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Author Topic: Blasphemy..... Solar power.  (Read 43121 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.