Author Topic: Blasphemy..... Solar power.  (Read 120175 times)

mike90045

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Re: Blasphemy..... Solar power.
« Reply #330 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 #331 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 #332 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 »

mike90045

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Re: Blasphemy..... Solar power.
« Reply #333 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.

BruceM

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Re: Blasphemy..... Solar power.
« Reply #334 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.

AdeV

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Re: Blasphemy..... Solar power.
« Reply #335 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 #336 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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1x Lister CS Start-o-Matic (complete, runs)
0x Lister JP4 :( - Sold to go in a canal boat.

BruceM

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Re: Blasphemy..... Solar power.
« Reply #337 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 »

BruceM

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Re: Blasphemy..... Solar power.
« Reply #338 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 »

BruceM

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Re: Blasphemy..... Solar power.
« Reply #339 on: January 23, 2018, 03:44:59 PM »
High AC voltage sensing with hysteresis is what you're asking for.  I would do this by doing a somewhat filtered peak voltage circuit (transformer, bridge diode, resistors, capacitors) and analog comparator with trim pot for set point and trim pot for hysterisis.  The fiddly bit is getting the peak voltage sense to ignore spikes and other line transients and have good immunity from inverter generated EMI.  This is an electronics build project for an intermediate skilled technician.   

An arduino could be used instead for the AC voltage sensing (peak would suffice or RMS if you wanted to get fancy) and is handy in that hysterisis and time delays can be programmed. 

I'll have a look around online to see if someone is making and selling some bits of this which would make your task easier.  Either analog or arduino would be fine, it's just a matter of cost and difficulty for you to build.


 

BruceM

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Re: Blasphemy..... Solar power.
« Reply #340 on: January 23, 2018, 04:27:23 PM »
Had a look and your best bet is to use a voltage monitoring relay. Macromatic makes some nice ones, but you may be able to find a china clone for a lot less $.  The macromatic units are self powered, which helps simplify the setup.

These relays have a set over/undervoltage which trips the relay, with an adjustable time delay as well.  Since the water heater is a sizeable load you would want to use the monitoring relay output to operate a second relay to switch on the water heater. 

https://www.macromatic.com/products-main/voltage-monitor-relays

This would eliminate the need for any fiddling with arduino or analog circuits, both are significant time and patience eaters, and give you something that anyone could maintain.

Give a holler if you need help on a specific unit you might find available to you there in Australia.


BruceM

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Re: Blasphemy..... Solar power.
« Reply #341 on: January 24, 2018, 04:23:59 PM »
Yes, that voltage monitoring relay looks like it should suffice.

I think it will be a challenge to find a current limiting device for your water heater.

Here in the US you can get water heater elements of various wattages.  Replacing the lower element with something suitable might be an easier solution-  plus adding a separate thermostat for it. 

Normally, the lower element (only) goes on at a higher temperature, and the upper comes on at a somewhat lower temperature to provide faster recovery of the water at the top of the tank.  A single thermostat has the bimetal switches to do this and turn on one or the other element.  So the lower element could be disconnected from the upper thermostat and used separately, or with a contactor could be diverted for your use only when needed.  You'd have to add a thermostat for the lower element to avoid boiling the tank.

Heavier wiring from inverter to the meter might an easier solution if voltage at the meter isn't going too high but it is going high measured at the inverter.

BruceM

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Re: Blasphemy..... Solar power.
« Reply #342 on: January 26, 2018, 10:11:02 PM »
Glort- The PV Edge unit doesn't do battery, that's a separate inverter product according to their diagram. 

I don't know of a piece of power regulating electronics suitable for limiting current to your water heater; it may exist, I'm just not aware of it. A variable speed motor drive might do it so perhaps that's the sort of thing you are referring to when you say PWM.

A 2000 watt, 230V variac might be a simple reiliable solution. The latter would let you dial in whatever voltage you need to get the desired current draw.  It would also be possible to use a variac, modified with more than one lead soldered in place to the windings instead of the adjustable graphite wiper, to have two or more voltages to switch between via relay, to get you more than one fixed current.  You can determine the location(s) to solder via the adjustable wiper...just use a clamp on amp meter and dial it to where you get the desired current.  Sand and solder tin the marked winding spot and then solder on your wire(s).  A variac is a very handy form of toroidal transformer and is often at 95% efficiency.







BruceM

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Re: Blasphemy..... Solar power.
« Reply #343 on: January 27, 2018, 03:53:05 AM »
Good find, Glort.  That dimmer unit is very high capacity!  If it doesn't confuse the grid tie converters with waveform distortions and EMI it should be a very simple and low cost solution. Good chance it will do the job nicely. Bravo!






 

ajaffa1

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Re: Blasphemy..... Solar power.
« Reply #344 on: January 27, 2018, 09:12:16 PM »
Here in Australia, we only get six cents per Kilowatt hour from the utility companies. We also have to pay $150 a quarter for the man to come and read the meter.  Grrrr.

Bob