Inverter/ batteries without solar panels

10fords10fords Registered Users Posts: 9
I have a new neighbor that has asked me to help them out with a project. Their house is too far from grid power to make it feasible, and, according to our local solar contractor, no feasible spot to put in a solar system. So, the Idea is to install a battery bank with an inverter to run the small loads, and a propane generator to charge the batteries when pumping the well or running the washing machine. While I am an electrician I am not a solar expert. I do have a completely off grid house with a small 540 watt solar setup that works great for me, but I would appreciate any input/ advice on how to set them up the best way. Ideally I would like to setup the inverters for 240volts so I dont have to completely redo all the wiring in every structure on the property. Thanks for any advice- Scott

Comments

  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: Inverter/ batteries without solar panels

    Scott, you will need to list the loads that need servicing first, everything will flow from that number(s)
     
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  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverter/ batteries without solar panels

    Not a problem. :D
    More than once I've helped design systems that recharge from generator only (usually either they're waiting for enough $ to buy panels or just want "quiet power" for emergencies).

    Basically you do it the same as with solar panels, only the charge source differs.
    Magnum inverters are a good choice for this as they have PF corrected chargers built-in and have 240 VAC capability (4 kw version): http://www.solar-electric.com/maensiwainac.html They also have auto gen start ability.
    So you need to come up with a reasonable average daily Watt hour need to plan the battery bank size. The 48 Volt version has a 60 Amp charger which with a 600 Amp hour battery bank would be around 14kW hours power max.
    Sizing the generator is going to be a matter of being able to supply maximum charge power and loads at the same time. The biggest drawback is the need to run the generator for full recharging: low load uses a lot of fuel to finish the Absorb stage.
  • 10fords10fords Registered Users Posts: 9
    Re: Inverter/ batteries without solar panels

    Thanks for the quick replies! I will get some more info tomorrow as I have to go to my weekly fire drill now. Keep the info coming please! - Scott
  • BB.BB. Super Moderators, Administrators Posts: 29,497 admin
    Re: Inverter/ batteries without solar panels

    Xantrex and Magnum (others?) now offer native 120/240 VAC 60 Hz inverters--So you don't have to play with the "stacked" 120 VAC inverters or auto-transformers for 240 VAC from 120 VAC inverters.

    The real question is what are the "off peak" loads. We talk about running batteries from afternoon through the night, and running a genset in the morning (if needed) to help an undersized solar array.

    Some places I have read about (Africa for one) are doing the "hybrid power" systems. Run the genset from evening until bedtime (people cooking, needing lights, home work, washing clothes, etc.) and then run the inverters/batteries for the rest of the time. The idea being that you run the generator when you have steady and "heavy loads" (50% or more of rated genset capacity, including battery bank charging--would be my first suggestion).

    I tend to suggest a "small genset" running a couple more hours than a large genset that quickly settles well below 50% rated output (kWH per gallon of fuel drops with most gensets).

    With diesel gensets, there is the ~40-60% minimum load recommended for many (avoid "wet stack", carbon build up, glazing cylinder walls--so much, that sometimes load banks are needed to keep the diesel engine well loaded). Using a "hybrid" system of generator + battery bank + inverters can help minimize fuel waste with load banks.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • 10fords10fords Registered Users Posts: 9
    Re: Inverter/ batteries without solar panels
    Not a problem. :D
    More than once I've helped design systems that recharge from generator only (usually either they're waiting for enough $ to buy panels or just want "quiet power" for emergencies).

    Basically you do it the same as with solar panels, only the charge source differs.
    Magnum inverters are a good choice for this as they have PF corrected chargers built-in and have 240 VAC capability (4 kw version): http://www.solar-electric.com/maensiwainac.html They also have auto gen start ability.
    So you need to come up with a reasonable average daily Watt hour need to plan the battery bank size. The 48 Volt version has a 60 Amp charger which with a 600 Amp hour battery bank would be around 14kW hours power max.
    Sizing the generator is going to be a matter of being able to supply maximum charge power and loads at the same time. The biggest drawback is the need to run the generator for full recharging: low load uses a lot of fuel to finish the Absorb stage.

    That inverter looks like the one I need. I like the autostart of the generator if the batteries get low. I am going to estimate that they will need around 3 kwh per day from the batteries at this point. What would be a good size for the battery bank? Also any generator recommendations? It will be propane powered. I am pleased with my Onan 7.5JB but I don't think they are made anymore. Thanks- Scott
  • 10fords10fords Registered Users Posts: 9
    Re: Inverter/ batteries without solar panels
    BB. wrote: »
    Xantrex and Magnum (others?) now offer native 120/240 VAC 60 Hz inverters--So you don't have to play with the "stacked" 120 VAC inverters or auto-transformers for 240 VAC from 120 VAC inverters.

    The real question is what are the "off peak" loads. We talk about running batteries from afternoon through the night, and running a genset in the morning (if needed) to help an undersized solar array.

    Some places I have read about (Africa for one) are doing the "hybrid power" systems. Run the genset from evening until bedtime (people cooking, needing lights, home work, washing clothes, etc.) and then run the inverters/batteries for the rest of the time. The idea being that you run the generator when you have steady and "heavy loads" (50% or more of rated genset capacity, including battery bank charging--would be my first suggestion).

    I tend to suggest a "small genset" running a couple more hours than a large genset that quickly settles well below 50% rated output (kWH per gallon of fuel drops with most gensets).

    With diesel gensets, there is the ~40-60% minimum load recommended for many (avoid "wet stack", carbon build up, glazing cylinder walls--so much, that sometimes load banks are needed to keep the diesel engine well loaded). Using a "hybrid" system of generator + battery bank + inverters can help minimize fuel waste with load banks.

    -Bill

    The generator will be propane powered. Any suggestions on a good one in about the 10kw range? Thanks- Scott
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverter/ batteries without solar panels
    10fords wrote: »
    That inverter looks like the one I need. I like the autostart of the generator if the batteries get low. I am going to estimate that they will need around 3 kwh per day from the batteries at this point. What would be a good size for the battery bank? Also any generator recommendations? It will be propane powered. I am pleased with my Onan 7.5JB but I don't think they are made anymore. Thanks- Scott

    3 kW hours per day is not unreasonable, but it is probably low. I use almost that much daily at the off-grid cabin and we've had a lot of practice at keeping consumption down. This includes running a refrigerator, satellite modem, computers (laptops), lights, water pumps, basically everything.

    On a 48 Volt system 3kW hours AC will be at least 80 Amp hours. If you go for a 25% maximum depth of discharge that's an easily obtainable 320 Amp hour battery bank. If it needs to go to 50% DOD (6kW hours) it would still work. The Magnum would have no trouble charging it either. Likewise if the daily need was 6kW hours and you did need a 640 Amp hour 48 Volt bank.

    The only other issue is maximum loads. You need to have a number for the most power that will be demanded at any given time. With big things like washing machines and water pumps being powered this can get quite significant. You may want to change the wiring a bit so that heavy loads are on "strictly generator" lines and can't be mistakenly used from the inverter, or you may find that 4kW is enough for everything (people usually don't turn it all on at once). If necessary, the Magnums can be stacked up to four in parallel providing 16kW @ 240 VAC.
  • 10fords10fords Registered Users Posts: 9
    Re: Inverter/ batteries without solar panels

    The refrig is propane and I am going to put the well pump on generator only. The washing machine will be the largest load on the inverter. Other than that only lights and computer stuff. I am trying to build some cushion into the system though as I know that everyone ends up using more than they say they do! So you think a 320 ah bank at 48v would be a good size? If it proves insufficient could more batteries be added later with the same inverter? Thanks- Scott
    3 kW hours per day is not unreasonable, but it is probably low. I use almost that much daily at the off-grid cabin and we've had a lot of practice at keeping consumption down. This includes running a refrigerator, satellite modem, computers (laptops), lights, water pumps, basically everything.

    On a 48 Volt system 3kW hours AC will be at least 80 Amp hours. If you go for a 25% maximum depth of discharge that's an easily obtainable 320 Amp hour battery bank. If it needs to go to 50% DOD (6kW hours) it would still work. The Magnum would have no trouble charging it either. Likewise if the daily need was 6kW hours and you did need a 640 Amp hour 48 Volt bank.

    The only other issue is maximum loads. You need to have a number for the most power that will be demanded at any given time. With big things like washing machines and water pumps being powered this can get quite significant. You may want to change the wiring a bit so that heavy loads are on "strictly generator" lines and can't be mistakenly used from the inverter, or you may find that 4kW is enough for everything (people usually don't turn it all on at once). If necessary, the Magnums can be stacked up to four in parallel providing 16kW @ 240 VAC.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverter/ batteries without solar panels

    Without refrigerator and water pump? 3kW hours is probably too much. This is the trouble with not having a definite power use reference figure; you either buy more capacity than is needed or the everything shuts down at an inconvenient moment.

    You can add more batteries later, but for a given value of "later". The longer the time and/or the more use the faster batteries age. So a set of 320 Amp hour L16's bought one year an be sufficiently lowered in capacity by next year that it is not a good idea to add more batteries. This is especially true if the reason for doing so is that the batteries are being cycled too deeply.

    If this is a full-time residence an electric refrigerator will be more economical than propane (especially if the 'frige needs replacing). Plan for that even if it isn't the case now. Depending on what the well pump is, it may be a good idea to run that off the inverter too. It can be done: I do it.

    You might also want to revisit the solar possibilities. Just because an installer has said it can't be done doesn't make it so. It could just mean it doesn't have the typical Southern exposure most of them think is necessary to make panels work. Panels only have to face the sun; they don't really care in which direction or at what time. Considering how low the price is on panels now, even an inefficient array can be worth the money over fueling a generator for that last couple hours of charging.
  • 10fords10fords Registered Users Posts: 9
    Re: Inverter/ batteries without solar panels

    Good points! The well is 240v 12 amps. It will be a fulltime residence. I will probably suggest that they get a second opinion on the solar. Either way they will need a generator and I could use some advice on that. In my researching there doesn't appear to be any new ones in the 7-10kw range that are as heavy duty as my old Onan 7.5JB. Any suggestions?
    Without refrigerator and water pump? 3kW hours is probably too much. This is the trouble with not having a definite power use reference figure; you either buy more capacity than is needed or the everything shuts down at an inconvenient moment.

    You can add more batteries later, but for a given value of "later". The longer the time and/or the more use the faster batteries age. So a set of 320 Amp hour L16's bought one year an be sufficiently lowered in capacity by next year that it is not a good idea to add more batteries. This is especially true if the reason for doing so is that the batteries are being cycled too deeply.

    If this is a full-time residence an electric refrigerator will be more economical than propane (especially if the 'frige needs replacing). Plan for that even if it isn't the case now. Depending on what the well pump is, it may be a good idea to run that off the inverter too. It can be done: I do it.

    You might also want to revisit the solar possibilities. Just because an installer has said it can't be done doesn't make it so. It could just mean it doesn't have the typical Southern exposure most of them think is necessary to make panels work. Panels only have to face the sun; they don't really care in which direction or at what time. Considering how low the price is on panels now, even an inefficient array can be worth the money over fueling a generator for that last couple hours of charging.
  • BB.BB. Super Moderators, Administrators Posts: 29,497 admin
    Re: Inverter/ batteries without solar panels

    It is is getting very difficult to find smaller prime mover designed gensets these days... I wonder if it is not all of the laws/regulations on fixed installation and off/road internal combustion engines that is pushing the smaller/lower profit systems out of production. In California, if you buy parts for a fork lift/old genset, the parts dealers send the information back to the state--who puts you in their data base and starts mailing you questions about your engines to see if you have to upgrade for pollution control requirements (from what I understand/have heard).

    You might look in wrecking yards that have RV equipment and see if you can find a used genset that meets your requirements--or at least cheap enough that when it fails in 5-10,000 hours, that you don't feel bad replacing it.

    You might also look at marine systems. Or two gensets--One smaller (throw away) to keep your batteries charged in a fuel efficient manner... And a second larger genset for your major loads/backup to the first.

    Anyone who knows of good quality, smaller gensets (any fuel), please post them here. It would be helpful to many folks.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverter/ batteries without solar panels

    The Magnum inverter should be able to run that well pump directly. One hint: make sure there is a very large pressure tank on the pump. This will reduce pump cycling and thus the frequency of start-surge demands. It is even possible to wire it so it can't come on unless the battery Voltage is high enough just to be sure.

    Generators are quite an issue in themselves. Most of the systems I deal with have one or two small gasoline generators because it is not the primary charge source. This is different. Diesel gen sets are more suited to this kind of usage, but you want propane. Have to say I'm not a big fan of propane generators. But I'll bet there's someone on this forum who has a good recommendation or two.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverter/ batteries without solar panels
    BB. wrote: »
    In California, if you buy parts for a fork lift/old genset, the parts dealers send the information back to the state--who puts you in their data base and starts mailing you questions about your engines to see if you have to upgrade for pollution control requirements (from what I understand/have heard).

    Why do people live there again?
    We have some pretty intrusive laws up here but if they tried something like that they'd get another lesson in "civil non-compliance". Or possibly a hockey stick in the teeth.

    Anyone who knows of good quality, smaller gensets (any fuel), please post them here. It would be helpful to many folks.

    -Bill

    Ditto. Good quality small gensets are becoming very difficult to find. Not everyone can use "disposable" generators.
    Maybe adapt a Lister to propane, something like that.
  • 10fords10fords Registered Users Posts: 9
    Re: Inverter/ batteries without solar panels

    A quick update: After getting a second opinion from another solar contractor it looks like they might be going with solar panels on the project. Basically we will put about double the amount of panels that would normally be required as the sun exposure is poor. I'll keep everyone updated with the progress -Scott
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