Author Topic: Blasphemy..... Solar power.  (Read 71684 times)

mike90045

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Re: Blasphemy..... Solar power.
« Reply #420 on: January 09, 2018, 02:46:27 AM »
It's not the panels  - it's the controller

Most MPPT controllers are most efficient with the solar Vmp voltage at about 2x the battery voltage.  Higher voltage, and you suffer more conversion losses in the controller.

See page 12 of this doc for the moringstar curves
https://2n1s7w3qw84d2ysnx3ia2bct-wpengine.netdna-ssl.com/wp-content/uploads/2014/02/TechTip-EnclosureHeatDissipation.pdf

BruceM

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Re: Blasphemy..... Solar power.
« Reply #421 on: January 09, 2018, 05:01:53 AM »
Mike, I'm not using commercial gear, I'm using a linear controller of my own design, not a MPPT buck converter (EMI bomb),  so actually fitting panel voltage to the 120V battery voltage is more important.  Anything much over battery voltage when limiting charge current must be dissipated as heat in my TO-247 darlington power transistors.

The Morningstar MPPT controller manual link you provided was very helpful to review...they show a 6 volt drop (for a nominal 24V panel with the typical 36V max power voltage at 77F) in the max power voltage at just 96F.  I didn't realize that panel temperature affected the max power voltage so much.  It means I need a lot more rated max power voltage for summer as my panel temps will be more like 150F.  In fact this big temperature related change in MPPT is the best rationale for MPPT that I have ever seen.  I'll have to confirm this data elsewhere but given the quality of the engineering data and tech writing Morningstar provided, I think they are likely quite trustworthy.

Thanks for this much appreciated food for thought!






BruceM

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Re: Blasphemy..... Solar power.
« Reply #422 on: January 09, 2018, 05:12:33 AM »
One additional thought-  I suspect that while the Morningstar buck converter is 2% more efficient at PV voltage about 2x battery, the PV wiring losses might well exceed that 2%, so it's probably not a penalty for this controller to go  with the higher PV voltage.  Wire sizes get pretty nuts for lower voltages, which is why everyone has been moving to higher voltages  . 

A decent article with calculations for temperature coefficients:
https://www.sunwize.com/tech-notes/temperature-effects-on-pv-modules/

I'm going to have to reconsider my 4 panel string carefully based on lower voltages at summer temperatures and the specific panels selected.  My tests were with cool winter temperatures so Vmp was high...

« Last Edit: January 09, 2018, 05:33:30 AM by BruceM »

glort

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Re: Blasphemy..... Solar power.
« Reply #423 on: January 09, 2018, 08:17:46 AM »

I have read about the panel losses due to temp and I have to say I take it with a BIG grain of salt.
mucking round with panels on the lawn taught me a lot real fast and one of those things was the panels will nearly always exceed their rated temp whenever clear sun is shining on them.  Might be different where there is snow on the ground but where I am, any sun made the panels too hot to comfortably hold. Given for me that's above 50oC, they are going to spend a LOT of their time above their rated temp.

I don't actually know why they are in fact rated so low. it has nothing to do with real world output but I suppose like most things they push for the highest numbers they can because people like to buy big numbers more than anything else. Everyone one knows though it is extremely rare to get full rated output from panels and this is probably one reason why.

One thing I had concerns about with putting the panels flat on the roof was lack of air circulation but then I figured the thing will be so hot anyway, probably don't matter.  As with all things solar, just put up a couple more panels and don't count them in your array and you'll have good efficiency as cheap as you will ever get it.

Before you get too worried about 4 panels strings Bruce, I'd test and monitor them. You may find your panels when you did your cool weather tests things were a lot hotter than you thought.  Lets face it, anything black heats up will in the sun no mater how cool the ambient temp. Look at those solar window heater things. work great even in winter and produce a stack of heat just through having a black surface.

glort

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Re: Blasphemy..... Solar power.
« Reply #424 on: January 12, 2018, 06:07:20 AM »

Finally managed to buy some more panels this morning. Only 4kw worth but the price was cheap for the panels themselves and I got microinverters and racking ( which I might sell) so a good deal.  About an hour away so not bad.

Anyone know anything about these micro inverters? I know the theroy but I'm wondering about the practacality of them.  Do they REALLY make a difference to oputput? I have learned that there are a lot of things in the solar world that are touted to be one thing but reality is a different story and I have deep suspicions these could be the same.

My golden rule of solar efficiency is there is none,  just add a couple of more panels to what you have and don't count them in the array and THEN you will have the cheapest efficiency possible.
If they aren't any big deal I might try and offload them and put the money towards another single inverter.

Did a deal with a guy earlier in the week for 11x 190 panels but so far getting any response as to when I can pick them up has been absent.
It's always a lottery buying used stuff and what sort of people you are going to get to deal with.
thankfully the ones this morning were very easy, co operative and helpful .

I'll go back down the solar place this weekend and check out their Dumpster for any more old inverters or cracked panels


mike90045

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Re: Blasphemy..... Solar power.
« Reply #425 on: January 12, 2018, 07:14:09 PM »
Micro inverters are great if you have large patterns of shade, marching across your array during the day.  That shade would mess with a string inverter, but with the micros, only the shaded panels are down.

In full sun, no difference between micros and string inverters, except the string inverter is in a much easier place to work on or replace.  Electronic modules baking in the sun, are either very expensive to withstand the heat, or cheap and have to be replaced a lot.

glort

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Re: Blasphemy..... Solar power.
« Reply #426 on: January 18, 2018, 12:53:12 PM »

I hooked 7 of the panels up with the micros and have them in the yard slightly tilted so they don't kill the grass. Again.
Still have a cricket pitch where the last lot were even though I have been pumping the fertiliser and water onto it like no tomorrow.
Think I'll have to re seed it all.

Have been making an extra 7KW the last few days which has taken me to new high combined outputs of 44 Kwh for the day. Given I should be making around 15 Kw+ from this array when they are all up, should start catching up well on the next bill.
The setup with the micros is a bit Meh. Hook the panels to each micro then hook the micro to a block connector. The ones I have are 4 spot so you have 3 panels and one extension lead going to the next connector for another 3 panels and so on.  Seems a bit of mucking about and extra install time and accessories if you were paying for it as original purchaser would.

Making good progress on the power meters although with the next 2 days forecast to touch the '40's again, the AC will make short work of any headway made.
I'll try to get the new system  on the roof next week and see how that goes. I'll not worry about the micros as that will be clear sun and just use a standard inverter and hook them up in 2 strings of 8 panels.  Hope the roof is not as steep to work on as it looks.

And while I'm on a roll, I bought some more panels again today.
3 kw worth for $250 and  3 or 4 KW inverter for another $100 with all the rails and fittings thrown in.
Bit of a step backwards, these are only 180W panels  but the price for the output was waay too good to refuse.
My Dad has become interested in my solar exploits and has said he'd like to get some. Like everyone else, his bill is going up even though his usage is amazingly constant. I might yet take these and set them up for him and hold out for some larger capacity panels. May not matter though.

Main array atm is 5.5 Kw.  Last weekends purchase was 4KW, today's is 3 Kw and I have 1.5 Kw as my play panels.
Would really like to get another 5KW setup but might be waiting for that a while.  I'll definitely put the 4 kw up and then see how I feel about the 3 Kw array.

If something else with the right output at the right price comes up I'll grab that too. I only ever buy at a price  I know I can easily get my money back on so no problems if I want to get out of anything.

BruceM

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Re: Blasphemy..... Solar power.
« Reply #427 on: January 18, 2018, 06:18:26 PM »
Glad you keep finding such amazing deals, Glort, though I am quite envious.  I had to buy new panels from Sunelec.com, couldn't find anything in used here.  I ended up paying $1100 including $250 for freight shipping and a $40 packaging (pallet and wrap job) fee for my five "310 watt" (200 realistic watts) panels.  We got the new rack posts concreted in place, plus the new posts for the modified old rack, and all welding complete.  We will start mounting panels on the new rack Monday assuming they test out OK.

glort

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Re: Blasphemy..... Solar power.
« Reply #428 on: January 18, 2018, 08:22:55 PM »

That is an unreal price Bruce.
I looked up the new prices with a panel supplier. Trina 320W $181.  Any out dollar is about .70 of your cents ATM.
Why are panels so expensive and seemingly hard to get there going by shipping costs. Must have come a long way!

Seems panels are one thing we beat you guys on. They all come from China now so don't know why.

I'm a bit surprised at my luck of late but also been screwed around badly a few times so maybe due for a win.  Dealing with people on these sales sites is always a lottery no matter be you selling or buying.  Had a few now I have done a deal with but then gone silent when I say " OK, where do I pick them up from?"
This is an interesting thing too.  SO many people put ludicrous prices on stuff but I'm experimenting with dealing with them.  Got one Guy atm who was asking $900 for 6x250w I have bargained down to $300.  That's about the right price here but I reckon I caqn get him down some more.  There is another twit atm that wants $2K for an incomplete 2KW setup.  I messaged her and said if you are taking this one down to put a new one up, you must know the prices. You should go on what new stuff is worth today not what you paid 7 years ago.

Said that to someone  earlier in the week and to my surprise they came back and said you are right, I'll take your offer.  Wasn't really interested in what they had but interesting to experiment wheeling and dealing.

With the panels I am aquiring, i'd like to offset the Power I'm Pulling from the 3 phase leg with the smart meter.  Been looking at something on another forum and was thinking of a limited power Grid tie inverter connected to the electronically metered leg of of the AC.
I'm thinking I could put a clamp meter on it, measure the draw of each leg which I believe to be around 1.5 to 2 KW and connect the GTI to that leg so when the AC is powered up, the inverter boots up and supplies power.
This should offset what I'm using.
If the AC is pulling say 1700W and I out a 1500W GTI on it, I'm only paying for 200W. Solar will deliver whatever it is capeable of grid will supply the rest.

Thing is though, I don't want panels and an inverter doing nothing  any other time so I'm wondering If thee is a way to switch the output from the array to different phases? When the AC was off, the inverter would be connected to an active phase. When the AC was turned on, that arrays output would be switched to  feed that demand and revert back when switched off.

Don't know if there is such a devise, " Dual switching relay??"
2 Relays working together from different signals/ outputs?
Doing the limited available power might be OK, Switching it automatically may be a bit more difficult.

                                                                                                                                                                                                                                                     

AdeV

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Re: Blasphemy..... Solar power.
« Reply #429 on: January 19, 2018, 11:00:04 AM »
Here in the UK, second-hand panels are virtually unobtainium - and of those I've found, they're the same price (virtually) as new panels, so it's a waste of time buying them.

A new 300W panel (individual panel) costs anything from around UKú230 second hand & damaged, to UKú450 brand new. Twin 150W panels come in a bit cheaper at around UKú240-270 brand new.

Those prices in other currencies:

UKú230UKú270UKú450
US$320US$375US$625
AU$399AU$468AU$780

Systems cost $$$more. Installation costs $$$$extra. It used to be possible to get a "FREE!" system, when the feed-in tariffs were good; but they've been whittled away to the point now where you have to have a gigantic south-facing roof preferably with a large magnifying glass on a tower in your garden before they'll consider it these days.
Cheers!
Ade.
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1x Lister CS Start-o-Matic (complete, runs)
0x Lister JP4 :( - Sold to go in a canal boat.

AdeV

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Re: Blasphemy..... Solar power.
« Reply #430 on: January 19, 2018, 11:08:19 AM »
OK, some additional eBay-fu reveals that if you're willing to buy a larger system (1.5kW to 5kW), it's a bit cheaper than buying individual panels...

So, for a 5kW system, consisting of 15x330W panels, one inverter, no mounting hardware (that's separate apparently), but you get a pile of MC4 connectors worth pennies... you'll shell out a mere ú3,295. And you have to go pick it up, they won't ship it, so factor in another ú150 to hire a van & fuel it.

Anyway, that base price in US & AU dollars, for shits & giggles: US$4580. AU$6853.

Not to mention the fact that solar in the UK is crap compared to much of the US and virtually all of Australia... The sunniest place in the UK (the "delightful" Bognor Regis) gets 1902.9 hours of sunlight per year (apparently). No idea what that translates to in power terms though, considering that for much of the year our sunlight arrives at such a shallow angle it expends most of its energy just getting all the way through the atmosphere to here...
Cheers!
Ade.
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0x Lister JP4 :( - Sold to go in a canal boat.

glort

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Re: Blasphemy..... Solar power.
« Reply #431 on: January 22, 2018, 07:45:12 AM »


Picked up my latest panel purchase today. Definitely the best value score so far.

16x 185W panels, 2.5Kw inverter and rails and mounting fittings.  a few of the panels have the leads cut off but they are all there. Bought a heap of Mc4 connectors a while back so I can either rejoin the leads or just put a new connector on. No biggie.

I am laughing to myself a bit.
The panels I paid $250 for ( 3Kw worth) and the inverter, $100. Inverter is old and kinda weird but I was assured it worked so all good if it does.

I asked the guy what size setup he replaced this one with. He said 3 KW. I'm thinking but this is a 3 Kw, if it's working as said why replace it? I said nothing and  as we chatted he let it slip that the reason he replaced the system was it wasn't generating like it used to. Soon as he said it he changed the subject obviously not wanting me to think he'd sold me something dodgy.

My mind was very quickly at rest when I was putting the panels in the ute.  They all had lichen like moss growing on them.  Smiled to myself and thought I know what the problem here is.  Sure enough when I got them home and stared unloading them, I reckon at least 12 of the 16 would be 5% minimum covered with moss.  A few even more and the other 4 not so much but all had it.
I thought there is the fall off right there. They are older panels so I'm sure not what they used to be but I guarantee after the scrap and the wash I gave them their will be a lot closer to their rating then when they came off the roof.

Guy selling them did notice it when I was packing them up and remarked on it but I don't think he realised the effect this can have.
In any case I set my benchmark at $200 per Kw. If the things put out half their rated power I won't have wasted my money. A quick volt/amp test after I washed them on a few showed my the things are close enough to the full output I'd expect than half their rating.

I did want to stick to 250W panels or above but there are so many around 180-190w going so cheap and I have so much roof, they are definitely the best bang for the buck atm.  the fact I will get my money back on them in probably 3 months makes them something I can easily throw away or use for the roofing on a pergola or something later if I do come across larger more efficient panels. Thing will be unless these do fall over markedly, really can't see a reason to change them if I'm making the power I want which is more than I need.


BruceM

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Re: Blasphemy..... Solar power.
« Reply #432 on: January 23, 2018, 12:15:04 AM »
Glad you found another fantastic bargain, Glort.

I got my new panels and rack mounted today, and got the old rack of 175 watt panels on the new "one man tilt" posts as well. The 300 watt panels dwarf the old 175's.  Both work great, the seasonal tilt adjust will now be easy for me to do alone. We managed to move the old rack without removing the panels with just a pry bar for shifting it, no small feat.

Testing the panels was only late and cursory due to high clouds much of the day.  The open circuit voltage was below spec at 42.1v vs 44V, but the short circuit current was high at 9.25 amps instead of spec'd 8.7 amps. Rather strange (!) so I'll do some further testing of the array when I get it wired up Wednesday.  I'm waiting on an MC-4 tee and some cable. My linear charge regulator needs a tiny bit of the the nominal 24V as well as nominal 0, 120V.  The +120 is directly tied to the positive 120V battery terminal.  The negative is below 0V in operation, no more than about -90V at float.  This keeps the max DC volts to ground anywhere in the system to 146V or less, which isn't a bad zap for DC.  DC takes about 4x the current to stop your heart compared to the same voltage in AC.

With the extra power, I can (on sunny days) use my new ultra low conducted EMI inverter to run my well pump fill my gravity feed storage tank, or run the washing machine.   The old 875 watt rack has done fine for my incandescent lighting and computer/projector and low wattage cooking use.  (My refrigerator, the usual off grid power hog, is propane.) 

It will be fun to have more PV power to play with.



« Last Edit: January 23, 2018, 12:36:54 AM by BruceM »

glort

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Re: Blasphemy..... Solar power.
« Reply #433 on: January 23, 2018, 04:35:17 AM »

Looks great Bruce.
If I were where you are and could get panels as cheap as I can here, I'd have half that hillside covered. :0)  Why did you have to move the old array?

You are spot on, it will be good to have more power. You have certainly made a big jump that's for sure. You can never have too much power,  only not enough. No doubt the real win will come on the overcast days.  Are you going to be able to match the strings Voltage and amperage wise and put them together or run them as 2 separate outputs for different jobs?
If your rack is really easy to tilt you could orientate the panels flat on the cloudy days and bump up the generation a bit more.

Speaking of which, I have learned clouds do weird and wonderful things to panels.  I'd be pretty sure that would explain your under voltage/ over current you are seeing.

Will be interesting to see what sort of outputs you get on a clear, sunny day. My bet is you will see better outputs under some haze/ certain cloud conditions like I do.
This is certainly not a cheap investment for you but I hope it pays off for you which I'm sure it will.

BruceM

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Re: Blasphemy..... Solar power.
« Reply #434 on: January 23, 2018, 05:24:24 AM »
I only lifted the old rack about 4 inches onto the new supporting posts which are centered under the panel.  Now the tilt is easy and a one man job.  The old design tilted from the bottom and it was a heavy 2 man job to tilt.

The new rack will be wired in parallel (nominal 120V, 24V, 0v) with the old one; a big boost in current.  Presently my Listeroid 6/1 is my only AC power and air compressor power source. Since I only average $100/yr in AC generation fuel costs (and that much again for compressed air), this upgrade isn't economically justifiable.  I'll have about $2000 in it including paid labor help.

I wanted the power to seriously test life and durability of my ultra low EMI inverter prototype design.   It's a tech-hobby thing.

I agree home PV power is a lot like shop size...no man has every complained of having too much.

Your question about switching your grid tie inverter ouput to different phases or meter panels is a good one.  If the grid tie inverter design was made to tolerate a grid outage and the on-off glitches that often entails,  it should be able to do it.  You can get double or triple pole relays that could do the switch-over.  Let me know the specifics and I can try to help you with it.




« Last Edit: January 23, 2018, 05:32:58 AM by BruceM »