what size backup generator

bleedingbluebleedingblue Registered Users Posts: 3
Putting my first solar setup. Have 12-335 watt panels, 24 trojan L-16 batteries in a 48 volt system. Have a midnite classic 200 and an aimes 10,000 watt pure sinewave converter.
I also have 2-1600 watt wind turbines as well that will be going up eventually.
Now during times where the panels cannot charge the batteries what size propane generator do i need to buy? Any recommendations?
Also i might buy another string of 8 L-16 batteries in the future to store power if what I have now is not enough. here is a site that I was looking at trying to figure out on what size generator I needed .

http://solarhomestead.com/charging-batteries-with-a-generator/

Comments

  • VicVic Solar Expert Posts: 2,958 ✭✭✭✭

    Hello bleeding..,

    Welcome to the Forum.

    You are pretty far along in buying hardware ...

    To your real question,  here is some reading:
    http://forum.solar-electric.com/discussion/16206/choosing-a-good-generator/p1

    The size of the generator depends on a number of factors.  Am not familiar with your particular AIMS inverter.  I assume that it has a built-in fast transfer switch to automatically switch from inverter power to generator power,  and also assume that this inverter has a battery charging function.  What is the maximum charge rate that any charger in the AIMS produces?

    Sizing the genset depends upon the battery charging rate that the inverter can supply,  the AC loads that need to be supplied,  the charger efficiency,  the elevation of the site,   the maximum temperature that the genset will experience when it is needed,  and so on.

    From your statement that you might want to add 8 more L-16s perhaps later,  assume that your existing L-16 are 6 volts,  and you already have three strings of batteries,  is this true?  Three strings of batteries can be real trouble,  and four would be even worse,  although  am just guessing that these batteries are 6 V,  and not 2 V.

    Also,  adding batteries later is often a poor choice,  as batteries age,  from the time that they are manufactured,  and batteries of differing ages connected together,  especially in parallel strings,  will often result in poor performance.  Opinions differ on what age difference might be tolerable.

    Just to get the ball rolling.    Opinions from Vic


    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • bleedingbluebleedingblue Registered Users Posts: 3
    Yes it supposed to have a gen option on it where it automatically starts the gen.

    Here is what i ended up getting
    http://www.aimscorp.net/10000-Watt-Inverter-Charger-48-volt-to-120-240vac.html

    Why are 3 strings of 8 batteries a bad thing? Yes they are 6 volt.
    When i was in the store i was going to purchase 2 volt batteries that were over 1100 amp hr at 20 hrs. He convinced me that 3 strings of 8 was cheaper and more powerful.

    Elevation here is right around 250 ft above sea level and maximum temps if gen is placed outside would be around 102 maybe in a yr out of 10. This year the hottest has been 97.

    Here is the controller

    http://www.midnitesolar.com/productPhoto.php?product_ID=257&productCatName=&productCat_ID=21&sortOrder=2&act=p
  • Marc KurthMarc Kurth Solar Expert Posts: 450 ✭✭✭✭
    I may have missed it, but what your daily load? How do you plan to use the system and what do you expect from it?
    Everything starts there when discussing equipment sizing.

    Marc
    I always have more questions than answers. That's the nature of life.
  • VicVic Solar Expert Posts: 2,958 ✭✭✭✭

    Hi bleeding..,

    Thanks for the info on your inverter/charger.  Assume this is an off-grid system,  or perhaps Back-up for the Grid.

    bleedingblue said, " ... Why are 3 strings of 8 batteries a bad thing? Yes they are 6 volt  ..."

    Parallel battery strings can be a problem,  because one/some strings can hog most of the charge current,  leaving others poorly charged,  especially with off-grid systems,  where the Solar charging day is relatively short.  Undercharging can damage  the lagging string/s,  and can also mean that one string that hogs much of the charge can experience charge currents greater than is good for them.

    You DO own this system,  so you will want to make the best that you can of what you have.  Please get two pieces of test equipment  --  a good Hydrometer to measure and record in your battery log book the SG readings of EACH battery cell,  and a DC Clamp Ammeter  --  to measure the balance of charge current in each battery string.  Knowing the string current balance can allow you to take steps to rotate batteries among strings,  or perhaps allow  a string that has been undercharged to get THE charge by taking the strings with the best charge off-line on occasion,   and so on.

    Here is a good Article on measuring SGs,  from Surrette Battery.  Your Trojans probably use 1.277 SG electrolyte,  but,  generally this difference in SG will be about the only difference between your batteries and the Surrettes.

    Parallel strings on systems that are charged from the Grid are not so problematic,  as,  the lagging strings will eventually become fully-charged,  as the grid charging will charge batteries 24/7,  in most cases.

    That Linked Thread is fairly long,  but probably covers almost every aspect.  Your elevation of about 250 Ft will not be a factor in choosing a generator.

    Just be certain to have a schedule for monitoring your batteries  --  checking water levels,  topping up the levels with Distilled Water,  measuring SGs and recording these readings in your battery Logbook.   It is a good idea to number each battery,  and use a letter for each cell of the batteries.  A felt-tip pen works well.  Keep batteries clean,  and treat them as a valued member of your family.  Just like family members,  batteries have a long memory,  and most likely will remember every thing that you have done for them,  and to them.

    FWIW,    Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • bleedingbluebleedingblue Registered Users Posts: 3
    null

    plan is to run as much as possible off of it. Got 2 200 amp boxes in the house side by side one with power from the grid and the other power from the batteries. Going to run the central air from the grid and everything else off the batteries. If its too much then i can just click off some breakers and transfer the load to the grid. Its just me so its not like im using a ton of power. Typical electric bill is 70-100 bucks sometimes in the 50 buck range. Before i had new duct work and a new 16 seer dual fuel unit installed it costs around 200 bucks more per month to run the older unit and that's with keeping the inside temperature around 55. Now in the winter I keep it at 68.
    I also put in an instant water heater, new stove and new dryer all off propane.
    For 18 months i only used $27 in gas at .75 a gal summer fill. Got a 1000 gal tank so why not power a back up gen???
    typically here the power goes out at least three to four times a month and will be off for several hours at a time that usually happens when I am coming home from work. When I try to open the garage door and it will not open and I will have no hot water or anything like that. It is pretty aggravating. a couple of years back we had a severe ice storm where we did not have power here for over a month. luckily my parents had a generator and a propane wall furnace and I just stayed with them for a month sleeping on the floor. But everything at my house was ruined and both my deep freezers and fridge etc.
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