I get questions from people who build experimental (or not experimental) solar devices, and would like to measure their performance. Measuring performance can be very helpful to see if the device is working well, and/or to measure the benefits of design changes.
So, here are some simple ways that I use to measure stuff. Since most of us do not have the test budget of a GE or Boeing, the emphasis is on cheap ways to get good data.
There are probably better, easier, and cheaper ways to do all of this, so if you know of any lets hear about them! Gary.
Since most of my work is in the solar thermal area, there is not much (nothing in fact) on measurements for PV systems, wind generators, or the like. If you have some experience in these areas and would like to pass along some tips, techniques, or advice -- please do. |
Directory to this Measurements page:
Air Flow measurements
Temperature measurements
Water Flow measurements
Pressure measurements
Power measurements
Light intensity measurements
Force measurements
Some sample test setups
Measuring collector performance
Air Flow Measurements | |
Dwyer $25 Vane
Air Velocity Meter
http://www.dwyer-inst.com/
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Micro Turbine
Wind Meters www.nkhome.com/ww/wwindex.html Other suppliers make similar meters -- a search under "Wind Meters" will turn some up.
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I have used the one in the picture for several years and think it works quite well. There are several brands and many models. This model is about $80. They also come in models that include other sensors for temperature, humidity, altitude, ... I think that some now even offer some form of logging. |
Garbage Bag
Airflow Measurements Evaluation of Flow Capture Techniques for Measuring HVAC Grille Airflow Or, how to use garbage bags and laundry baskets to measure airflow Lawrence Berkeley National Laboratory Full How-To Report (pdf) More on Same (pdf) |
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This is a great and practical piece on how to measure airflows accurately using timed filling of garbage bags, or simple pressure difference across a flow resistance, where the pressure difference is generated with a simple laundry basket. |
Adventures in Measuring Airflow for a Solar Collector... |
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Temperature Measurements | |
Ordinary
Thermometers
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![]() When you buy the thermometers, try to select ones from the bin that read the same temperature. In most cases, you will be interested in the difference between the readings on two thermometers, so the absolute accuracy is not usually critical, but having thermometers that are all off by the same amount helps. When you place them, try to get the bulb into the air stream you are measuring, and keep them out of direct sun (this may require a shade of some type). For most projects, you will get better results if you take and record several readings over a time span. If more accurate measurements are needed, the thermometers can be calibrated as described below. Every once in a while, bring them all together and see if they read the same temperature -- throw away any that don't. Here is what happens when plastic thermometers get a bit too warm :) |
Better thermometers
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This is the Hanna Checktemp. It is thermistor based with a stainless proble that can be inserted in air or liquid. It maintains an accuracy of +- 0.5F over its -58F to +302F range. It comes with a calibration certificate and it has a built in calibration test you can run any time. About $25. |
Thermistors
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Picture of logger with
thermistor above, and
If you decide to invest in a data logger, the loggers that use thermistor sensors tend to be among the most affordable. The picture shows a thermistor sensor enclosed in a stainless steel can, and connected to a cable that is plugged into a data logger. |
Thermocouples
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IR Thermometers |
![]() IR thermometers measure surface temperature by measuring the IR radiation emitted from the surface. About $50. You can use them for measuring surface temperatures in solar thermal experiments, and also to see if your tires are overheating, or your beef stew is up to temperature -- no household should be without one. They are often the easiest way to measure surface temperatures. Some caution must be used, in that they assume that the IR emissivity of the the surface is 0.95. Many surfaces are close to this, but some surfaces (e.g. polished metals) are much less. In some cases this ambiguity can be removed by putting a piece of dark colored tape on the surface, and doing the measurement on the tape. You can get air temperature by waving a sheet of paper around in the air, and then measuring the paper surface temperature with the IR thermometer. I have a little matchbook size one that I carry around some of the time -- they are great for getting a better understanding of the thermal physics of the world around us. The matchbook size model costs $25.. |
Thermal Imaging Cameras |
![]() They have been almost prohibitively expense, but over the last few years have come down a lot as some entry level lines have been introduced with lower prices that have been steadily dropping. The lowest priced ones are now a bit over $1000 -- still a lot, but much better than $10,000. I recently took the plunge and got a FLIR IR camera. My impressions of the FLIR so far are here... |
Instead of the array of sensors that most thermal imagers use, it uses a single IR sensor that is scanned over the target object, then an image is put together from the set of readings taken during the scan. The upside is the price and the downside is the time it takes to scan an image (about 6 minutes?). Pretty clever. |
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Water Flow Measurements | |
Timed Filling of
A Bucket Gary |
![]() In the picture, there is a submersible pump in the bucket that pumps water around the collector, and back into the bucket via the line with the flow control clamp on it. To measure flow, the line going back into the bucket is redirected to the 2 qt measuring bowl in the background, and the fill time measured. |
Using the DLJ Water Meter for Flow Measurement
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$5 DIY Flow Meter Gary
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Some Commercial Flow Meter Possibilities
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Pressure Measurements | |
Water Manometer
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A water manometer can be used to
measure pressure differences in inches of water. A manometer can be easily
made from transparent plastic tubing bent into a U shape. The
height of the U should b a bit greater than the maximum pressure
differential you will want to measure. To use
it:
Ordinary ink pen ink can be used to dye the water. Adding a little bit of detergent prevents breaking up of the water column.
Accuracy is excellent, and cost is near zero. |
Dwyer Magnehelic
Differential Pressure Gage
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Power Measurements | |
Kill-A-Watt
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The claimed accuracy is 0.2, which is amazing. If you bought the equivalent of this as a "lab instrument", it would probably cost a thousand dollars. www.NewEgg.com often has them for about $20. |
The Electric Clock Method |
The picture shows using an electric timer to record how many hours my water heater runs each day by powering the timer from the fan that runs whenever the burner flue exhaust fan is on (which runs only when the burner is on). |
Using your house
electric meter to estimate power used by a load http://staff.washington.edu/corey/power.html And, reading your electric and gas meters
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![]() The 2nd link tells you how to read the totals on your electric and gas meters. |
Reading your gas meter... | ![]() |
Power Cost Monitor http://www.save-electricity.ca/display.html
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![]() The idea being that getting instant feedback when you turn on lights, appliances, ... will help you cut down on electricity use. Kind of like driving a Prius and seeing what your current mpg is all the time. |
Solar Intensity | |
Apogee
Pyranometer
http://www.apogee-inst.com/pyr_spec.htm
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![]() Shown here set up to determine if the corrugations on SunTuf glazing reduce its transmission Details ... |
Measuring
Sunlight at Earth's Surface: Build Your Own Pyranometer, David Brooks www.instesre.org/construction/pyranometer/pyranometer.htm Update: I built one of these kits and tested it against my Apogee Pyranometer for recording solar radiation during collector tests....
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![]() Material on how to order and assemble a $20 pyranometer kit. |
Measuring Solar
Radiation -- A Cheap Solar Radiation Meter http://chuck-wright.com/projects/pv-measure.html
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![]() From Chuck Wright's website -- other interesting solar projects, and renewable energy project data logging systems: http://chuck-wright.com/projects.html |
Micro Circuit
labs Solar Meter and Logger
http://www.microcircuitlabs.com/index.htm
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![]() Battery powered logger has a silicon photodiode as the sensor, and will log up to 16K sun measurements over up to 170 days. Said to have 5% accuracy. Price -- $70 to $150. |
Onset Pendant
Light Meter
(search their site for "Pendant" if you have trouble finding them) |
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Motor On Time | |
Logging Motor On Tim |
This Onset motor on/off monitor is the one I use -- I'm sure there are others. It is very easy to use -- just tape it to the side of the motor. Price of this one is $79 + software. Lots of uses -- some examples ... |
Force | |
"Fish" Scale |
![]() Inexpensive digital versions of "fish" or "game" scales are now available. The one I have is reliable and accurate. |
Gravity and
pulleys
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The weighted bucket applies a known force to the edge of the heliostat
via the rope over a pulley.
Not very elegant, but it works!
Used to estimate the heliostat beam displacement for high wind conditions.
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Data Loggers Data loggers allow you to record temperatures, voltages, events, ... at regular intervals. The interval can typically range from once a second or less to hours, and the time period over which data is logged can be minutes to months. Values recorded by the logger are typically transferred to a computer for processing or plotting. Data loggers are typically NOT required for most solar thermal experiments -- you can get equally good results by just manually reading and recording sensor values -- the loggers just make life easier. |
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Onset Computer
Data Loggers
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More... I mention this specific brand, because it is the one have used, and have experience with -- I am sure there are other very capable loggers out there. |
Home made
temperature logger from AnotherURL.com www.anotherurl.com/therm/logger.htm
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![]() There are other versions of loggers that make use of the "One Wire" sensors. Try a google for the latest. |
Measuring Energy
Usage for Inverter & Battery Bank Sizing Mark Patton www.HomePower.comSearch HP archives for issue 76
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![]() This is a year 2000 article, so some of the hardware may be a bit out of date, but the techniques are still applicable. |
1-Wire HVAC Monitoring
System for a Residential Geothermal System The system logs many sensors and provides real-time and historic data over the internet.
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![]() Phil sells kits for the logger main board, and for some of the sensors. He also provides the software, including source code (so you can customize if you wish). Our Cool House is Phil and Lisa's very interesting, passive solar, earth sheltered, geothermal house -- their website provides lots of good information on the design an building of their house. Its in our "I Did It" homes section. |
myDTC
controller/logger www.mydtcstore.com/ |
![]() One of the sensors offered is a solar radiation sensor, which can also be logged. |
Some Sample Measurement Setups Here are a few sample test setups that I had some pictures for. This is not rocket science -- one of the nice things about Solar Thermal is that you can do good work with simple test setups. Here are some simple examples that might be helpful to folks who have not done much of this stuff. |
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A Test Solar
Water Collector
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Some Additional ones: |
Some Additional ones: Grey Water Heat Exchanger In A Barrel Temperature Stratification i Tall Room Combined Collector and Thermal Shade |
Measuring Collector Performance | |
How to measure: - Collector Heat Output
- Collector Efficiency
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A very rough way to estimate collector efficiency. A list of common collector design misconceptions. More... |