Rooftop Savonious Discussion

I'd like to talk a little about a vertical axis wind turbine positioned on its side. Yeah, I know, it becomes a HAWT when you do that. The main problem is that, in that position, it doesn't spin from all wind. But there are some advantages. Firstly, it is low profile and neighbors are less likely to complain. Secondly, it is technically easier to mount this way. Standing straight up means the mount point has to be way stronger due to massive torque effects. And thirdly, you can link several wind turbines in a row to share shaft power to one powerful generator.

There is also an advantage to putting a VAWT on the rooftop. When the wind comes, it is compressed upward and effectively gives the savonious more surface area of wind collection. If the wind is traveling perpindicular to the axis then you will get your maximum power potential. In the below example, there is a VAWT 8 feet long and 4 feet wide and it s laying down on its side at the rooftop. In this example the roof rises 8 feet. That means that whatever power the wind turbine would generate in a given wind is multiplied by 3. Of course, a different roof and sized wind turbine would generate different results. So, if it ran at 15 % efficiency normally, then on the rooftop it could be up to 45% efficient. Also note that wind at the peak of the house is stronger than wind at the ground level.

In the below picture you will see wind angles at 45 degrees from perpindicular to the axis. At 45 degrees, the wind turbine should appear to have half the surface area. So, half of 45% would be 22.5% efficiency, still good. At some angle greater than 45 degrees the silouhette would become one third of full and, due to the roof, would make the overall efficiency become 15%. In other words, you can get normal power even at extreme angles. An at perpindicular angles, get 3 times the normal power output.

Some roofs have sections that are perpindicular to each other. Another VAWT could be mounted there as well. That way you generate power no matter what direction the wind comes from. And even if you only have one, whenever the wind direction changes back to a better angle, the power increase more than makes up for the times when no power was generated. Just make sure that your predominant wind is the right direction, otherwise this just wouldn't work for you.

Richard

DC Motor Analyzer Finished

Well, it looks like I've finished the updates on my DC motor analyzer software. I still have to do some more testing before I make it available but here are some screenshots. The yellow highlighted sections are new parts to the program. They are only highlighted here for you to see, the program normally doesn't show that. The first picture below is in the HAWT mode, or horizontal axis wind turbine. The second picture is in VAWT mode. So, you can do savonious or other vertical axis wind turbines.



Something to be aware of if you go to the VAWT calculator web page on my website, is that those computations also account for about a 55% efficiency dc motor. So, if you take a savonious and the blades are 15% efficient and the motor is 55%, then on the new motor analyzer software you would put in 8% efficiency. On the website, this was done in the background. But the new program gives you more control.

For instance, if you have blades that are 30% efficient for a HAWT and your DC motor is 60% efficient, then you can put 18% in the efficiency field and get a nice "real world" expectation. Especially when you put in the cable length and gauge.

I should have my testing done by this weekend at the latest and the new analyzer should be available for purchase.

Richard

Cardboard Solar Oven

This is the third solar oven that I've made over the last few years. But this is the first cardboard one I've made. This first pic is the oven without the lid and the second picture is with the lid on.


I still have to paint the inside with some flat black paint. I'll leave the top back 1/4 or so unpainted.

My first test will be without any insulation, just like you see in the pictures. Then I will try the hot box cooker approach. I will take a bigger box and a thick blanket or two and push this down inside so it will be surrounded by the blankets except the glazing section. Then I will add a reflector and see if it improves. Although a reflector mounted on the back of a slant face oven is almost pointless unless the sun is really high, or unless you have a flat top glazing.
And something to be aware of is that (as is true for all solar) size is king, or in this case, surface area of the glazing is king. Here is a picture of a small solar oven that has a 1 square foot piece of glazing letting the sun in.
With the reflector put into position and if it is facing the sun perfectly it will have 3.5 square feet of solar collection. You could make a solar oven with a slanted face that has 3.5 square feet of glazing and you would get the same efficiency without the reflectors.

Also, be aware that reflectors can get in the way. If you don't rotate that funnel type every 30 minutes to an hour, then you will get shadows from the reflectors.

Earlier testing with a thin plywood solar oven with no insulation showed temperatures from 190F up to 225F on a sunny summer day. I expect about the same with the cardboard one.
I'll keep you guys posted.

Richard

Rocket Stove

I was talking about hot box cookers the other day and thought this would be an appropriate method for bringing food to a boil and then using the hot box to finish it off. This one is really simple and made with just some adobe bricks.

I like the rocket stoves because they make a lot of heat with very little input. They fact that they are smokeless tells me that they are very efficient. And combined with the hot box method, this is an off the grid dream come true.

See ya Monday,
Richard

Update on DC Motor Analyzer

Most of you are aware of the DC motor analyzer program I wrote. I have been in the process of upgrading it to visual basic dot net. The old version was written in vb 5. As you can see, in the picture above, I've added a few things.

Now you can select Motor1 to Motor3 and hit save for future use. You can also select it and hit load. This is great for comparing a few motors and configuration settings.

I've also added an efficiency setting. The older program defaulted to 30 %. This is really handy for more real world applications. For instance, the blades may be 30% efficient, but the motor may only be 50%. In that case, set the efficiency field to 15%. In other words, it is an overall efficiency measurement. Everything except voltage drop. That is handled separately.

When you move your mouse over the chart area it now displays watts and amps.

I've also added a field in the bottom left to show the wind speed that battery charging starts. If you set it up to start charging at too low a wind speed and you don't have enough torque, then you will get an error now.

I have a few small changes to make and I still have to get the print function to work. But it will be available sometime in the next couple of weeks. Any customer that purchased the older program can upgrade to this version for free. You will just have to send me an email and the date of your purchase.

If you don't have the older version but would like to see it operate, you can see some of my older videos on youtube. You can also see a video of the updated software there as well. It doesn't have all the changes yet because I made the video yesterday.

Richard

Slow Sand Filter

I prefer the ceramic filter over a slow sand filter, but in an emergency it would be good to know how to make these.

Something to remember is that there is a layer at the top couple of inches in the sand called the hypogeal layer or Schmutzdecke. It contains all the bacteria that help clean the water. Just pouring the water in too fast can wreck it. And it takes a couple of weeks to repair. The same is true with the backflushing. It would be a good idea to have 2 of these, that way if you have to backflush, then the other one is still functioning. Some people use a top diffuser to limit the disturbance when putting water in. And you don't have to use activated carbon. That is mainly for clearing up odors and tastes.

Richard

Hot Box Cooker

I just read a great article and interview on Wretha's blog.
http://wretha.blogspot.com/2009/07/new-old-way-to-cook-book-review-video.html

The premise is simple. Heat your food to boiling temps for a few minutes, then turn the heat off and take the food and place in a very insulated box so it can slow cook for the next 3 plus hours. I know it is a simple concept but I am totally amazed by how much power or fuel you can save this way. Not to mention the facts that you can't burn the food, it tastes better, food keeps it's shape and yet is fully cooked, and doesn't heat up the kitchen.

With my limited wind and solar system I wouldn't want to waste power for cooking. But if I ran the stove top for 20 minutes and used 1500 watts, then that would be 500 watt hours or 42 amp hours. That is only 10 % of my golf cart batteries or about 6 % of my forklift batteries. But, if I tried to slow cook something all day on the stove, it would drain my batteries. This is huge, people!!! Another thing you could do is to take the black pot and put it in the sun so it preheats. If you have a solar oven you can just cook in that. But in the winter time, you could just place the pot of water in the sun to preheat it. This will save some more energy.

This simple concepts of hot box cooking and solar ovens will help us tremendously in the near future. So, check out the post and watch the video. Thanks, Wretha, for a great article.

Richard