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  • solar panel ideas

    Last night I put together one of my panel assemblies. I used 6 panels- each being 8-3/8 wide I figured to stay within about 4 or 5 feet in length for ease of build and use, etc. It became 50 odd inches in length and about 11 inches wide- a reasonable size.

    Today just for fun I wired the panels in series and did a voltage check. We don't have sun here today, and it's quite dark for mid afternoon, but I was getting over a hundred volts from it. While thinking about this whole 'powering something' thing, I started wondering about actually using it in a high voltage mode. Keep in mind this is academic, and I have no unrealistic expectations of getting useful amounts of power out of it- aside from the original use which will be as a 'top-up' source in my vehicle, and all panels wired in parallel for this, with nothing more than a voltage cutout circuit to control overcharging.

    So back to this high voltage idea- a person could make up a simple circuit to detect voltage, then switch a series transistor on at the high voltage point, then off at the low voltage point. The high point would be the panel voltage at the peak power point (times the number of panels) and the low point would be something less than that, perhaps about 2 volts less per panel. The array would charge a capacitor, and the output through the series transistor would feed through an inductor to a battery bank. The switching of the transistor would have some hysterisis so the switching action is sharp. The charging action would then be done in pulses, which suits batteries fine. The battery bank determines the voltage on one side of the inductor, and the two switched voltage points would keep the panels working in a small range where the maximum power point is.

    Offhand, this doesn't seem much different than any MPPT controller, except that the input voltage is much higher than the output voltage, and the switching losses would be less. Virtually every circuit I've seen uses a panel voltage that's only about 30% higher than the battery bank voltage- typical from what I've seen is a panel voltage at MPP of about 18 volts, with the battery bank at 14.4 or so- my large panel is rated at 17.6 v or so at maximum power, and my latest panels are rated at 18.8 volts. You've basically got about 4 volts of difference, and a loss of 1 volt in switching represents a 25% loss. Why not lose that 1 volt from an excess voltage of perhaps 100 volts, for only a 1% loss. That's the basic idea anyway.

    I see that one spec for solar panels is maximum system voltage. One spec said 200, another said 600 volts. I'm sure that just reflects the breakdown potential at any point where electricity could jump a gap or destroy a reverse-biased cell, something like that. But it does suggest the possibility of using a higher system voltage, like 120 vdc for instance. Your battery bank could be 10 12v batteries in series, with conversion for powering appliances being a directly switched output without an inverter.

    As I said before, this is academic at this point and just for discussion. Basically a discussion regarding using panels wired in series rather than parallel, both for low voltage battery bank or high voltage battery bank.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    Sounds interesting. Please continue to post your progress: I'll be watching.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

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    • #3
      Almost every serious MPPT controller I am aware of uses at least up to 120V or even more. See Outback solar, etc.

      It is an absolutely standard way of operating, and allows optimum power output. Utility systems use a voltage up to 600V, possibly more, although the UL recognitions for panels and connectors, etc only go to 600V.

      Most of them do MPPT, to get all the power available.

      This one uses a max array voltage of 145VDC. A friend of mine has one of these, as I recall. (He might actually use a Xantrex product, but the specs are about the same). His system currently is at about 125 VDC in good sun and a cool day.

      http://www.outbackpower.com/download.../specsheet.pdf
      1601

      Keep eye on ball.
      Hashim Khan

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      • #4
        Well that shows how little I knew about 'real' solar power systems. Glad that what I was talking about actually makes some sense-

        Largest system that I've seen is a bank of 12 2 volt cells from a railway switchyard. His panels are 36 volt, but all in parallel. The controller has everything though, from what I saw. While I was there it was displaying input voltage, charge current, and battery voltage. I thought the numbers were impressive- charge current at the time was over 30 amps, 37 I think it was.

        I'll keep tinkering, and learning.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          My take on it is that you are a pretty sharp character, (which we already knew) and that you have a good sense of practical engineering (which we probably also knew).

          Nothing wrong with finding that your good idea is in production, it proves that you can come up with good ideas.
          1601

          Keep eye on ball.
          Hashim Khan

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          • #6
            One problem with wiring so many panels in series, is that if any one is shaded or otherwise putting out less current than the others, it may limit the total amount of power that can be extracted. AFAIK, MPPT controllers are most efficiently implemented on a one-per-panel basis, and the outputs are matched so that they can be connected in parallel with a fixed voltage or charging current for storage batteries. It should be possible to use a switching type battery charger that works similar to what you describe. In most cases, it would probably be a buck current/voltage switching supply with the output lower than the input. You can use most any line-operated switching supply on 120-370 VDC corresponding to 85-264 VAC. If you connect panels in parallel, you should use a low Vf Schottky rectifier rated higher than the maximum panel voltage.
            http://pauleschoen.com/pix/PM08_P76_P54.png
            Paul , P S Technology, Inc. and MrTibbs
            USA Maryland 21030

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            • #7
              If a panel is out of commission, it simply gets bypassed. It's possible to bypass each panel with a parallel diode. When the panel is producing, the diode is reverse-biased. If a panel is not producing, then the current simply goes through the parallel diode as a lower-voltage path than the forward voltage of a series of cells.

              When a panel is bad, you lose about the same amount of power, one panel worth, as in the parallel case, but you generally have a lower loss in the "ON" voltaqe and forward voltage of devices and diodes under all conditions. Overall it should be lower loss.

              You also lose less in the panel system wiring, due to the considerably lower current, and you require only one switching device for a number of panels. Plus, you get to choose your battery voltage, which can be anything less than the panel string produces.
              1601

              Keep eye on ball.
              Hashim Khan

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              • #8
                Series wired PV cells have a problem when the total voltage exceeds the forward breakdown voltage of a single cell. This can happen with smaller cells that lose light as when a bird or large leaf blocks it. Because they have a very large area, series arrays are vulnerable to shadows from any source shutting down the entire array. I'd be interested in what ever purpose somebody might have for doing this. Inverters do the same thing without introducing shading problems.

                Our Blues Band did a show at a remote venue last summer on what is called the Solar Stage. It has an array about 2 meters on a side, a box of batteries, and an inverter to drive our amplifiers. Epic fail - the batteries were unable to maintain adequate power for our band, stage lights. We're in a desert with very long summer days being just at the Canadian border but we have thunder storms and heavy rain all weekend. I guess that is why solar is considered unreliable. The solar is also augmented with a wind turbine but had no impact on the reliability. Even the luggable 2KW portable generator didn't help. The other stage had a large fossil fuel generator and they didn't miss a beat. Fortunately our band played that stage too so the day wasn't a complete bust. None of us were happy about having our very expensive gear investment exposed to that lashup.

                So the lesson is size it appropriately and keep a battery charger handy that uses grid power if reliability is at all important.

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                • #9
                  Solar is NOT "considered unreliable". It is FAR more reliable than wind power.

                  Every panel is a series connection of cells, as many as 30 or more, depending on the panel voltage. So a series array is simply more of the same.

                  NO.... A bird or large leaf does NOT "shut down" the array. Or the panel. All that happens is a reduction in power output. My own array continues to put out power at the times of day that it is as much as 20% in shadow. Reduced power, of course, the shadowed parts are not producing as much as the others.

                  EVERY large installation is made with series panels. Your objections are simply unfounded hearsay that is proven to be silly by installations all over the globe. Including mine, and the one my friend has. He has no grid power at all, and has been living there with solar for many years, finding it quite reliable.

                  Edit: I have no idea what you mean about "inverters". They are for making AC from DC, and nothing to do with solar panels other than using their output.

                  As for the "solar stage fail"......

                  From your description, the array was simply an abysmally poor design. For reasonable power, it should have been more like 2 or 3 meters by 10 meters.

                  At your estimation of 4 square meters, it hat a raw arriving power of about 6kw maximum. The efficiency of about 12% would lead to a net output of about 700 watts. Not enough to keep up with a band.

                  You do not say what the inverter power was, nor the battery capacity, but my suspicion is it was similarly stupidly small.

                  The system was not adequate for the usage, THAT is why it did not work. Apparently your usage was too large even for the 2KW genset, let alone the silly 700 watt array.

                  My friend has had a yearly 2 day music fest for the last 12 years at his place, all solar powered. He has never had a power failure, but his array is about 3 x larger than what you describe, and there are not full bands with PA, its a folk fest.
                  Last edited by J Tiers; 01-23-2016, 11:33 AM.
                  1601

                  Keep eye on ball.
                  Hashim Khan

                  Comment


                  • #10
                    I'm reading that your measuring the total voltage of the series strung panels.
                    The high voltages are cool but what about current?
                    Voltage times Amps equals Wattage which is what we really need to know to get usable work out of a system.

                    I'm really missing something about your ideas on using a parallel diode for bypass.
                    If a Panel is producing power, it's parallel diode will short it out.
                    If you turn the diode around, it does nothing.
                    Upon some more reflection, I think you need to add a series diode with the panel and then bridge those with an additional diode.
                    Do the panels themselves act as diodes and block reverse current flow? In which case the parallel diode may work after all.

                    Tom M.

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                    • #11
                      Originally posted by dp View Post
                      Even the luggable 2KW portable generator didn't help.
                      If anything like the Honda EU2000is, it doesn't produce anything close to 2000 watts continuous either.

                      Comment


                      • #12
                        The parallel diode allows one panel to be non-productive while others still produce. The diode bypasses the weak panel, allowing current to still flow from the others. Imagine that you have a series of water valves and one closes- no current will flow. In the solar array the diode blocks current flow when the panel is producing, so it doesn't short out the panel, but when the panel is not producing it will be 'reverse biased'- in other words the other panels will impress a voltage on the weak or dead one, in a reverse direction. The diode passes the current in this direction, thus completing the circuit so current from the producing panels can still flow.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                        Comment


                        • #13
                          I just did a test. I hooked up a power supply to one of my panels, then varied the voltage up to the limit, which with this power supply is 21.5 volts. With the panel in room light, it's showing about 5 volts output. As I raised the voltage level to it, the 'leakage' current was zero up to about 19 volts or so, then rose to about 30 ma at 21.5 volts. When I hooked it up in reverse, the leakage current never rose above a few ma, if it was there at all. It's hard to read this low of a current on my power supplies scale, so it may have been zero or maybe a few ma. There is no reverse diode on the panel- otherwise the current would have assumed a very high value even with less than one volt applied. What I did not test, and what could be an issue, is a higher applied reverse voltage. This could happen with a series connected array- but then I would assume that any 'better quality' array would have the reverse diode installed, and probably a forward diode as well per string, where more than one string would be connected in parallel. A consideration here would be when using a forward diode you'd want to use one with a low forward voltage drop- this is usually a shottky diode, which may not have a very high reverse voltage rating. You would consider this when putting several panels in series for a higher voltage output. Of course as you series the panels and get higher voltage output, the forward voltage drop of the series diode becomes less important and you would probably use a regular silicon diode, which can have a reverse rating of 1000 volts or more.



                          In any event, my current panels will be wired in parallel, since they will be used to maintain 12v batteries. I will probably not use either a reverse diode or a forward diode, since the voltage is not high enough to damage a cell in reverse bias, nor damage a weak parallelled cell.
                          Last edited by darryl; 01-23-2016, 05:31 PM.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                          • #14
                            Originally posted by J Tiers View Post
                            Solar is NOT "considered unreliable". It is FAR more reliable than wind power.
                            Solar is unreliable. There is no question about it. Solar cells quit working every day requiring transfer to battery backup. Solar cells have to power the inverter(s), battery charger, and the primary load while the sun is shining. The people who built the system are bad at math. That is obvious. That is why I said you have to size the system appropriately.

                            Solar panels fail miserably, depending on design, when panes are shadowed. There is no question about this. Series panels (where there are no parallel panels) are the worst.

                            Proper panels are arrays of parallel and series cells that can survive with minimal energy generation loss. Solar as built and installed on an annual basis is at best 50% efficient relative to the placard rating. That is because the sun goes down on average half the time. Seasonally it is far worse. Daily it is worse yet. Anything that quits working once a day is unreliable.

                            NO.... A bird or large leaf does NOT "shut down" the array. Or the panel. All that happens is a reduction in power output. My own array continues to put out power at the times of day that it is as much as 20% in shadow. Reduced power, of course, the shadowed parts are not producing as much as the others.
                            Actual field test. It all depends on the array geometry what the degree of output failure will be.
                            https://www.youtube.com/watch?v=-WGU5j7Rh1g

                            In a series wired array where the total array voltage is greater than the forward voltage rating of a single panel that is shaded, that panel behaves like an open circuit and the entire voltage of the remaining active cells is impressed upon the inactive array. That is bad.

                            EVERY large installation is made with series panels. Your objections are simply unfounded hearsay that is proven to be silly by installations all over the globe. Including mine, and the one my friend has. He has no grid power at all, and has been living there with solar for many years, finding it quite reliable.
                            The OP is describing a single high voltage series wired array. Try to follow the conversation were having and not the one you imagine.

                            Edit: I have no idea what you mean about "inverters". They are for making AC from DC, and nothing to do with solar panels other than using their output.
                            Inverters are what make solar arrays useful. Solar DC output direct to load are unusual but not impossible. They are what make solar arrays useful as general purpose energy sources. The OP hasn't mentioned them and this part of the conversation is general as applied to solar array in lieu of grid energy.

                            As for the "solar stage fail"......

                            From your description, the array was simply an abysmally poor design. For reasonable power, it should have been more like 2 or 3 meters by 10 meters.
                            I already said in my post that you have to be careful when designing solar power systems to size them correctly. There is more wrong with the solar stage that you and I have discussed. The real problem is they don't have enough money to buy what they need. They do have enough money to buy a proper generator, though.

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                            • #15
                              I agree there is a lot of misinformation regarding solar systems- perhaps misinformation is not the right word, maybe over-optimism describes it better. I did a mental calculation a couple weeks ago when trying to explain the reality of the situation to a young lad. I came up with 5% of the solar panel rating as an average of the power output. Even that might be optimistic. I guessed at the cost of hydro and came up with a payback period of 16 years- and that's for the price I paid, not what these would be retail. Our cost for hydro is 1/2 of what I used for my calculation, making the payback period 32 years. Talk about sizing the system correctly- it would be virtually impossible to power a stage setup including lights with any system that you could reasonably set up on site. I do applaud the effort to do so, and it probably would have been the highlight of my day to see this being set up and used to power a stage- I've set up enough stage gear and lights in my time for this to have been a unique part of the experience. I've had my share of 'not enough power' when it comes to running everything, and had my own ideas on how to supply enough juice for everything when all that was offered was a 14/3 50 ft long extension cord from a 15 amp outlet- and even for that, how many sq yds of solar panel would it take, even with full sun, to develop even that much (or little) power-

                              One of the outdoor concerts we powered up had it's own generator on a trailer, probably a 20 kw unit, and it was barely adequate. Makes what I'm doing seem like an expensive alternative to a single AA battery.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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