Solar Site Evaluation Tool

We're using a solar site evaluation tool to help with siting some solar thermal and pv arrays. If the "fuel" is the Sun, then it makes sense to find a location to mount your panels that has little or no shade for the hours of at least 9am to 3 pm. Shading solar thermal is not a huge issue, if you are partially shaded you will just get a proportional decrease in thermal output. Solar pv (ie. solar electric panels a.k.a. Photovoltaic) on the other hand has a bad habit of producing very little energy at all if they are even partially shaded.

So how do you measure how often a site is shaded? Setting up the lawn chair for a year-long vigil in a location under consideration is not practical. Luckily, if you recall astronomy 101, the Sun's path in the sky is absolutely predictable for any day of the year! Traditionally, a solar site evaluation would be done with a neat tool called the Solar Pathfinder. This simple instrument can show you exactly when objects on the horizon will cast shadows on your site for any month of the year. Neat. You start with some paper templates that are specific to your latitude. These templates show the suns path for every month and every (daylight) hour. You insert the template under a plastic dome and make sure the assembly is level and pointed due south. Standing directly above the pathfinder dome, you look straight down and you'll see the reflection of objects around you in the dome. Using a pencil, you trace the reflections of the objects onto the template. Seeing where the objects you've drawn on the template intersect the solar path lines on the template tells you exactly when those objects will cast a shadow on your location.

We took this one step further with a really cool instrument that uses a digital camera and custom software to replace the plastic dome and paper template. It uses a special mounting bracket that holds a camera and attaches to your tripod. It has 15 degree detent stops that allows you to take a series of pictures from east to west in 15 degree increments. You save these pictures onto your computer and you use special software to "stitch" these pictures back together in a panorama. After you enter your latitude, the software overlays the sun's path for the entire year over the panorama. Of course, the sun takes a different path across the sky depending on the season, so what you see is a series of arcing lines across the photo. The software tries to identify when an object intersects these arcs and thus would present a shadow on your array. A red line indicates when the software thinks shadowing will be an issue. This isn't an exact science - sometimes one photo of the sky might be a little darker than the others, and the computer interprets the contrast change as a sun-blocking object instead of the sky. A little touch up in photo shop or some other photo-editing program will blend the sky and help the software interprets the photo correctly. What can you tell from this analysis? Quite a bit. The simplest and most important thing is when you can expect your site to have a shading issue. Take a close look at the blowup of the right side of the solar panorama photo. You can double-click the photo to open it full size in a new window. Notice the "horizontal" lines are labelled with months of the year. This is the path that the sun will take in that particular month. Notice also that the "vertical" lines are labelled by hour. You can see that the equipment garage will present a shadow on the location that the picture was taken, at around 1:30 pm in December all the way to around 4:30 pm in June. See - you don't have to camp out in your lawn chair all year long after all! Now this isn't all this product can do - it has a nifty .csv output that has all kinds of interesting and useful information like how much energy you can expect to capture given the shading at this site, how much more energy you could expect if you had a tracking mount versus a fixed mount, or how much more energy you could expect if you cut down your neighbours tree!!

The software creates a .csv file with a lot of great information including the potential monthly energy production of the array. While I haven't yet been able to independently verify the proposed energy production (this survey was not a "real" location) I'm assuming that the differences between fixed, 1 axis tracking and 2 axis tracking are reasonable. 954 kwh /1159 kwh/1309kwh shows a fairly significant increase in energy production with the tracking arrays. Tracking arrays can be pricey however, and it may make more sense to make a 30% larger array on a cheaper fixed mount.

Update: fixedArray 1-axisArray 2-axisArray

Wind Energy Basics

I've been interested in wind energy for some time now. My plan is to use a wind generator to cover some of my electrical consumption of the net-zero energy home I've been building. Wind turbines are a very romantic technology for generating electricity. It's easy to appreciate the concept of harnessing the wind that you can feel on a breezy day and, unlike solar, there is something interesting to watch.

There are 2 main things to consider when trying to determine how much energy a wind turbine will produce on your site. The first is the wind resource itself. If there is not much wind - you will not harvest that much energy. This seems obvious but how many people know what a 10m/s wind feels like? Not many. We tend to be very anecdotal about wind. We think that we live in a very windy area, only to be disappointed when our turbine isn't producing the 1200 kwh a month we were counting on. So how do you know for sure how much wind you really have? For starters, you could go to http://www.windatlas.ca/en/index.php . You can find your location on the map and get a general idea of your wind resource. Notice I said "general" idea. Your specific location and particular spot you want the wind turbine to go, cannot be modelled specifically from the wind atlas. For that matter, if you are in a windy area, your specific location could be less windy(or more windy) than the general area. If you are at the top of a hill, you would likely get more wind than your neighbour at the bottom of the hill. Or, maybe you are at the top of the hill, but you want to place the turbine on a short tower between some large trees and a grain bin which may give you less energy than your neighbour at the bottom of the hill who has a taller tower and an obstructionless location.

If you want to know for sure, you could consider measuring the wind at your site. Best done over a full year, you can buy relatively inexpensive wind dataloggers to let you know for sure. Most of us are too impatient to wait for a full year so at least plan to mount your turbine on a tall tower in an area where there is a minimal amount of obstructions to block the wind and cause turbine-killing turbulence.

The second factor in determining your wind resource is the swept area of the turbine. How much wind is captured by the wind determines how much energy you get. Sounds simple, but you'd be surprised how many wind turbines are sold with power outputs that don't relate to their physical size. Resist the vendors efforts to sway you with comparing the turbines rated output and instead compare the swept area. A bigger wind turbine will make more energy than a smaller one. Sure, the efficiency of the particular machines matter, but if you are comparing legitimate turbines, their efficiencies will be close (typical efficiency will range between 25 and 35%).

Ram Pump

Imagine if there was a way to pump water without having to supply any external energy. No gas-powered pump, no solar pump, no manual effort etc. Sounds like an impossible dream doesn't it? Well, the Ram Pump doesn't violate any of the laws of Thermo Dynamics and in fact depends on the law of Conservation of Momentum to operate. So what the heck is it anyway? It's a pump. It requires a constant flow of water into it - with a head of at least 3 feet. For this input, you will get a constant supply of water pumped to a height of up to 30 feet at about 1/10th the flow rate of the input water source. They are reliable. My pump typically operates 24/7 for the entire summer. They require no outside power source other than a supply of water at least 3 feet above the pump. The water supply can be a spring, river, even a beaverdam can give you the 3 feet of head needed to drive the pump. They work 24/7 and are ideal where electric power is not available and a low-cost solution is needed. Ram pumps are an old though not-quite-ancient invention. Invented in Europe in the late 1700's, they were fairly popular until the widespread use of electricity and specifically electric pumps hampered their value-proposition considerably. In my case, I have a small artesian well that produces between 3 - 10 gallons per minute year round. Unfortunately, this spring is 30 or so feet down a ravine and thus at a lower elevation than the garden and trees I need to water. After some research, I discovered the Ram Pump. I pieced one together with various off-the-shelf plumbing parts (only one part requires moderate modification). I now have a pump which delivers about 500 gallons of water per day to a height of about 40 feet above the source. I store this water in a 1000 gallon tank and use battery-operated irrigation timers to drip irrigate several hundred trees and shrubs as well as the garden. It made a tough job easy.

How does it work? It's not easy to explain in words. Essentially, the water which is driving the pump is allowed to build up speed while spilling out of a special valve on the pump. Within a second, the flow is moving fast enough that it lifts the valve and effectively shuts off this exit. Now you have a moving column of water that has just been brought to a standstill. The kinetic energy of this moving water column is enough to overcome the higher static water pressure on the delivery side and so a little squirt of water makes it out the delivery pipe at a higher elevation. The entire column of water (the supply and delivery sides) is now at a standstill and soon realizes that it should be actually heading up the supply pipe because it has less head pressure than the delivery side of the pump. So, the entire water column starts moving towards the source when the check valve which seperates the supply and delivery sides closes behind him. Since he is still moving, this inertia creates a small suction on the waste valve which causes it to open. Now the water realizes that it shouldn't be heading uphill into the supply pipe - it should be heading downhill towards the open waste valve. The cycle now starts again. Relentlessly, ram pumps continuously cycle, each time sending a small pulse of water up the delivery pipe to a higher elevation. Because this is happening 24/7, even a small flow can add up. I get about 1.8 litres per minute out of my delivery pipe - which is about 500 gallons per day!!! Not bad for a very small investment in time and money!