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  • #16
    Originally posted by DanS26 View Post
    In my case I dump excess power into heating ceramic bricks. Yes, using PV to create resistance heat is inefficient on a whole house scale, but it is very efficient when heating smaller spaces.

    Its low tech but using timers and properly adjusted thermostats, I can convert many kWhs into comfortable heat in the space I'm in and do it efficiently.
    Scale does not effect efficiency. Practicality yes but not efficiency.
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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    • #17
      Originally posted by ButchDeal View Post

      Scale does not effect efficiency. Practicality yes but not efficiency.
      But scale does affect cost, if you can gain the same result with significant less input.

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      • #18
        Nice ideas and adopting the KISS approach.
        I certainly have good control but it comes at the expense of significant increase in complexity - out of proportion to the gains.

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        • #19
          Originally posted by wrsnz View Post
          Proffessional engineering forum, bring it on!
          OK Mike Holt Code Forum. I am a moderator along with about 15 other moderators. You have to be able to prove your credentials to be a member. We have more than 200,000 members. All licensed professionals and even a Solar Sub Forum. You will have to prove every word you say because we know what can and cannot be done.
          MSEE, PE

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          • #20
            Originally posted by wrsnz View Post
            Other than Sunking:

            Thanks for your comments. It would be good if the PoCo's in my country were more on board with distributed generation like most other countries. NZ is a very small country with a high % of power coming from renewable resources. It has fairly poor infrastructure milked by high overseas ownership of almost everything. Our power price is also relatively high. We have no nuclear power.

            I like the idea of credits for export power - that really makes sense.

            In my situation there is no point exporting power since you get so little for it ($0.08/kWh export vs $0.299kWh import).

            It would seem there is little need to optimise self-consumption outside NZ since the PoCo's are more reasonable.
            For me this was more about a fun project and a challenge to see how far I could go with the power control...
            Nice to see someone else doing something for the fun of it. I designed my own MPPT controller and BMS for my LFP battery. As you say, if you take all the time needed to design and build such devices into account you would be better going out and buying something off the shelf. I agree that building your own stuff gives you far more flexibility and you can get high precision with some careful design and it doesn't have to cost a fortune in parts.

            Here in Australia we have the same problem with high power prices, low feed in tariffs and high supply charges.

            I have seem costings from an organisation i am not allowed to mention of AU$0.22 per kWh for power cycled through a Tesla Powerwall 2. The 2.1kWh/day I cycle through my battery works out at ~AU$0.50 if the battery lasts for ten years and only ~AU$0.25 if it lasts twenty years.

            For off grid systems if you utilise most of the power during the day and have a much larger solar panel array than you need you can reduce the size and cost of the battery.

            Where it is practicable to be on the grid I would like to see a situation where you are paid the spot wholesale rate for power exported. This would make the economics of time shifting solar power generation with batteries far more viable and may bring power prices down. In Australia it seems there are many vested interests that don't want this to happen ...

            Simon

            Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
            BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
            Latronics 4kW Inverter, homemade MPPT controller

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            • #21
              Originally posted by DanS26 View Post
              In my case I dump excess power into heating ceramic bricks. Yes, using PV to create resistance heat is inefficient on a whole house scale, but it is very efficient when heating smaller spaces.

              Its low tech but using timers and properly adjusted thermostats, I can convert many kWhs into comfortable heat in the space I'm in and do it efficiently.
              But, unless the building heat loss/gain changes, and/or the existing delivery system is improved, the inefficiency of using resistance heat stays the same.

              I wrote more, but I'm not at home and the computer I'm using ate a more detailed response. More when I get home.

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              • #22
                Yes I used the wrong word in my post.....let me fix it........

                "In my case I dump excess power into heating ceramic bricks. Yes, using PV to create resistance heat is inefficient on a whole house scale, but it is very "effective" when heating smaller spaces.

                Its low tech but using timers and properly adjusted thermostats, I can convert many kWhs into comfortable heat in the space I'm in and do it "effectively"".

                Geeze....you guys are tough. haha

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                • #23
                  Originally posted by J.P.M. View Post
                  But, unless the building heat loss/gain changes, and/or the existing delivery system is improved, the inefficiency of using resistance heat stays the same.
                  Where oh where has critical thinking gone and disappeared too? In the USA it went away when public schools quite teaching math, science, and handing out F's with Dunce caps. Some poor little Darlings got their feelings hurt being stupid, so public schools decided to make everyone stupid in the name of PC.

                  With a Grid Tied system or sometimes called Interactive the user has little to no control where power is sent. The whole idea is for excess to be sent out to the grid for your neighbors to use and thus lesson the burden on utilities and slow down using limited fuel reserves.

                  Certainly you can monitor and tell if you are Importing or Exporting as that is easy to do. But why would you try to control it, and what can be gained in your favor? Almost nothing can be gained except for costing you more money. Example an electric Hot Water Heater you could turn on right? Not so fast because unless it is turned off when not exporting you will likely put you rlife in danger by over heating water that is already hot enough. Instead of getting a credit on your bill you just wasted energy you did not need to begin with.

                  How about turn on the HVAC system? Just as silly as turning on the hot water heater making you either colder in summer or hotter in winter. Again loosing money by not exporting and wasting energy that does not need to be used in the first place.

                  Really smart folks would turn on lights when none are needed. Then you have really brilliant folks who would store excess in a battery. That way they lose money twice and waste more energy. Any of that power you dump in a battery is costing a a dollar a kWh instead of making 8 to 10 cents per kWh sending it out on the grid and having credit to use later when the sun does not shine.

                  [Moderator note - the rest of this post was off-topic, moved into its own thread, here]
                  Last edited by sensij; 01-11-2018, 05:02 PM.
                  MSEE, PE

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                  • #24
                    Originally posted by Sunking View Post

                    Certainly you can monitor and tell if you are Importing or Exporting as that is easy to do. But why would you try to control it, and what can be gained in your favor? Almost nothing can be gained except for costing you more money. Example an electric Hot Water Heater you could turn on right? Not so fast because unless it is turned off when not exporting you will likely put you rlife in danger by over heating water that is already hot enough. Instead of getting a credit on your bill you just wasted energy you did not need to begin with.
                    Neither the OP, nor anyone commenting in this thread, has suggested self-consumption is more cost-effective than a net-metered grid tie system, and the OP has been very clear that the system was not built for financial gain. This system has been presented as an engineering project, not a path to get rich quick.
                    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                    • #25
                      Let me just throw out some numbers that will flesh out this discussion somewhat. It is important to compare energy sources on an apples to apples basis. The best way to do that is to compare the equivalent BTU capability of all available energy sources.

                      Here is what I experience in IN....your mileage may vary: (from lowest cost to highest)

                      Wood.....1 rick hardwood....cost $65 per rick delivered.........value per mBTU $5.20
                      Coal......1 ton Anthracite....cost $225 per ton delivered.........value per mBTU $8.09
                      Propane..1 gal ..................cost $0.99 per gal delivered........value per mBTU $11.85....(yes summer fill for the last 3 years was under $1 per gal)
                      Nat Gas..1 Therm..............cost $1.20 per therm delivered....value per mBTU $12.00
                      Electricity..1 kWh..............cost $0.042 per kWh wholesale..value per mBTU $12.31........(my sale price to POCO)
                      Gasoline....1 gal................cost $2.36 per gal......................value per mBTU $20.70
                      Heating Oil #2..1gal............cost $2.89 per gal.....................value per mBTU $20.87
                      Electricity..1 kWh..............cost $0.135 per kWh retail..........value per mBTU $39.55


                      So now when I need to make a decision on which energy source to use I just consult my mBTU comparisons. As you can imagine some energy sources also have to be evaluated by their ease of use and other characteristics. Do I use my excess PV energy to charge my car or heat my house or heat my water or sell back to the POCO? What is efficient/effective for me? I just like to have choices.
                      Last edited by DanS26; 01-11-2018, 07:25 PM. Reason: Added #2 Heating Oil

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                      • #26
                        What I failed to mention and which is critical to any decision on what to do with excess production is know your LOCE (levelized cost of energy) for your PV power. Anyone who produces power should know this cost. If you are not familiar....Google is your friend.

                        In my case my LOCE is $0.033 per kWh. The reason it is so low is that I did not assign any costs to my own labor to design and install my PV system. Not that I wanted to, but the IRS was adamant that I assign a zero value to my own labor. I'm sure they have good reasons for that position. I also took advantage of the generous tax credits that my fellow citizens gave me.

                        So now if I apply this $0.033 per kWh to my mBTU calculations my value per mBTU is $9.67. Yes my analysis is simplistic and cost/benefit based but it works.

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                        • #27
                          Originally posted by DanS26 View Post
                          What I failed to mention and which is critical to any decision on what to do with excess production is know your LOCE (levelized cost of energy) for your PV power. Anyone who produces power should know this cost. If you are not familiar....Google is your friend.

                          In my case my LOCE is $0.033 per kWh. The reason it is so low is that I did not assign any costs to my own labor to design and install my PV system. Not that I wanted to, but the IRS was adamant that I assign a zero value to my own labor. I'm sure they have good reasons for that position. I also took advantage of the generous tax credits that my fellow citizens gave me.

                          So now if I apply this $0.033 per kWh to my mBTU calculations my value per mBTU is $9.67. Yes my analysis is simplistic and cost/benefit based but it works.
                          Over how many years is your LCOE analysis done ?

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                          • #28
                            My LOCE is based on 25 year life for panels, wiring, switches, etc. and 10 year life for the Fronius string inverters. Replacement cost for the inverters was at current cost since it appears that these costs are actually decreasing. No salvage value assumed and minimal annual maintenance. I do keep an inventory of spare parts....five extra panels, fuses, wire, etc and those values are included. I also included the cost of my monitoring system.....a TED Pro system.

                            I use .71% per year degradation on panel production over the 25 year period (ie panels will be producing ~18% less at year 25). I'm basing that information on advice from Kyocera and I have no reason to doubt since the panels have been performing great over the last 6 years.

                            Payback for the system based on cash flow including SRECs is projected to be 7.5 years.....almost there.

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                            • #29
                              Originally posted by DanS26 View Post
                              My LOCE is based on 25 year life for panels, wiring, switches, etc. and 10 year life for the Fronius string inverters. Replacement cost for the inverters was at current cost since it appears that these costs are actually decreasing. No salvage value assumed and minimal annual maintenance. I do keep an inventory of spare parts....five extra panels, fuses, wire, etc and those values are included. I also included the cost of my monitoring system.....a TED Pro system.

                              I use .71% per year degradation on panel production over the 25 year period (ie panels will be producing ~18% less at year 25). I'm basing that information on advice from Kyocera and I have no reason to doubt since the panels have been performing great over the last 6 years.

                              Payback for the system based on cash flow including SRECs is projected to be 7.5 years.....almost there.
                              Interesting how low your system costs/kWh.

                              The latest data from the DOE is that solar is more expensive on homes then from a utility sized array. The range is about: $0.11/kWh homes, $0.08/kWh commercial, $0.06/kWh utility.

                              What is nice is that those values have come way down the past 5 years and are expected to go down a few more cents/kWh.

                              Although a small home array (5kw - 10kw) is still going to be more costly then power from a MW utility array even after adding in distribution costs.

                              Comment


                              • #30
                                Originally posted by SunEagle View Post

                                Interesting how low your system costs/kWh.

                                The latest data from the DOE is that solar is more expensive on homes then from a utility sized array. The range is about: $0.11/kWh homes, $0.08/kWh commercial, $0.06/kWh utility.

                                What is nice is that those values have come way down the past 5 years and are expected to go down a few more cents/kWh.

                                Although a small home array (5kw - 10kw) is still going to be more costly then power from a MW utility array even after adding in distribution costs.
                                The longer the time frame, the lower the LCOE becomes. My assumptions are different than Dan's, but using a 12 yr. lifecycle and post incentive cost, my real LCOE is ~~$0.1274/kWh. If I stretch that out to 25 years, the LCOE drops to $0.073/kWh. Cash purchase. Zero salvage value, 6% discount rate, electric rate inflation = 3.28/yr. = general inflation.

                                Not arguing numbers here, just pointing out that the longer the lifecycle, usually, using common assumptions, the lower the LCOE.

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