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Post by horsall on Oct 27, 2012 8:56:25 GMT -5
Hello All Let me first introduce myself. We live in a cottage that is off grid(except for a telephone line)
We have been here for 37years so all our systems have evolved? over time.
We have 2 diesel generators(4.5kva and 3.5kva lister start o matics) 2 wind turbines which on a good windy day will show charge up to 1/1.5kw.
We also have about 1kw of PV panels most of them tracking the sun for max output.
We have a 3.5kva inverter system(Outback type)24volt type which is all singing and dancing. ie it starts on demand, starts the generator if batteries are low or on high load and then charges the batteries while the generator is running.
We have 1100amp/hours battery capacity @ 24volt(fork lift truck type very heavy)in 2volt cells.
We have 2 solar panels I made 30 years ago! they in an aluminum frame about 2150mm x 730mm x 50mm.
I made the collectors out of 28mm copper pipe top and bottom with 15mm running vertically between them at about 150crs and on to these I soldered copper sheet which I had formed a 15mm half round impression and then etch primed and sprayed matt black(cant remember what type of paint but it still looks ok) and glazed in front with horticultural glass(it was cheap) They were constructed like this because I wanted them to thermosyphon(no constant power then)
This heated a separate cylinder which we could use direct or feed to existing cylinder.
I later modified it to a pumped system on a closed loop with expansion tank(which increased the efficiency) But now I an upgrading? the system as I want to change the bathroom and tanks.
So I have fitted a twin coil solar tank(Telford type bought off ebay) I have bought one of cye,s pumps(TS5 15PV) and a solar controller off Peter(decided my home made one was a bit to simple)
I am going to connect the solar panels with 10mm copper pipe to cut water capacity down now its not a thermosyphon system(cant do much about the panels) We use to get up to a max of 185degF on our old tank(30" x 18") so I know it works.
Now after all that my question.
Is it better to control the the pump flow by altering the voltage to the pump or by valves?
I would think voltage adjustment but I am not sure it would be easy enough to fit a small variable chip something like an LM317T What is everyone's thought on the matter? Thank,s Roger
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Post by cye on Oct 28, 2012 10:26:49 GMT -5
hi there. using a gate valve to control flow rate to me is like applying the brakes on a car to reduce speed whilst continuing to keep the foot on the accelerator. it will work, but it's making unnecessary work for the pump and using excess energy. so your thinking is sound about using another method.
are you trying to reduce power to the minimum or is there another reason you wish to vary the flow rate?
i have a spare 12v pwm motor speed controller pcb lying about somewhere in the shed. if you like i can root it out & see whether it works on the PV pumps and if it works you can have it to play with? i know it works on the 6w non PV pumps but have not tried yet on the PV pumps (the latter have mppt circuitry which may not be compatible???).
your other way of varying the supply may also work i'm not an expert, just make sure the voltage stays in the rated range of 6-24v. those pv pumps are designed to run directly from pv panels and have no surge protection, and whilst they do have some overvoltage protection, this is limited to 30v.
please tell us more about your other systems - e.g., the pv tracking! several of us here are very interested in small scale tracking.
your flat panels have stood the test of time. a lot of the commercial ones i see on roofs have problems with condensation - have you vents to manage this or did you just seal them well? and you used ordinary solder?
regards
cye
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Post by horsall on Oct 28, 2012 13:01:06 GMT -5
Hello Cye Thank.s for the reply. The reason for reducing the pump flow is to obtain the 10deg temperature drop through the solar coil and get best efficiency! The panels do suffer a bit of condensation but it seems to clear after a short time I also I used glass and not plastic as they are still clear not all opaque like all the ones I see on other roofs. I don,t see why adjusting the voltage won,t do the job unless there is some very clever circuitry which keeps the pump at set speed in which case it would need a different approach? I have 3 different tracking systems! ( as I said it has all evolved! over time) I will try and post photos and a few details when time permits and links to kit used (but some is home made) Roger Attachments:
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Post by cye on Oct 28, 2012 15:32:52 GMT -5
hi there.
they're nice looking panels!
regarding pump speed adjustment i agree that adjusting the voltage should do the job, as the PV pumps pump at a slower rate in lower light. adjusting the voltage would be a better plan that my earlier suggestion of pwm adjustment , which i believe pulses rather than lowers the voltage.
regarding efficiency, whilst you will indeed get a better heat transfer efficiency with a greater temperature difference between the coil and the surrounding tank water, you are however in turn running the panel at a higher temperature as a consequence. this in turn reduces the energy capture efficiency of the panels. the higher the difference between the panel temp and the ambient air the lower the energy capture efficiency. The efficiency drop with increasing panel temp is greater for flat panels than with tubes by virtue of their lower levels of insulation. i'll dig out a graph from a study for you if you like?
so it always a balancing act whereby one tries to avoid using an unecessarily high powered pump for the job (which is wasteful of energy), versus minimising the difference between the panel temperature and the surrounding air. inevitably we all compromise. food for thought anyway!
we've been thinking a lot about tracking recently. i have just 80w into a grid tie and the panels are almost useless unless tracked. when tracked manually the difference is enormous, far greater than the 30% improvement i've read about. this may in part be due to the fact that i'm using a 300w grid tie inverter with only 80w of pv, and i'm probaby already operating at the extremes of the inverter's efficiency curve! cavemen has built a nice tracking sensor and circuitry and i've bought a 12v Linak linear actuator originally for a hospital bed. all the makings of a tracker! very keen to see what others have done.
all the best.
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Post by horsall on Oct 28, 2012 16:21:00 GMT -5
Hello Cye That,s given me more to think about it wasn't this complicated when I built them 30years ago I just built what I thought looked right and would fit the position I fitted them in. This was just before I built our first 25foot wind turbine tower after having carried home a load of angle iron home on the the roof of our Morris Minor Traveller(completely overload)and that is still standing! My first tracker is powered by a small 24volt motor(the one that delivers your receipt on older ATM,s) and a nut on a piece of all thread via a small reduction gearbox(off an ATM again) guess what I used to service and repair? I will post some photos of the setup in the next few days. It makes the panels a lot more efficient plus they are all feed through a MPPT charge controller which again makes a lot of difference(but it is still very expensive electricity so not to be wasted) Roger
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Post by cye on Oct 29, 2012 3:57:08 GMT -5
is the Traveller also still standing or just the turbine tower? I hope both . Many good projects start with an overloaded car! Well your panels look good and i would point out for others the wisdom of where they have been located. i.e., somewhere preferably both in a good location for catching the rays as well as somewhere accessible. our neighbours had the commercial installers out to visit a few years back when the grants were good and they told her they could do nothing as the roof of her house was pointing east and west - yet she had a perfectly good south facing garage roof, very accessible into the bargain, which was totally ignored. they missed it because they were programmed to look only at the house roof, & the perfect solution was right under their noses. East/West was possible too but perhaps a little more complicated and expensive but again was not highlighted as an option. what sort of improvement did you see with the tracker compared with untracked? rgds cye
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Post by horsall on Oct 29, 2012 4:51:06 GMT -5
Hello cye No that Traveller has gone but we have another one now along with triumph Spitfire, and TR2 plus 3 velocette motorcycles and a Moto Guzzi(Boys and Toys?) There is quite a lot more power gained from tracking but the down side is the cost of doing it and the extra complication(but if you are like me its the challenge that makes it fun everyone would do it if it was easy) If you don't want to go down the road of trackers I would definitely look for a MPPT charge controller as they will give you anything up to 30% increase in power depending on the battery state etc. I have 2 of the 200watt kits they were not as expensive when we got them www.solar-pv-systems.com/pv-solar-sun-tracking-kit-c-92.htmlThey are quite good they just work out mathematically were the sun is so no so good on cloudy days when there may be more power at the edge of the clouds which the solar tracking type would find(in theory) we have 2 solar tracker types here is a photo of the home made tracker Attachments:
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Post by caveman on Oct 29, 2012 5:27:46 GMT -5
Hello Roger, Welcome to the forum. You would not be the only one to have to own up to a large collection of vintage motors (eh Cye?). I live in a glass house in that respect also and shall be throwing no stones.
If you try to control the pump with a regulator be careful not to operate the pump close to stall or the current through the pump will rise and cause overheating. PWM control will not cause this problem usually. Also PWM is more efficient in so far as there is less heat produced in the regulator. I know it is small fry in the overall load and the problem occurs when you have plenty of solar input, but it is worth mentioning. A common or garden switching regulator is a PWM device and is fit for 90% efficiency.
conor
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Post by cye on Oct 29, 2012 17:41:00 GMT -5
Roger, Do you want me to check whether the spare PWM controller works with a 15PV pump? If it does you are very welcome to it if you wish to experiment. I am in ignorance as to how the mppt circuitry built into the PV pumps operates. My layman's guess is that it somehow (trial and error?) varies the load that the panel 'sees' and determines which of the loads gives the highest rpm.
That tracking mount looks very robust. Looks like motorcycle chain, sprocket and hub? Pillow block bearings look fit for very heavy wind loading. Conor was considering a car hub on a vertical axle, and i had been eyeing up one of the designs of satellite dish tracker.
A recent study had concluded that inclination + orientation tracking added only 3% to orientation tracking alone, so the idea was to provide a manual adjustment for the inclination and automate only the orientation in the horizontal plane.
I'll try and dig out some pictures I have somewhere of the satellite dish based tracking mechanisms.
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Post by horsall on Oct 30, 2012 8:54:37 GMT -5
Hello All Thank,s for the replies. I am not sure how MPPT works in these pumps but on batteries it looks at the battery voltage and adjusts the charging voltage to match there fore giving you more watts into the batteries(or something like that?) I assume it does the same on grid connect? As for the PWM controller I am interested I have ordered one of these to power the solar controller. www.ebay.co.uk/itm/300725897866?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649I am not sure if the same device would do for the pump as they are so cheap easier than building one. I have attached a photo of our set up the middle 4 panel array does not track at the moment as the gearbox is broken and you can,t get spares so I am thinking of turning it east/west with a satellite actuator but at the moment it is just set due south. Yes I agree inclination is probably not worth the extra trouble(expense) just alter it manually 3 or 4 times a year to suit your latitude . Roger ps I wish the water solar system was working today as there is plenty of sun and we are getting about 800watts/hour into the battery bank but no wind unfortunately. Attachments:
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Post by cye on Oct 30, 2012 15:14:50 GMT -5
that looks like a substantial power plant!
re the step down device, are you stepping down from 24v to 12v? that 94% efficiency quoted looks good. i will root out the pwm pcb tomorrow and see if it works.
is it peter crayfourd's picaxe-based controller you have or his 12v commercial model? (i have both here).
is that 800w into your batts when the sun is shining or 0.8kwh in one day in this weather? either way i'm jealous! i got 50wh (.o5kw) into my grid tie on saturday and on a good summer day (rare) i was getting only .3kwh per day (albeit untracked). i know 0.3kwh is rubbish but it's enough to run a 1.5w led lamp for 200 hrs though in theory which puts it into perspective!
will let you know how i get on with pwm and PV pump tomorrow
rgds
cye
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Post by cye on Oct 30, 2012 15:23:35 GMT -5
food for thought -showing efficiency dropping off when running panel hotter Attachments:
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Post by cye on Oct 30, 2012 15:24:35 GMT -5
and a similar graph from a differnt report, this time showing the effect of cloud cover Attachments:
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Post by horsall on Oct 30, 2012 15:53:52 GMT -5
Hello Cye Thank,s for the info it looks as though I should aim at keeping the panel temperature down so maybe the pump running unrestricted maybe ok? I bought one of Peters commercial units, could have bought it off Ebay for less but may have been caught for VAt etc so would not have been much cheaper and also have someone to send it back to if it fails. I wanted one were I could see temperatures(which will help me aim at getting panels more efficient ) and tell it to top up tank temperature with boiler or immersion heater(depending on battery state) We had 4.5kwh of power from panels today The photo is the Inverter and charge controller plus all the various switches and breakers to control!!!! all the systems. Attachments:
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Post by cye on Oct 30, 2012 16:30:20 GMT -5
roger
4.5kwh is more than enough for most things.
i use one of peter's picaxe controllers myself which does what i need it to do. peter is a reliable fellow and will stand over whatever he supplies. the derry solar installation (George Row's) pictured on this forum uses one of peter's 12v versions of the same controller, and i think the galway installtion (Dermot Leonard's) uses the 240v version. I have a 12v commercial version here still in the box which we take to workshops to show folks that DIY solar thermal doesn't all have to look heath robinson!
in stark contrast to my usual experience of fishing about the shed for ages in vain, i was able to lay my hands first time on the PWM controller. it seems to work grand on the PV pumps. if you still want to try it out pls confirm that i've got the right address for you (postcode beginning DY9) and i'll post it off tomorrow.
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