heat. By 9:45 it was at 310F. Opening the top to place the food inside dropped the temperature to 250F. It quickly heated back up to 310F and that seemed to be our maximum temperature inside the two pyrex glass pieces. We cooked blueberry rhubarb bars in the oven for 50 minutes. The recipe calls for 350F for 30 minutes.

We placed a cast iron skillet into the center of the parabola to see how hot it would get.

The initial temperature read:  77 F  and after 1/2 hour it read 225 F - daytime temperature was still 80F. It did not get above 225. Would this be hot enough to cook eggs?

I capped it with a pyrex lid to see if we could raise the temperature. We did not get a higher temperature and started to run out of sun. I will reattempt a lidded skillet in the future.

A lidded, cast iron dutch oven could also work and would probably benefit from being wrapped in an oven bag or placed inside a large pyrex bowl with lid.

In the shade, the deck boards registered temperatures between 76 and 80F. In the sun - 136-150 F.
The reflectors of the solar oven - 92  F.
 The outside of the oven itself  between 150-170s. F.

To see if the heat from the dark deck boards made a difference, I moved the oven to a tan colored patio in full sun. The temperature heated up the same. On the patio, I put 4 cups of water inside the oven - directly into the black bowl.

With an outside temperature of 80F - it took 140 minutes to bring the water to a boil. For comparison - a direct flame will usually heat the same quantity of water to boil in 15-20 minutes. But the sun was free.

This means we could cook rice or noodles easily in the solar oven (with enough time to plan - actually: I think it would be better to heat the water in the solar oven and finish the cooking in a thermos like I did here.) It also means we could easily sanitize water and cook stews/soups, braise meats over a long period of time, and much more!

This is the most successful solar oven set up we have used in a northern climate. It is small and portable. It heats up well and maintains a consistent temperature. With the clear glass and the grill thermometer, it is easy to see the temperature inside the oven.

It cooked well with slightly longer cooking time compared to an indoor oven (but with free heat from the sun and no electricity.) The max temperature seems to be 310 for our climate. I will be adding a fresnel lens to a portion of the top (above the black bowl but beneath the glass lid) in another rounds of tests to see if I can up the temperature even more.  I will also attempt to cook meat. At 300F,  it's going to take a few hours, and I'll have to rotate the oven to chase the sun.

In case you were wondering, the box style solar oven worked okay in our area. This is one I built from two shoe boxes (one shoe, one boot,) some shredded paper, duct tape, black spray paint and a fresnel lens.

We baked cookies inside this oven one year. The cookies were mostly done and burned in random areas (due to the fresnel lens focusing beams of light in certain places.)
The inside was insulated with paper. I always felt this was a fire risk - especially with the fresnel lens and would probably use sand or pebbles in the future. I have had good success using a clay pot for the base instead of the box - as long as it has a glass top (pyrex lid!) and there is a solid base of pebbles/sand holding and insulating the cooking vessel.  That oven was dismantled so I could grow plants in the clay pot.

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Blackcurrant said...

What's your latitude please? I am UK southern half and wondering whether this will work

Blackcurrant said...

What latitude are you please. 80F by 9am sounds fairly warm to me! I live in southern half of UK and wonder whether this will work. Thanks

Angela said...

44.9778° N, 93.2650° W

Angela said...

It was summer when we cooked in the solar oven so it did get warmer earlier in the day. It is now the end of September and we are in the 40sF

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Thank you for your comments! I appreciate all your tips, advice, and well wishes!


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