Circuit Schematic Info Library Construire Desulfator
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Earth
er Letters
Spreading the Word
A little over a year ago, I was asked to offer a community education class on Alternative Energy. We had done many tours of our home over the past eight years for local schools, but nothing for the adults in the community. I thought this would be a good opportunity for people who had heard about our home to see it and learn about the technology. I put together a Microsoft PowerPoint presentation that was a photo tour of our home and a general presentation on alternative energy technology.
I'm not sure what my expectations were for attendance at that class, but eight very interested people came to hear about alternative energy. Since I had put the effort into the presentation, I called another community education program in the area to see if I could offer the same presentation to a different community. The reaction has been incredible. My second and third presentations were completely filled just days after the classes were offered. In fact, the interest was so strong that people who were denied registration because the class was full, came anyway.
I was somewhat shocked at the interest level, and started the class by asking why people came. The responses varied from general interest in renewable energy to contractors looking at building more efficient homes to people who had already decided to build off the grid. Lots of people are very interested in hearing from someone living off the grid. The community education classes have been a great way to spread the word! Tom Markman, Avon, Minnesota
Energy Star Problems
Dear Editors, I agree with Joe Schwartz's refrigerator suggestions in HP88, page 131, in response to Pete Gruendeman's letter "12, 24, or 48?" But there are a few problems with the Energy Star program that should be considered.
First, the Energy Star program excludes all manual defrost refrigerators. Only automatic defrost appliances are rated, although they generally waste more energy than the manual defrost types. Anyone looking for the most efficient refrigerator by referencing the Energy Star Web site would be left seriously uninformed.
Second, the scoring parameters and classifications used for appliances are sometimes influenced by mainstream manufacturers, to the exclusion of niche builders. Staber clothes washers come to mind. As the only top-loading horizontal axis washer, Staber doesn't neatly fit any of the industry classifications, and gets compared to what it ain't.
Third, dishwashers are tested only with a load of clean dishes. This measurement decision distorts results in favor of washers equipped with dirt sensors. These types are programmed to adjust their cycle times according to need. If you make the silly mistake of introducing dirty dishes into your washer, sensor-equipped machines will ratchet up to use as much water as dumber machines, which always run full throttle, even during "clean dish" tests. The placards for comparing energy use that you see in appliance showrooms falsely penalize some equipment based on this imaginary difference.
Fourth, I have heard numerous reports of inaccuracies in the energy consumption figures quoted on the yellow placards attached to all new appliances in showrooms. I don't know who, if anybody, audits these numbers, which probably are unsupported manufacturer's claims.
On a related topic, Consumer Reports magazine never seems interested in testing the super-efficient appliances available direct from niche manufacturers. They will only report on merchandise available in large retail chain stores. These mall stores will not be carrying the sort of stuff advertised in Home Power magazine any time soon. Kind of puts a new spin on the word "consumer," eh? Joel Chinkes
Payback on RE
Dear Home Power, I was disturbed after reading the article about professional wrenches and their responses to the question of system payback (HP87, page 44). I agree that the primary reason to purchase an RE system should be based on the environmental cost and not financial cost. However, it seems that the professionals who we rely on to give honest straightforward answers to our direct questions all appear to pride themselves on how they can turn the question of financial payback back on the customer.
Not a single representative response from this large group of professionals stated that they would answer the question about system payback, and then perhaps remind the customer of the more important reasons to use renewable energy. Shame on you all! Trying to twist the question back on the customer or attempting to shame or belittle them for asking about payback in the first place relegates you to the level of shifty, dirty-dealing, used car dealers. When I make a major purchase, I expect straight, honest answers to all my questions, not just the ones you think I will like the answers to. This is simply a matter of respect. Kurt Kiewal, College Station, Texas
Dear Kurt, The whole point of the article was to reframe the entire question of payback itself. And yes, most people are talking about monetary payback; as in "how much time has to pass before my investment in solar electricity will pay me back in avoided utility bills?"
I offer the following in the hope that you will better understand the inherent absurdity of trying to make a comparison like this. 1. The true cost of electricity is not reflected in your bill, not by a long shot. 2. Why ask the question of payback with solar electricity, when you don't question it with anything else? In my opinion, that is what the article was most urgently trying to say. You don't ask for payback for a car or a roof, or anything else for that matter, but you ask it of an investment in renewable energy. 3. Where you interpret a "twist of the question back on the customer or attempting to shame or belittle them for asking about payback," I see a genuine attempt to give customers who would ask such a question a reasonable context to their question. In other words, the question of payback for solar electricity is culturally influenced and not necessarily based in reason, or as I mentioned above, compared equally to utility rates. I hope this helps. Colin Mitchell, for Allan Sindelar, Positive Energy • allan@positiveenergysolar.com
Hi Kurt, I think there's definitely some validity to your point. I have also frequently been disturbed that we can't first answer the financial payback question before going on to the more important issues and clarifications. I agree 100 percent with Colin and many others that subsidized dirty energy makes the comparison wildly skewed. But we should recognize that many people asking the payback question don't know this, and are expecting a straight answer. They deserve a better explanation up front. It's too easy for people familiar with the question to skip over this essential step. The wrenches discussion we published came from a professionals' forum, where all share a grasp of the underlying issues.
I also am getting tired of hearing the couch and car analogies. People contemplating buying a couch are not looking to save money—they are looking for household comfort. People who ask the payback question are looking to save money on their energy bills—that's why they ask! It's the same as someone asking about the payback on investing in a more efficient furnace—they want to know when their savings will outweigh their investment. My normal answer to these folks is that if their only interest in RE is to save money and they are on-grid, forget it. Then I go on to talk about energy efficiency, and explain why comparing RE to subsidized dirty energy is not fair. Regards, Ian Woofenden • ian.woofenden@homepower.com
More Payback on RE
I am new to your magazine and was disturbed by the attitude of your respondents in the article "Payback on RE? How Wrenches Respond." When I engage an industry professional about any complex technical problem, I would expect them to be able to detail the cost advantages of one system over another. How the experts explain the solution, including the cost benefit, is important in determining if I want to hire them for a project as large as powering my home.
I was confounded by the response you got from Larry Elliot of kattel.org. Especially since he is apparently the director of an educational organization. If answering a legitimate question about the cost benefit of a solar energy system is pandering, I don't want anything to do with Kattel or any of its graduates. Kent Morris, Bellevue, Washington
Hello Kent, I believe you misunderstood my position on PV payback. As a new reader, I can understand why. First of all you, must understand that in pure economic terms, there really is no payback for PV. Most utility electricity is so cheap that on a cost per KWH basis, you're not going to save money.
Payback? Is that in my lifetime or my great-grandchildren's? In present or future inflated dollars? What will weather trends be in ten years? Is that before or after all oil wells run dry? Statistically, will utility outages become more or less frequent in the future and to what percent? If you can first establish a concrete set of ground rules, perhaps we could make a feeble attempt at quantifying payback. Better odds are on turning lead to gold or making water run uphill.
When I said "to hell with pandering" it was a reflection of my intense frustration with dealing with certain customer questions for close to twenty years. Two guesses as to what those questions have been. Even though PV produces electricity just like what you get from a utility, the similarity simply ends there. Thus my comment of"compared to what?" When was the last time someone calculated the payback on cruise control or leather seats? Better yet how about a hot tub or swimming pool?
My goal is to educate people about RE technologies. Most people require many hours of intense question and answer before they can become satisfied customers. I feel that if I must spend any additional time on payback issues, the person really is not a good prospect for becoming a customer. Obviously, they don't see any value beyond dollars.
If I was paid simply for my customer education time, I would now be retired and living comfortably. I have never lost a customer because I refused to pander. Hope this has cleared up a misconception. Larry Elliott larry@energyoutfitters.com
RFI Problem
Dear Home Power, I have noticed that since we installed our Trace DR2424 inverter, the interference on AM radio stations has been bad enough to prevent listening to them. This is not a serious problem, but it does bring up further questions. Recently our neighbor who has a similar inverter started investigating the source of these high frequency radio waves, and found that they emanated not only from the inverter, but also from all the DC wiring of the system, all the way out to his solar-electric panels. Do all inverters produce this radio interference? Since inverters are often located in the house, is there any possible health hazard to be considered? Thanks in advance for any light you can shed on this. Bob Kidwell, Michigan
Hello Bob, All inverters make some radio frequency interference (RFI), and so do most charge controllers. The RFI is actually transmitted by any wires attached to the device—the wiring acts as an antenna. While the RFI produced by inverters is intense enough to blitz AM radio reception, the signal level is far, far too weak to present any health hazard.
Your best bet for reducing the RFI in your AM radio is to locate the radio as far from the inverter as possible. Putting up a good outside AM radio antenna will also increase your received signal strength and help to override the RFI. I hope this helps. Richard Perez • richard.perez@homepower.com
Hot Water from Wind
Dear HP, I have a bee in my bonnet to build a domestic solar hot water system. I also want to add wind generation to the equation. A flat plate, closed loop, drainback system would be OK here in northeast Ohio, but in the winter, the "sun don't shine, but the wind sure blows." It seems that a solar storage tank with an electric heating element would round out the system—what are your thoughts?
Would the heating element actually work with infinitely variable, 240 volt "wild" AC output, say from 5 to 1,000 watts that a small wind generator might produce? Does anyone manufacture such an element? I'm an avid reader of your inspirational magazine. Keep up the good work! Steve Miller, Chardon, Ohio
Hi Steve, Using a wind generator in winter to heat hot water is a great thing to do. In fact, it is the most cost effective use of wind power, since there are no expenses for a controller, battery bank, or inverter.
I've used my grid intertied 3 KW Jacobs to heat hot water for a number of years. I used the water heater as a dump load when the grid went down. During such occurrences, with the Jake running hot and heavy, and a 50 gallon tank of cold water, the Jake could heat the water to the point that the pressure relief valve blew. In fact, this could happen four or five times a night during a good wind. Not that I'd recommend you do that!
You need to answer several questions. Do you plan to use the wind heated water only for potable domestic purposes? Or do you have plans to circulate the water for radiant heat as well? If the latter, note that most houses need extra heat when the wind is blowing the hardest in winter. This is because wind causes negative pressure in a house, increasing the infiltration rate. Again, there's a good correlation between the resource and the need for heat. If you're interested in this type of system, check out Tom Simko's system in HP36. Tom heats his home hydronically with wood and wind.
As far as the element that you'll need, I'd suggest using a standard 110 VAC heating element, rated at the same wattage as your wind genny. While three-phase elements are available, they are difficult to find, especially in such low wattages. To use the AC element, add a three-phase, full wave bridge rectifier to convert the three-phase wild AC wind genny electricity to DC. The heating element will do the rest, since resistive elements don't care if the energy is AC or DC. If you add a voltmeter and ammeter so you know what the wind genny is generating, you'll have all you need to heat your water. Mick Sagrillo, Sagrillo Power & Light, E3971 Bluebird Rd., Forestville, WI 54213 • Phone/Fax: 920-837-7523 • msagrillo@itol.com
Hi Steve. I'd like to add that you should try hard to not overheat your water heater. First, the pressure relief valve is designed as a backup for if a water heater temperature control fails. This wind application effectively bypasses the temperature control feature, causing reliance upon a backup as the primary and only method of preventing pressure build-up. If the valve fails to open, dangerous pressures could build up in your tank and plumbing system. Second, standard pressure relief valves are not designed for continuous duty. Once they release pressure, often they will not properly seal again, causing constant leakage. Michael Welch • michael.welch@homepower.com
Question about PVs
Hello Richard, Do solar-electric panels need a charge controller or blocking diode to keep them from causing battery drain when the sun is down? I was thinking yes; my neighbor says no—what's the truth? Thanks, Ron Hudson
Hello Ron, You are correct, PVs do need some type of device, either charge controller or diode, to prevent them from withdrawing energy from the battery overnight. The amount of energy that a PV takes from the battery at night is small and depends on the PV technology. Single crystal PVs will discharge the battery only a few milliamps, multicrystal PVs discharge in the range of tens of milliamps, while thin film PVs will discharge on the order of a hundred milliamps or more. These are small numbers, but hey, this energy is wasted, so use either a charge controller or a diode to prevent the battery from discharging into the PVs at night. Richard Perez • richard.perez@homepower.com
Solar Powered Travel Trailer
Hello! I discovered your magazine a while back. I have been inspired by it. I plan to build a solar home in about three years. Right now I want to either construct a livable building or install a travel trailer temporarily on the property. I plan to visit this shelter for about a week each quarter as I begin my experience with solar electricity, decide where I will build the house, start landscaping, and simply enjoy the property.
As I read articles in your magazine, I notice that dealing with batteries seems to be a murky, nasty issue. But I'd love to begin living with solar energy in this shelter. Tying to the grid is simple, since a utility line runs through the property. But the state is not yet a net metering state, and I have found no knowledge about net metering or renewable energy among the utility employees I've spoken with. So for now, I'd rather live off the grid.
Once I am set up with a solar powered system for this shelter, I'll be happy to spend time there. But what do I do with the batteries when it's time to leave for a few weeks? Is it possible to have an independent system I can turn off and on at will? Thanks for your great resource! Cordially, Claire Calhoun
Hey Claire, A properly designed and installed PV system requires virtually no maintenance. And PV systems are very commonly used in vacation cabins that aren't occupied full time. The PV panels charge batteries via a charge controller, which automatically regulates the batteries' state of charge
(how full they are), and keeps them from being overcharged. It's all automatic.
Flooded lead-acid batteries require watering about four times a year. They produce hydrogen gas when charging, which needs to be vented to the outside because it's flammable. Sealed batteries do not require watering, and do not produce hydrogen gas when charging. They are maintenance free, and a great choice for a small PV system. Joe Schwartz joe.schwartz@homepower. com
36 V Forklift Batteries
Greetings Home Power crew, Kudos for all the good work on RE. I have been a subscriber and RE wannabe for many years. I just got some acres and buildings up on a mountain, and I'm looking forward to putting to practical use all of the good info I have archived from HP over the years.
I have a source for new 36 volt replacement batteries for forklifts in the US$1,800 to US$2,500 range. Could these be used in an RE system? Would they last longer than golf cart type batteries? I know they are good for a lot of deep-cycle charges and recharges. Other than the weight and difficulty moving them, I would think they would be a great way to store a lot of energy. Are there inverters that will take 36 volts? Also, can you recharge a battery bank from a DC welder? My friend has a portable unit that puts out about 36 volts. Is there a charge controller that could be adapted for this purpose? Thanks for the help, and keep up the good work. Charles Evans • cevans9@tds.net
Hello Charles, Forklift batteries are deep cycle types, and well suited for use in RE systems. They will last longer than golf cart batteries. Exeltech makes inverters that will run in the 36 volt range. You can use a DC welder to recharge batteries. B.Z. Products makes a charge controller that will handle 36 V, and charge controllers are not difficult to homebrew.
Also, if the individual battery posts are accessible, consider configuring the forklift batteries as a 24 volt system rather than a 36 volt system. This will give you access to a much wider range of RE equipment. Richard Perez richard.perez@homepower.com
Is Biodiesel Really Green?
Dear Home Power, After looking into electric cars and propane conversions, I read about biodiesel in HP. I bought From the Fryer to the Fuel Tank by Joshua Tickell. I am in the last stage of shopping for a diesel VW. I have a couple of questions before I take the plunge, if you could help.
1. Is biodiesel really green? 2. I intend to purchase 500 gallons, the minimum delivery from Worldenergy.net for US$1.50 a gallon. Do you know if they are a good company? Will World Energy be here next year when I need more?
3. To burn 500 gallons a year, I will either have to buy a second diesel for my wife, run biodiesel in my home furnace, or both. I have been trying to buy a Chrysler Voyager minivan with a CRD Diesel (43 mpg) in Europe. They don't sell them in the U.S., but you can read about it on the Chrysler UK Web site. Do you know of a way I can get one in the U.S.? Thank you for any info you can give. Gordon Palmer Gordair2@aol.com
Hi Gordon, 1. Biodiesel is about as green as it gets for now. Each gallon made from vegetable oil has embodied energy at least 3.1 times the energy required for production. If it is made from recycled vegetable oil, the net energy yield is much higher. Fossil fuel based components of biodiesel are limited to about 20 percent methyl alcohol, made from natural gas, plus a minimal amount of energy required for processing. Make your own at home and there isn't even energy required for distribution.
2. World Energy Corp. is the largest manufacturer of biodiesel in the U. S. They converted several factories built by Proctor & Gamble that were originally intended to make Olestra, the nonfat fat. While this is still a small industry, it is growing at more than 100 percent per year, and with new subsidies from the government, it is likely to be more available in the future.
3. The EPA doesn't make it easy to import overseas vehicles. Look at their Web site at www.epa.gov for some ideas as to the restrictions. Search for"import cars" or similar topics. Tom Leue, Homestead, Inc. Tilapia@aol.com
Taming Wild Power
Greetings Richard, In two articles in HP86, the term "wild" is used to describe three-phase power produced by Whisper wind generators (schematics on pages 15 and 33). What does the term "wild" mean in relationship to three-phase power? As always, thanks for your help. Regards, Stan Strickland • stanncarol@juno.com
Hello Stan, "Wild" power is AC electricity where the frequency is not constant. Normal utility electricity is 60 Hz or 50 Hz depending on where you live. The frequency of the AC power produced by most wind generators is proportional to the propeller speed. The faster the prop spins, the higher the frequency of the AC power. The fact that the AC power is "wild"is not important since it is converted to DC for use in the system. Richard Perez • richard.perez@homepower.com
Bigger Plug-N-Play Guerrilla
I really enjoy your magazine. I was very interested in your many guerrilla solar articles about people supplying electricity back to the grid. I would love to do something along the same lines. After researching your magazine and other references, it seems that most people are using OK4U inverters, and only putting a 150 watt or so panel on them. I would like some info on a system with that much simplicity but maybe a little larger—say 300 to 600 watts. The cost of the OK4U and the two smaller panels required for the 24 volt system seems cost prohibitive for such a small gain.
I understand that people want to do what they can to contribute, but if there was a simple system with a little larger gain, I think it would catch on just as much. The larger panels are cheaper and readily available. I have heard about the OK5 inverter, but nothing since last fall. A recommendation of a simple 12 or 24 volt system in the 300 to 600 watt range would be greatly appreciated. I can even be more specific for my use. I have four, 120 watt panels that I would love to hook up to a cost effective inverter with the plug and play simplicity of the OK4U. Any suggestions? Thank you, Rick • B707PHX@aol.com
Hi Rick, A good inverter choice for this size system is Advanced Energy Incorporated's GC-1000. This is a batteryless, utility-interactive inverter and is not designed to provide backup during utility outages. The GC-1000 has a 48 VDC input, so you can work in four, 12 VDC nominal panel increments. Grid synchronized AC output is 120 VAC. The inverter includes integral DC series fusing and disconnects, ground-fault protection, and an AC output breaker. And you can add another four, 120 watt PVs down the road! Take it easy, Joe Schwartz joe.schwartz@homepower. com
Efficiency Rules
Dear Home Power, I've been following with interest the letters you've had on the philosophy behind big RE systems. I want to address the claim by one gentleman that a big, home PV system is doing "more to help the environment than a hundred families replacing lightbulbs with compact fluorescents." Not only is the claim wrong, it betrays a misunderstanding that a lot of folks still seem to share.
If a hundred families each replace three or four of their most-used lightbulbs with CFs, the drop in their collective load is on the order of 100 KWH per day. That's a lot more than even the fanciest rich man's PV system can provide (the biggest systems profiled in your magazine run 10-40 KWH per day). Total upfront cost of all those CF bulbs is around US$2,000, or less than a tenth the cost of any sizeable PV system.
I know Home Power often points out that efficient appliances are a better buy than RE systems—but it takes a specific example like this to make people realize just how much better. Don't invest in RE, people—until after you have all the load-side efficiency money can buy! Regards, Geoff Pritchard, Auckland, New Zealand.
Desulfator Notes
Greetings, After the article I wrote for HP77 describing a homebrew battery desulfator, I have been in contact with people around the world. The circuit has been a success on numerous small systems, and many kits of parts have been sent out. I have often been asked about what to do for larger systems, and now I have placed a design for a high power desulfator/maintainer on my Web site. It should answer the needs for all those wishing to reclaim monsters like submarine batteries, and to maintain large systems. Check out the latest at www.shaka.com/~kalepa/desulf.htm. Alastair Couper • kalepa@shaka.com
Wishing for Quiet Wind Genny
Hello Home Power, Today in Dallas, Texas, the wind is blowing a constant 30 mph. I wish I had a wind generating device on my house. I read once in your magazine that those propeller type wind generators make a lot of noise. That guy out in west Texas wrote that it sounded like a vacuum cleaner running. Can't they make a wind generator that works without so much noise? Why can't they use the design of the turbines on my roof to help keep my attic cool? Dale Crawford • dalelani@airmail.net
Hi Dale, If you want a very quiet wind generator, buy a low-speed machine, and check out any machine you are considering, since there are other factors that affect wind turbine noise. Low speed machines available today are the African Windpower machine, rebuilt Jacobs turbines, and the Proven. I don't have personal experience with the noise level of the Proven, but the other two are extremely quiet. These are all substantial and robust machines. If you buy a lightweight, high speed machine, you'll tend to get more noise and reduced longevity.
I don't advise putting any wind turbine on your roof. Noise and vibration will resonate in the structure, and it's not the best place to capture the wind. The standard rule of thumb is to install wind turbines 30 feet higher than anything within 300 feet. Siting a turbine lower than this will decrease output dramatically, and the turbine will have to deal with lots of turbulence, which is hard on it. Regards, Ian Woofenden ian.woofenden@homepower.com
Laptop Puzzler Comment
In HP88, Q&A, on pg 139, right hand column, Dan Bisbee asks about laptop charging. Some laptop chargers limit charge on the basis of time. Dan may have such a unit. His mod-square peak output voltage is lower than a sine wave inverter's, which would result in lower overall charge into the laptop battery in the allotted timeframe. This issue is avoided with a true sine waveform.
This possibility is further bolstered by Dan's mention of a five minute charge cycle on the modified square wave inverter vs. one hour on the grid. My $.02 worth. Regards from rainy Fort Worth. Dan
Laptop Power
Richard et al, I have scanned previous issues for guidance on powering my laptop directly from my home battery bank. My Tecra 8000 draws 3 amps at 15 volts coming in from the 120 volt adapter, yet my laptop battery is only 10.5 volts. I suspect there must be a stepdown voltage regulator in the laptop to give a stable 10.5 V from the 15 V supplied.
I have seen two HP articles on buck converters, one that is just the LM and a few resistors running at 52 kHz (considered an inefficient voltage waster), and another that uses an inductor and runs near 220 kHz. (I also read the great article on your travel pack for the Mac, Richard.) What are the constraints on using one of these linear converters for running a PC laptop directly through the laptop battery connection and skipping the 15 volt feed in from the 120 VAC converter? I suspect the frequency the buck converter runs at would have some effect on the laptop processor innards. Can I do this? Will I fry the innards? Thanks for your computing thoughts. Jim Marquardt, St. Paul, MN marqu009@tc.umn.edu
Hello Jim. Most laptop manufacturers offer a 12 VDC car cord for their computers. These power supplies are the way to go if you have 12 VDC nominal available. Since they are designed specifically for that particular computer, there is no problem with noise or voltage parameters.
In terms of aftermarket car cords, I can highly recommend those made by Lind Electronics at www.lindelectronics.com. These are high efficiency switching power supplies that accept very high voltages (over 24 VDC) on their input. This allows the laptop to be operated and recharged from a full-sized PV module if you are in the field. Richard Perez richard.perez@homepower.com
EVA Disease
I have some old Arco Tri-lams (I believe that's what they were called) with three rows of twelve, square cells per panel. Carrizo Solar Corp. is printed on the back of them. I heard that they were used/salvaged and pulled from some utility test project. I understand that they had a Fresnel lens focused on each cell. They are badly solarized and have a brown color except for a very thin margin around each cell that is still blue. The open circuit voltage on these panels is 6.7 volts, which I think is normal. But the short circuit current is only 666 mA. As I recall, when they were sold to me, they were supposed to only have lost 10 percent of their capacity due to the baking that they had received.
I am wondering if anyone knows about these panels. Since they all have this same failure mode, I am wondering what the problem is. Is it the cells themselves or the glass or plastic covering them, or is it the interconnects that connect them together? If it's the cells themselves, what happened to them? And finally, are the entire panels, or at least some of the cells within them, salvageable for small projects? Thanks, Clyde Feral • wobblie@skyhighway.com
Hello Clyde, Your Tri-lams have what is know as EVA (Ethyl Vinyl Acetate) Disease. The EVA is used as a backing pottant to the cells. Over time, it out-gases acetic acid and corrodes the metalization on the cells' surfaces (both metal electrical traces and the metallic anti-reflective coating). Alas, EVA Disease is fatal, as you have discovered. The metallic traces lose electrical connection with the cells' substrates. These modules should put out more than 4 amperes at short circuit. With only 666 mA output for your cells, they are effectively dead.
These modules were originally made by Arco Solar, and used in PG&E's Carrizo Plains generating plant. The facility did not use Fresnel lens concentrators, but did use reflectors on each side of the modules to increase the light on the modules. Upon this plant's closing, these modules were bought secondhand by Carrizo Solar. Richard Perez richard.perez@homepower.com
Alternator Question
I have just set up a Trace SW4024 using six Group 27 Costco batteries. It works great, and the batteries are being charged from a 120 volt AC hydro generator. When water is scarce this summer, I hope to convert the source power to a Chrysler type, 12 volt alternator, driven by a 5 inch diameter cast iron Pelton wheel. I have been testing it with an electric motor, and can get 30 amps at 30 volts through a portion of dryer heating coil with no apparent alternator overheating. However, to get this 900 watts, I am using 4.3 amps through the field winding at almost full 12 volts from a battery. I have found no information on the characteristics of alternator field coils. Will the alternator field be able to handle this current on a continuous basis? Do you know of any sources of alternator information? Thanks, Jim Peterson
Hello Jim, Automotive alternators are incredibly rugged. They are designed to work under the hood of a car during the summer with a hot engine. You can run up to about 5 amps through the field without damaging the alternator. The worst thing that will happen is short brush life. The Internet is full of alternator info, but unfortunately, nothing applies to your unique operation situation. Richard Perez richard.perez@homepower.com
Amps & Watts per Hour
Hi Ian, I just received my HP88, and was glad to see an explanation for the correct use of amp-hours and watt-hours. As you would expect, however, someone has to find a "flaw." This time it's me! It's nothing serious, but it does provide a certain amount of entertainment when watching folks do the mental gymnastics.
Amps per hour and watts per hour do exist. I admit, however, that I've never had the opportunity to work with them. They are simply the electrical analogy of acceleration. As an example, watts per hour is a description of the rate of change of power. If power at time 0 is 1 watt and at time 0 + 1 hour it's 2 watts, the average rate of change of power was 1 watt per hour. I wonder if there's any techno-discipline that actually uses these units! Regards, Alain Chuzel, SunCat Solar • ahmchuzel@aol.com
Hi Alain, Thanks for your message. This text was cut from the first draft of my column: "(OK, you nitpickers, there is one instance I can think of where "watts per hour" and "amps per hour" could be used. If we were talking about the rate of increase of the output of a PV array as the sun came up and grew in intensity, we could conceivably (it's a stretch) say that the output increased by X watts per hour or X amps per hour.)"
So I agree with you, but I decided this was so unreal that it isn't real. I have never heard these terms used in this (correct) way. Every time I've heard or read these terms, the speakers have either meant amps or watts, or amp-hours or watt-hours. I just did a "Google" search on the net, and found hundreds of hits for these terms. So far, I've only found one that seems to be referencing acceleration. The rest are misuses (mostly), and folks trying to correct the misusage. A surprising number of the misuses are perpetrated by RE companies, which is frustrating. Thanks for your help and encouragement. The point of all this is to help people understand electricity better, and these misused terms make it harder. Regards, Ian Woofenden ian.woofenden@homepower.com
Speedometer; Odometer
Ian, Thanks for your column on "Watts Per Hour" in the April/May Home Power. I've spotted "hour" confusion in such varied magazines as Scientific American, E magazine, and Dr. Dobb's Journal. Perhaps HP could run a "watt-spotting" contest. Points could be awarded based on circulation—an error in the New York Times would bring more points than one in Podunk Times.
When I show people the meter on my PV system, I sometimes skip the units and say "This is like the speedometer and this is like the odometer." This seems to help, though I'm not sure how to carry the concept into general usage.
Maybe a new name would help—if we anagrammed "watt-hr" to "thwart," then a watt is a "thwart per hour" or tph. Electric bills would then be measures in "kilothwarts", or "kt" for short. Cheers, Mike Morton • mike@mikemorton.com
Hi Mike, Thanks for your comments. The names are certainly not intuitive, and I don't know what the answer is, beyond continued education. I especially like your speedometer/odometer (watt-meter/watt-hour-meter) comparison. This is a very helpful image, and I plan to use it regularly. Thanks, Ian Woofenden ian.woofenden@homepower.com
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