A Parvati Solar Cooker

Damn, is solar cooking easy! Put some rice in a pot, place the pot in this simple panel cooker, made with cardboard and aluminum foil, stick it out in the sun and two hours later you have lunch.

We built our “Parvati” solar cooker with plans designed by Shobha Ravindra Pardeshi that can be found here. Pardeshi, who runs an “appropriate technology” company with her husband in India has another design for a similar dish-shaped cooker here. We found both of these cookers (and many more) via the amazing Solar Cooking Archive.

For the Parvati cooker, we cut the cardboard according to the plans, and affixed the aluminum foil with spray glue. For our first pot of rice we used a black enamel pot to better absorb the heat of the sun’s rays, and wrapped it in a roasting bag to increase the efficiency of the cooker. A five gallon bucket made a convenient stand and did not have to be rotated in the two hours it took to cook the rice. Longer cooking times would require re-aiming the cooker as the sun moves across the sky. Temperature in the pot quickly went over 180º F, the point at which food begins to cook. The two hour cooking time is much longer than it would take on a conventional stove, but with a solar cooker there is no danger of burning, making the process, in our opinion, easier than stove-top cooking. Consider a solar cooker a kind of low-powered crock pot for lazy and cheap people–good for things like rice, beans, soups and stews, but not good for sauteing. Just remember the oven mitts–this thing gets hot!

When the sun gets higher in the sky, as we move into summer, this cooker will reach even higher temperatures. We don’t remember where we read this but some folks say that panel cookers like this one cook best when your shadow is shorter than you are which, here in Los Angeles, is right about now. We tried this cooker back in January and it performed well, but did not get above 140º F, which is not hot enough to cook.

Perhaps here around the Root Simple compound we’ll get around to turning our Parvati Solar Cooker into a low rent attraction. Just add some ostriches and we’ll repeat this early 20th century tourist trap in nearby Pasadena (click to biggify):

Planting a Mini-Orchard

Ignore the bucket in this illustration! See update below.

Update 3/13/2011: I met Brad Lancaster last night and he told me that he and Art Ludwig no longer use the upside down bucket described in this post. The reason is that detergents can build up in the hole. In my experience the bucket was also an unnecessary step. While I have a clay soil, the hillside drains fairly well. A properly sized mulch basin should suffice to allow greywater to infiltrate. Also, the new generation of washing machines use a lot less water than the old one that I still have. Other than the unnecessary bucket and the persimmon tree (died, for some unknown reason) this greywater application has worked very well. Our fruit trees are lush and happy.

With the news that Lake Mead could go dry by 2013 we figured it was about time to figure out how to grow food with very little water in a Mediterranean climate that gets on average 15 inches of rain a year (3 inches last year). Our water worries sparked the beginnings of our draught tolerant mini-orchard. Thankfully greywater and some tough, water sipping trees make it possible.

Step one was figuring out how to reuse our washing machine water (read our earlier post on the washing machine surge tank we built). Step two was matching that washing machine water output to the right kinds of plants for the mini-orchard. We settled on the three “Ps” — pomegranate, persimmon, and pineapple guava, plus a mission fig tree to replace the substandard one we cut down (even though God Hates Figs!). The advantage with these four trees is that they can survive, once established, should we find ourselves unable to use any water due to the aforementioned bad-ass draught scenarios.

Our house sits on a small hill, with the front yard sloping down towards the street. We placed the trees at the top of the slope and made mulch basins like the one illustrated above. The outlet chamber consists of a upside down three gallon bucket with a bunch of holes punched in it. The purpose of the outlet chamber, which is buried in the mulch basin, is to help the greywater infiltrate our heavy clay soil. To use it we simply place the hose coming from the surge tank into the hole in the top of the outlet chamber. We cover this hole with a brick when not in use. The photo below shows the digging of the mulch basin and the installation of the outlet chamber in progress:

The completed mulch basin and (hard to see) pomegranate tree to the right. We used straw for mulch We use wood chips for mulch (replaced the straw):
These craptacular photos don’t show the details very well, but the mulch basins were dug in such a way to also catch rainwater as it flows down the hill. Both rainwater and greywater work their way into the soil and slowly move down the hill over the course of many months. Since installing the greywater system we’ve seen previously sad plantings we did years ago of rosemary, wormwood and Mexican sage thrive. And we’ve got lots of nopalitos coming our way from the prickly pear plants.

For more information on these simple, water saving strategies see Brad Lancaster’s excellent book Rainwater Harvesting for Drylands.

Greywater Linkage

Outlaw water activists the Greywater Guerillas have added a nice set of examples to their website showing some creative greywater strategies. As figuring out how to get greywater out to your garden depends a lot on, say, if your shower is higher than your bamboo grove, it’s great to see some real world examples.
Next step around our little crackhouse will be to figure out how to reuse our shower water. The GGs have given us some ideas . . .

Using Greywater from your Washing Machine

With our current bad drought conditions it makes no sense to pour perfectly good water down the sewer. So we just joined the greywater underground with our illegal washing machine surge tank, and the installation was a piece of cake.

We built our washing machine surge tank based on the design in Art Ludwig’s book Create an Oasis with Greywater. The purpose of the surge tank is to prevent the built-in pump in the washing machine from burning out, which might happen if you tried to pump the water through pipes. The tank also slows down the flow of water going out to the garden, allowing more time for it to percolate into the soil. In addition the tank lets the water cool a bit, should we run a load in hot water.

Bottom of barrel showing fittings Top of the barrel where the hose from the washing machine comes in

For the tank we picked up a used and cleaned 55 gallon plastic drum with two “bung holes”, and plumbed it based on a design from Aquabarrel.com. The folks at Aquabarrel offer kits or a DIY video. We put our barrel together ourselves with a couple of common pvc fittings from the hardware store and omitted the overflow pipe, since our washing machine load will never exceed 55 gallons. The basic idea behind the Aquabarrel design is to turn the barrel upside down and use the preexisting threaded bung holes to connect up a garden hose. It took just a few minutes to complete, and our washing machine surge tank was ready to use. We highly recommend the Aquabarrel design, and you could combine a washing machine surge tank with a rain barrel with the addition of the overflow pipe and a fitting for the gutter.

When we do a load of laundry the waste water that collects in the barrel flows immediately out the garden hose and down towards the front slope of our little compound. Ludwig warns against keeping grewater around as it will quickly turn septic. We use Oasis Biocompatible detergent which is manufactured specifically for greywater systems. Regular “eco” detergents, while not harmful to aquatic plants, often contain substances that will kill terrestrial plants so you must use a greywater specific detergent.

Our next step will be to figure out some plantings that will take advantage of our laundry schedule, and to construct some simple earthworks and mulch basins to accommodate the water flow. Right now we just let the water percolate into the front slope, and our rosemary and Mexican sage look a lot healthier for it.

Our Rocket Stove

  • Editor’s note: we have a new design for a portable rocket stove here.

Low-tech is the new high-tech, and the best example of the low-tech revolution is the miraculous rocket stove–a stove that makes it possible to cook with small twigs–no logs needed! Best of all rocket stoves are easy to build. We liked the idea so much that we decided to build a permanent one just off our back deck for entertaining and as a backup to our gas stove should an emergency take out our utilities.

The rocket stove was developed for use in poor nations where wood used for cooking has led to the vast, wholesale, deforestation of large swaths of the earth’s surface. Rocket stoves can be built out of metal or masonry and consist of a L shaped tube, at the bottom of which you place your wood. The chimney effect creates a highly efficient, largely smoke-free burn. There’s no need to cut down a tree to cook your dinner–all you need is a few small branches or twigs.

Before we built the rocket stove we considered making a cob oven, a mud domed wood fired oven in which you can cook bread and pizza. There’s a trend in the eco-world to build cob ovens and we felt a certain pressure to keep up with the eco-Joneses. We started to build the base for one and then began to think about how often we would actually build a fire, especially considering that it has to burn for several hours before a cob oven gets hot enough to cook in. Also, where would we get the logs? And how good is it to burn such a fire and contribute to Los Angeles’ already smog choked air?

Staring at the bricks we had scavenged to build the base of cob oven, we realized that we could re-purpose them for a permanent backyard rocket stove that we would actually use. Furthermore we realized that our rocket stove could burn some of the palm fronds that regularly tumble down from the iconic palm trees that line our old L.A. street.

Here’s the materials we used:

36 bricks
4-inch galvanized steel stove pipe elbow
4-inch stove pipe
ash (scavenged from park BBQs)
1 tin can
50 pound bag of premixed concrete for the base
mortar mix
grill (scavenged)

The first step was to make a small foundation for the rocket stove. We fashioned a 18 by 18-inch by 4-inch slab with 2 x 4 lumber and a bag of premixed cement. Folks in cold places will need to make a deeper foundation to avoid frost heave.

Next we built a brick cube, leaving a small hole for the bottom of the stovepipe. For advice on how to build with brick we recommend taking a look at this. As you can see our masonry could use some more practice, but the results are not too bad–we like to think of our stove as being a bit “rustic”. You can avoid the hassle of brickwork by making a simpler rocket stove–check out these two instructional videos, one for a metal model, and another version using bricks. We chose brick largely for aesthetic reasons and we’re satisfied with the results.

Drawing from Capturing Heat

The next step is to put the pipe together fitting the elbow up into the longer pipe, and sized so that the top of the pipe is just below the bottom of the grill. Check out our earlier post for a video that can help with this part of the assembly. Serendipitously, on a bike ride, we found a grill in the middle of Sunset Boulevard that fit the opening in our brick rocket stove exactly.

You pour the ash into the completed brick cube to fill the space between the pipe and the inside wall. The ash acts as insulation to increase the efficiency of the stove. You could also use vermiculite but note that sand or soil will not work. Insulation works because of small pockets of air between particles, hence the need for ash or vermiculite, which are also non-combustible. We used a piece of scrap sheet metal with a 4-inch circular hole cut in it to keep the ash from spilling out the gap between the pipe and the squarish opening at the bottom.

Lastly you use a tin can sliced down the side and flattened out to form a shelf which you insert into the elbow at the bottom of the stove. Note the drawing above for the shape of the shelf. You put your twigs and kindling on this shelf and start the stove up with newspaper underneath the shelf. As the twigs burn you push them in over the edge to keep the fire going.

Our first test run of the stove was very successful–we boiled a pot of water and cooked some eggs in a a pan. The fire burned cleanly with little smoke except during start up. For more info on rocket stoves check out the Aprovecho Research Center.

And please people don’t burn wood inside and watch out for embers. Make sure you put the fire out completely when you are done cooking!