Off_Gridder: Inverter/ batteries without solar panels

Hi folks. I'm new to the forum but have been looking for info to set up a system like this myself... so I wanted to bring up a couple of points that have been concerning me and looking for a solution around them..and I think this relates to potential solutions to the original post as options/considerations of course:

1. I've contemplated setting up generator-only powered lines for the heavy loads and I thought I had a good solution to avoid over doing the battery bank... then when I got into the issues of 'pure-sine' vs. 'dirty AC' out of generators (and the motor/electronics burn-out case), it led me back to an inverter:

2. I've read bits and pieces about setting up a generator and inverter so that the inverter will pull power as needed from either battery bank or generator (assuming for simplicity--or possibly need--that both gen and battery bank are at same DC voltage---let's say 12 for simplicity)... so when the battery bank gets low then the auto start kicks in and charging occurs... when heavy loads are present (water pump, fridge or other), then you can start the gen yourself (ie, assuming bank is topped up and does not need charge), so that the generator feeds the inverter directly which then produces 'pure-sine' output... BUT

3. The well-pump is the thing that one can't really schedule around---or is it? So, if #2 above is possible... then is the only way to get the generator to kick on is when the bank runs low vs. when a very heavy load kicks in? So scenario being: Bank is full, generator is off... well-pump kicks on making a heavy impulse draw... 1) Pure-sine inverter is large enough to meet the high-load draw from the start of the pump (better to have the inverter do a pass-thru of 'clean' pure-sine power to the pump), and then 2) generator kicks on to serve the heavy full cycle load of the water pump. Then well pump switches off, gen keeps running to top up batteries..then shuts off.

Also... I'm thinking I'll need more power than what I've seen in the inverter-generators like the Honda's... and I'd also like to keep them separate so if I want to change my generator then I can easily do that while keeping a separate Inverter.... I'm thinking of a 7KW propane generator because I'll have propane for heaters, etc... so will have a 500 gallon tank and I don't want to deal with multi-fuel types of diesel/gas and don't like the gumming nature, evaporation issues, etc... Propane is ideal for me for these reasons.

So, my question really focusing on 'unscheduled loads' and how to leverage generator power to avoid over-investing in batteries ... while also avoiding 'dirty-power' from generators that decrease the life of electronics/motors/etc...

I would think these considerations go directly into this main question ... because the rest of it is very similar to what I need...

Anyway, I hope these considerations/concerns add to the core post...and thanks in advance for any insight!

Cheers

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Off_Gridder: Inverter/ batteries without solar panels

    Welcome to the forum Off Gridder,

    I moved this to your own thread--That way we can discuss your needs without confusing the original thread. Feel free to guide the discussion along the lines that are helpful for you.

    Typically, I would suggest keeping your discussion all in this thread--That way it is easier for us to follow the conversation.

    First--I am not quite sure I understand your needs. And that may be the problem for you too. Any off grid power is 1) measuring/logging your loads (kill-a-watt type meter) and 2) define your needs (weekend cabin, full time, etc.). Then finally 3) pick the equipment.

    And for 1)--This may be an interitive approach. Measure what you have, then see if you can find something that will do what you need using less power... For example water pumping. Many people start with a 3/4-1 HP in well pump that will use a 2,000 watt + inverter just to start the pump and run for 10 minutes a day, or run 30 seconds at a time to fill a pressure tank.

    There are other options out there... You can pump to a cistern with a "slow pump" (lower power) and then use a small DC (or AC) pump+small bladder tank to provide water to your home/cabin. There are other pumping options too that we can discuss--But while many of the pumping solutions are not "cheap"--Many will save you fuel (generator runtime) and/or allow you to dramatically reduce the size of your inverter/battery bank (less peak power, more efficient pumping, etc.).

    And this gets back to your needs--How deep is your water, how many gallons per day, do you have a cistern/elevated tank (or tank site) available, do you need to pump for four seasons, etc...

    Similar questions with the Fridge... A typical energy star full size refrigerator will use around 1-1.5 kWH per day and need ~1,500 watt inverter to start it (assuming auto-defrost heaters, ice maker, etc.). You can get refrigerator/freezers designed for off grid DC power--But they tend to be very expensive and less features (manual defrost, etc.). So expensive--you probably would save money to buy an energy star fridge+larger inverter+a couple more solar panels instead.

    Or--if you are there only weekends for spring/summer--perhaps a used RV propane fridge would be a better option...

    Anyway--Don't get too wrapped up in solutions just yet--Define your loads (and conservation opportunities) first. Then we can look at some options to power them.

    By the way--is there some reason solar is not viable for your needs? Running a genset will get expensive for your long term power needs if you cannot use solar to reduce the fuel usage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Off_Gridder: Inverter/ batteries without solar panels

    Add storeage capacity so you can time the pump cycle to when want it. A larger p tank or a series of tanks. Monitor and gauge your daily (or weekly ) useage and design accordingly, or as Bill suggests do a larger unpressurized holding tank, (cistern) and use a smaller pump to pressurize the house. That does have sanitation issues however if the cistern is exposed to the outside environment.

    Good luck, welcome to the forum,

    Tony
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Off_Gridder: Inverter/ batteries without solar panels

    i think i may know where he's going with this. he wants an inverter with a built in charger and automatic genny start. while the genny is on it will power your ac circuits as well as charge the batteries, if the genny is large enough to handle it all. you would then shutdown the genny and run from battery and if the batteries reach a certain point it can automatically kick the genny back on. there is some degree of manual operations with this setup as you will be needed to shut down the genny for whatever reasons, like the batteries are charged fully, unless you let it run until it's empty.

    now there are some out there that fit this and one example may be like the magnum mms1012. (yes, for 12v operation, but there's others as well and for differing voltages and wattages) if one attaches the remote like the me-rc it can be used to help remote fire the genny. now i don't use mine in a genny autostart so i can't say what else may be involved with that if anything and i'll let others chime in on that if i'm on the right tract of what you are after.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Off_Gridder: Inverter/ batteries without solar panels
    3. The well-pump is the thing that one can't really schedule around---or is it? So, if #2 above is possible... then is the only way to get the generator to kick on is when the bank runs low vs. when a very heavy load kicks in? So scenario being: Bank is full, generator is off... well-pump kicks on making a heavy impulse draw... 1) Pure-sine inverter is large enough to meet the high-load draw from the start of the pump (better to have the inverter do a pass-thru of 'clean' pure-sine power to the pump), and then 2) generator kicks on to serve the heavy full cycle load of the water pump. Then well pump switches off, gen keeps running to top up batteries..then shuts off.

    You can do this with some inverter/chargers. In fact they can auto-start and stop the generator not only based on the battery state of charge, but also on the current draw. The catch is that the inverter must be large enough to sustain that current draw initially. Bare in mind that all inverter/chargers have an internal transfer switch, and once the generator is started they'll pass through generator power to your loads and use the spare energy for charging the batts. I.e. your loads will run on the "dirty" gen power through the inverters transfer switch. If you really only ever want to see clean inverter power then you'll have to buy a separate DC charger to put between the gen and battery.

    And about this "dirty" generator power. The quality depends on the quality of your genset, even non-inverter type generators can produce a good quality sine wave using AVR and a good quality governor.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Off_Gridder: Inverter/ batteries without solar panels
    BB. wrote:
    By the way--is there some reason solar is not viable for your needs? Running a genset will get expensive for your long term power needs if you cannot use solar to reduce the fuel usage.

    If you add solar panels to the mix, the system (batteries, battery box, inverter, cables, fuses, electrical panels, meters, solar panels, etc, but not the generator) is eligible for 30% federal tax credit. The credit on the inverter and batteries alone may be enough to pay for the solar panels.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i