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  • How many watts in solar panels do I need for my grid tie system

    I use about 1000 kilowatts a month in summer and 1200 kilowatts in the winter. This is really not very much, but I would like to cut it in half. I am thinking of a direct grid tie. My small house draws about 1000 watts during the day/night hours during summer and 1200 watts during the day/night in winter. These are averages I have taken with a meter.

    What would be the total watts I would need in solar panels to cut my kilowatt use in half using direct grid tie?

    Would the Enphase Micro inverter or the SMA Sunny Boy 700u work for me? Where do they tie-in to my grid?

    Thanks
    Azel

  • #2
    Need -

    1) Your approximate location - and or zip code

    2) Any shading problems?

    3) Good southern exposure?

    Russ
    sigpic

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    • #3
      Originally posted by russ View Post
      Need -

      1) Your approximate location - and or zip code

      2) Any shading problems?

      3) Good southern exposure?

      Russ
      Central Texas
      No shading problems
      yes

      Comment


      • #4
        Go to PV watts (link on home page)
        Plug in your zip code, tilt of roof and azimuth of array and play around with array size to come up with a system size that would work for you.
        In most cases the PVwatts will come up with a larger array than actually needed as the derate factors are fairly high but we can go into that once some system parameters and equipment is chosen.
        Rich
        WWW.solarsaves.net

        NABCEP certified Technical Sales Professional

        http://www.solarpaneltalk.com/showth...Battery-Design

        http://www.calculator.net/voltage-drop-calculator.html (Voltage drop Calculator among others)

        www.gaisma.com

        Comment


        • #5
          Another online calculator with a few more buttons comes from Sharp http://sharpusa.cleanpowerestimator.com/sharpusa.htm
          sigpic

          Comment


          • #6
            I want to thank you both for the links.

            It looks like I would need to install 5000 watts in solar panels to cut my monthly electric bill in half. That is a lot more than I had planned on.

            I may go to my Plan B. I had thought about installing electrical conduit in my trailer and making a second power circuit that is solar/battery only. I would plug in small wattage draw appliances like refrigerator, lights, computers, but not big wattage drawers like air conditioners, electric heaters. I would leave heavy watt drawing appliances on gird circuit and run the small watt drawing appliances on solar circuit. In a house this would probably not be practical, but in a trailer, it would not be much trouble to install conduit externally where wall and ceiling meet the full length of the trailer with conduit branch downs to appliances. This would include:
            Lights
            fans
            conputers
            microwave
            refrigerator

            I don't suppose this would help lower the monthly electric bill to half as I had planned, but it would help. My air conditioner (in summer) and electric heater (in winter) are the appliances that really draw the watt hours.

            Comment


            • #7
              Originally posted by Azel View Post

              I don't suppose this would help lower the monthly electric bill to half as I had planned, but it would help. My air conditioner (in summer) and electric heater (in winter) are the appliances that really draw the watt hours.
              Actually, it would come out a lot worse than the same amount of panels in a grid-tie application since you would have the extra cost of the batteries, which would not last forever either. You will end up paying at least 5 times as much for the solar electricity for your trailer as you would to leave the same appliances on the grid.
              SunnyBoy 3000 US, 18 BP Solar 175B panels.

              Comment


              • #8
                Originally posted by inetdog View Post
                Actually, it would come out a lot worse than the same amount of panels in a grid-tie application since you would have the extra cost of the batteries, which would not last forever either. You will end up paying at least 5 times as much for the solar electricity for your trailer as you would to leave the same appliances on the grid.
                Thank you for the information.
                I better go back and do some more reading in my solar power books.

                I think I will end this string and make a post in the General section with my thoughts about the use of solar energy.


                Thanks
                Azel

                Comment


                • #9
                  Axel, don't give up yet. I live in central Texas as well (round rock). Depending on who your electrical provider is there are some really nice rebates available to help you get solar installed, as well as the tax credits. I just finished my install of a 10kW system on my roof. Total cost was 37 and some change. By the time I got all the rebates the cost to me was about 13k and I will get 4k and some change tax CREDIT on my returns next year. Bringing my total cost to about 8k. Let me know if you want more specifics and I will give them to you.

                  Originally posted by Azel View Post
                  Thank you for the information.
                  I better go back and do some more reading in my solar power books.

                  I think I will end this string and make a post in the General section with my thoughts about the use of solar energy.


                  Thanks
                  Azel

                  Comment


                  • #10
                    Please don't get mad.

                    Originally posted by inetdog View Post
                    Actually, it would come out a lot worse than the same amount of panels in a grid-tie application since you would have the extra cost of the batteries, which would not last forever either. You will end up paying at least 5 times as much for the solar electricity for your trailer as you would to leave the same appliances on the grid.
                    Please do not take this the wrong way, I've already had that happen here. I'm just curious, I understand the old "truth hurts' thing but... you guys here are Big solar guys, why do you poo poo other people when the have an interest in going solar. Like I said to start please don't get mad. I'm just wondering why I keep hearing "It's too expensive, you might as well stay on the grid."

                    I believe there is always a way you just need to find it.

                    Is it that you guys are just sick of explainig that there is more involved in getting started than most people think?

                    Comment


                    • #11
                      Sadly (or it's good) Texas has cheap electric rates. That means solar will have a long break-even period. Some areas in Texas do not even allow selling back power.
                      spreadsheet based voltage drop calculator:
                      http://www.solar-guppy.com/download/...calculator.zip
                      http://www.solarpaneltalk.com/showth...oss-calculator

                      http://www.mike-burgess.org/PVinfo_2.html

                      solar: http://tinyurl.com/LMR-Solar
                      gen: http://tinyurl.com/LMR-Lister ,
                      battery lugs http://tinyurl.com/LMR-BigLug
                      Setting up batteries http://tinyurl.com/LMR-NiFe

                      gear :
                      Powerfab top of pole PV mount | 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

                      Comment


                      • #12
                        Originally posted by daveb View Post
                        you guys here are Big solar guys, why do you poo poo other people when the have an interest in going solar.
                        We do not Poo Poo on people, we give them both the Pros & Cons or Fair & Balanced so they can make an informed decision. If you are only looking for the Green Side only responses then there are other Forums like Northern AZ Wind & Sun. There the moderators and contributing members are salesman and activist that will only present one side, and then sell it too you.

                        Originally posted by daveb View Post
                        Like I said to start please don't get mad. I'm just wondering why I keep hearing "It's too expensive, you might as well stay on the grid."
                        Well if you are already connected to the Grid then it would be very foolish to go Off-Grid Battery system. We have had hundred of people come here who say: I am tired of paying the POCO and I want to stick it to the Man". Well I can understand that, but it clearly demonstrates they have no idea of what they are asking for. In reality what they are asking for or saying is: I am tired of paying dirt cheap prices for all the electricity I can use and enjoy the comforts that come with it. I want to pay 10 to 20 times more for electricity the rest of my life with limited supply, a new part time job worrying & working daily on my system and a life time of maintenance and replacement". Granted they do not use those word's, but that is basically what they are asking for and just do not know it yet. I do not know about you but I would be thankful for someone telling me before I did something stupid.


                        The other scenario is Grid Tied which can be of benefit to the homeowner, but there are a lot of factors that go into the decision, and most of it depends on your location. Where i live in TX electric power is dirt cheap @ about 9-cents per Kwh down from 13-cents a few years ago and will continue to go down. TX does not have Net Metering Laws except for the Austin area. Since TX has no Net Metering Laws utilities are not even required to connect you with a solar system, and will only pay Wholesale prices. Couple all that along with no state incentives and it would be decades before you just break even with 0% ROI.

                        Where I live I pay 9-cents I can Grid Tied. For that privilege TXU will come out and install the dual meters for the system, raise my rate to 15-cents per Kwh, and pay me 7-cents for the excess I generate and give to them to sale to my neighbor for 9-cents. So for me my electric bill would go down about 20% (from $100/month to $75 to $80/month), and I would be out $30K in cash. Not going to happen. Oh, and if I want to stick it too the MAN and go off-grid battery I am looking at a cost of right around $100,000 initial investment, with $40,000 of that in batteries that need replaced in about every 5 years. No Thank You, I prefer to just keep paying the Mean Ole Greedy POCO $6000 every 5 years, and invest the rest so I can retire comfortably.

                        As for Austin TX that does have Net Metering and Local incentives. To get that those folks pay 50% more for electricity than the rest of TX does. Who does that hurt in Austin? Everyone living there especially the poor and Blue Collar workers who cannot afford to take advantage of the free money they are paying. Are you a biz looking to relocate in TX. Scratch Austin off your list, because energy and taxes are too high there. Your money is welcome in Dallas, Fort Worth, Houston, and San Antonio, but not in Austin.

                        So if someone wants to go Grid Tied or Off-Grid, once they know the facts and still want to proceed, I will help them.
                        MSEE, PE

                        Comment


                        • #13
                          As has just been stated - if grid power is available grid tie is the only way. If it costs to much to connect (power line extension etc) as in Mike's case then a battery system might be of use.

                          Even grid tie only makes sense if very generous incentives and feed in tariff are available. Without big time financial assistance solar PV is not ready for prime time.

                          For off grid systems people have to change their life style big time - do away with many luxuries and wasteful items - most (99%?) are not interested.

                          Start small? Expanding systems is generally not practical as components need to be sized to fit in with other equipment.

                          Residential wind? Far worse - commercial wind is useful in a few places but residential is generally a waste of money.

                          There are a million scamsters out there trying to make a case for their junk - difficult for people to avoid them.

                          As Sunking said, we get people wanting to 'stick it to the utility' - a rather silly viewpoint - I guess their barber told them how they were getting screwed - if anyone figures it out for themselves it is easy to see that commercial power is a very big bargain today. Even where I am electricity is a little under 20 cents US per kWh while gas and diesel run about 10$ US per gallon.

                          Small is great as a learning experiment and DIY the same. For real power larger and commercial grid tie is the only practical solution.
                          sigpic

                          Comment


                          • #14
                            Well first I must say sorry again, should have slept on that one. I guess my question should have been Why not start out small. I saw you said something about problems with upgrading size later, but there are problems with everything...they just need to be addressed and resolved.

                            As I see it if you start with a small grid tied system that doesn't make all the electricity you need but just cuts down on what you must buy from the poco, thats a good thing. Why do you guys always suggest the largest system possible, demanding that it meets your entire power need. If you dont make excess, who cares what the power co. pays.

                            And I dont get the payback time. Even if it takes 10 years, so what. If you stayed on the grid, the Power Co. isn't going to start paying you in 10 years.lol

                            Comment


                            • #15
                              Originally posted by daveb View Post
                              Well first I must say sorry again, should have slept on that one. I guess my question should have been Why not start out small. I saw you said something about problems with upgrading size later, but there are problems with everything...they just need to be addressed and resolved.
                              Lots of reasons. If talking about off-grid will likely require you replace everything except for the panels. Maybe even the panels because there is a good chance when it is time to upgrade your panel count, the manufacture is out of biz.

                              For grid tied system you are going to have to go through the whole permitting and inspection process which is expensive. In addition using contract labor is going to be very high on small scale jobs upgrading, and inflation will cause it to go even higher.

                              Lastly and this is a big one. All those rebates and incentives to force your neighbors to pay for your system is a one time deal. Next time all the expense is on you. So instead of your neighbor being extorted to pay for up to 75% of your system, you get to pay up to 400% more for the addition.

                              Originally posted by daveb View Post
                              And I don't get the payback time. Even if it takes 10 years, so what. If you stayed on the grid, the Power Co. isn't going to start paying you in 10 years.lol
                              Probable because you have no idea of how money works either for you or against you. Invest that same amount of money, not only will it pay for your electric bill with interest, it will also compound and grow. So in 10 years it paid for all the electricity you used and grew into real cash you can use to retire on and go on a permanent vacation. If it takes 10 to 20 years to break even, you have 0% ROI and nothing to cash out.
                              MSEE, PE

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