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  • Whole House Generator vs. Hybrid System

    We will be installing 64 Sunpower 327W panels with SMA inverters at our home within the next few months. We chose SMA inverters in part because they'd be compatible with a Sunny Island battery backup system if we wanted to add one in the future. We have lived in this home for 7 months and need to address backup/emergency power at some point. Our area has had power outages of 8 days or more several times in the past few years due to weather events. Our options are a battery system tied to solar with a smaller standby generator, or a 22KW whole house standby generator. I've read many of the posts making the case that battery backup systems are not cost effective. The one advantage I see is that we'd be much less likely to run out of propane during a long outage. My guess is that battery options will improve and decrease in cost in the future. Do others agree/disagree with this? I'd like to have some in depth information comparing the economics of each option.

  • #2
    Dglavin,

    The SMA inverters as you know have a power port for use during outages to support lights and small appliances - when the sun is shining. Generally speaking batteries are much more expensive per KW than a generator - others here will have better cost/usage estimates I am sure.

    When looking at Generators a 20KW system with 200AMP disconnect is roughly $5K and a 14KW is $4K. The difference in LP consumption of the 20KW (3.7GPH) to 14KW (2.2GPH) is at full load so you probably would want to install a 500Gal propane tank unless you already have one?

    Another option is a 20KW diesel generator, $12K if you heat with oil, it could run off that source. It will take a lot of hours operation to make up the difference of $7K to a propane unit IMO.

    Sum and substance, the $ delta between a lower KW (14 to 20) is so small I can't see the benefit of a hybrid approach, since the installation costs of either size will be the same, and then you add cost of batteries, maintenance and installation of a hybrid system.

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    • #3
      Originally posted by Carl_NH View Post
      Dglavin,

      The SMA inverters as you know have a power port for use during outages to support lights and small appliances - when the sun is shining. Generally speaking batteries are much more expensive per KW than a generator - others here will have better cost/usage estimates I am sure.

      When looking at Generators a 20KW system with 200AMP disconnect is roughly $5K and a 14KW is $4K. The difference in LP consumption of the 20KW (3.7GPH) to 14KW (2.2GPH) is at full load so you probably would want to install a 500Gal propane tank unless you already have one?

      Another option is a 20KW diesel generator, $12K if you heat with oil, it could run off that source. It will take a lot of hours operation to make up the difference of $7K to a propane unit IMO.

      Sum and substance, the $ delta between a lower KW (14 to 20) is so small I can't see the benefit of a hybrid approach, since the installation costs of either size will be the same, and then you add cost of batteries, maintenance and installation of a hybrid system.
      I have quotes for installation of a Generac 22KW standby generator ranging from $10K-$13K. This is turnkey--includes cement pad, trenching, etc. The generator and transfer switch alone is $4650.

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      • #4
        Originally posted by dglavin96 View Post
        My guess is that battery options will improve and decrease in cost in the future.
        Don't fool yourself with false assumptions. Batteries have never gone down in price, and no real improvements in the last 100 years as it is a mature technology. Batteries are a commodity made from lead, plastic, and electricity and will go up in price at a rate greater than inflation.

        With a hybrid system you will be extremely limited in the amount of power it can supply, and requiring you to completely rewire you home electrical system. With a battery system you will not be running any electric heat, air conditioning, electric hot water, cooking, clothes dryer, or any high demand items. Batteries also have a shelf life and need replacement even if you do not use them.

        So make sure you know the facts to make an informed decision. Not one of false assumptions and wishes.
        MSEE, PE

        Comment


        • #5
          It's all about the loads. Do you need to keep the beer in the fridge cold, the ice cream frozen, the spa bubbling along and the air conditioning going at all times. Just the sauna ? The iron Lung for grandma?

          Once you have your ESSENTIAL loads, then you know the size of the genset.

          Beware of Generac , they are known for NOT honoring warranty claims (oh there was a power failure, so really you used it off grid. Void! ) And because they are not good engines, there will be claims.

          if your loads can be managed by a manual start genset, something like the honda eu series can be a pretty reliable power source.
          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

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          • #6
            Originally posted by dglavin96 View Post
            I have quotes for installation of a Generac 22KW standby generator ranging from $10K-$13K. This is turnkey--includes cement pad, trenching, etc. The generator and transfer switch alone is $4650.
            Several things, 1) doing a generator at the same time as the solar may save some $ on the wiring and interconnections at the same time. 2) checkout the Kohler brand systems (they get better reports than Generac) and will a 20KW system support your load? Most here quote about 2x generator cost - or $9K range. I had a quote for 12KW at $5.6K installed.

            Rarely does the home draw 80+ amps (that's a 20KW system) unless you have a lot of AC/Heat Pumps/Geothermal load?

            Comment


            • #7
              Battery Technology

              Originally posted by Sunking View Post
              Don't fool yourself with false assumptions. Batteries have never gone down in price, and no real improvements in the last 100 years as it is a mature technology. Batteries are a commodity made from lead, plastic, and electricity and will go up in price at a rate greater than inflation.

              With a hybrid system you will be extremely limited in the amount of power it can supply, and requiring you to completely rewire you home electrical system. With a battery system you will not be running any electric heat, air conditioning, electric hot water, cooking, clothes dryer, or any high demand items. Batteries also have a shelf life and need replacement even if you do not use them.

              So make sure you know the facts to make an informed decision. Not one of false assumptions and wishes.
              Exactly why I'm reading the threads and posting here. I want to learn enough to make an informed decision. This may be completely ignorant, but is it possible that battery technology from companies like Tesla could change the landscape?

              Comment


              • #8
                Originally posted by Mike90250 View Post
                It's all about the loads. Do you need to keep the beer in the fridge cold, the ice cream frozen, the spa bubbling along and the air conditioning going at all times. Just the sauna ? The iron Lung for grandma?

                Once you have your ESSENTIAL loads, then you know the size of the genset.

                Beware of Generac , they are known for NOT honoring warranty claims (oh there was a power failure, so really you used it off grid. Void! ) And because they are not good engines, there will be claims.

                if your loads can be managed by a manual start genset, something like the honda eu series can be a pretty reliable power source.
                I am set on a standby generator fueled by my existing propane tanks. For a variety of reasons, I don't want a portable gas generator. Can you recommend a better alternative to Generac?

                Comment


                • #9
                  Originally posted by dglavin96 View Post
                  I am set on a standby generator fueled by my existing propane tanks. For a variety of reasons, I don't want a portable gas generator. Can you recommend a better alternative to Generac?
                  Kohler.
                  MSEE, PE

                  Comment


                  • #10
                    Originally posted by dglavin96 View Post
                    Exactly why I'm reading the threads and posting here. I want to learn enough to make an informed decision. This may be completely ignorant, but is it possible that battery technology from companies like Tesla could change the landscape?
                    Yes, it is possible, but not foreseeable. Any major improvement will come in a battery chemistry other than Lead Acid. And there will be a gradual implementation unless a major consumer with deep pockets like Tesla gets behind it.
                    At this point I think that Musk's role will be more in the form of financial backing than in basic battery research. But I do not know what is going on behind their closed doors.
                    SunnyBoy 3000 US, 18 BP Solar 175B panels.

                    Comment


                    • #11
                      Originally posted by dglavin96 View Post
                      Exactly why I'm reading the threads and posting here. I want to learn enough to make an informed decision. This may be completely ignorant, but is it possible that battery technology from companies like Tesla could change the landscape?
                      Well good that is the way it should be done.

                      But don't hold your breath waiting for lithium. Lithium is still in its infancy and still has a lot of issues to work out. Those with a deep understanding of the challenges can work with lithium using solar, but comes with great expense and risk. It will be a long time before lithium is ready for solar main stream use. Right now the only applications that can justify the cost and risk is small electronics like cell phones, laptops, battery power tools, and automotive applications. But lithium still has serious issue for those applications to be ironed out.
                      MSEE, PE

                      Comment


                      • #12
                        Originally posted by dglavin96 View Post
                        Exactly why I'm reading the threads and posting here. I want to learn enough to make an informed decision. This may be completely ignorant, but is it possible that battery technology from companies like Tesla could change the landscape?
                        Yes, we hope this pans out well with the battery Giga-factory in the west and the fact that Elon's cousin is the CEO of Solarcity and they are building a panel plant in Buffalo NY makes this very interesting.

                        So, yes solar and battery technology will change in 3-5 years and Musk is going after the holy grail - getting the sun to work 24 hrs a day over the long term at an affordable price.

                        Comment


                        • #13
                          when making your decision about hybrid vs generator, consider how long of an outage you want to protect yourself from, if only a week, then generator is cheapest route, if you want to protect yourself from longer term grid outages, then 2 Sunny Islands and several batteries may be appropriate, Sunny Islands only put out 120VAC plus you seem to want capability of lots of watts. You can use 2 SI for 240VAC or use one SI with a step up transformer.

                          Comment


                          • #14
                            Originally posted by sulfur View Post
                            when making your decision about hybrid vs generator, consider how long of an outage you want to protect yourself from, if only a week, then generator is cheapest route, if you want to protect yourself from longer term grid outages, then 2 Sunny Islands and several batteries may be appropriate, Sunny Islands only put out 120VAC plus you seem to want capability of lots of watts. You can use 2 SI for 240VAC or use one SI with a step up transformer.
                            I wouldn't use the length of an outage or even the number of outages a year to justify between using a generator or battery system.

                            A generator that is properly exercised and maintained will still be available and useful if it has been used only once for an extended period or 10 times for an extended periods after 5 years.

                            Batteries on the other hand, used only once or every day will be near death after 5 years and need to be replaced.

                            Comment


                            • #15
                              The point of my comment is that if she is trying to protect herself from long term outages, say 3 months, she will not have enough propane and will have no power. Just depends what the goals are.

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