Robert Isted

Here’s another link to a description of the scheme.

http://ipsnews.net/news.asp?idnews=106927

In this article they state that the system does have an aquaponics cycle, with fish included into the scheme to provide improved filtration and more input for the digester.

Marcos,

I heard the story first hand from a friend who is one of the engineers behind the company that makes the biogas digester.
See www.biogaspro.com.

There’s a brief description of the project here:
http://biogaspro.com/download/case-studies-read-about-our-installations/item/school-three-crowns.html?category_id=2

Yes I agree.

Ideally, to fully exploit the latent energy of the phase change, you would have to tune the freezing point of each bottle of the thermal mass fluid to be the average temperature of that bottle. You could do this by adjusting the amount of salt in each bottle of water. Or you could forgo the optimal solution and simply have a few more cold beers on hand and slightly less space in the fridge.

The BEST solar energy system? Well if by “best” you mean “does does the most good”, then the best specific example of a solar energy system is one that includes the following components: a school, a bio-gas generating sewage digester, an algae pond and a vegetable garden. I’ll explain.

I recently heard a lovely story about a school in a poor rural part of South Africa. It used to be a typically dismal third world community with hungry malnourished and sickly kids, no sanitation, polluted local water and a terrible shortage of cooking fuel.

Then a foreign charity funded a sewage processing system which captures the bio-gas (mostly methane) from the anaerobic decomposition of sewage in a digester vat similar to a septic tank. The water discharged from the vat, which is very rich in nutrients and also organic contaminants, is then fed into a series of shallow algae ponds. With all the nutrients and lots of sunlight the algae grows prolifically, capturing the energy of sunlight to create algae biomass. The algae is collected and fed back into the digester vat to create yet more bio-gas. Meanwhile the water that flow from the algae ponds is no longer polluted but still contains quite a lot of nutrients. This water is then used to irrigate and fertilize the school’s vegetable garden. Here more sunlight energy is captured to create nourishing healthy vegetables. These vegetables are cooked in the school kitchen, using stoves running on the bio-gas. And now they have healthy, happy kids with decent sewage, clean rivers and plenty to eat.

You could use bottles of salt water for thermal mass but from a Thermodynamic point of view beer will work just as well. And beer comes conveniently packaged and can be useful to have on hand in case of unexpected emergencies like a sudden barbecue.

Why not just keep the fridge inside the freezer? Just be careful that you don’t overpower the system and nothing ought to freeze.

Refrigeration is the exception where batteries need not be the heart of a solar system. Instead of storing energy chemically in batteries you can use thermal mass to store cooling potential. Minimal battery power might be needed to provide compressor motor startup current and the batteries can be protected with a simple electronic relay system.

Dale
Fortunately, I am in an area where farms are quite small and close together and also political and racial tensions are not particularly bad here and so personal safety is not really an issue. We have no security at all.

But in much of South Africa being a farmer is a very risky business. I believe it is rated as the most dangerous profession in the world outside of a war zone. More deaths per capita than Mexican policemen. Only war reporters and soldiers on combat duty get killed more often. Your friend was not exaggerating. Farm security systems are impressive and necessary.

If you are coming from Canada and want cheap land and a novel experience farming in Africa you are probably better off going to one of the countries North of here like Mozambique or Zambia or Malawi. I have too many family and social ties to Cape Town and am not up for all that comes with emigrating to another country.

Morgan

Talking of useful succulents, a thorn-free variety of Cactus Pear is getting a lot of local interest lately:

http://www.farmersweekly.co.za/article.aspx?id=14959&h=Theamazingcactuspear


This is a South African derived variety of a plant originally introduced here from America in the 1700‘s.

Leila,

I am aware of Allan Savory’s work, and so are more and more South African farmers. Many are having a lot of success by applying the principle of managing grasslands by allowing very intense but short duration grazing with long recovery periods. But these ideas are more relevant to the extensive savanna and natural grassland ranches well North of here. But its great to see how ideas that were considered radical, like so much of permaculture, is slowly being accepted into mainstream farming.

I’m in the South-Western corner of Africa that gets winter rain. The remaining natural vegetation in this area is too valuable from a nature conservation point of view to be used for grazing, and besides the soils are too nutrient poor for sheep and cattle to survive on the stuff that grows around here. The more fertile lands have all been plowed and are quite intensely farmed, mostly wheat and wine.

We’re planning to turn a patch of ex-wheatlands into a permanent pasture for sheep and maybe pastured poultry, a classic Permaculture zone three strategy. Many farmers here simply plow annually and plant a monocrop of something like oats or barley for grazing and fertilise heavily. For planning what to grow and how to manage this pasture I have found that the most useful information comes from Australia. The area around Perth I think is very similar to here. I don’t think we could do this without the Internet.

In wet temperate zones, like where you are in NZ, pastures are mostly White Clover and Ryegrass and are quite easy to establish. But in areas with lower rainfall and seasonal droughts and weak soils it gets much more complicated. Pasture management and especially the selection of suitable blends of plant species becomes quite an advanced science. I am struck by how much of what get published by Australian agri academics sounds like Permaculture. Much of what they are doing is simply looking for suitable guilds, though they don’t use that word.

Just a couple of weeks ago we planted 20kg of seeds of four different types of pasture legumes. The seeds all come from Australia, but the species originate from all over the world. And instead of using a $64000 no-till planter, we made seedballs!

For a solar system I think that the following recipe ought to be cost optimal:

Decide how much fridge volume you need.

Then buy an ordinary chest freezer of at least twice that size.

Fill the bottom and line the sides with lots of cans of beer to provide thermal mass. Tape them into place until at least half of the volume of the freezer is taken up. Line the remaining space with card board so you now have a usable cold food storage space of the desired volume. The sides of the freezer might well go below freezing, but because it takes so much energy to freeze beer the zone in the middle where you store food will never get to freezing temperature. This will work as long as you don’t provide enough energy for the refrigeration mechanism of the freezer to run 24 hours per day. And this is the trick - scale the solar panels to provide current to power the system only when the sun is shining. During the day the beers will get really cold and at night they will slowly take up heat from the food storage compartment.

You might be able to simply get an inverter matched to the max power of the freezer and directly connect the solar panels to the inverter, without using a charge controller or a battery.

Unfortunately it is probably not quite that simple - there is one more trick. Ordinary electric motors require a much bigger starting current that what they need when they are running normally. You probably will have to add a battery to the system to provide this brief power kick. This won’t cost anything because the power spurt is quite brief and an old car battery that is too feeble to start a car and too old to store much energy will still be quite sufficient for this application for many years after it has been retired. But then you need to make sure that when the solar panel is not providing enough power that you don’t drain the battery. A simple solution would be to add a relay so that when the voltage on the DC system get to below about 14 volts then the AC circuit gets shut off. An electrician/engineer ought to be able to put this together for a few pennies.

I haven’t done this yet, but I intend to do so someday.

Thanks for the welcomes ...

There’s a few pics here:

http://www.facebook.com/media/set/?set=a.10150444326613653.416831.531553652&type=3&l=d9d290abe1

The ground is gently sloping down to a river that flows only in the rainy season. We get about 750mm annually, almost all falling in Winter. The climate is quite mild, quite similar to Southern California and South Western Australia. Temperatures are normally 15C to 25C but extremes are about -2C to 40C. Soils are terribly infertile and quite acid. Nearby commercial farms produce mostly wheat or wine.