Help with Solar system sizing

Discussion in 'General Technical Questions and Answers' started by K2POP, Jan 18, 2012.

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  1. K2POP

    K2POP Ham Member QRZ Page

    I want to build a small solar system to power my FT-897D radio (22A at 100W transmit) and a few other small things. I am using 25A as my max. load. Just receiving, my load is probably 3A or less. Max. usage is about 3 hours per day – mostly listening. How many watts of solar panels do I need and how many Amp Hours of battery capacity do I need? What size controller and wire do I need?

    Does anyone know how to calculate the answers to these questions? I have found quite a few solar sizing calculators on the internet, but the results they generate vary greatly. I would think there are some good rules of thumb for this – solar power for a 100w transceiver. Any suggestions?

    73, Richard
  2. KA9VQF

    KA9VQF Ham Member QRZ Page

    Hummm,…. How many planets do you plan to have in your solar system?
  3. NN4RH

    NN4RH Subscriber QRZ Page

    First, the smart-ass answer: You really should ask this in the Astronomy Forum.

    Now the real answer: Get ahold of the February issue of QST.
  4. K1CD

    K1CD Ham Member QRZ Page

    last time I offered anything on a query like this, I found that direct advice was not what folks here wanted to discuss. That was disappointing. -- seems the case here, too.

    See 1 to 10 kWh battery systems – rules of thumb for some ideas that might help.

    3A at 12v is 36 watts. 3 hr per day means about 100 watt hours per day. With a 3 day reserve, that's about a 300 usable watt hour battery. The 25A or 300 watt transmit pull is a consideration primarily as peak load but probably insignificant as far as energy storage in the context you describe.

    300 watt hours implies about a 30# battery. That means that even a couple of the gel cells you find in UPS devices will do although a small car or RV battery would probably be cheaper.

    A 100 watt hour solar harvest per day implies a solar panel of about 50 watts. You can find 30 cell solar panels of this size intended for direct connection to lead acid batteries as trickle chargers (30 cells peaks at 15v). More common is the 36 cell 18v panel and that would need a charge controller.

    One of the biggest problems is going to be battery maintenance. Lead acid batteries need some activity to stay healthy. When not in use, they need a full charge that doesn't overdo it and they need a sulfation inhibiting technique applied. I am using a charge controller by BatteryMINDer(tm) that wasn't that expensive (~$90), handled 100 watts, and uses their pulse charge battery maintenance technique. I also have a 20A battery charger I can use now and then to help with the activity level.

    As for wire size, 10g is usually good for up to 30 amps if the run is rather short. Look at the power cable that comes with your rig as an example.

    The articles in the February QST on this topic were rather disappointing as they repeated some old myths and didn't really offer anything useful in practical terms. There is so much bad and misleading advice and information out there on this topic you do need to be careful. Read critically and think through the implications and context carefully.
  5. KU7PDX

    KU7PDX Ham Member QRZ Page

    Hey Richard,

    If you're receiving 90% of the time (10% transmitting), in a 3 hour span you would consume roughly 128 watt hours in a typical day (receive is @ 1 amp, transmit is @ 22 amps on the FT-897D; 1 amp for 2.7 hours is 2.7 amps, 22 amps for 0.3 hours is 6.6 amps). With this in mind, I would recommend starting with a very basic solar setup.

    For the battery, I would use something around a 20 to 30 amp hour sealed lead-acid battery (like this). To size a solar panel, you'll want to consider the average number of hours of sunlight you have available and the size of the battery (in watt hours). A 180 watt solar panel could charge up a 26 amp battery in roughly 2 hours. Something like this would work...

    The last (very important) thing you'll need is a solar charge controller. It's job is to keep you from cooking your batteries once they're full. I definitely recommend the CirKits SCC3. It's a fun kit to build and it even adjusts the voltage based on temperature. Just set it to turn the green light on at 13.85 volts and you'll never cook the battery.

    For a 24 amp load, be sure to use 8 AWG wiring (based on this chart) and don't forget the fuses (something like a RIGRunner 4005)!

    Hopefully this gives you a good start for a very basic solar setup!
  6. KE3WD

    KE3WD Ham Member QRZ Page

    Sizing the solar system?

    Lessee, the Sun is aprox. 80,000 times the diameter of the Earth...
  7. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    There has to be at least 50 web sites dedicated to solar energy calculations, replete with plug in formulas—including average and peak loads, array size, Lat-Long adjustments, solar-days adjustments, and a few more so esoteric, even electrical engineers will be confused. Based on this, I suspect the vast majority of amateur radio operators mis-enter the requisite data. This includes your estimates—they're way low!

    Just like you, I thought joining the Green Crowd might be a good thing. So, I did a bit of reading, and in the end, I was more confused than I was when I started. That was because I didn't understand the real parameters. So, I contacted someone I knew. He owns three commercial radio sites (cellphone, repeaters, etc.) which all rely on solar power. I got a real rude awakening! It turns out, that a decent system that one can rely on to provide a decent operating time (we are talking about emergencies too, aren't we?), cost many more dollars than most amateur operators are willing to spend. Digressing....

    A solar powered station is a whole lot more than just a storage battery or two, a solar panel(s) of some sort, a regulator, wiring, fusing, mounting hardware, and a few miscellaneous parts. Just one or two of these devices is not enough!

    With his help, I set about getting to the bottom line of what was needed if I used my IC-7600 for just 4 hours per day—a very low estimate in an emergency situation (I selected 12 hours without Sun which is about average for my Lat-Long). I wanted to make sure that the voltage supplied to the transceiver was within its IMD specs, which meant I'd needed a battery booster. And, although I live in Roswell, NM where the sun shines a lot in the Summer, that's not the case in the Fall, and Winter months. That obviously changed the formula. As I got deeper into the subject, things started to get really expensive!

    The end result was, I needed nearly $4,000 worth of solar panels, $1,500 worth of batteries, an expensive regulator, wiring, battery house(ing), and a host of other hardware. Total cost? Just over $9,400! I therefore decided, that my mobile installation was much more economical, even with $4 per gallon gasoline!
  8. K2POP

    K2POP Ham Member QRZ Page

    Thank you to those who offered thoughtful answers. Like K0BG, the more I read about Solar PowerSystems the the more confused I get. Getting a generator would be easier and maybe cheaper. Nevertheless, thanks for the recommendations.

    Does anyone know of any good websites, computer programs, books, etc. that might be of help to me? Aside from the "garbage in" problem, all this stuff should be pretty straight forward math - if you know how to do it. It should be pretty easy for a computer program to do it - I would think. Like K1CD, I found the February QST articles interesting, but disappointing in terms of useful information. The ARRL book, Emergency Power, is similar. It contains a lot of interesting information - but never really pulls it all together in a user friendly manner.

    I am still open for helpful suggestions.

    Thanks, Richard
  9. KK4EDU

    KK4EDU Ham Member QRZ Page

    Richard, you are on your way and have gotten some good pointers. As you are finding out, there is quite a bit of detail and its not a small project. My post in the Tech Forum got some good pointers from others also but the most helpful things was finding someone local that has actually pulled something together. If you can find someone local, it helps. I was able to look at sites and information with my friend's help, which helped me make choices. The issue is really not your radio, whose power draw is not substantial. The issue is sizing a decent solar photovoltaic system with the right storage that can handle your radio or perhaps a few other things -- a little oversizing will prove handy. So when I sized mine, I did the calculations for a radio, but the radio turned out NOT to be the driver. It was other things. Long and short of it: if you have a decent sized panel (they can range from 100W to 300W), that will feed a storage battery, which is your power source for anything you conceive of. I oversized my system for one 245 watt panel and one AGM battery (decent sun will charge it in one average day). But that runs a small freezer for a few hours a day (to act as a refrigerator in power-out longer emergencies) to other things that, combined, might run about the same power. Or, I could substitute a laptop (running via the inverter), a few phones, and a few LED lights. So if you choose a single average decent sized panel and an appropriate AGM with someone helping you size them, then the other things get added: a good charge controller (keeps the battery healthy and tells you about it with a display of some sort), a few switches/disconnects, a few fuses (sized for where and what they do to protect equipment or you), disconnects, and some sort of 12V dc-out rig (I am using a rigrunner). But I can tell you, that what I know, which was limited, needed the assistance of that friend who new solar....and could cut through all the too-much-information that is everywhere on the web. Even with his help and my getting started, its been several hours together and several hours separately...and we have a ways to go. In the end, your radio will get powered, but as I said, it probably will not be the driver for system design, unless you really transmit a lot constantly, which is doubtful. You mentioned a generator. Yes, in most cases they are cheaper. The issue is what you are trying to do. We do disaster assistance (comm is just a part) and we were in parts of the Katrina thing -- where gas could not be gotten easily without driving 100 miles during the first two weeks following the eye crossing the coast. But if you are not concerned about such things and you just want power without the grid, a generator IS an easier solution.
  10. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Richard. These guys have been in business for decades, have a real store front and sell both locally and on line. I used them for reference when bidding some jobs a number of years ago. I think you can find reliable information and see what products are actually used.

  11. K7JEM

    K7JEM Ham Member QRZ Page

    If someone told you that, they were leading you astray. A solar power system to run a single HF radio wouldn't cost anywhere near that amount. Five 100 watt panels would probably be enough, and the batteries would have to be able to last through how ever many dark days you would estimate. You might be able to put a whole system together for 2K or so. If you had someone design and install it, that might go to $5K.

    What many people do is have a solar system that can also be charged with a small generator in times of low panel output, which can save money on batteries and panels, too.

  12. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    I agree with you about the cost Joe, but I didn't go out and see just how low ball I could go. The prices were list, and the duty cycle was set at 50% for no less than 24 hours of dark time, and that the battery voltage would still be above the 10.5 volt level under load at the end.

    There is a solar panel, inverter unit on the market that sells for just under $800 including a 20 Ah Li-ion battery. It certainly will run a 100 watt transceiver, and it might be okay for a light duty emergency. However, I wouldn't rely on it to complete a Field Day exercise, no matter the solar days index at the time.

    I think you have to be guarded when wishing for champagne, on a beer budget.
  13. KD0CAC

    KD0CAC Ham Member QRZ Page

    A good place to start in alternative energy is your project , something that is part time , hobby and low cost , till you get a handle on consumption & production and have it be 2nd nature in your mind .
    Then you can realistically build a larger system , for like full time home etc.
    Then there is a lot of advice from many that have not lived with it , some of it hear .
    There appears to be a lot of intended disinformation on alternative energy out there that makes getting started difficult .
    One of the 1st things is defining the terms , labels etc. - what a true deep-cycle is , the best dollar per watt spent is a true FLA = flooded lead acid 6 volt [ not 12 volt ] deep-cycle battery , like Trojan .
    Stay away from glass mat , AGM , 12volt , marine starting /deep-cycle etc. , you could play with a regular car starting battery - if you have one around for free .
    The point being that for a new-be , the 1st thing your going to do is kill at least one battery system from lack of knowledge / experience of care & feeding of batteries .
    And even with an almost perfect system , batteries have the shortest life in a system , with the highest frequency of replacement and cost .
    Sorry 0GB , but your costs in this thread are so far off that , we could call them deliberately misleading .
    One of the issue in giving info in a non-alt. energy forum , is that we are talking about many systems added together , kinda like ham radio , and it is not something you can gather up overnight , or cram for a test and pass if you take it the next day .
    You have study & know the material to be able to make it work .
    One of the single best sources to go to is , magazine , but again it takes following the info for some time .
    I have lived on solar power full time with airconditioning , and all the modern conveniences for yrs. at a time .
    Also , my last system used Trojan L16 batteries , that for the entended use [ comercial floor scrubbers ] and well taken care of had a normal life of 4 yrs.
    In my system that I designed and put together , they lasted 11 1/2 yrs. , that is probably the single best proof of a good system , long lasting batteries .
    My 1st choice for the next battery bank , when I need one , would be nickel-iron batteries , they were used in submarines , and were just about impossible to mis-use and destroy , also should be able to last 50+ yrs.
    I did some pricing a few yrs. ago when I new that the Trojans were coming to an end , I paid $650 for 4 of the L16 [ about 15 yrs ago now ] , the replacement 2 yrs ago was about $900 , I found a couple of sources for the nickel-iron batteries , and for the same capacity would cost about $1,100 2 yrs ago .
    Also there is a massive falling of panel prices for some yrs. now , you can buy almost any of the top brands of panels for .99 cents to about $1.89 per watt , I still see available at some of the big box stores [ Home Depot , and here Menards , Nothern Tool etc. ] rebranded panels go for $9 - $14 a watt , this just plain bull-hocky .
    I do not mean to offend , but I have been around many types of alt. energy for over thirty yrs. , and it just piss's me off that mostly because of corruption , that the general public is BSed into blowing it off .
    The world has gotten to the point of , having to prove everything to your self , I am not interested in proving to others , I know it works , just saying go find out for yourself .
    Just like anything , there is no reason to pay retail for any of this .
    I like to think as ham radio types , we can home-brew :)
    Last major point , do not try to make cheap chineeze junk do a quality job , unless your trying to prove that it doesn't work .
  14. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    John, I did qualify where the costs came from. But while were hashing things out here, and hopefully learning from one another.....

    There are a lot of bargains to be had. One of the locals here, was given a set of batteries from a cell site. They are suspect for that service perhaps, but for battery backup, they're wonderful. They are flooded, so it isn't something you want to put in your house. Yet, a lot of amateurs do just that, and we both know what could happen. Whether it does is moot, however, if they are placed inside, AGM's make a lot of sense, as long as you choose the correct one. I don't believe SLI batteries are the answer in any real serious case. You can buy (so-called) stationary batteries that are AGM style, which are designed for use in UPS systems. Lynch, and others supply UPS systems equipped with same.

    I am appalled at the common suggestion to use batteries designed for marine use. For some unknown reason, amateurs think the term "Marine" means deep cycle, or some other esoteric, non-provable claim of long life. No matter the type, name on the outside, post configuration, or whatever, any lead acid, nominal 12 volt battery, flooded or not, is considered discharged when the voltage reaches 10.5 volts under load at the nominal C rating. For most SLI batteries that's C20. For industrial-sized ones (>200 Ah), that's usually C50. Discharging past this point greatly reduces charge/cycle life. Unfortunately, no one seemingly thinks about this issue. Just for the record, the BCI says a marine rating means that the battery can sit for up to two years without charging, get have enough reserve charge to start the engine.

    There is another issue to be considered, and one which is almost always overlooked. A nominal 12 volt battery, isn't 12 volts. Depending on the type (flooded, AGM, intended use, etc.), the resting, no-load voltage may range from 12.0 to as high as 13.2. But once you put a load on the battery, the voltage drops. This seemingly isn't a concern for a lot of folks, but consider that an Icom IC-7000 or IC-706 will shut down if the input voltage reaches 11.6. Other brands and models aren't much different. A battery booster is in order in these cases, but we still have to be cognizant about the lowest partial state of charge (PSOC). Even when we're not, we need to look at another significant issue—IMD.

    It is a tough nut to crack to keep IMD within the FCC guidelines when the transceiver in question operates from nominal 13.8 volts. Lower this to the cutoff point mentioned above (≈11.6), and the IMD is about 20 dB worse than it is at 13.8. Except for Tom Rauch's, W8JI, and my own web site, you almost never see this fact mentioned. The usual answer is, it doesn't matter. Well, it does if we really want to be amateur-band civil.

    All of this points out the fact that choosing a battery for some specific use, is not a hit or miss scenario. Unfortunately, that is exactly the case in most instances to the detriment to us all!
  15. K2POP

    K2POP Ham Member QRZ Page

    Thanks Bill. I found this company on the internet. I'm glad to hear that they are good to deal with.

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