Solar Updraft Tower

I started this blog in order to share ideas on small scale alternative energy devices. In this post I am going to discuss a very interesting device. The idea is nothing new. It has existed for over a century. Let me explain the basic principle.

The Solar Updraft Tower

The solar updraft tower is basically just a large heat collector with a chimney in the middle. It works on the principal of convection. The heat collector is similar to the solar cooker or the solar water heater. It's consists of a glass canopy spread over the ground. It collects and traps sunlight and heats up the air underneath the canopy. We all know that hot air rises. Since the hot air has nowhere else to go, it rises straight through the chimney in the middle of the canopy.

The purpose of chimney is to create a draft. The temperature at the top of the chimney is much lower than the temperature of the hot air (heated by the solar collector) at the bottom. This temperature difference causes a difference in pressure, which in turn causes the hot air to rise rapidly. This is called updraft.
Those of you who are technically oriented can read more about this phenomenon here:
http://en.wikipedia.org/wiki/Stack_effect

All you have to do is to place turbines at the mouth of the chimney such that the turbines face the air flow. The air rising through the chimney will rotate these turbines and viola, you've got electricity. its quite a simple device. Read more about the Solar Updraft Tower here:
http://en.wikipedia.org/wiki/Solar_updraft_tower

My Thoughts And Ideas I Want to Experiment With

Now suppose I want to build something like this on a much smaller scale, say, just big enough to provide electricity to a small household, maybe 300-500 Watts. I want to improvise the design since I think that the maintenance of a glass canopy would be too much hassle. Glass is expensive and breaks easily.

So I have some ideas. Suppose we lay down some metal sheets very close to the ground(maybe half an inch above the ground). We paint the top surface of this metal canopy black, so it absorbs sunlight and gets really hot(I think 60 degree Celsius is easily attainable in tropical regions like southern India). We spread these black painted metal sheets over an area of a few square meters(maybe 100). At the centre of this canopy we make a hole and place a 10 feet tall chimney and inside the chimney we place a turbine. So I am hoping that heat absorbed by the metal sheets will be transferred to the thin layer of air underneath the sheets. The hot air will rise through the chimney and rotate the turbine.

The reason I like this device so much is because of its simplicity. It can be built and maintained by people anywhere in the world. There are very few moving parts. And there is no need for complicated devices like heliostats (sun trackers) and heat engines. Of course, this simplicity comes at the cost of efficiency. There is always a trade-off between simplicity and efficiency. But since I plan to build small scale devices, it is better to keep it simple. Plus sunlight is free. So efficiency is not the most important thing.

Your Thoughts?

I urge all those who read this post to share their thoughts on the ideas mentioned above. Also feel free to suggest your own ideas.

Our current hypercomplex fossil fuel energy paradigm

In my previous post, I mentioned that I attribute my high(relatively, I mean, when compared to the average Indian) standard of living to the access to the Indian electric grid. I also said that I would like to preserve my high standard of living. So the question is, what wrong with the grid? This post is meant to highlight some of the problems with our current energy paradigm.

The Energy Source Issue 
Here's a breakdown of the various sources of electricity in the country

                                                                   

As you can see, about 2/3rd of our electricity is generated using thermal generation facilities. These facilities use coal or natural gas for fuel. Both of these are non renewable fossil fuels. Once you burn them, they just disappear into thin air. Actually coal (especially Indian coal) does leave behind a large amount of ash. But that's not very useful.

The problem is that the price of both coal and natural gas, has been rising in recent years. Here's a chart for coal prices.

The reason for this is largely geological. Mining of natural resources is usually done by the lowest hanging fruit principle. The easiest cheapest deposits are mined first. After centuries of mining, all those easily accessible deposits have been depleted. More energy, effort and money (capital) has to be invested to access the deposits that are discovered today. That cost has to be recovered from the consumers (you and me). This is true for oil and natural gas as well.

The Complexity Issue
Even if we ignore the rising prices, there is another problem. Our current energy systems are way too complex. Basically, that is true for all modern systems. The entire progress story of human species has been nothing but a quest to add new layers of complexity on the previous ones. We call that complexity - technology. To be sure, computers are not becoming simpler just because they are getting smaller. People should see how a modern microprocessor is made, in order to understand just how complex a modern computer is.

As mentioned earlier, fossil fuels like coal are becoming harder to access. So how was this problem solved? Well, by using larger and larger machines for mining. Actually, these days they use a process called mountain top removal. Where large areas of land are simply blasted off using explosives, in order to expose the coal deposits underneath.

There are two kinds of energy resources- High Grade and Low Grade. Fossil fuels and Hydroelectricity are high grade energy resources. They provide very large amounts of energy per unit volume. Solar, wind etc are low grade energy resources. When you have high grade energy resources, it makes sense to centralize generation and distribution as much as possible. That way, it's more efficient and comfortable. Its better to have 1000 MW power plants and then distribute that electricity using a highly interconnected and complex national grid.

Now, the problem with this arrangement is that complex system always have single points of failure. Recently, entire North India suffered a black out because of a single faulty line. Black outs like that are seen even in western countries. An analogy can be seen in the financial world where a few failed companies in USA caused a worldwide recession.

It would be prudent of us the curtail our dependency on these hyper-complex systems. I believe that low grade renewable energy resources provide us with an opportunity to do that. We have to find ways to building small stand alone energy systems that can be easily maintained and replicated. And that is what this blog is dedicated to.

Prologue

This blog is meant for sharing ideas on alternative ways of generating electricity. Primarily, small scale energy technology. Now, that does not mean that I have boycotted fossil fuels. But lets keep it to sub-kilowatt scale.

I would be sharing some designs of devices that I have in mind. I also welcome ideas from readers. The purpose of this site is to freely exchange thoughts and opinions on whether the ideas are feasible, their utility, cost effectiveness, practical applications and so on and so forth.

Let me share the reason for starting this blog. Even though I live in India, which is considered to be a developing country, I consider myself a citizen of the developed world. I enjoy almost all the amenities that you would normally associate with the people living in advanced countries. My house is hooked up to the electric grid and the internet. I consider that to be a great privilege and the primary reason for my high standard of living. I would like to preserve that.

In the coming post, I will discuss some of the problems the current energy paradigm that we live in.