Boiling a Kettle with Goat Poop!

I would like to use biogas for cooking in the house, so I built a pilot project to check if and how it works. We have the feedstock, being goat manure so I decided to give it a try.

I wasn’t going to spend any money on the project, so I built a crude digester out of junk lying around on the farm. It comprises a 220 litre drum filled with goat manure slurry, a 100 litre drum upended in the larger drum with a valve and a rock on top, and a piece of gas pipe, wedged into the valve with a plastic bag. Behold its precision engineered glory!


I filled the big drum about one third full with goat manure, topped up the drum with water and mixed it up into a nice slurry. I then put the small drum upside down inside, covered it with black plastic and waited.

For a week nothing happened.

In the next week the smaller drum started to lift a little, but the gas produced did not ignite.

In the following week a foul stench was noted.

And after about 3 weeks the contraption was producing gas every day, and I could make flares of gas flame out of the pipe.

Apparently the bacteria first ferment the mixture to produce CO2, then H2S is produced and finally methane production commences as the methane producing bugs establish themselves.

The next test was to see if anything useful could be done with the gas, so I connected up a camping gas cooker, but it wouldn’t light. It took a lot more google research to figure out that biogas (being mainly methane and carbon dioxide), behaves quite differently to your normal propane or butane gas that you buy in cylinders.

An important difference is that propane and butane liquify under pressure, so they occupy a lot less space as a liquid than as a gas. You can’t compress methane into a liquid, so you need relatively large storage volumes. Methane’s burning characteristics are different so you can’t just use a normal gas burner, it needs some tweaking.

I then bought a small one ring cooker that I could modify. What needs to be done is the jet needs to be opened up to much larger than for normal gas, and the amount of air restricted. I opened up the jet in the stove from about 0.5mm to 1.5mm, and blocked up the air intake with a piece of plastic with one 6mm hole drilled in it.


So, I opened up the gas, applied a match and hey presto! It works!

Next thing is to boil a kettle, which I duly did (OK, only 1cm of water in it, but it boiled nonetheless). You can’t see the flame or the steam in the pic, but it is boiling, trust me….


So I’m quite pleased that the experiment worked. The digester is probably making about 30 litres of gas per day, probably quite a lot is lost due to the small drum not filling nicely in the big drum.

My next step will be to make a 1000 liter digester so that we can use the single ring burner in the kitchen to make a cup of coffee in the morning. I am going to use the design from this website and see how it goes : Solar Cities IBC Digester

I will keep this digester bubbling as the bacteria are established in this system, so you can take this material to quick start the new system, without waiting for the whole process to establish from scratch again. Seeing as IBCs are fairly cheap, I will probably be able to get a small working system going for less than $50, hopefully enough to do some of our cooking on, but we’ll keep our normal gas stove as well. Based on the experience of this pilot system I would anticipate about 100 litres of gas per day from the 1000 liter system.

There are many variables that dictate how much gas a biogas system will produce, like type of feedstock, ambient temperature, water hardness and so on, which is why I wanted to see it work on a small scale first, but I am very pleased with the results!

I found these websites quite helpful in this process :

ATTRA – Sustainable Agriculture

DIY Methane Generator

Biogas Plant in a Plastic Drum

Biogas Start Up

Backyard Biogas

Biogas from Kitchen Waste

Modifying a Gas burner for Biogas



Going Off Grid

This has been a long process starting some years ago and culminating with going fully off grid in June 2015. My wife and I have a lodge – which has 3 cottages we built to be off grid, all have solar water heaters, 2 have candles and paraffin lamps for lighting and the other has solar PV (12V running a few lights), gas fridge (an antique), a gas stove, and a wood stove for heating.

Since the beginning of 2015 we started taking our house off grid as well so as to finally say goodbye to utility power.

We already had a 300l solar geyser which we had used for years, and a gas stove and oven for summer and a wood burning stove for winter:



The first step was to get a generator for when everything goes pear shaped (sun doesn’t shine etc). So I was hunting around for a reasonable priced genny. I then came across this advertised secondhand, and couldn’t resist it!


I didn’t know anything about these type of engines when I bought it, but figured it out over time. They are very simple with very few moving parts and will run on a variety of fuels including diesel, veg oil, old engine oil and various blends of all of these.

Apart from reconditioning the head, the engine was working. It also took some time to figure out the the packet of brushes I got amongst all of the other spares, were actually supposed to be inside the generator, so once they were in I had lights!

Reconditioned head and new OEM Lister head gasket :

Eventually the copper head gasket turned out to be a problem as it leaks a bit of coolant from between the copper sheets, but I have a more modern gasket on order to replace it.

Generator Room

Now I had to build a room for the genny to live in, and for the PV panels to live on top. The old bathroom/kitchen on the original house had the main distribution board where the Eskom feed can in so that was the obvious place:


I removed the rusted old roof, and broke down some walls for a new door. Then I built a concrete block to mount the generator on:


And finally install the genny. Note the electric light!


Solar Panels

So now the genny was working, next was to get the solar up and running. I built a frame for the PV panels from angle iron on the roof of the generator room. The best fit for the roof was 6x300W panels:





And finally, hook the genny, panels and some batteries together:


Currently I have a 6KVA JSM Power inverter/charger to charge the batteries from the generator and supply the 220VAC for the house, 1800W of panels into a Microcare 60A MPPT charge controller. At that stage there were 4x 150Ah Trojan T1275 batteries in series to give 48V, which I have since increased to 8 batteries.

The generator is now installed at the other end of the room and I am busy with a waste heat water heating system which I will describe when it is complete. The cooling for the engine is by thermosiphon through a 150 litre water tank. After you have run the generator for about  one hour, you end up with 150l of water at 50 degrees celcius. This water I would like to circulate through radiators in the house for winter heating.



In total we have the following free energy/energy saving gizmos:

Water pumping:

Wind pump – 6ft Climax

Solar pump – Watermax OB with 200W of panels

700W 220V pump connected to house inverter (failsafe for when the other 2 don’t work)

Water heating:

Main house : 300l Sun tank high pressure flat panel indirect geyser

3 Cottages : 3x 150l low pressure tube geysers (various suppliers)

Big kettle on the wood or gas stove….

House heating:

Wood fire


Extra jersey : :)

Cottage heating:

Wood burning fireplace x2

Wood burning oven x1


Smeg 5 plate gas stove & oven

Jewel wood burning cast iron stove

Braai :D(barbeque)


House – 220V LEDs throughout

Cottages:  Candles and paraffin lamps x 2

12V solar setup – 50W panel and 2x 100Ah batteries 12V LEDs and 12V flourescents (LED is much better than flourescent so these will be replaced soon)


Bosch AA+ rated 220V fridge

Chest freezer 220V


1800W of solar panels

5KW of generator.

Lifestyle Changes

So 8 months down the track we have not had to change much. Power usage is modified so that all of the high power drawing appliances run during the day. So for instance we still run a standard top loading washing machine, we just wash in cold water. Power tools are no problem, since you rarely use them for a long time continuously. The microwave oven can only be run during the day. The electric toaster is also no problem, as it draws about 1000W, but only for 3 minutes.

The fridge and freezer are on a timer so they only run during daylight hours. We have an electrical outlet on the same timer circuit with which we charge all cellphones, tablets etc during the day. It makes no sense to charge batteries from other batteries.

Because the cycle depth of the batteries is inversely proportional to their lifespan, I try to keep the batteries as fully charged as possible. I have set the inverter to kick out if the batteries drop to 50%, but this has only happened once. I run the generator from time to time keep the batteries topped up, like on cloudy days or if I am doing a lot of welding for instance. The odd bit diesel is currently our only power expense so it has been very worthwhile going this route. It was expensive to install, but now power is essentially for free!