Chasing down power loss, and other newbie questions

cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
Newbie here so be patient with me!

I am living in Mokanji, Sierra Leone where I am working with an NGO drilling water wells a d renovating a hospital.

Where we live there is no grid power and there won't be any in the forseeable future so we are on solar power.

I made some guesses about what we might need and that when we were home in Canada and it appears my guesses were not quite on the mark and I need more panels and/or batteries.

I currently have two Carmanah 125w panels. I tried to see the specs but I can't see that right now. I'll get that info before buying the additional panels so I can follow whatever advice is offered. If I get additional panels should I put them in series or parallel with what I have? I assume I'd use one of my current panels and a new one in series and then connect those two strings in parallel. Am I right? What should I be looking for (besides the exact same panel) when buying additional panels? Is voltage, amperage or watts output most important to mate different panels?

Secondly, I have two Deka 260amp gel solar batteries in series to my 24v inverters. I have one 110v 600w GoPower Pure Sine wave inverter for my 110v stuff and one Su-Kam 220v 1400w Pure Sine wave inverter for the rest of the stuff and lights. The main stuff that is on all the time is a Kenwood "bar" fridge off of 110v (90watts nameplate). I'll charge the laptop most of the time also on 110v. We'll run some fluorescent lights for 3-4 hours at night. Not more than 2 4' lamps at any time and not for more than 3-4 hours a night. We also would like to run the ceiling fan in our bedroom and possibly the guest bedroom as necessary. Are the two 260amp batteries sufficient or do I need a second set in parallel with these?

Lastly, the house was wired while we were out of the country by an "electrician" who lives here in the community so he doesn't have much opportunity to practice his trade. There seems to be a parasitic draw somewhere in the system such that if I leave the 220v inverter on over night the batteries are down to 22v by the morning (from 25.4v). If I leave the 220v inverter on but NOT connected to the house wiring I'm only down 0.2v. Any ideas of where to look for the power drain? We've checked ohms across the power leads to the house after unplugging it from the inverter and they all show an open circuit (ground to load, ground to line and line to load).

That should be enough questions for a newbies first post!
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Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Chasing down power loss, and other newbie questions

    Welcome to the forum.

    I wish you had asked the questions before you spent the money; it's easier that way.

    You're not going to be happy with gel batteries. No matter what it says on the label, they're not suitable for solar applications. Plus you've got a battery bank of 260 Amp hours @ 24 Volts and only 250 Watts of panels. That's roughly 1/2 the minimum amount of panels you need to recharge those batteries.

    As for how much power you can expect, some "ballpark" calculations:
    260 Amp hours @ 50% DOD = 130 * 24 Volts = 3120 Watt hours maximum, not including inverter efficiency. Probably 2.6 kW hours AC potential.
    Whereas the panels have a potential of about:
    250 Watts * 5 hours "equivalent good sun" / 2 = 625 Watt hours AC. That is not very much. About 7 hours of actual run time on the refrigerator - with nothing else drawing. In other words, not enough panel to supply the amount of power that's being used in one day. Deficit charging leads to premature battery death, and if there isn't some other source of charging your gel batteries are probably already ruined.

    You really need:
    A). accurate measurement of load requirements with a Kill-A-Watt meter
    B). back-up power/charge source such as a small inverter-generator like the Honda EU2000i
    C). enough battery bank to supply the power requirements, including running the inverters and their conversion inefficiencies, for 50% DOD or better 25% DOD
    D). enough panels to recharge the battery bank properly. Shoot for 10% peak charge current, as in:
    Amp hours * 0.10 = peak charge current. Multiply by charging Voltage and divide by efficiency derating (0.77 typically) to get array size.
    E). enough money to pay for the steps above.

    As for the mysterious parasitic load, you could try a clamp-on AC ammeter. Put it on the line with everything disconnected, then hook things back up. Most likely something that's plugged in but turned off is drawing current.
  • mike95490mike95490 Solar Expert Posts: 8,607 ✭✭✭✭✭
    Re: Chasing down power loss, and other newbie questions
    ...that if I leave the 220v inverter on over night the batteries are down to 22v by the morning (from 25.4v). .....


    The bad news is the batteries are going to need to be replaced, 22V is essentially DEAD and you need to avoid such deep cycles. The batteries can only do a few dozen cycles to 0% like that.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 30,037 admin
    Re: Chasing down power loss, and other newbie questions

    Also, a plain TSW 1,400 watt sine wave inverter may draw 20-40 watts with no load on the output at all... Run the inverter overnight turned on/without any loads, and you may be looking at using most of the power you generated with the solar panels during the day (idle inverter still can consume a lot of power).

    For example, say you have 2x125 watt panels and get 5 hours of "full noontime sun" a day. The end to end efficiency of an off-grid inverter system may be around 52%... So:
    • 2*125 watt panels * 5 hours of sun * 0.52 efficiency = 652 WH per day
    • 40 watt inverter idle load * 10 hours on/no load = 400 WH per day wasted
    That leaves you ~252 WH per day of "useful power"... Not very much (enough to run your fridge for, perhaps 4 hours per day or so.

    Recommend you backup up a bit, measure/define your loads. Define your needs, figure out how much sun you have (4 hours a day is sort of average for North America--some places can have a year round average of 5-6 hours a day--but that is usually limited to very dry climates and near the equator).

    Then we can work out the size of the battery bank, size of solar array, and the rest of the support equipment.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Chasing down power loss, and other newbie questions

    OK, in answer to some of the questions.

    We are in Sierra Leone, about 7 degrees north of the equator so we have good sun most every day. I assume we're in the 5-6 hours of sun a day region?

    The batteries have been down to 22v twice or three times, not more. These are the only "deep cycle" batteries I can find in country. Am I better with some standard lead-acid truck batteries? The lead-acid truck truck batteries are certainly cheaper but not "deep cycle"!

    I have a Honda EU1000i generator but it is a 110v model not a 220v model so I'd need to change out the inverter section or get a different one. Can I run a generator to charge the batteries at the same time as the solar panels are going? I was concerned about back feeding to the charge controller and damaging things (I told you I'm a newbie). I can also find a 220v generator here but not using one was one of my goals.

    If I shut off the inverter over night to avoid power losses while idle then I will not be able to use the ceiling fans at night either. That's not a great loss and I can live with that if necessary.

    Our power use is/will be as follows:

    one small refrigerator at 1.2 amps, 115v 85w
    laptop computer
    cell phone charger x2
    small kitchen appliances (blender) on 220v very occasionally, not more than 15-30 minutes/day
    standard fluorescent lighting of not more than 2 or 3 40w tubes for not more than 3-4 hours/day and probably less.
    ceiling fans for overnight use, say two fans for 12 hours (probably my energy hog I'm guessing as they run continuously overnight). I these are impractical we can deal without them.

    Unfortunately I don't have my nice Fluke 83 meter here. I didn't think I'd need it and I didn't want to loose it to the baggage handlers. Maybe I need to send for it?

    We'll be replicating this in one other house with probably more power use than us so any info can be used there as well. For the other house we only have the panels right now which are 6 old 80w panels I think (probably not enough either by the sounds of it).
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Chasing down power loss, and other newbie questions

    You can use this online tool to estimate daily energy harvest: http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php?map=africa

    With 250W of panel at the ideal inclination you'd get about 1.28kWh in Feb and 660Wh in August. Taking the worst case, 660Wh from panels * 0.8 (losses to charge battery) * 0.85 (losses in inverter) = 448Wh per day for your use.
  • mike95490mike95490 Solar Expert Posts: 8,607 ✭✭✭✭✭
    Re: Chasing down power loss, and other newbie questions

    You can use your honda genset to power an ordinary battery charger, (don't bother with it's wimpy 12V DC output) and hook that right to the batteries - attaching charge controllers in parallel to batteries is fine, when you notice the solar controller has dropped from BULK to absorb, you can cut the charger and generator off.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Chasing down power loss, and other newbie questions
    mike90045 wrote: »
    You can use your honda genset to power an ordinary battery charger, (don't bother with it's wimpy 12V DC output) and hook that right to the batteries - attaching charge controllers in parallel to batteries is fine, when you notice the solar controller has dropped from BULK to absorb, you can cut the charger and generator off.

    My batteries are 2 @ 12v in series as my inverters are both 24v models. If I charge just one at a time isn't that a problem? Is a 24v battery charger available?

    The ceiling fans are rated at 80w each on 220v so that sounds like a pretty hefty power hog for a 10 hour a day run on batteries. Let me know if it is possible and what it will cost me in panels and batteries but I imagine it won't be worth it.

    The solar panels are 125w and 17.6v Vmp, 7.11A Imp, 21.4Voc and 7.67A Isc and are currently in series. I have two of these.
  • BB.BB. Super Moderators, Administrators Posts: 30,037 admin
    Re: Chasing down power loss, and other newbie questions

    There are other voltage chargers available. From our host:

    http://www.solar-electric.com/bach1.html

    If you are really into optimizing charging/small genset/efficient fuel usage--Take a read from this thread:

    Question about battery charger selection with EU2000 generator

    Next--I would suggest some tools next time you can do some shopping:

    A Battery Monitor (Victron should also be nice). Almost a requirement for Sealed Batteries to monitor the state of charge. Very simple for anyone to use:
    1. >75% state of charge=Everything OK
    2. <75% state of charge=Perhaps start the genset early next morning and charge to 80-90% state of charge if heavy loads/little sun is expected.
    3. <50% state of charge=Start genset and/or start shedding loads
    4. <20% state of charge=Turn Off loads, check why genset is not charging, get technical help. Battery bank may be ruined if discharged further
    If you have flooded cell batteries, get a couple hydrometers (somebody always breaks the first one or two).

    I would suggest a DC Current Clamp Meter so you can debug DC problems. This one from Sears is ~$60 and will work well for your Digital Meter Needs (cheap enough to get a couple, and if one walks/gets damaged--you are not out $300-$450 or so). And if you need to measure AC/DC current--it is much safer than having to insert a hardwired current meter into the circuit.

    You may want to hunt down a MorningStar 300 Watt TSW inverter for your day to day AC power needs (especially for a smaller system). Very efficient, has a "standby mode" (low idle power), and a remote On/Off switch (you do not have to have a huge switch to turn on/off DC power to the inverter). It is available in both 120 VAC 60 Hz and 220v 50Hz (you may have to shop around for the overseas version vendor). Unfortunately, this is 12 volt inverter and would require you to convert to a 12 volt battery system. If you did not have the refrigerator, I look at going to 12 volts + the MorningStar inverter.

    For a 24 volt system, you are pretty much looking at much more expensive (and probably larger) inverters with similar features.

    If you need a larger inverter once in a while (power tools), then fire up the big guy.

    And your refrigerator is usually a killer for power usage... 1.2 amps at 120 VAC all of a sudden becomes 12 amps at 12 VDC (or more).

    For example, just to run a 1.2 amp 120 VAC refrigerator, assuming it is running 50% of the time, 5 hours of sun per day, 52% end to end PV to AC power system efficiency:
    • 1.2 amps * 120 VAC * 24 hours per day * 0.50 frige duty cycle * 1/0.52 eff * 1/5 hours of sun = 664 watts minimum solar array
    And, realistically, you would probably want 2x that size of array for reliability and to support other loads/losses. And to power a refrigerator, you are probably looking at a 1,500 watt inverter minimum (more losses).

    An alternative to refrigerators is to convert an efficient chest freezer to refrigerator (just add a new thermostat that operates at just above freezing). Some people have reported ~250 WH per day vs the typical 1,000 to 2,000 WH per day of a standard energy efficient refrigerator.

    Chest freezer as a chest refrigerator

    Yes, you can parallel solar+AC battery chargers without problem (just watch that you do not over charge if you have lots/big chargers on smaller battery banks).

    A couple of things to read:

    Choosing an inverter for water pumping
    All About Inverters
    Deep Cycle Battery FAQ
    www.batteryfaq.org

    A choice between truck batteries and GEL batteries--close call there. Neither are "right" for the job. If the truck batteries are cheaper and you can keep their daily discharge to less than 25% (75% state of charge), I probably would go with locally available truck batteries.

    You might also look around the port area and see if there are any battery companies that have forklift/pallet jack batteries. May be a good source and it is possible you can get some donations of used batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Chasing down power loss, and other newbie questions

    There are indeed 24 Volt battery chargers. One example: http://www.solar-electric.com/iodl24vo15am.html
    Alternately, you could use two 12 Volt chargers - one on each "half" of the 24 Volt bank. Even cheap automotive type chargers. It would be less than perfect, but should manage the Bulk charging. Ideally you'd disconnect the batteries to do this, as automotive chargers are not very sophisticated internally (can have poor regulation, not fully rectified current, no 3-stage charge settings).

    80 Watts is 80 Watts whether from 220 or 110. The problem is 80 Watts * 24 hours = 1920 Watt hours.
    Again with your panels only able to collect around 600 Watt hours per day, it isn't going to work.

    You still need more panels just to meet the charge requirements of the batteries you've got, or else run the gen with the battery charger(s). You'll also need to examine your over-night use in respect to the battery storage capacity; if they're being brought down to 50% between charge periods then you're running on the edge. You need to at least multiply out the Watts of each item by its run time to get Watt hours. That's the all-important number. Using factor ratings is not as accurate as taking actual meter readings, but it's a start.
  • conntaxmanconntaxman Solar Expert Posts: 125 ✭✭✭✭✭
    Re: Chasing down power loss, and other newbie questions

    Hello .glad to find this tread. I just hook up my panels to a battery. and a coleman 2000 xd 4000 inverter.The battery is only a small optium 55ah yellow . Every thing is working fine / i think. lol. But this morring the alarm on the coleman went off and it shut down. Voltage at the battery was 10volts. I only had a computer pluged in but it was shut off. So did the coleman inverter draw down the bat. in the night? I didn't check on how much it draws yet as this just happened today.
    The 520 watts of panels charges the battery back up in about 2 to 3 hours up to about 13.9 volts.
    The coleman is about 10 years old,and not the full sine wave.
    So it looks like these just on all night draw alot. I know that a new colemen draw about .45amp in idel.
    Ya almost need another battery just for these and the led's that stay light and like a fax machine that is in stand by mode.
    Just love this fourm.
    tks BB
    John
    Im going to start out with 2 of costco's deep cycle 115ah.,their cheap $85.00 but a 3 year Full Warr..
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Chasing down power loss, and other newbie questions

    How bad can inverter idle draw be? Very bad. Some of them use 45 Watts! In this case it looks like around 6 just sitting there, but that's half an Amp. If you go with the 4 hours sun/20 hours without plan that adds up to 10 Amp hours (more or less). The Optima yellow top is rated as 75 Amp hours. 10 Amp hours would be about 13%. You should still have power in the morning.

    However, a computer plugged in and "turned off" is not necessarily drawing zero current. In fact anything with a transformer will draw something as long as it's plugged in. Gone are the days when the off switch disconnected the line cord. :cry:

    Power bars are a good cure for this. ;)
  • conntaxmanconntaxman Solar Expert Posts: 125 ✭✭✭✭✭
    Re: Chasing down power loss, and other newbie questions

    I checked and realized that I had 2 computers and one lcd monitor pluged in but off.And when I checked the wattage on my wattameter it read 1 amp. So thats ALOT. Pluse the inverter, i think that drew 1 amp.Holy smokes.Need one battery just to run the "Stand by" stuff for all this new fangle stuff. LOL. well really it's not funny.
    question they asked???:D did you turn it off? reply :grr um yes and no.I turned off the power switch,but the Stand by" stuff is Still running. :confused:
    John
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Chasing down power loss, and other newbie questions

    A couple of answers and a couple more questions.

    First, if the port had pallet jacks and fork lifts then there might be a source for those batteries but alas the port does not own a fork lift or pallet jack!! They you strong (thieving) backs to move things around.

    The standard truck batteries are significantly cheaper than the gel cell deep cycle batteries so I guess it's the truck batteries from now on. I do have a battery hydrometer so I can check state of charge on lead acid batteries using that.

    I'll send for my Fluke meter so the next folks coming out can bring it here. I like that better than the cheap meter I have here anyways.

    Before my first post I had more or less consigned myself that I needed more panels and possibly more batteries so I am not at all surprised by those comments. I guess what I don't know is how to connect dissimilar panels. Do I go series, parallel or what? I know I will loose some efficiency but I imagine it's better to have the dis-similar panels than simply leave them in a store room somewhere?

    In the power loss. When I went to switch off the inverter last night I noticed the fluorescent light starters glowing. I don't know much about fluorescent lights with starters but a glow means power use, that much I DO know. Is that normal with the fluorescent lights that use starters (that probably needs an answer from an old timer since we haven't had lights with starters for years in Canada/USA)? If that is not normal how do we go about fixing it?
  • mike95490mike95490 Solar Expert Posts: 8,607 ✭✭✭✭✭
    Re: Chasing down power loss, and other newbie questions
    ....... When I went to switch off the inverter last night I noticed the fluorescent light starters glowing. I don't know much about fluorescent lights with starters but a glow means power use, that much I DO know. Is that normal with the fluorescent lights that use starters (that probably needs an answer from an old timer since we haven't had lights with starters for years in Canada/USA)? If that is not normal how do we go about fixing it?

    Wow - I didn't even know they still made ballast with "click and glow" starters. There are more efficient ballasts, with good power factor, that will consume less power - but more expense up front.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 30,037 admin
    Re: Chasing down power loss, and other newbie questions

    Are your inverter MSW or TSW type? Florescent fixtures with starters and magnetic ballasts may not like MSW too well (could overheat the ballasts). If you see the starting lamp lighting while the lamp is running--that is probably the result of the MSW inverter and/or other problems. The running starting lamp will be an additional power lost (running the lamp heaters) and probably will dramatically shorten lamp life.

    Longer term--if you stay with MSW inverters, you might want somebody to setup a similar inverter back at "home base" and experiment with various brands/models of CFL and LED fixtures and see which will work out well for you. If you use a good RMS reading current meter, I would measure the amperage usage of different lamps on grid power and MSW inverter---Those that use more current (20% or more) than sine wave power, I would suggest they will not last/be a good choice for MSW inverter use (ballasts will overheat with excessive current draw). Perhaps some others here have suggestions for good lighting sources on MSW inverters (or look for native 24 VDC fixtures--large trucks/boats frequently use such lamps).

    Regarding battery types--you probably will have to do your own experiment and see which ends up a better solution/bang for the buck. Neither is really that great of answer.

    I would still see if you can get a DC Clamp type current/multi-meter. It will be much easier to use than anything else (let you decide how much money to spend--obviously a $400+ Fluke is going to be much better than anything else/cheaper).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Chasing down power loss, and other newbie questions
    mike90045 wrote: »
    Wow - I didn't even know they still made ballast with "click and glow" starters. There are more efficient ballasts, with good power factor, that will consume less power - but more expense up front.

    Welcome to the developing world where every store is racing to sell the cheapest product and who cares about quality and energy use! Yes, these are still alive and well and very much available new. It's the good stuff that I can't find so easily. Should the starter glow when the lamp is switched off or has the electrician possibly swapped the line and load to the lamp?

    Apparently LED lights for 220v are available in Freetown but I have yet to find the store.
    BB. wrote: »
    Are your inverter MSW or TSW type?

    I would still see if you can get a DC Clamp type current/multi-meter. It will be much easier to use than anything else (let you decide how much money to spend--obviously a $400+ Fluke is going to be much better than anything else/cheaper).

    -Bill

    Both the 110v and the 220v boast as being "pure sine wave" as opposed to being a modified or square wave inverter. I paid for the better one and if I run the square wave inverter you can hear the lights buzz. With the other you don't get that buzz so I'm pretty confident that they really are a true sine wave.

    I've got my kids chasing down my Fluke meter back home. We'll see if they are successful.


    It appears that the 135w panels available locally are very close in ratings to the ones I currently have. When I get some additional panels how should I connect them with the old ones?
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    How many more panels do I need?

    I figure I'll have about 6kw/day energy use in a worst case scenario. That's with all our rooms occupied and fans running all night long. Each fan is nearly 1000watts each day and there are three of them.

    I currently have 2 - 125w panels which everyone tells me is not even close to enough and I know that. I can get 135w panels locally which have a very close rating to those I currently have and those are the panels I'd like to get.

    How many additional panels do I need and how much battery do I need to carry all this load? I currently have two Deka 12v Gel batteries with a 260amp hour capacity (I know that these apparently are not the best but that's what I have now). If I need additional batteries can I mix lead-acid flooded batteries with the current gell cell batteries?

    My current charge controller can take in 25 amps and 56 volts from the solar array so I'd like to stay within those parameters if possible. That would be a 9 panel array in a 3 x 3 arrangement.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Chasing down power loss, and other newbie questions

    You can not mix battery types. The charge Voltage set points and current requirements will be different. You'll end up either over-charging one (the gels) or under-charging the other (the FLA's).

    As for adding more power, you have to look at it like this: the batteries supply the power, the panels recharge the batteries. So the first step is to increase the battery bank to where it can handle the load. Then make sure you have either enough panel or a generator that can supply the recharging.

    6kW hours per day is significant. On a 24 Volt system that's at least 250 Amp hours, meaning you need a minimum of 500 Amp hours @ 24 Volts. To recharge that you'll need about 1800 Watts of panel. It is difficult to be more precise because panels do not put out their nameplate rating but rather an average percentage of it which varies with local conditions. High temps will reduce the output more. Another thing to look at is the Watt hour yield. Basically to get 6kW hours per day you'd need to figure on over-all system performance of about 50% efficiency which means 12 kW hours from the array. This number is divided by the average hours of "equivalent good sun" which ought to be around 5 there, so you get a 2.4 kW array.

    How are we doing so far?
  • BB.BB. Super Moderators, Administrators Posts: 30,037 admin
    Re: Chasing down power loss, and other newbie questions

    Cruiser Guy,

    I moved your last post back into your other thread--It keeps things less confusing to have the same discussion subject(s) in the same location.

    If you have a simple/inexpensive PWM charge controller, your only option is to connect the two "12 volt" (should actually be Vmp~17.5 volts) in series, then connect that series string in parallel to the existing solar array.

    With a PWM controller, you can probably use a Higher Vmp-array voltage (larger panels tend to have Vmp higher than 17.5 volts)--However, the farther Vmp-array is from ~35 volts, the more power will be wasted with a PWM controller (it will still work, but less efficient power harvest from panels).

    If Vmp is not equal to ~17.5 - 18.0 volts for your panel, let us know.

    As the array grows (over ~400-800+ watts), you may eventually want to look at MPPT charge controllers--you can connect more panel in series (upwards of Vmp-array = 100 VDC). This allows you to use smaller gauge wire and/or mount the solar panels farther away from the charge controller/battery bank/battery shed. Having a 24 volt battery bank does help keep losses/wire size down.

    24 hour per day loads are actually quite daunting for solar PV/off grid power... A microwave may only run 30 minutes a day so:
    • 1,500 watts * 1/2 hours = 750 WH per day
    • 3 fans * 100 watts * 24 hours = 7,200 WH per day
    So--First suggestion is to measure the actual fan loads, and if they are multi-speed fans, see how much power they use on a lower speed setting and see if a lower speed will "work OK" for your needs.

    Obviously, if you could find lower power ceiling fans that moved enough air--it would help a lot.

    So, for the calculations. First you need to add up all your watt usage and hours per day power needs. A Kill-a-Watt type meter (230 VAC for your needs) would be helpful--but probably one of those things not easy to get for you.

    For the sake of discussion, assume 3 fans * 80 watts * 24 hours per day.
    • 3 fans * 80 watts * 24 hours per day = 5,760 Watt*Hours per day
    Now, frankly, that is a lot of power from a small off-grid PV system... In the US, we would normally be planning on ~100 kWH per month or 3.3 kWH per day as a smallish system to supply the needs of an off-grid cabin/home for basic needs (no fans, no A/C, fridge, few lights, laptop computer, maybe a washing machine every couple days, small well pump, etc.).

    Anything moving air/water/etc. tends to be an "energy hog"--and doing it 24 hours per day makes it that much worse.

    Anyway, some other assumptions. Minimum (average) of 5 hours per day of full noon-time equivalent sun and 0.52 end to end system efficiency.
    • 5,760 WH per day * 1/0.52 system eff * 1/5 hours of sun per day = 2,215 Watts of solar array
    • 2,215 Watt array / 125 watts per panel = 17.7 panels = 18 panels minimum
    Note, your Vmp-array must be constructed in series/parallel for Vmp~35 volts with a PWM controller... No other Vmp will be acceptable (something like 2 panels in series by 9 parallel strings). For fire safety, each series string should have a series protection fuse/breaker to prevent a panel short from causing a fire (powered by the other panels in the array).

    Lastly, a couple battery calculations. Assume 2 days of no sun and 50% maximum discharge (if using truck batteries, assume a maximum of 25% discharge for longer life--or 1/4 discharge). Assume an 85% efficient inverter and 24 volt battery bank:
    • 5,760 WH per day load * 1/0.85 eff inverter * 1/24 volt battery bank * 2 days of no sun * 1/0.50 max discharge = 1,129AH @ 24 volt battery bank
    Again, a very large battery bank. And with large battery banks, you need to meet some minimum/maximum rate of charge calculations. For solar charging, we recommend 5% to 13% rate of charge (GEL cells usual recommend 5% maximum rate of charge) and 0.77 solar panel + charge controller derating:
    • 1,129 AH * 29 volts charging * 1/0.77 panel+charger derating * 0.05 = 2,126 watt minimum array
    • 1,129 AH * 29 volts charging * 1/0.77 panel+charger derating * 0.13 = 5,528 watt maximum cost effective array
    And for an AC backup battery charger/generator, the charger ratings should be around 5% to 25% rate of charge (again, 5% maximum rate of charge is recommended for GEL):
    • 1,129 AH battery bank * 0.05 rate of charge = 56.45 amps
    • 1,129 AH battery bank * 0.13 rate of charge = 146.7 amps maximum cost effective charge rate
    • 1,129 AH battery bank * 0.25 rate of charge = 282 amps maximum charge rate
    Note, if you are within ~20% of the above calculations (panel/battery bank/chargers/etc.)--that is usually close enough. I carried the digits so you can reproduce my math.

    Also, never plan on using 100% of your systems predicted output every day... There are too many variables in system and weather. If you monitor the system/battery state of charge closely, you could probably use 75% per day on average--but you will have to shed loads by season and based on weather patterns.

    So--anyway, the above is the basic math I would suggest using to size your system... You will need to provide accurate loads, hours of sun per day, and make the cost decisions (new, more efficient fans vs larger PV system).

    Hope it all makes sense.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Chasing down power loss, and other newbie questions

    What is a PWM or MPPT charge controller?

    The 6kW daily load is an absolute worst possible case scenario, likely it would never be that bad and if it were then I could justify a generator to give things a boost during the day. This also assumes I make NO changes to my installed equipment.

    I think we could safely assume our loads on an average day would not even be 1/2 of the 6kW, ie: less than 3kW and probably alot less.

    We are considering going to Germany for Christmas and if we do that we'll be returning with LED lights and ceiling fans with 1/2 the power use of the ones currently installed. Here in Sierra Leone if it cost more it isn't for sale because the average guy on the street can't afford it anyways.

    If we assume the fridge, at 85w runs during daylight hours, I have LED vs. fluorescent lights and the ceiling fans use 50w at high speed vs. 80w (they would only be run at night to make sleeping less sweaty), I'd still have the various items to charge and an occasional use of the kitchen appliances, what are my needs?

    Vmp of the current panels is 17.6v.
  • BB.BB. Super Moderators, Administrators Posts: 30,037 admin
    Re: Chasing down power loss, and other newbie questions

    A PWM controller is just an On/Off type charge controller... It may cycle in seconds or 10,000's of times a second. The longer the average "On type per cycle", the higher the average current.

    The "switch" just makes a direct connection from the solar array to the battery bank. So, no matter what the array voltage is (Vmp=15 volts, 18 volts, 32 volts, etc.), the battery clamps it to ~12-15 volts (12 volt system).

    You can do that with solar panels because they are (roughly) constant current sources... the solar panels will out (for example) 8 amps at 0 volts, 6 volts, 15 volts or 17.5 volts. As the voltage goes above Vmp (voltage maximum power) to Voc (voltage open circuit), the current drops down towards zero amps.

    The typical efficiency equation is Vbatt-charging / Vmax-power-array

    As you see, the higher Vmp-array gets from Vbatt, the less efficient it becomes.

    With a MPPT type charge controller, they are a digitally controlled switching power supply. Basically, they use an Inductor to store and transform the energy from High Voltage / Low Current (from the solar array) and down convert it to Low Voltage / High Current used by the battery bank.

    A MPPT type charge controller can with ~95% efficiency down convert energy to the battery bank...

    The MPPT controller is a "constant power" converter, and ignoring losses, its equation is:
    • Power = Volt * Amp
    • Vmp * Imp = Vbatt *Ibatt
    Or, more or less like using a transformer to take high voltage power lines and drop it down to house voltage or even low voltage for toys, computers, etc.

    Some more reading:
    All About Charge Controllers
    Read this page about power tracking controllers
    And about switching power supplies:
    Buck converter
    Switched-mode power supply

    17.6 volt Vmp is fine for use with PWM supplies (one panel in series for 12 volt battery bank, two panels in series for 24 volt, etc.).

    How much power will you use--I have no clue. You have to measure/estimate your usage and what power you can shed when needed. But, it general, this is very expensive power and you will want to do all the conservation you can first.

    The occasional mixer, microwave is not too bad (although, you do need a large enough battery bank + inverter to power those heavy, but short, loads).

    Since you already have a solar pv system--I would suggest either a full blown Battery Monitor (or Victron out of Europe) or you start monitoring your loads with meters or DC WattHour/AmpHour meters.

    In the end, monitoring your system and logging the results will tell you a lot more than I can from 1/2 a world away.

    You can get DC Ceiling fans and they will use only 20 watts or even less... Now will it move as much air as a 230 VAC 80 watt ceiling fan? Probably not.

    DC motors in general (pumps, fans, etc.) have the advantage of not needing an inverter (with its losses)--However, many DC motors are "Universal Motors" (same as cheap electric drill motors) with commutators and brushes. The problem is brushes do wear over time and commutators need turning... A typical universal motor may run 3-6 months at rated speed and power (or less) before needing brush servicing. How long will a DC Fan run--I have no clue (year or years?).

    There are also electronically commutated DC fans (like the fans in all of the personal computers). They can last much longer--but you may have to hunt those down for your application (and your part of the world).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Chasing down power loss, and other newbie questions

    PWM = "Pulse Width Modulated" That's what I currently have.

    There is a new development in that we will be constructing a childrens home near here as well so I think I may put the charge controller over there. It will be a lights only system and I have proposed they use 12vDC LED lights from an RV place for low energy use and the 12v will mean that power cannot be easily used elsewhere. I'll get the MPPT type charge controller at my place where the loads will be greater.

    I have worked out a realistic energy use based on getting some more efficient equipment and the probable average energy use per day.

    I figure we'll be around 1.5kW per day energy use and we can arrange that the biggest energy pig (the fridge) operates only in the daytime and would consume about 1kW/day. Night time use would likely be about 400-600 watts/night. With guests the night time use could double. I propose changing out the lights to LED lamps which I could source in Germany if I cannot get them locally. Based on that info and the fact that I currently have 250watts of panel (2 at 125w each) what is the recommended system?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Chasing down power loss, and other newbie questions

    If you're going for 1.5 kW hours per day on a 12 Volt system you need at least 250 Amp hours of battery (1500 Watt hours / 12 Volts = 125 Amp hours). You will need a lot more panel than you have: 1500 Watt hours * 2 (50% over-all efficiency) / 5 hours "equivalent good sun" = 600 Watt array at least. Or you run the generator a lot.
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Chasing down power loss, and other newbie questions

    My system is a 24v system since my inverters are both 24v.

    OK, so I need 6 panels if I use a PWM charge controller since I must use an array of 6 panels with 3 parallel groups of 2 panels in series. 2 panels in series to get a nominal 24v to the batteries.

    Am I going to have much benefit from a MPPT charge controller since it is so warm here anyways? From my reading it has greater benefits in colder climates that in hot climates. I assume that the MPPT charge controller is a significantly more expensive device than the PWM controller so it might not be worth it in warmer climates. Help me out if I am interpreting it wrongly.

    On the battery end of things. 1500w / 24v = 63amps I have 260amp batteries so am I OK then?

    My only real pressing need at this time is efficient equipment and 4 additional 125w or close panels?

    My power loss might have been bleeding through a poor quality switch. The electrician was just here and he changed out the switch and the starters don't glow any more. We'll see what the battery voltage looks like in the morning.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Chasing down power loss, and other newbie questions

    You can see a benefit from MPPT with larger arrays, because it will squeeze out a bit extra charging current from the difference between Vmp and charge Voltage. You will see an advantage with running a higher Voltage array (as in a 48 Volt array on 24 Volt system) or where the panels have "odd" Voltages (not ideal for the system Voltage). You will see an advantage with cold temps where the panels V goes up. Is the advantage in any of these situations worth the extra money? Could be. The bigger the system, the bigger the advantage, the more worthwhile it is.

    260 Amp hours @ 24 Volts should work for your expected load demands. You will need a slightly larger array to accommodate charge current concerns. Looks like about 950 Watts. And then we get back to the MPPT question.
  • mike95490mike95490 Solar Expert Posts: 8,607 ✭✭✭✭✭
    Re: Chasing down power loss, and other newbie questions

    The other thing MPPT is good for, is reducing the amps, in a long run from the array to the charge controller. Panels could be wired in series, for 130Vdc @ 9.5 amps, and the charge controller downconverts that to battery voltage, and more amps. Woo Hoo !!
    Instead of 35V @ 35A
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 30,037 admin
    Re: Chasing down power loss, and other newbie questions

    I am not quite sure what your question is here?
    • On the battery end of things. 1500w / 24v = 63amps I have 260amp batteries so am I OK then?
    There is usually no reason to make "this" calculation unless you are looking for running a 1,500 watt load at 24 volts.

    There is the "maximum current"--say it is 1,500 watts on an 85% efficient inverter and 24 volt battery bank:
    • 1,500 watts * 1/0.85 inverter eff * 1/24 volt battery = 73.5 amps peak
    Normally, for an average battery bank/configuration, I would suggest a maximum of C*0.4 maximum surge current:
    • 260 Amp*Hour * 0.4 = 104 amp max peak
    So, your system would be good for (example) starting a pump motor with a 1,500 watt starting surge.

    However, if you are looking for long term average power use--We like to use an 8 hour rate (C/8 or 0.125*C). This is the typical maximum discharge rate before the batteries overheat and have high losses (this is for typical flooded cell batteries. For AGM, some can sustain up to 4*C sustained load--but that is really not useful for a typical off grid system--but for a cheap UPS with 15 minutes of emergency power):
    • 260 AH * 0.125 = 32.5 amps @ 24 volts long term average current output
    • 32.5 Amps * 24 volts * 0.85 inverter eff = 663 Watts long term 230 AC load
    And, if you are using truck batteries where you only discharge to a maximum of 75% state of charge (or use 1/4 of the capacity)--that is 1/4 of the 8 hour discharge rate or 663 watts for 2 hours

    Anyway, there are lots of ways of slicing and dicing the math to represent/check against your needs...

    But, as you can see, even "moderate" loads for a modern home are "huge" compared to what a "typical/smallish" PV off grid system can supply.

    Hope this is more of a help than confusion. Please let us know what is confusing or what more you may need.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Chasing down power loss, and other newbie questions

    We're making headway here! Thanks for the help to a newbie solar guy.

    We fixed our power leakage problem. As I said the electrician came by yesterday and swapped out the switch and that seems to have fixed the problem. I left the 220v inverter on, connected to the 220v house wiring and every device switched off, all last night and we dropped 0.2v on the battery bank in that time (I attribute that to the inverter idling losses and I can live with that). Previously that would have killed the batteries with leakage current.

    Back to batteries.

    The only item running at night would be a ceiling fan besides a few hours of a couple of LED lights. The ceiling fan I am proposing is rated at 50 watts full speed and would run for about 8-10 hours at night. How many batteries, or better, how many battery amps do I need to run that without killing the batteries every night? I'll multiply that by the number of fans.

    I assume the math will look like this based on Bill's example.

    50 watts * 10 hours / 0.85 efficency on the inverter / 24v on the battery bank * 8 hours battery discharge

    for a total amps of 200

    That looks like we need more batteries then so I don't draw them down all the way each night. Am I right in putting in the 8 hour discharge in my calculations above?
  • BB.BB. Super Moderators, Administrators Posts: 30,037 admin
    Re: Chasing down power loss, and other newbie questions
    I assume the math will look like this based on Bill's example.

    50 watts * 10 hours / 0.85 efficiency on the inverter / 24v on the battery bank * 8 hours battery discharge

    for a total amps of 200

    That looks like we need more batteries then so I don't draw them down all the way each night. Am I right in putting in the 8 hour discharge in my calculations above?
    Glad to hear you found the problem with loosing power (switch?).

    I would write it like this (note: 1-3 days of no sun with maximum of 50% battery discharge for long life):
    • 50 watts * 10 hours running * 1/0.85 inverter eff * 1/24 volt battery bank * 2 days no sun * 1/0.50 max discharge = 98 AH @ 24 volt battery bank
    The "8 hours" is not appropriate in this equation... 8 hours is about as fast as you would want to discharge or recharge a flooded cell battery bank (C/8 rate of charge/discharge).

    Note, if the inverter has more than 6 watts or so minimum operating power (large inverter, small loads), you will need to include it in your 50 watts (worse than 85% efficiency with light loads). For example, assume your TSW inverter has a 30 watt minimum operating load (tare loss):
    • (30+50 watts) * 10 hours running * 1/0.85 inverter eff * 1/24 volt battery bank * 2 days no sun * 1/0.50 max discharge = 157 AH @ 24 volt battery bank
    Small loads with larger inverters can really play havoc with battery and solar panel sizing. In the above (pretend? guesstimate?), the lightly loaded inverter itself is consuming a third of your system power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Chasing down power loss, and other newbie questions

    On inverter loss. I know it is not a scientifically accurate measurement but last night I left the 220v inverter on in idle mode (no loads were on). It lost about 0.2v on the 24v battery bank over a 10 hour period. That is measured on the charge controller display as my cheap meter was swiped at the port when my container arrived. Does that give any indication of the inverter efficiency at all?

    My inverter is a Su-Kam "Smiley" 1400 watt 24vDC - 220vAC Pure Sine Wave inverter. I also have a "Go-Power" 600 watt 24vDC - 110vAC pure sine wave inverter for 110v applications.
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