Announcement

Collapse
No announcement yet.

Use of spare 500 Watt from Solar Panels

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Use of spare 500 Watt from Solar Panels

    I typically export 500 Watt to the grid during normal day operations.

    I have a 1500 watt hot water element in my hot water tank. I don't want to change the element for awkwardness reasons.

    I would like to use my excess 500 Watt to heat the water. A transformer to drop the voltage down could be expensive.

    Is there any alternative?

  • #2
    I think you might be confused on this.
    First off, do you really mean 500Wh? or 500W continuously? There's a big difference. If it's 500Wh, then you could power your water heater for about 20 minutes.

    You don't need a transformer to change the voltage if you are already sending it to the grid. That 1500W heater is going to you 240V, just like you're sending to the grid. It's just going to use more amps. You can power that heater with less amps, it just won't get as hot.

    Comment


    • #3
      Originally posted by emartin00 View Post
      I think you might be confused on this.
      First off, do you really mean 500Wh? or 500W continuously? There's a big difference. If it's 500Wh, then you could power your water heater for about 20 minutes.

      You don't need a transformer to change the voltage if you are already sending it to the grid. That 1500W heater is going to you 240V, just like you're sending to the grid. It's just going to use more amps. You can power that heater with less amps, it just won't get as hot.


      Thanks emartin00 for the swift response. I meant that I typically have 0.5 kW continuously available which I export to the grid. My tank requires 4 kWh to heat fully. I would like to use the spare power to heat this tank. So it would take about 8 hours at 0.5 kW per hour.

      If i reduced the voltage using an expensive transformer from 240 to 120 volt, say, then I could use the same heating element but it would take about 4 times longer to heat the water. However the big advantage is that I would need to import less electricity from the grid and hence get charged less on my electricity bill. I pay 28 cents per kWh for imported electricity and get credited 5 cents per kWh for exported excess electricity from my solar panels.

      I would like to use the excess power from the solar panels and heat the hot water more slowly rather than heat the hot water at a rate of about 2000 kW continuously but for a shorter time.

      Thanks again for your response.

      Comment


      • #4
        As I understand it, my parents house was the same.

        You have a grid connect system,

        You pay for the electricity you use,

        You get paid for the electricity you export.

        Even if you export more than you use you still pay, as you cant generate enough to make up the difference between the 28c you pay and the 5c you get paid.

        You dont get to use your own power that you make as such.

        So no you cant do what you want.

        Comment


        • #5
          Thanks Bala. I want to make use of the excess energy i am exporting by using it to heat my hot water. At present I heat the hot water "quickly" as my heater uses 1500 watt, so as I only have 500 watt spare I still import 1000 watt. However if I used 500 watt only to heat the hot water I would not import electricity from the grid. If I replaced the 1500 hot water tank element with a 500 watt element this would achieve this.

          I would use the same amount of electricity to heat the hot water, however I would not be importing it from the grid.

          Thanks again Bala.





          Originally posted by Bala View Post
          As I understand it, my parents house was the same.


          You have a grid connect system,

          You pay for the electricity you use,

          You get paid for the electricity you export.

          Even if you export more than you use you still pay, as you cant generate enough to make up the difference between the 28c you pay and the 5c you get paid.

          You dont get to use your own power that you make as such.

          So no you cant do what you want.

          Comment


          • #6
            Give up you have a grid tied system. You do not get to choose where power goes.
            MSEE, PE

            Comment


            • #7
              Originally posted by solardarity View Post
              Thanks Bala. I want to make use of the excess energy i am exporting by using it to heat my hot water. At present I heat the hot water "quickly" as my heater uses 1500 watt, so as I only have 500 watt spare I still import 1000 watt. However if I used 500 watt only to heat the hot water I would not import electricity from the grid. If I replaced the 1500 hot water tank element with a 500 watt element this would achieve this.

              I would use the same amount of electricity to heat the hot water, however I would not be importing it from the grid.

              Thanks again Bala.
              You did not understand,

              You import all the power to heat your water, and for all other appliances.

              All the power your solar makes is exported

              They are two different systems, they dont work together.

              My parents put in a system, without speaking to me and with the belief that they would not have a power bill to pay. At 8c kw they still had a power bill even though they were producing a lot more that they were using. And no hope of even ROI.

              When it first came in it was about 50c kw, my inlaws make money, but now its reduced to 8c, or 5c its just a scam.

              Comment


              • #8
                Originally posted by Sunking View Post
                Give up you have a grid tied system. You do not get to choose where power goes.
                I don't think you understand what I was saying.

                Comment


                • #9
                  Originally posted by solardarity View Post
                  I don't think you understand what I was saying.
                  He does,

                  You still have not come to terms with how your system works.

                  Comment


                  • #10
                    I think you are saying, if the heater ran at a much lower power level, your energy would
                    cancel the expensive energy you would have to buy at a high power level.

                    I suggest, many electric water heaters have 2 heating elements, in parallel. If you
                    have 120V elements, you could replace them with 240V elements, which would draw
                    1/4 the power at 120V.

                    If you have 2 elements, you might put them in series instead of in parallel. However,
                    not sure how the operation of the thermostat attached to each is affected. Really, an auto
                    transformer or perhaps Variable transformer/powerstat rated at your line voltage and 500W
                    could be adjusted to the level you had in mind. Turn it up too high and it will burn out.
                    Bruce Roe

                    Comment


                    • #11
                      Originally posted by solardarity View Post
                      I don't think you understand what I was saying.
                      I understand perfectly. The issue is you do not understand how grid tied systems work. A grid tied system is passive. It generates as much power as the conditions permit.

                      If your system is generating more power than you are consuming at your home, the excess goes out on the grid. If you are consuming more power than the panels are generating the shortage in power comes from the grid. There is nothing you can do to change that. You have no control whatsoever where power is going. Only thing you can control to some degree is how much power you are using at any given moment in time.
                      MSEE, PE

                      Comment


                      • #12
                        Originally posted by Sunking View Post
                        . Only thing you can control to some degree is how much power you are using at any given moment in time.
                        I believe that this is what the OP is asking to do. Phrased another way: OP wants to setup his hot water heater to draw 500W when his solar system is producing. This will allow his demand to equal his generation and thus not have energy exported to the grid as is happening now.

                        I would suggest a 500w element on a timer to coincide with solar production hours could do this though not sure how cost effective it would be.

                        Comment


                        • #13
                          If you have net metering it really doesn't matter whaT size element exists. If you produce 30 kwh per day and you only use 20 kwh you have a net credit of 10 kwh to use at night or a cloudy day. So I don't understand the problem..

                          Comment


                          • #14
                            Originally posted by LucMan View Post
                            If you have net metering it really doesn't matter whaT size element exists. If you produce 30 kwh per day and you only use 20 kwh you have a net credit of 10 kwh to use at night or a cloudy day. So I don't understand the problem..
                            It would matter, if the (instantaneous) rate at which he buys is higher than the rate he sells. Bruce Roe

                            Comment


                            • #15
                              The net metering usage here is calculated month to month, you can carry credits for 1 year from your anniversary date. If you then still have kwh credits the utility pays you the wholesale rate for those credits.
                              Any consumption over the amount of power produced every month is billed at approximately 20 cents a kwh total for supplier and delivery.
                              If the utility is billing for instantaneous consumption and production that doesn't make a lot of financial sense to install pv as you are paying retail and selling at wholesale rate.
                              What's the advantage?

                              Comment

                              Working...
                              X