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  • Expandable Solar Panel Starter System

    I'm not looking for cheap (i.e. chinese). I'm not looking for expensive. I'm looking for quality and reliability.

    But more importantly, I'm looking to start small and build. This is not only for a real application, but also as a learning experience

    I'm an Electrical Engineer. I'm 100% sure I could figure this all out. But I'd like to save some time, by asking those who have already been there.

    Requirements:
    1) eventual design goal, 12-15K
    2) designing for off-grid, and battery storage
    3) I'd like to minimize replacing components as system grows
    4) I'd like to start with 2-4 panels, and generate around 1000W to start with.

    What I would like to know are a few basic things. I understand the architecture of the system, but I'm not familiar enough to the components to know what the best way to go is. For instance, an inverter that can't work at 15K doesn't do me any good. One that will work well at 15K might not work well at 1K.

    * should I use 100W, 250W, 500W panels,
    * what technology for the solar panels
    * what inverter should I consider (brand, model)
    * what charge controllers should I consider (brand, model)
    * do I need charge controllers or does the inverter do all the work to go from Panel to battery, and back to AC? (might be stupid question)
    * and what are the best batteries, considering reliability, and length of time they will work.

    What I would like to do, is buy a quality minimum set of hardware and be able to expand it as I need. Starting small is so I can learn to work with all of this. Like I said, I'm an electrical engineer and have a basic understanding already. But don't have the experience to know what to consider at the get-go.

    This is my basic understanding what a solar system should require. Did I leave anything out?

    solar_system.jpg

    I will add panels and batteries as I expand the system for increased output, but I'd like NOT to have to change out any of the other components.

    Thanks
    Last edited by MikeSD; 04-21-2021, 06:29 PM.

  • #2
    Well Mike I don't know where to start.

    First off expanding a solar/battery off grid system can be quite costly. That is because you can't just add more batteries to an existing set. Old and new batteries on the same system tend to kill off the newer ones so if you want to make the system bigger you would need to start with a totally new set of batteries. They should also be low voltage type (2V ,4V or 6V) and high amp hour rating so you can wire them all in series then in parallel.

    Next I see a problem if you want to go off grid then you can't have your batteries connected to your main electric panel if that panel is also connected to the grid.

    So if you want a totally off grid system then your inverter will be different for a grid tied system. If you want to add batteries then that inverter needs to be a hybrid type that will send power to the grid and charge your batteries.

    So first determine if you want a totally off grid system or a hybrid grid tie system. Then also determine what you want to use in watt hours on a daily basis. That allows you to size your battery system and then your panel wattage to charge it.

    As for getting the correct equipment then stay away from the cheap Chinese stuff and purchase a quality CC and inverter. Also go with grid tie panels which are at least 250 watts. Using small wattage panels end up costing you more $/watt then higher wattage panels.

    A generator is needed for an off grid system to help keep the batteries happy but it is usually connected to a separate battery charger or through a transfer switch at the load panel.

    Comment


    • #3
      Based on your ultimate goal you may want to also look at All In One hybrid inverters. That would save you the expense of changing out components as you grow, especially charge controllers. Unfortunately the minimum string voltages would require more than 1000 Watts of panels. The cost per Watt of larger panels is a better value.

      The unknown is whether you have a grid connection or not. If so then starting with a simple grid tie system would be optimal. Later that could be AC coupled to a hybrid to leverage the GT system.
      Some of the All In One hybrids can initially be configured as a grid tied inverter until you are ready for batteries. In that scenerio the increased cost of panels would more than be offset by not having to buy batteries for starters. I have a similar system and while I am still connected to the grid I operate mostly in self consumption mode. My system could handle 16 kW of solar. I started with 5.7 kW of GT solar, added the hybrid with some used batteries. Then I added another 3kW of solar, replaced the used batteries with 28kW of LFP and am evaluating the next step based on my needs. I did add a sub panel when I installed the hybrid. It is called a critical loads, essential loads or backup loads panel depending on who you talk to. I don't use a generator but another benefit of an All In One hybrid is that there is often a Generator Input and an included transfer switch.
      9 kW solar, 42kWh LFP storage. EV owner since 2012

      Comment


      • #4
        Originally posted by SunEagle View Post
        ...

        First off expanding a solar/battery off grid system can be quite costly. That is because you can't just add more batteries to an existing set. Old and new batteries on the same system tend to kill off the newer ones so if you want to make the system bigger you would need to start with a totally new set of batteries. .....
        That is definitely true for Pb batteries. Expensive Lithium batteries with self contained BMSs and communucation systems can be incrementally added. SimpliPhi and Fortress Power are just a few names and they are pricy but also UL approved.

        9 kW solar, 42kWh LFP storage. EV owner since 2012

        Comment


        • #5
          The only way I can recommend expanding your system is with the end goal battery bank and grow your panels, SCC and inverters to meet it.

          I did a lot of calculations to figure out my power needs, and got that correct enough for battery size. In sunshine I had enough panels and SCCs, but with the my second trip, in rolls the clouds, and I'm a little too close for comfort with the amount of amps going into the battery bank on several cloudy days in a row. I was able to add a third string of panels and SCC and now I'm happy.

          There's no way I could of added more batteries later. I looked at this many, many ways, but it just did not work or was not very efficient. Most of my power consumption is on the 12 volt side, so I could keep my current system on 12 volts, and add a second system, at 24 volts to run an inverter on my AC side, but I just do not have a lot of AC draw to make it worth it. 24 volts is good to run a microwave, but I just don't turn it on enough to justify getting a second system just for AC use.

          The only way I could see it working is adding a second system later on to power the "East" outlets in the house, and the other the "West" outlets, but this would not be very efficient and probably some challenges with code.

          Comment


          • #6
            Originally posted by SunEagle View Post
            Well Mike I don't know where to start.

            First off expanding a solar/battery off grid system can be quite costly. That is because you can't just add more batteries to an existing set. Old and new batteries on the same system tend to kill off the newer ones so if you want to make the system bigger you would need to start with a totally new set of batteries. They should also be low voltage type (2V ,4V or 6V) and high amp hour rating so you can wire them all in series then in parallel.

            Next I see a problem if you want to go off grid then you can't have your batteries connected to your main electric panel if that panel is also connected to the grid.

            So if you want a totally off grid system then your inverter will be different for a grid tied system. If you want to add batteries then that inverter needs to be a hybrid type that will send power to the grid and charge your batteries.

            So first determine if you want a totally off grid system or a hybrid grid tie system. Then also determine what you want to use in watt hours on a daily basis. That allows you to size your battery system and then your panel wattage to charge it.

            As for getting the correct equipment then stay away from the cheap Chinese stuff and purchase a quality CC and inverter. Also go with grid tie panels which are at least 250 watts. Using small wattage panels end up costing you more $/watt then higher wattage panels.

            A generator is needed for an off grid system to help keep the batteries happy but it is usually connected to a separate battery charger or through a transfer switch at the load panel.
            All good info.
            First this will be completely for off grid. I'm planning to buy some property that is nowhere near power.

            Batteries. Would it be possible to buy all batteries at once. But add panels as I need them? I need to find a wail, piecemeal vs. All at once. Initially I won't need much power.

            Comment


            • #7
              Originally posted by Ampster View Post
              That is definitely true for Pb batteries. Expensive Lithium batteries with self contained BMSs and communucation systems can be incrementally added. SimpliPhi and Fortress Power are just a few names and they are pricy but also UL approved.
              I agree that Li chemistry batteries are more forgiving when added to existing. Unfortunately most people come here looking to go at a lower cost to start out and then "grow" their system. That usually means Pb batteries. But if the OP wants a robust system that can be enlarged and cost is not a factor then by all means go with an Li chemistry battery.

              Comment


              • #8
                Originally posted by Ampster View Post
                Based on your ultimate goal you may want to also look at All In One hybrid inverters. That would save you the expense of changing out components as you grow, especially charge controllers. Unfortunately the minimum string voltages would require more than 1000 Watts of panels. The cost per Watt of larger panels is a better value.

                The unknown is whether you have a grid connection or not. If so then starting with a simple grid tie system would be optimal. Later that could be AC coupled to a hybrid to leverage the GT system..
                Looks like I need to do a little more research, at least to come up with a minimal system. 1k was a number out of the blue.

                It's definitely no grid ties.


                Comment


                • #9
                  Originally posted by MikeSD View Post

                  All good info.
                  First this will be completely for off grid. I'm planning to buy some property that is nowhere near power.

                  Batteries. Would it be possible to buy all batteries at once. But add panels as I need them? I need to find a wail, piecemeal vs. All at once. Initially I won't need much power.
                  Again if you are thinking about Pb batteries then you will need at least a C/12 charge rate where C = battery system Amp Hour rating. Unfortunately that means a lot of solar panel wattage especially if you live farther from the Equator and plan on using the system in the Winter.

                  As I stated before, first determine your daily watt hour usage and that will allow you to properly size your battery system. From there you then size your panel wattage and charge controller.

                  Comment


                  • #10
                    Originally posted by SunEagle View Post

                    Again if you are thinking about Pb batteries then you will need at least a C/12 charge rate where C = battery system Amp Hour rating. Unfortunately that means a lot of solar panel wattage especially if you live farther from the Equator and plan on using the system in the Winter.

                    As I stated before, first determine your daily watt hour usage and that will allow you to properly size your battery system. From there you then size your panel wattage and charge controller.
                    I guess what I will do is size my system for highest wattage and determine the panels and batteries needed. I can do this for several ratings (5W, 10W, 15W) and see if there is a lower rated system that could be expanded.

                    Worst case, which is best case, is just build it right rhe first time.

                    Thanks, I'll do my work then update this thread with more realistic goals.

                    Comment


                    • #11
                      Originally posted by MikeSD View Post
                      I guess what I will do is size my system for highest wattage and determine the panels and batteries needed. I can do this for several ratings (5W, 10W, 15W) and see if there is a lower rated system that could be expanded.

                      Worst case, which is best case, is just build it right rhe first time.

                      Thanks, I'll do my work then update this thread with more realistic goals.
                      There are some books out there called Solar for Dummies. Don't let the title turn you off. It can provide some good basic knowledge concerning solar.

                      Also don't let your EE degree get in the way of learning all you can about solar. It is an interesting subject and is constantly changing.

                      I got my EE degree back in the early 70's. But I was also lucky to work in a solar panel research center at the U of D. It made understanding of solar equipment that much easier for me. And boy has it changed in the last 4 decades.

                      Comment


                      • #12
                        you estimate your ultimate loads and seasonal hours of usable sunlight
                        Then you figure how much solar you will eventually need. Install for now just what you need -keeping in mind it will grow. Get a 60A MPPT charge controller, that will handle 3000w for a 48V battery bank. If your need is beyond what a single 60A controller can handle, you buy another one in the future when you add more panels & batteries
                        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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