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Is it economical for a home owner to add storage to already existing rooftop PV?

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  • Is it economical for a home owner to add storage to already existing rooftop PV?

    One of friends from Northern California is looking to add storage. Is it beneficial? How to evaluate it and are there any calculators? I also posted this question here http://renewableelectron.com/questio...ng-rooftop-pv/

  • #2
    How does storage reduce your cost of electricity? If you are looking at using batteries to shift demand under a TOU plan, I think it might make sense someday, but not under the residential tariffs that exist today.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #3
      Based on the current battery technology and costs unless you have a lot of power outages or can save a lot of money by offsets the high cost of the POCO's power through a TOU plan the payback for any home energy storage system is very long and IMO not worth the investment until the price comes down and the output (kWh) goes up.

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      • #4
        If you are net-metering, then I doubt it would ever make sense economically. If your grid goes down a lot, it may make sense for your lifestyle, but it is still not economic.

        I have a neighbor who is net-metering, They have no batteries. They seem to be content with one or two power outages every month. They have no intent to ever get batteries.

        If you are off-grid and you are discussing expanding an already existing battery bank. That is a different kind of discussion.


        4400w, Midnite Classic 150 charge-controller.

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        • #5
          Until rates reach $1.10 per KWh, battery backup will COST you money (replacing many expensive batteries every 8 years)
          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 Mike90250 View Post
            ... (replacing many expensive batteries every 8 years)
            Why would anyone choose to replace their batteries every 8 years?

            4400w, Midnite Classic 150 charge-controller.

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            • #7
              Originally posted by organic farmer View Post

              Why would anyone choose to replace their batteries every 8 years?
              Well the systems that are currently being offered by Tesla and others only have a 5 year warranty so I would guess 8 years might be the existing life time.

              What is the lifetime for any type of EV battery? Probably much less than 8 years and that is what is being advertised for these home systems.
              Last edited by SunEagle; 05-06-2016, 03:15 PM. Reason: added last sentence

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              • #8
                Originally posted by organic farmer View Post
                Why would anyone choose to replace their batteries every 8 years?
                Not actually a choice, it's when they eventually fail and go bad, unless it's a bad design and the batteries fail year 2.

                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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                • #9
                  Originally posted by Mike90250 View Post
                  Not actually a choice, it's when they eventually fail and go bad, unless it's a bad design and the batteries fail year 2.
                  I checked out the latest ad concerning the Tesla PowerWall. It now has a 10 year warranty but is only rated 6.4kWh. But they did say you could discharge it 100%.

                  So I did some quick calculation and if it can delivery 6.4kWh every day for 10 years that came to about 23400kWh. For me to purchase the same amount of power at $0.11/kWh (that price actually is lower now for me than 8 years ago) would only cost me ~ $2600. I seriously doubt that battery will ever cost $2600 or less to install.

                  So even with all of their claims, it would never be a good investment for anyone that pays $0.15/kWh or less. And that is assuming it only costs $3500 to install one.
                  Last edited by SunEagle; 05-06-2016, 07:10 PM. Reason: spelling

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                  • #10
                    Originally posted by starsun View Post
                    One of friends from Northern California is looking to add storage. Is it beneficial?
                    If you:
                    -have frequent and costly/dangerous power interruptions
                    -are no longer allowed to backfeed the grid
                    -are paying astronomical rates for power without grid tie
                    -cannot get on the grid (i.e. far from power lines)

                    Then it might make sense. But for someone on the grid in (say) Sacramento - it doesn't make economic sense.

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                    • #11
                      From talking with my neighbors, it seems that first-time batteries last between 10 and 15 years.

                      Among my neighbors, the shortest battery lifespan has been 10 years, when one guy allowed his batteries to freeze [a toilet ran all night, which drained his batteries, once they were flat those froze].

                      The shortest lifespan is 10, the longest is 15 years. I have neighbors who have been off-grid 30+ years.
                      4400w, Midnite Classic 150 charge-controller.

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                      • #12
                        Originally posted by organic farmer View Post
                        From talking with my neighbors, it seems that first-time batteries last between 10 and 15 years.

                        Among my neighbors, the shortest battery lifespan has been 10 years, when one guy allowed his batteries to freeze [a toilet ran all night, which drained his batteries, once they were flat those froze].

                        The shortest lifespan is 10, the longest is 15 years. I have neighbors who have been off-grid 30+ years.
                        Those must be some very interesting battery systems. I am not saying I know all about off grid and how to keep a system happy and long life but most FLA battery manufacturers do not warranty life spans more than 5 years unless you use less than 10% every other day.

                        As for any Lithium type chemistry the lifespans maybe longer but at a much higher up front cost which equates to a very expensive way to generate power and being much more than FLA with its shorter life.

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                        • #13
                          One online retailer charges $4500, so that's $4500 / 23400kWh = $0.19 /kWh for storage if you are an electrician and install it yourself onto a system that can already handle it.
                          With the ITC, it's 30% less, or $0.13.

                          Hawaii's considering offering another 25%: http://www.thestate.com/news/busines...e74562142.html
                          That would bring the price down to $0.09.

                          That very well might make sense in Hawaii.

                          http://arstechnica.com/business/2015...lls-in-the-us/ quotes the installed cost of a powerwall plus inverter (presumably solaredge 7600?) as $6500. If a solaredge installed is $2000, that suggests the installed price of a powerwall is $4500. So maybe the estimate above is valid for non-diy, too.
                          Last edited by DanKegel; 05-07-2016, 09:52 AM.

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                          • #14
                            Originally posted by DanKegel View Post
                            One online retailer charges $4500, so that's $4500 / 23400kWh = $0.19 /kWh for storage if you are an electrician and install it yourself onto a system that can already handle it.
                            With the ITC, it's 30% less, or $0.13.

                            Hawaii's considering offering another 25%: http://www.thestate.com/news/busines...e74562142.html
                            That would bring the price down to $0.09.

                            That very well might make sense in Hawaii.
                            Maybe. What makes you think Tesla will allow someone to DIY? And would you really spend $4500 on the hope it lasts 10 years providing full nameplate output? I see you like to gamble with your money.

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                          • #15
                            Originally posted by SunEagle View Post

                            Those must be some very interesting battery systems. I am not saying I know all about off grid and how to keep a system happy and long life but most FLA battery manufacturers do not warranty life spans ...
                            Manufacturer warranties are like life insurance policies or any game of chance in a casino. The odds are in the favor of the house. If they say 5 years, that means they know that none of the product will fail before 5 years. One of every thousand will fail in 10 years. And by 20 years 50% will fail.


                            4400w, Midnite Classic 150 charge-controller.

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