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  • #31
    Originally posted by SunEagle View Post

    I guess the word "race" is not appropriate. What I meant was that with our low electric rates it is very hard to justify solar in Florida. My calculations put my ROI out beyond 10 years. But I will probably spend much less for power then those in CA with solar.
    The reason I mention California is not to create completion, but rather so people understand the context of my examples. You probably will pay less, but based on what I am seeing about the installed base, close to 50,000 people have reached the conclusion that solar makes sense for them in Florida. The low kWh rates for electricity may account for the fact that Florida has one of the lowest costs per Watt to install solar. By my calculations that means the point where solar gets a less than a 10 year payback is when electricity costs approach $0.15 per kWh. I am not trying out for a job as a solar sales person, but rather trying to better understand the market trends.
    As for websites that try to encourage solar in Florida, I think you have to understand who gains and who loses on that stage. Some of the local adds still have that 30% credit from the FED's so I think they are just trying to convince the people not really aware of the costs that the Sun is "free" which it isn't.
    I pointed to that website because I thought it was ironic that it is the sponsor of this forum. Here some of the dialogue contradicts the message of the sponsor. Their business model is to generate leads and the dialogue on the forum attracts viewers and some of those viewers are going to click on the title bar. Clearly the sponsor wins with that business model.
    9 kW solar. Driving EVs since 2012

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    • #32
      Originally posted by J.P.M. View Post

      Is that a typo ?
      Yes, correct the unit is kWs, I corrected that post.
      To put the above in context, that system generated 7.14 mWhrs during the past calendar year. Also I should clarify that the metric I used to compare Bruce's system was annual generation divided by inverter capacity. In my case my inverter capacity is 3.8 kWs and my ratio is 1875 to 1. Another metric that is used is STC capacity and that ratio is 1250 to 1. (7140 divided by 5.7) Most commercial solar farms use the inverter ratio when describing their systems.
      Last edited by Ampster; 02-26-2020, 05:34 PM.
      9 kW solar. Driving EVs since 2012

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      • #33
        Originally posted by Ampster View Post

        Yes, correct the unit is kWs, I corrected that post.
        To put the above in context, that system generated 7.14 mWhrs during the past calendar year. Also I should clarify that the metric I used to compare Bruce's system was annual generation divided by inverter capacity. In my case my inverter capacity is 3.8 kWs and my ratio is 1875 to 1. Another metric that is used is STC capacity and that ratio is 1250 to 1. (7140 divided by 3.8)
        Thank you for the clarification on the units, but I'm now confused by the numbers in your last sentence above. Are you saying that 7,140/3.8 = 1,250, or another typo ?

        I'd suggest the more common and also more useful measure of system performance - the one you seem to have in mind - might be the annual system generation (either actual or modeled) divided by the array STC kW size. That would be 7,140 kWh/yr./ 5.7 kW = 1,253 kWh/(yr.*installed STC kW).

        For several reasons, and maybe a little like building a car around the transmission, I'm not sure what array output as f(inverter capacity) gets you besides the a trivial result of array output vs. inverter size, unless what's sought is perhaps a measure of inverter underutilization. Or, if not underutilized, then as perhaps an intermediate measure on the way to an analysis of how much less than, or how far off optimal (for whatever reason(s) chosen) in terms of system output per time, like per year or month, an array orientation might be.

        Seems to me most PV systems or arrays are described by their total STC panel rating with the inverter sized for the duty, with the array price then normalized in some fashion, usually or often in terms of $$/ installed STC W of panel rating, or as you seem to have attempted, output per time period per installed STC W (or per STC kW).

        I repeat, I appreciate what Bruce is doing and has done. As I've stated before, I do stuff that's probably as or more eccentric than he does in some respects, and I can't and never did intend to justify a lot of it on the basis of efficiency or cost effectiveness.

        But, I'm of the pretty strong opinion that most folks come here and most folks get involved with solar and other alternate energy applications primarily for the purpose of saving money on utility bills, and I try to keep that in mind.

        To the degree that my opinion may be correct or at least useful, unless there is some other compelling reason such as utility restrictions on system sizes using inverter size as the criterion, or demand rates somehow that can and do sometimes get in the picture or some other such less common reasons, using inverter size alone, or even as the primary metric for system size can easily make examination of what I believe is most important to most users (system cost effectiveness) more difficult to gauge.

        If one of the big, or biggest goal in getting PV for most folks is getting the most bang for their buck, doing things like sizing the array for a high DC/AC ratios or using multiple orientations when not necessary, and doing so thinking such measures alone will result in a more cost effective array, puts the cart before the horse. A choice - for sure - and hail the freedom to choose, but thinking such measures ensure a more cost effective system when just the opposite is probably closer to the facts of the matter is probably not what most people who investigate PV have in mind.

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        • #34
          Originally posted by J.P.M. View Post

          Thank you for the clarification on the units, but I'm now confused by the numbers in your last sentence above. Are you saying that 7,140/3.8 = 1,250, or another typo ?

          I'd suggest the more common and also more useful measure of system performance.........

          .
          Yes you are correct, the correct formula should be (7140 divided by 5.7) with the resulting ratio being 1253 to 1.
          The relationship between the inverter ratio of 1875 to 1 and the STC ratio of 1253 to 1 is the AC to DC ratio.

          There is no need to rehash the AC to DC ratio discussion again. The opinions about Bruce's array has been discussed over and over again and I should have predicted that even mentioning it would result in another hijack. My apologies to the original poster.
          To me the important answer to the OP's question is that he gets to make financial trade offs as he pursues this project.The important issue in either of those ratios is the accuracy of the numerator when used prospectively. He can also use any metric that works for him. I am sure he has already figured out there will be a diversity of opinions.
          Last edited by Ampster; 02-27-2020, 01:49 AM.
          9 kW solar. Driving EVs since 2012

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          • #35
            Originally posted by Ampster View Post
            The reason I mention California is not to create completion, but rather so people understand the context of my examples. You probably will pay less, but based on what I am seeing about the installed base, close to 50,000 people have reached the conclusion that solar makes sense for them in Florida. The low kWh rates for electricity may account for the fact that Florida has one of the lowest costs per Watt to install solar. By my calculations that means the point where solar gets a less than a 10 year payback is when electricity costs approach $0.15 per kWh. I am not trying out for a job as a solar sales person, but rather trying to better understand the market trends.

            I pointed to that website because I thought it was ironic that it is the sponsor of this forum. Here some of the dialogue contradicts the message of the sponsor. Their business model is to generate leads and the dialogue on the forum attracts viewers and some of those viewers are going to click on the title bar. Clearly the sponsor wins with that business model.
            I agree with the action of some people going to solar in Florida. I see more and more installations around my area. My problem is that as much as I want to install a grid tied system so far the only prices I have gotten are above $3 per watt and unless I can get it below $2 per watt I would rather spend my money else where. I hope the installers change their pricing so more people install but I having seen a big drop in prices even with the lowered FED credit.

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            • #36
              Originally posted by crashintoty View Post

              Nice, that's much more budget friendly! Should I go with the CAN enabled version if I want the programmable stuff or is the CAN version meant for EV vehicles?
              Sorry for the late response. I think they are both programable. The version I have is older and I interface with it via my PC and a USB/Serial interface. Even that version has CAN communications, which is how I connect the remote wifi monitoring.
              9 kW solar. Driving EVs since 2012

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              • #37
                I'm looking at $0.86 to $0.79 per watt for my DIY installation with used panels (10 or 12 panels, respectively plus grid tie or regular inverter, unistruts, cables & condiuts). I'm paying a little over $0.11 per kWh from utility ($0.08, $0.13 for non-peak and peak rates, respectively). Not sure what the break even point would be, but the installation would cost $2600 to $2880 and we pay a little over $2500 a year for electricity. Since it's far below $3 to $2 per watt does this make it a more favorable project?

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                • #38
                  A back of the envelope calculation suggests that you may use as much as 23,000 kWhs or more per year. I got that number by dividing your bill of $2500 by your average rate. If that is correct then the next step is to estimate solar generation.

                  For that I suggest you go to PV Watts and plug in your location, tilt and azimuth to see what a crude estimate of annual production would be. The elephant in the room is how much you will lose from the shading you mentioned earlier. There are devices that you can rent that will plot the sun and give you a crude estimate. Clouds might be considered in the PV Watts estimate. Sometimes they use weather data that might be miles away and not account for micro climates. FWIW you could run an estimate of your main roof and see what an simulated result would be. You can increase the installed Watts on that roof to see some tradeoffs on size.
                  Last edited by Ampster; 02-29-2020, 03:57 PM.
                  9 kW solar. Driving EVs since 2012

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                  • #39
                    Originally posted by Ampster View Post
                    Clouds might be considered in the PV Watts estimate. Sometimes they use weather data that might be miles away and not account for micro climates.
                    The solar irradiance data in particular, and lots of the other weather data and atmospheric variables PVWatts uses is, for the most part, modeled and not actual historic data for a specific site, which data is (dirty little secret), for the great majority of sites, nonexistent.

                    With the hope of avoiding possible misinformed assumptions leading folks astray, regardless of the origin, or uncertainty of the irradiance data and lots of other weather data PVWatts uses, rather than "might be", the fact is clouds are always a big part of the PVWatts modeling process.

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                    • #40
                      Originally posted by J.P.M. View Post

                      The solar irradiance data in particular, and lots of the other weather data and atmospheric variables PVWatts uses is, for the most part, modeled and not actual historic data for a specific site, which data is (dirty little secret), for the great majority of sites, nonexistent.

                      With the hope of avoiding possible misinformed assumptions leading folks astray, regardless of the origin, or uncertainty of the irradiance data and lots of other weather data PVWatts uses, rather than "might be", the fact is clouds are always a big part of the PVWatts modeling process.
                      Yes, thank you for confirming that the data is only modeled and that clouds are part of the model. I was not sure about the relevance of the model with respect to his microclimate and did not want to raise his expectations, particularly in light of previous comments about "proper use" and that his location was "not an irradiance hotspot". The low cost of energy also adds bias to the payback calculations.
                      This projects seems to have progressed from a science experiment of a few panels to a serious attempt to cut costs.
                      9 kW solar. Driving EVs since 2012

                      Comment


                      • #41
                        Originally posted by Ampster View Post

                        Yes, thank you for confirming that the data is only modeled and that clouds are part of the model. I was not sure about the relevance of the model with respect to his microclimate and did not want to raise his expectations, particularly in light of previous comments about "proper use" and that his location was "not an irradiance hotspot". The low cost of energy also adds bias to the payback calculations.
                        This projects seems to have progressed from a science experiment of a few panels to a serious attempt to cut costs.
                        Well, you're welcome. Unless I misinterpreted what you wrote, you apparently didn't know irradiance data (or, in your word, clouds) is a necessary input to most solar process design modeling.
                        Otherwise, what were you thinking ? The way I learned it, requiring information about how sunny (as the inverse of how cloudy) a location might be was and continues to be one of, if not the most significant input a PV design model needs to the point of being a no brainer.

                        After I read "clouds might be considered in the PVWatts estimate" and stopped shaking and scratching my head at the ignorance of that statement, I figured I might mention some of what I think I might know about the matter and maybe help others who might be confused on a take it/leave it basis.

                        Aside from tilt, azimuth and latitude, what do you think is the largest single factor in determining the specific output (as expressed by kWr/yr. per installed STC kW), or the LCOE cost effectiveness of a PV array at a location ? Ya think it might have something to do with how cloudy it is ?

                        BTW, do not try to link me by implication or innuendo to statements about proper use of PV. I do think there's a lot of ignorance around about the subject and that's a shame, and even more wasted effort and wheel spinning, but I'm a libertarian at heart and if/how folks waste their time/money/effort is none of my concern. What I do here, like cleaning up the ignorant spoor from the likes of you and others of your ilk, is an attempt to eliminate some of that ignorance.

                        If you are interested in alleviating some of your ignorance about models for solar devices and solar resource modeling, try reading and reviewing the PVWatts help/info screens, and then, peruse one of the TMY data manuals, particularly if your interested in maybe learning something about modeled data and its extent.

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                        • #42
                          To Ampster and JPM

                          I think you both need to either fight it out somewhere else or get your posts deleted. Please stop sniping at each other because I am tired of responding to the complaints from other members.

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                          • #43
                            So it looks like I can only put 12 panels (305 W, 64.2 V Voc, 5.96 A Isc) on this roof that will get mid-to-late afternoon shade. They'll have to be split up and installed in two locations on this roof to avoid an obstacle (two groups of 6, roughly 3 to 4 feet apart from each other). Considering the panels' specs, the installation layout, the late afternoon gradual shading only affecting one group of panels (6 total) and the fact the cable run from the solar panels to the combiner box/charge controller will be at least 20 to 25 feet, what's a recommended series and parallel configuration for this setup?


                            P.S. - In case this matters, the battery will be 48 V, 24 kWh (eventually expanded to 72 kWh).

                            P.P.S. - As for the charge controller, I initially thought about going with a 200 V, 100 A controller for a 1s12p solar panel config, but worry about finding cable and equipment big enough to carry that current (71+ A). Then I thought maybe a 600 V 60 A controller for a 4s3p solar panel config (and to cover any other configs, if I learned of a better one), but worry about the voltage being over kill (256.8 V) and dangerous for this short cable run. Then I thought I better ask the forum.

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                            • #44
                              Originally posted by crashintoty View Post
                              So it looks like I can only put 12 panels (305 W, 64.2 V Voc, 5.96 A Isc) on this roof that will get mid-to-late afternoon shade. They'll have to be split up and installed in two locations on this roof to avoid an obstacle (two groups of 6, roughly 3 to 4 feet apart from each other). Considering the panels' specs, the installation layout, the late afternoon gradual shading only affecting one group of panels (6 total) and the fact the cable run from the solar panels to the combiner box/charge controller will be at least 20 to 25 feet, what's a recommended series and parallel configuration for this setup.
                              What is the obstacle? If it is a vent, can it be moved to get more panels?
                              It gets tricky with shade and you may want to arrange your strings so that the shaded ones don't effect the other strings. Micro inverters or optimizers are a workaround but with optimizers you still need to be concerned with shade as it affects minimum string voltage. From your panel specs it sounds like you may be using 96 cell panels and that may limit your options.
                              I used a combination of microinverters where I had shade and a string inverter where I only had shade in the morning. It all depends on the pattern of shade including seasonal differences.

                              Does your property have any other south facing unshaded areas that could better utilize those panels. Your driveway looks like a candidate?

                              What analysis got you to the conclusion that a battery system would be more economical than using the grid as a battery? I have a combination of Grid Tie and Hybrid inverters on my system. My batteries, were also less than $100 per kWhr but their main value has been to get me through power outages. In the future they may provide some hedge against erosion of Net Energy Metering beneficial time periods. I still have 3 years left on a great TOU plan that allows me to be credited at good rates. I have some time before I will need more batteries but in the meantime I have stored a lot on the grid and used it later at very little cost.
                              Last edited by Ampster; 03-17-2020, 02:36 PM.
                              9 kW solar. Driving EVs since 2012

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