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Forum Index : Solar : Stage One to grid power independence
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LadyN Guru  Joined: 26/01/2019 Location: United StatesPosts: 408 |
Stage One to grid power independence for a complete newcomer: Warpspeed version Stage One uses solar to supplement rectified dc grid power to drive an inverter (without a battery). Unlike a conventional grid tie system, it feeds nothing back. This is phenomenally capital efficient. Some reasons: 1. By not having grid feedback it removes the risk of islanding so you are not putting line workers at risk reducing your own liability. 2. By not having a battery you tremendously reduce your initial capital outlay. Lithium based chemistry is the most popular one right now with Lithium Cobalt being the favorite. That said, new contenders are gaining momentum. 2019 has a lot in store as less risky and most stable chemistries gain wider acceptance. 3. By not having to choose between either PV output or rectified dc grid power you have the best of both worlds. Here, solar energy is used to supplement the rectified dc grid. The most efficient would have been to load share ac grid with ac out of PV output but the highly variable nature of PV would complicate the design and to minimize complication we trade it off with efficiency. |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
Placeholder now that I have edit privileges |
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| BenandAmber Guru Joined: 16/02/2019 Location: United StatesPosts: 961 |
That's a really amazing idea be warned i am good parrot but Dumber than a box of rocks |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
If the grid went down for a week, you would still have full power during the day. At night it would be candles and flashlights though. But you would be infinitely better off than the neighbors that had absolutely no power at all for a week. Cheers, Tony. |
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| kanchana Regular Member  Joined: 08/05/2018 Location: Sri LankaPosts: 56 |
when we have no power from the grid , How to buffer the pv voltage fluctuations with out batteries? Regards kanchana |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Without either grid or batteries it gets tricky. It will need some large electrolytic capacitors to reduce the heavily pulsing load of the inverter so that the solar panels can just supply a steady constant current. Its all much easier to do at higher dc voltages, preferably at 100 volts or more. The inverter will obviously need to operate over a much wider input voltage range than with a battery, but that is doable too. The load on the inverter needs to be kept low enough so that the solar voltage will not be pulled down much below the maximum power voltage. With my own system, it draws no power at all from the battery during the day so unless there is so much cloud its almost dark outside, there is still enough power to run fairly light normal loads even with the battery switched off. Probably not an ideal system to use on a daily basis without either the grid or batteries, but it can and does work like that. Cheers, Tony. |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
The Warpverter (the designer of which replied above) achieves line regulation (as you desire above) through software by using the proper switching pattern from internal look up table. However, as energy can neither be created nor destroyed, you can only get out of the Warpverter the power you put in of course minus losses. If you have the ability to make an inverter and want to build a Warpverter, I will be very happy to work with you on that but it could be a pretty long project. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
It should also be possible to do exactly the same thing with a PWM inverter. I just do not know what sort of input voltage range those Chinese PWM boards can cope with. The dc input voltage range to the inverter will have some pretty dramatic voltage swings with step load changes, and whatever voltage feedback controls the ac output voltage needs to be extremely fast on its feet to cope. My own inverter does not use voltage feedback. What it does is measure the dc input voltage and make some very fast corrections. Its the speed of response that is the most important feature here. It doesn't really matter if the output voltage falls very slightly at very high inverter loading. The grid goes up and down a fair bit anyway. The problem with voltage feedback is that the output voltage has to actually change before any output voltage correction can even begin to work. Its then really all happening a bit too late. So you get voltage sags and voltage surges as heavy loads switch in and out. Light flicker when the refrigerator starts up being typical. Probably not too bad with a monster battery with fairly constant terminal voltage, but coming straight off solar its a really serious issue. The dc input voltage sensing technique, and a sufficiently large capacitor bank between the solar panels and the inverter slow down any sudden voltage swings so that the input voltage correction technique has sufficient time to track the changes. This all works a lot better than I expected and is well worth trying. As the energy stored in a capacitor increases with voltage squared, this all works far better at higher dc voltages. At lower voltages the dc current will be much higher and the capacitor bank will need to be impractically large (and expensive). My own system is nominally 100v dc, uses 36,000uF and uses a 5Kw inverter. It is normally very lightly loaded and that energy storage is quite sufficient. If I was going to start using a 4.8Kw airconditioner I would probably need a lot more microfarads than that, but at the moment I don't have enough either solar or batteries to run loads like that, even though the inverter itself can. If using a rectifier for grid power at night, the same capacitor bank can smooth that too, through a suitable choke. Cheers, Tony. |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
I wonder if trying to sync the Warpverter to the grid would require onboard frq. synthesis instead of look up table based DDS. Something to consider after my second or third Warpverter I guess. I believe this is a solved problem with the Nano version of the OZInverter? |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Poida has come up with a successful way to synchronize his PWM with the grid. The original intent of that was to synchronize an inverter to a small gasoline generator, which I believe is pretty much doomed to failure, unless its an inverter type generator which many of the newer ones now are. If running an inverter straight from solar panels during the day, and off a grid powered rectifier at night, there could be a distinct advantage in phase locking the inverter to the grid. The pulsing output from the rectifier would then coincide exactly with the pulsing current demand of the inverter, and any problems of very slow cyclic voltage variations caused by any beating of the two different frequencies would not occur. Just about all inverters have a crystal oscillator, and that could be replaced or modified to provide voltage control of frequency over a very narrow range sufficient for phase locking. I have no need of that here because my own grid powered rectifier runs off three phases and I do not have the frequency beat problem. Cheers, Tony. |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
It is very interesting that you brought up this point. I want to discuss this further: here https://www.thebackshed.com/forum/forum_posts.asp?TID=11198 Why would I want to run the inverter off a grid powered rectifier at night though? 1. Is it only to simplify the wiring so everything is fed off the inverter? 2. To allow the inverter to load share between the battery stored power and use that to offset grid reliance? 3. Some other reason I did not think of? For me, the only time it makes sense to sync to the grid is if I plan to backfeed to the utility to get credits. At no other point in time it makes any sense to sync to the grid if I am converting all my inputs to (rectified) DC. Then the only thing I need to worry about is matching their voltage to assure proper load sharing without wasting any energy. Maybe I am missing something. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The idea is that there is dc voltage from the solar panels, and also a dc voltage from a grid powered rectifier. The inverter is powered from whichever is the higher voltage (via two diodes) or if the voltages are the same there will be load sharing. During the day we arrange things so that the voltage from the solar panels will be considerably higher, and supply all of the inverter load. At dusk, the solar voltage falls and the inverter load is seamlessly taken over by the grid powered rectifier. At dawn, solar voltage rises and seamlessly takes over from the grid. If there is very heavy cloud cover and the inverter load high, solar will provide all that it possibly can, and any shortfall will come from the grid. That might only be very short bursts of grid power required to get through sudden heavy surge loads such as motor starts for example. Cheers, Tony. |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
This really sounds beautiful. Very simple and effective. Fantastic engineering! A possible (and wonderful) side effect of this design is that if there is a heavy load that causes the alternative inputs to sag (because they can't keep up), grid power picks up the sag automagically until the alternative inputs come right back up. The only real challenge I see is ensuring the outputs from the alternative inputs have the same amplitude (voltage) as grid power when load sharing. That could be tricky. Only experimentation will say how much I guess! |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The load sharing is automatic. During the night solar voltage is zero, during the day solar voltage will be considerably higher than the rectifier voltage. At both dawn and dusk the solar and rectifier voltages will cross over and it will load share at that point, and smoothly transfer all of the load one way or the other. During the day solar voltage will be higher, but as the panel loading increases the voltage is going to fall. Under heavy load (or poor solar) the panel voltage will be pulled right down until it gets as low as the rectifier voltage, whatever voltage that happens to be. It will again load share, and the grid will make up any shortfall. Its not tricky, it just happens all by itself. If the inverter can operate over a sufficiently wide dc input voltage range, you just get continuous power day and night out from the inverter without really knowing or caring which source it comes from. Cheers, Tony. |
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| kanchana Regular Member Joined: 08/05/2018 Location: Sri LankaPosts: 56 |
quite elegant design. how do you get the 100v from the mains ? Regards kanchana |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I am very fortunate in having three phase power available at home. And even more fortunate in having a suitable three phase transformer out of an old industrial battery charger that with the various tappings and windings gives me about 106v dc at several tens of amps. Cheers, Tony. |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
Was that from your transformer business? |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Its something someone gave me a very long time ago. It was a case of "I am going to chuck this out, do you want it?" There is no rating plate, so I really have no idea what the current or power rating is, but from the size its probably 3Kva to 5Kva. This is an old picture of the same transformer, but here its hooked up for a much lower output voltage, 30v as I remember, for 100+ amps with everything connected up in parallel.  What I have now is pretty much the same thing, except the three secondaries on each section are now in series, and I bumped up the primary tapping to give me about 106v dc instead of around 90v dc. Its no longer used, as I now run off a lithium battery at night. Although if I ever need to do any serious work on the battery, the rectifier will get plugged back into the system to give me some night time power. Cheers, Tony. |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
The picture looks beautiful! 1. What are those 3 things into which the windings feed into? 2. What the rating of the cap at top left and what does it do? 3. What's on top of the board and why do they connect to what looks like breakers? |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
1/ One hundred amp bridge rectifiers, mounted on an aluminium plate heat sink. 2/ Not really necessary, as the ripple out of a three phase rectifier is only about 2% without any extra filtering. Its there only as an "add on" to reduce any noise when run at very low load current. 3/ On top of the transformer are some connections to allow for different mains input voltages. In this case tappings are for 225v, 240v, and 255v. Yes there is a 10 amp three phase circuit breaker which is mainly to provide an on/off switch. The reason is more for safety, in fact it is a statutory requirement to have an on/off switch within three feet of "the equipment" but its also just common sense. Its much more convenient, rather than having to keep walking over to the remote power outlet to switch the thing on and off. Cheers, Tony. |
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