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  • A/C offgrid

    Well, we've gotten into the "dog days" of summer here. No wind, hazy semi-overcast conditions and very hot (yes, water vapor in the air is even more of a potent "greenhouse" gas than CO2).

    So we're running our A/C around the clock to keep the house nice and comfy. We ran the A/C yesterday on solar and wind power alone and didn't start the prime generator last night. That was a mistake:



    The system started the big genset between 1:00-2:00AM and ran it for about 2.5 hours. The system starts the standby generator when the battery gets to 35% SOC and shuts it off when the battery gets to 50% SOC. When we woke up this morning in our nice cool and de-humidified house the batteries were at 42% SOC.

    So I started the prime generator at about 7:50AM this morning and leaving it run all day. Our normal loads in the house, plus the A/C going 24/7 means we are using 70-80 kWh/day with no utility power here. Our loads are running 3-4 kW continuous. The little prime generator takes enough load off the RE system so it can charge batteries, and they been charging at 100-120 amps all day so they're up to 70% SOC as I write this.

    It takes a LOT of power to run A/C. As long as you don't have some sort of religious beliefs that prevent you from running a generator, you CAN power an A/C system off-grid. But that generator is the only way I've found that it can be economically (or practically) done.

    I threw this out because not too long ago there was a thread where somebody asked about this, but can't find that thread right now. And I've seen it from many other folks too - live in a hot climate, want to move off-grid and the big question is, "how can power that A/C?" Solar panels can't do it. The sun only shines part of the day and that means the rest of the day you're on batteries. Batteries can't do it because even a big bank gets killed by Peukert Effect in short order. Generators can do it.
    off-grid in Northern Wisconsin for 14 years

  • #2
    Great post Chris - Thanks!

    Russ
    [SIGPIC][/SIGPIC]

    Comment


    • #3
      I forgot to mention cost. This is a big issue for most folks.

      Typically, what we do is let the solar and what little wind we get during the day power the A/C without running the generator during the day. The reason we're running it today is because I screwed up last night, thinking we could run off battery power thru the night. So the bank was sacked out this morning and needs to be charged up.

      Normally we'll start the little genset at about 7:00PM and run it until 7:00AM to keep the load off the batteries at night. Then let the solar take over and run it during the day again.

      The little generator burns a quart an hour at the power setting we use. So we'll burn up 3 gallons per day @ (current price) $3.69/gallon. So it costs us $11 bucks a day in fuel for the luxury of having A/C. For us, that's a cheap price to pay to escape from being miserable in the heat.
      off-grid in Northern Wisconsin for 14 years

      Comment


      • #4
        Originally posted by ChrisOlson View Post
        I forgot to mention cost. This is a big issue for most folks.

        Typically, what we do is let the solar and what little wind we get during the day power the A/C without running the generator during the day. The reason we're running it today is because I screwed up last night, thinking we could run off battery power thru the night. So the bank was sacked out this morning and needs to be charged up.

        Normally we'll start the little genset at about 7:00PM and run it until 7:00AM to keep the load off the batteries at night. Then let the solar take over and run it during the day again.

        The little generator burns a quart an hour at the power setting we use. So we'll burn up 3 gallons per day @ (current price) $3.69/gallon. So it costs us $11 bucks a day in fuel for the luxury of having A/C. For us, that's a cheap price to pay to escape from being miserable in the heat.
        Better get some more gas in case the global temp goes up another 0.5 C.

        Oh. I also agree with russ. That is really good data for those that want to live off grid like you.

        Comment


        • #5
          Originally posted by SunEagle View Post
          Better get some more gas in case the global temp goes up another 0.5 C.
          Let's just say we're not gonna worry about that this year. If it starts getting too hot we got the backup plan. Diesel fuel. Turn the sky black and block the sun out, and cool the earth. We got a handle on it.

          off-grid in Northern Wisconsin for 14 years

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          • #6
            solar, or anti gov website?

            What does this to do with solar panels?
            Does this website have a mission statement that allows anti gov posts that have nothing to do with solar panels?

            Comment


            • #7
              Originally posted by GomezMiami3333 View Post
              What does this to do with solar panels?
              Does this website have a mission statement that allows anti gov posts that have nothing to do with solar panels?
              Read the thread - not anti government but anti BS

              Something you haven't read but don't agree with is anti government?
              Last edited by russ; 07-22-2014, 04:28 AM. Reason: added
              [SIGPIC][/SIGPIC]

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              • #8
                Originally posted by ChrisOlson View Post
                The system started the big genset between 1:00-2:00AM
                <snip>
                The system starts the standby generator when the battery gets to 35% SOC
                <snip>
                So I started the prime generator at about 7:50AM this morning and leaving it run all day.
                <snip>
                Batteries can't do it because even a big bank gets killed by Peukert Effect in short order.
                Originally posted by ChrisOlson View Post
                I screwed up last night, thinking we could run off battery power thru the night. So the bank was sacked out this morning and needs to be charged up.

                Normally we'll start the little genset at about 7:00PM and run it until 7:00AM to keep the load off the batteries at night.
                Hi Chris,
                It's been awhile since I read about your generator collection... and I know that it changes from time to time... please remind me what you've got now... you've mentioned big, standby, prime, and little generators in this thread.

                Also, please remind me what your battery bank is now... a couple of years ago, if I recall correctly, you were running six parallel strings at 48 volts (144 cells).

                Originally posted by ChrisOlson View Post
                The system starts the standby generator when the battery gets to 35% SOC and shuts it off when the battery gets to 50% SOC.
                Is that a voltage based AGS or SOC based AGS? If voltage based, what voltage starts the generator?

                --mapmaker
                ob 3524, FM60, ePanel, 4 L16, 4 x 235 watt panels

                Comment


                • #9
                  We got three gensets and the big one (standby unit) is started and stopped based on either load or battery SOC, not voltage. The system that starts and stops it on SOC is not available to the general public yet and I am beta testing it but bound by NDA on it until it is released. So I can't really tell you too much about that other than it works pretty good and is light years ahead of using voltage-based start/stop for low battery condition because it doesn't waste fuel. Once you get it tuned to work with the RE system it will only charge the battery with the generator to the point where the RE system can finish charging. This system will be appearing on the market sometime this fall, and then I can tell more about it and my experience using it.

                  Our battery wiring was changed some time back to reduce the number of strings to three, and we now have shunt-based battery monitors on each string and those battery monitors are what starts and stops the standby genset based on SOC. The XW System starts and stops it based on load. That is all the standby generator is used for.

                  The prime generators are much smaller units, and are run for extended periods of time when we get poor RE conditions in winter. And also for extended periods of time of high-draw operation on the system (using generator support) to prevent sacking the battery out due to the RE system not being able to keep up. One prime unit is a little Honda EP2500CX that we also added some time back. It is a conventional, a little bigger than a EU2000, with a GX160 engine. We were going to use a EU2000 but we are using a Outback PSX-240 autotransformer for split-phase from the 120V genset. The EU2000 will not handle the surge when the core in the transformer is magnetized (went thru this with one of the neighbors last spring and had to build him a soft start for his) and it faults. So we went with the conventional unit, which has no problems with the transformer, has better surge power, and higher continuous output rating.

                  The other prime unit is a twin-cylinder liquid-cooled Perkins rated at 3.0kVA that we recently replaced our air-cooled Robin diesel with. We went with that one because it can be pre-heated in the winter with a regular block heater and is our new winter-time prime unit when we need a larger genset for continuous loads due to reduced output from the solar in the winter to help it out.

                  Our system is not the conventional off-grid system like most people think of off-grid. I set out on a mission a few years ago to figure out how to live big off-grid without breaking the bank. Our system is a combustion generator/RE hybrid that uses genset power and RE power together just like a hybrid car uses electric and combustion engine power together. It allows us a normal lifestyle like anybody on utility power would have, but we have a regular monthly fuel bill in generators to support it. Our system was never designed to be "green" or reduce our "carbon footprint" or any other of that ridiculous stuff. It was designed to be able to live normal off-grid, like anybody else does on-grid, but without the costs of maintaining a huge battery bank that would cost $30,000 to support our lifestyle.
                  off-grid in Northern Wisconsin for 14 years

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                  • #10
                    Originally posted by ChrisOlson View Post
                    We got three gensets and the big one (standby unit) is started and stopped based on either load or battery SOC, not voltage.
                    Is the big standby generator the honda 4000 with the electronic voltage regulation (I think I remember that from another thread)?

                    Originally posted by ChrisOlson View Post
                    The prime generators are much smaller units, and are run for extended periods of time when we get poor RE conditions in winter. And also for extended periods of time of high-draw operation on the system (using generator support) to prevent sacking the battery
                    So you are managing gen support with two small generators, neither of which is an inverter generator? What's the secret to that?

                    --mapmaker
                    ob 3524, FM60, ePanel, 4 L16, 4 x 235 watt panels

                    Comment


                    • #11
                      Originally posted by mapmaker View Post
                      Is the big standby generator the honda 4000 with the electronic voltage regulation (I think I remember that from another thread)?
                      That is a Honda EM4000SX. It will produce 5.0 kVA on surge for 20 seconds and maintain 240V and 60Hz. It will produce about 5.8kVA on surge with voltage and freq drop. It produces 4.0 kVA for 30 minutes and 3.6 kVA continuous at up to 115F ambient. It is electronic controlled engine, as well as voltage regulation.

                      So you are managing gen support with two small generators, neither of which is an inverter generator? What's the secret to that?
                      Schneider Xantrex XW-series inverter. They are the only ones that ever got gen support right in a split-phase inverter.
                      off-grid in Northern Wisconsin for 14 years

                      Comment


                      • #12
                        Originally posted by ChrisOlson View Post
                        Schneider Xantrex XW-series inverter. They are the only ones that ever got gen support right in a split-phase inverter.
                        How tight must the voltage and frequency regulation (of the generator) be in order to use gen support?

                        --mapmaker
                        ob 3524, FM60, ePanel, 4 L16, 4 x 235 watt panels

                        Comment


                        • #13
                          You can set it to whatever it takes to protect your equipment. I'd have to look to see what I'm using on the low side, but I think I have it set to 110V minimum per leg, and 55 Hz.

                          Over-shoot of the governor is important too. I know have that set to 252 (126V per leg) and max 63 Hz. If the generator is loaded heavy and suddenly the load goes off, the over-shoot can damage equipment faster than being under voltage and freq, so I set the tolerance tighter on that.

                          Inverter generators do not work that well on gen support because the inverter expects the generator to be able to handle part of extreme surge loads up to 125% within the allowable voltage and freq drop. Inverter generators can't do that and conventionals can, so an inverter gen just faults on overload because it has no surge capacity to allow for "soft starting" heavy surge loads. An example is both the A/C compressor and well pump start at the same time. The surge amps probably approach 100A per leg with other normal loads on. You set the amps in the XW's menu that the generator can supply on surge, but the XW expects that to be at least 25% higher than the gen support setting for the time required to handle the surge and the inverter handles the rest. This snuffs an inverter generator as fast as you can blink your eyeballs, while a conventional generator handles it without even blinking an eyeball.

                          Inverter generators are great for camping, or running a few tools on the job site, or whatever. But they were never made for off-grid power, and to feed the input on a big inverter with generator support. And especially a split-phase unit. Our neighbor made the mistake of buying a little EU2000 with a PSX-240 on their XW to do the same thing we do so they can have A/C in the summer. I had to make a soft-start for it so it would power up the transformer. And now they got problems with it faulting all the time if the A/C compressor cycles. So they've "fixed it" for now by turning down the thermostat on their A/C so it doesn't cycle. But after messing with it for two hours a few days ago I told 'em they're going to have to buy a real generator and sell that EU on craigslist or something, because it just doesn't work.
                          off-grid in Northern Wisconsin for 14 years

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                          • #14
                            So you are managing gen support with two small generators, neither of which is an inverter generator? What's the secret to that?
                            It works easily (with the XW series). My main genset, is a 1930'ish clone 650 rpm diesel. Even with it's power stroke strobe light effect, the XW sync's fine. But my garage door opener wont work with it. The Subaru genset (diesel also) has much tighter controls, but my gas oven thermostat wont work with it.
                            Listeroid 58 - 61 Hz
                            Subaru 59-61hz (according to my kill-a-watt and XW control panel)
                            Powerfab top of pole PV mount (2) | 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

                            Comment


                            • #15
                              Originally posted by Mike90250 View Post
                              But my garage door opener wont work with it. The Subaru genset (diesel also) has much tighter controls, but my gas oven thermostat wont work with it.
                              I would guess that the reason those things don't work is THD causing problems with the electronics. The XW will sync with damn near any generator that puts out some semblance of a sine wave. But it mimics what it gets from the generator in order to do that. So if you got dirty power in, you get get dirty power out.
                              off-grid in Northern Wisconsin for 14 years

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