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Forum Index : Electronics : Grid tie with ultracaps, no batts
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| domwild Guru  Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Hi, Second post on this issue; no reply on my offer of the thesis but I certainly found it interesting: Kansas State Uni, Master of Science thesis. 2 x 220W PV into one Enphase M190, 208 VAC grid-tie PLUS an Air Breeze 24VDC wind turbine connected to a second M190 grid-tie. The M190 outputs on two phases of a three-phase grid connection, 190W max. Input voltage tolerance of 21 to 40VDC. Rather than buying two 12V, 200AH batts for US$300 each they decided to connect to 12 Maxwell BCAAP0100T07 2.7V, 100 Farad ultra caps costing $12 each = US$144 connected in series giving 8.33 Farads with a voltage tolerance of 32.4. Problems: 1. Start-up delay of one minute of the M190 means a 24VDC wall-wart power supply keeps the voltage at 21V. 2. M190 cannot respond to gusts and takes 3-6 secs to respond giving 45V spikes; solution is achieved via 1k Ohm resistor in series with 1N4751A Zener driving an IRF250 NFET which is full-on and clamps at 33V. Zener conducts at 29.3V and small current goes through 1kOhm resistor. 3. OMRON relay is normally open from grid and performs anti-islanding on grid failure and stops run-away. Schematic: Air Breeze mill - mill disconnect switch - OMRON relay - 24VDC trickle - spike suppressor - ultracaps with balancing circuits and drain switch - fuse - M190 grid-tie - three-phase grid Schematic also shows two DC measuring places before caps and after and one AC measuring site after the M190. Non-Maxwell caps were initially bought and rejected, however, the balancing circuits and "non-heatsinked" (!) over-voltage protection circuits were reused for the Maxwells. An aside: Ultracaps are going to become ever better as one scientist is working on growing vertical carbon nanotubes. Q.: 1. As the third L3 three-phase connector is not used but an "unbalanced" output is occurring, at which wattage are our power companies worried about unbalanced phases? 2. As this is a battery-less low-cost solution with a "solar" low-cost grid-tie micro inverter and no diversion load, that does the forum think about that??? Do not panic, this is not a cheap Chinese-brand grid-tie, it is UL, etc. certified for the US. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Hopefully this is the link to the ~45-page thesis: https://krex.k-state.edu/dspace/handle/2097/8754 Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I think there is still a big gap between the storage capacity of capacitors and batteries. Capacitors do offer a longer working life compared to a battery, but their price and size mean batteries will be around for many decades yet. You just cant beat the energy density of a chemical reaction in a battery, compared to the electrostatic charge storage in a capacitor. The only way to increase a capacitors storage ability is to increase the plates surface area, and/or bring the plates closer together. Both methods are reaching their limits in engineering in modern capacitors. I do think caps used in combination with batteries is a clever way forward, especially for automotive applications. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Glenn, You are right and I do not advocate getting rid of batts altogether, however, if you are on the grid, then the article describes a low-cost solution. Off the grid batteries are essential. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Hi Dom, Ultra-Caps are very viable option to add into a Grid Tie system. I have had this set up for a number of years now. I do not know why because some engineering student does a 45 page thesis all of a sudden make it a discovery as buses and other forms of electric vehicle applications have been using ultra caps for power recovery on regenerative braking for quite a while. With wind/solar it is no different, as gusts and solar bursts cause rapid power spikes and overpower batteries causing damage because of the slow response time of grid inverters to match these spikes. Before I added the Ultra Caps the voltage line on my logger over a day looked like it was recording a R9 earthquake, after adding the Ultra Caps the line is not totally smooth but everything reacts at a controlled pace , as well as reducing the lost power due to the solar being backed off and battery losses due to gassing . I have 25 x 2.7V 3000 Farad Maxwell Ultra Caps that are in paralell with a 48V / 225A/hr battery set , they can be switched to be run as separate systems or together which is normal. The ultra caps can absorb 8000W for a period of 30sec with a voltage rise of 53 to 60Vdc , so this easily absorbs wind gusts and solar bursts . Here is a pic of the Ultra-Caps / Batteries , there are 2 x PVE 1200 Grid Inverters feeding off the system , 2.5kw of Solar and at present I have 2 x 2kW Chinese wind turbines up for testing , one with the GOE Blades opposed to the Factory supplied blades. 
I posted some info some years back when I fitted them and after that Tinker also added them to his system , I do feel they have a place in grid tie systems such as mine but as for Off -Grid I can see no benefit. If you are getting rapid voltage Spikes means your batteries are to small or buggered. I also designed and incorporated them into a battery-less grid tie system for a customer a couple of years ago that worked very well. It used a small solar panel and battery to keep the grid connection. In my opinion " Thesis ", he should have bought 2x100A/hr batteries for the mismatched toy system he was playing with, he had too much solar and a wind turbine that will only output in force 10. If he fitted a standard solar voltage control and a dump or diversion system for the a bigger mill with much larger Ultracaps and it would be a sweet system with the ability to grid feed as well have some back up power for black outs. But its only a cheap experiment for him to become a Master of Science with not much "in the real world" value. PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Phill, Thanks for that. I am still learning and IMHO using a cheaper solar grid tie inverter and ultracaps for wind seemed like a new idea to me. Not too many companies seem to have successfully built MPPT wind grid-tie units; one can most likely disregard the Alibaba Chinese claims of wind/sun grid-tie units. From what I have read solar MPPT is an easier problem to deal with. I did not know that solar bursts also cause spike problems. From the little that I know I guess most solar grid-tie inverters are MPPT-based. Does the addition of ultracaps to absorb mill power spikes/drops get closer to the ideal of a MPPT wind grid-tie inverter? Did you worry about balancing circuits on your ultracaps? Thanks. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Dom, I do not know why there is need to chase the 1% extra for the "holy Grail " of small Wind MPPT, to me it is just a fruitless dream some have. A small wind turbine is racked by so many variables and to program in a power curve to some of the offered MPPT controllers like windy boy and Midnite Solar still means you have to keep well back from the optium power to allow for things like not tracking the wind ,sudden wind shifts , furling etc. A turbine will catch a gust then speed up and yaw then the MPPT will load and its all to late as the turbine is not at its optimum position to the wind so it gets over loaded and stalls. It is not like running the gen up in a test bench where- (x)volts Ac (X)Current draw, when the input power is constant , Solar is a given and can be easily tracked and plotted , so I think it comes to the point that you just accept that if you want wind, then it is is what it is and tune the mill to its best . If you want to waste $ on MPPT for a what is a probably poorly designed wind generator to get virtually no return then that's up to the individual. Yes , you can use Ultra Caps to absorb wind spikes and but its no good putting a undersized set in because of cost and expect it to work . From memory the 25 x 3000 Farad Ultra Caps cost over $700 , Batteries $1400 . Thats 9.5+ megawatts of power it has to make to break even, I am never going to see that day. As I mentioned , I put the caps in because of the lag time on the inverters , the PVE 1200 is the only one on the market that is low voltage . Latronics do make a unit that will connect a wind turbine to the PVE 1200 with no batteries , it is basically a set of caps but there will always be the problem with AS4777 connection time of 60sec +, which is useless for wind so batteries and solar/wind works. There are other options but none of which are legal , so if you want a legal and compliant wind grid feed in AUS there is not many options. To answer about the balancers , yes they are fitted with just basic LED / diode across each Cap, which I have just added a resistor in (advice from a friend GW@PE) to trial and it is working unbelievably and they seem to be settling at 10 ~ 50mV difference. I have just put them back into the system as I was using them as a test battery bank for setting up a stand alone Wind/solar/ batt 48Vdc deep bore pump control PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Commenting on the need to balance supercaps, my 12 x 3000F bank uses a balancing circuit with an adjustable voltage which is a little more complicated than a simple LED & resistor but also kept the difference to figures mentioned above. For my Lipo balancing mentioned elsewhere on this forum I just use a *green* LED with no resistor across each of the two 100F supercaps. Green LED's have a higher forward voltage than red ones and seem to work perfectly for me. The LED's are absolutely essential, I did not have any balancing for some time and when measuring each individual supercaps voltage one was rather too close for comfort to its 2.7V max rating. Klaus |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Phill, Please excuse my ignorance and follow my logic for a sec: 1. Most commercial solar grid-ties use MPPT. 2. Because of the cubic relationship wind mill grid-tie is much more complicated. 3. By adding caps in he smooths out surges and approximates wind MPPT as a cheap solution as solar MPPT grid-ties are "cheaper". 4. The connection time delay he circumvents by trickling the system with 21VDC. I fully agree with you re legality and solar capacity and IMHO if he was successful he did get his Masters easily as even I managed to follow the thesis; he only had one formula in it with a differential and one expects the maths to be much more complex in a thesis like that. The system he describes would most likely be illegal here as the anti-islanding system he describes would have to be approved first by the authorities. A university campus in the US might be legally on federal land and therefore any state laws would not be applicable? What do you think? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
I can expand a bit on your first point. Usually right down the back of the solar inverter grid tied installation manual there is a graph that shows the "butter zone" that the two strings of panels need to meet to get the 95+ efficiency and make the best of the MPPT. Sometimes that can be very hard to achieve, it is a very narrow window. Don't assume that every solar system that you see is averaging a high peak efficiency. There are also strict panel current and voltage limits to ensure the longevity of some of the harder working components, high ambient temperatures will also cause some inverters to severely restrict their output. Solar panels also operate at a fairly stable consistent voltage right down to very low light levels so they get above their lower voltage limit very early after sunrise. So grid solar is more about making the system components fit the MPPT rather that having the MPPT deal with whatever is thrown at it. conformity equals "cheapness" in this case. I'm confused, no wait... maybe I'm not... |
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| fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
1. Yep and you will find they run at very high DC voltages and as Yahoo threw a bit of light on , i would think it is done more for somplicity / components / keeps the amps low / Less wiring / lighter wiring. As for the " Butter Zone " nver heard of that.... Anyway totally usless for wind generators . 2.YEP 3. So if a solar MPPT runs at 135Vdc to 270VDC , that would be 50 to 100 Ultra caps in series and then you have to run a high voltage wind gen to match. Cost $$$$$ Not really the low cost solution he described it to be. 4. High VDC trickle ????? As I have said it's easy to do what he has did with one of the cheap chinese 1000W grid tie inverters as the low DC input range easily allows it. I have done it, had it working very well and as long as the wind gen is set up correctly and can deal with the voltage & loading paramiters set internally its a winner. As for legalities thats up to you, another purpose it could also be to feed into a Off Grid system where it is its own grid, this would be legal. I should write a story on how I did it and apply for a Masters 
SMA also made a LV 1100, karlJ advertized some left over stock in the for sale recently , they are ideal but 5 years ago they were not on the AS4777 list , they are now but only till the end of the year  ... Buy one and play with that they are a quality unit and run @ 22 ~ 60V and you could get one at a good price.. PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Phill, Tinker and Yahoo2, Thanks for the enlightenment. I have a "grey belt" in software (from punched cards to C++) but definitely no "black belt" in electrickery. Yes, Phill, you should apply to Kansas Uni for your Masters and point out that you can improve his system! I will check out the "For Sale" ads of this forum to see if this karlJ still advertises. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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