Grid Connect PV systems

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acmotor
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Post by acmotor » Sun, 06 Jun 2010, 05:38

Yes, basically sell the power when the sun shines and buy back in off peak times as much as possible.

Just a thought, in WA the PV installation must be used with smart meters i.e. the peak/off peak/high shoulder/low shoulder type. I assume this is the same in other states ?

So power bill is (for a month)
+ kWh at peak rate (27c/kWh)
+ kWh at high and low shoulder rate
+ kWh at off peak rate
- kWh fed in from PV/wind/hydro etc at 40c/kWh (60c in VIC)
Not really averaged, just cumulated kWh at the various rates.

This works well in summer for PV with peak times 11am to 5pm but less helpfull in winter where peak is 7-11am and 5-9pm. (I find it hard not to use power in those times !) In fact, run an aircond/ fridge/ freezer in summer and you likely won't get to export with a 1.5kW PV system but at least your bill is reduced.
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Post by weber » Sun, 06 Jun 2010, 05:40

I'm an accredited PV system designer and installer (grid and standalone) currently training other installers 3 days a week. Coulomb was my "apprentice" today as we installed a high quality 1.6 kW domestic system with Sharp panels and Latronics inverter. I love having an apprentice with a PhD. Image

What Coulomb says above is totally correct. Only NSW and ACT pay on gross generation. All the others pay only on "instantaneous net", also called export.

Handy Aussie FiT chart here

Net feed-in-tarrifs suck. Well, OK, they are better than no feed in tarrif. But it's the same benefit to the network, and the atmosphere, whether the solar energy is used by the house whose roof it's on, or the one next door. Gross feed in tariffs recognise this. With net (import/export) metering there is no (easy) way to tell what the household consumption actually is, so there's a loss of information too.

It would be completely unethical (and certainly illegal in Queensland) to store dirty power in batteries and then export it to obtain a FiT intended to reward clean energy. However, charging off peak and running your house off the batteries during the middle of the day so as to export all of your solar energy, to maximise a Net FiT, is quite OK. But it will not pay for the batteries.

If you were going to have the batteries anyway, e.g. for backup in case of grid failure, then it may make sense. Coulomb and I have designed and installed such a system for one customer.

ACmotor, the drop off in power when the sun is not at right angles to the panels is approximately cos(theta). This is much less of a reduction than most people imagine. Or to put it another way, trackers make much less of an improvement than most people imagine.

This cos(theta) is for the direct component. The diffuse component (e.g. from clouds) is pretty well unaffected, such that even a south-facing wall receives about 25% of the energy that an optimally tilted (lattitude angle) and oriented (north) roof does over a year.

See the tables at the end of this document, for derating arrays with non-optimal tilt or orientation in various cities in Australia.
http://www.cleanenergycouncil.org.au/ce ... %20CEC.pdf

Also for ACmotor: Latronics grid-connect inverters have a mode where they will charge a battery and then drop it back to float and put the excess energy out to the grid. This is quite efficient. Figures given above for typical charge discharge battery efficiencies are not relevant here as the battery is just kept on float and the inverter "skims the excess off the top".

The PVE1200 floats the battery at 54 V, the PVE2500 at 108 V.

[Edit: Minor rewording]
Last edited by weber on Sat, 05 Jun 2010, 19:47, edited 1 time in total.
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acmotor
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Post by acmotor » Sun, 06 Jun 2010, 06:11

weber,
Those tables are normalised to a fixed PV e.g. Perth,north,30deg=100% and NOT to the max possible PV output if it tracked the sun.
Take care with statistics !
A tracked system is another set of data.

Personally I would never charge batteries off PV if I could sell the power at peak rate and buy it back at off peak. The only real use for a GCI charging batts is for when the grid is down (e.g. during the Vic bush fires) and you had an inverter. (you did such a system ?)
BTW, do any of the GCIs provide island power when the grid is down ?
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Post by weber » Sun, 06 Jun 2010, 16:46

acmotor wrote: weber,
Those tables are normalised to a fixed PV e.g. Perth,north,30deg=100% and NOT to the max possible PV output if it tracked the sun.
Take care with statistics !
A tracked system is another set of data.
You're quite right. I thought I made it clear what the tables were for. Sorry if you were misled.

However the approximate cos(theta) relationship for direct radiation and approximate constancy of diffuse radiation are much the same whether it is the sun or the array that moves (relative to the earth).

Even in a flat desert (mostly direct radiation and clear horizons) the benefit of dual axis tracking is only 40%. In a coastal domestic situation it is likely to be only 20% to 30% and of course single-axis tracking will give even less benefit. Some drawbacks are that tracking mechanisms tend to fail after a short time due to being exposed to the weather and tracked arrays are far more vulnerable to wind damage. For wind-loading reasons they pretty much have to be mounted on the ground, raising their horizons even further.
Personally I would never charge batteries off PV if I could sell the power at peak rate and buy it back at off peak. The only real use for a GCI charging batts is for when the grid is down (e.g. during the Vic bush fires) and you had an inverter. (you did such a system ?)
BTW, do any of the GCIs provide island power when the grid is down ?

That's right. I've done several battery-backed-up grid-conect systems, but only one with the "load shifting" add-on for maximising the Net FiT.

Early systems used a single SunProfi inverter (which is no longer available) that has two AC outputs. When the grid goes down it disconnects its grid output, as required for the safety of line workers, and operates in standalone mode feeding its "emergency" output. A complementary contactor outside the inverter switches the household power and light loads (but not hot water, aircon or pool) from the grid to the inverter emergency output. The Selectronic SP PRO series are a currently available inverter that can work in the same manner, but they start at 3.2 kW and so are an expensive option for a 1 to 2 kW system.

My current systems use two separate Latronics inverters, one grid-connect and one-standalone. It is only with two separate inverters that the additional load-shifting function becomes possible.

We add a battery charger, a timer, a battery-state-of-charge-monitor, and some other bits and pieces. The battery is charged from off-peak power (charger must be permanently wired) and the house runs off the batteries via the standalone inverter during sun hours (or until the battery falls to 80% SoC) while the PV array exports 100% via the grid inverter. In the event of grid failure the house runs off the batteries (whether above 80% SoC or not) and the PV array is switched from the grid inverter to a separate MPPT charge controller to charge the (nominally 48 V) battery.
[Edit: Fixed up the quoting]
Last edited by weber on Sun, 06 Jun 2010, 07:59, edited 1 time in total.
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Post by Johny » Sun, 06 Jun 2010, 17:01

Thanks guys - great info.

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Post by acmotor » Mon, 07 Jun 2010, 03:30

weber, that's what I run. CGI + separate inverter and a 48V battery bank. I'd run hydro if the creek actually runs again !

I still wouldn't cycle the batts to timeshift energy. My calcs show that is a no win when amortising battery cost, particulary at only 40c net FIT in WA !!!

Your PV business sounds like fun. All those toys and other people buying them for you ! Image
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Post by weber » Mon, 07 Jun 2010, 03:49

acmotor wrote: weber, that's what I run. CGI + separate inverter and a 48V battery bank. I'd run hydro if the creek actually runs again !
Cool!
I still wouldn't cycle the batts to timeshift energy. My calcs show that is a no win when amortising battery cost, particulary at only 40c net FIT in WA !!!
Are you sure? Given that we limit it to cycling only the top 20% (lead acid). We're using 200 Ah SunGels from Battery Energy. 10 year warranty. According to their charts, the cycle life at that DoD isn't much shorter than their standby life.
Your PV business sounds like fun. All those toys and other people buying them for you ! Image

Yeah. But I have to admit I paid for all the load-shifter add-ons myself because it was something I really wanted to try, and there was a risk that it wouldn't work. Fortunately the customer is my father-in-law and willing to trust me. And I also have to admit I screwed up and fried a set of batteries because the 240 Vac charger was set to just too high a constant voltage for the absorption phase with gels, given that there was no temp compensation. It worked fine for a year, then we had a week of unusually hot weather that managed to trigger a thermal runaway. Sigh. That was an expensive lesson.

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Post by antiscab » Mon, 07 Jun 2010, 04:04

weber wrote:
I still wouldn't cycle the batts to timeshift energy. My calcs show that is a no win when amortising battery cost, particulary at only 40c net FIT in WA !!!
Are you sure? Given that we limit it to cycling only the top 20% (lead acid). We're using 200 Ah SunGels from Battery Energy. 10 year warranty. According to their charts, the cycle life at that DoD isn't much shorter than their standby life.


whats the round trip efficiency like when operating between 80 and 100% SOC?

from my own playing, I haven't seen any better than ~60%.

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Post by weber » Mon, 07 Jun 2010, 04:25

antiscab wrote:whats the round trip efficiency like when operating between 80 and 100% SOC?

from my own playing, I haven't seen any better than ~60%.

Sorry Matt. I haven't measured it. As you probably know, it doesn't depend only on the battery chemistry. It depends very much on the voltage profile produced by the charger. Almost all of the loss is due to "gassing" (i.e. water being electrolysed). So it depends heavily on how far above gassing voltage it goes and how long it stays there. But I don't doubt your 60% figure.

60% would mean that it costs about the same to charge off peak and power loads off the battery versus power loads directly off the normal tariff. So any financial benefit would come only from maximising the PV Net Fit, assuming the life of the battery (which the customer would have anyway) was not significantly reduced.

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Post by 7circle » Mon, 07 Jun 2010, 08:41

Weber - I have a question on getting cash for NET Fit
Grid Connect- Peak/Offpeak Load Shifting
You might be able to advise.
Thanks for the info on the load leveling system.
Ken

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Post by acmotor » Mon, 07 Jun 2010, 17:20

I must admit my calcs were based on lithium not lead acid as despite the low capital cost of lead, the combination of its aging and lower calorific efficency, made the economics of timeshifting even worse.
LBB will attest to this !
There is no question that the technology works with (almost) any chemistry. Its just the economics. Good luck claiming on a 10 year warranty ! I hope the 25 year warranty you supply on your PVs works out !

At only 20% DOD the lead acid should only be float charged over the 10 hours of off peak. So 2.3vpc max (temp corrected). No boost charge. Is that what you do ?

weber, are you planning a lithium timeshift system ?
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Post by weber » Tue, 08 Jun 2010, 15:20

acmotor wrote: I must admit my calcs were based on lithium not lead acid as despite the low capital cost of lead, the combination of its aging and lower calorific efficency, made the economics of timeshifting even worse.
LBB will attest to this !
There is no question that the technology works with (almost) any chemistry. Its just the economics. Good luck claiming on a 10 year warranty !
Yes. The warranty conditions are strict. But no other lead-acid manufacturer in the world even offers a 10 year warranty. These Battery Energy brand Aussie gel batteries were developed over 17 years in collaboration with CSIRO and scientist Dr David Brown. Search for "David Brown" within this page:
http://www.conferenceworks.net.au/13abc/abstracts.php
I hope the 25 year warranty you supply on your PVs works out !
Do you think I should be worried that panels made by Sharp Corporation may not last 25 years _and_ that the corporation may not be around if they fail?
At only 20% DOD the lead acid should only be float charged over the 10 hours of off peak. So 2.3vpc max (temp corrected). No boost charge. Is that what you do ?
No. Maybe I should, but I'm currently boosting (at max C/20) to 2.4 Vpc then floating at 2.25 Vpc.
weber, are you planning a lithium timeshift system ?
Not until the lithiums have first been used in an EV for many years. Image
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Post by acmotor » Tue, 08 Jun 2010, 17:02

Yep, you don't need to worry.
Its not the panels or battery that concern people with warranty, it is the installer (the first port of call for the customer). Not suggesting anything with your business, just acknowedging the transient nature of rebated industries in Oz !
Do you put your customers in direct contact with the suppliers and have the suppliers acknowledge the warranty with the customer ? Good.
Call this post 'customer feedback' Image

Yeah, the 'battery energy' offerings are good, for lead acid.
Makes you wonder though, if Oz can make those then why not some lithiums too ? But then a super tax will put the price of both up. Image
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Post by Tassie Mike » Mon, 14 Mar 2011, 04:14

Hi People, Since you all seem to be very innovative, I would like to drop this into your respective laps! A tracker will boost your PV's output --some say as much as 60% (must be on a strange day!) BUT here is one that will really work -- virtually service free, and will NOT blow away in a wind, (Tornadoes excepted)

Since I have never put a spoke in before, hope it will serve someone well.
Here is the killer, I have not built mine yet, a toilet comes first!

I have however seen one at work and it was magic!!!!
Enough chatter here is the pic
Bother! will not upload!
OK will post this and try to post the pic separately!

Cheers Mike

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Post by Tassie Mike » Mon, 14 Mar 2011, 04:16

Microsoft VBScript runtime error '800a0035'

File not found

/forums/functions/functions_upload.asp, line 455

Bother

HELP!! please
image 42 kb will not go!!
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Post by woody » Mon, 14 Mar 2011, 06:25

Tassie Mike wrote: Microsoft VBScript runtime error '800a0035'

File not found

/forums/functions/functions_upload.asp, line 455

Bother

HELP!! please
image 42 kb will not go!!


Try renaming the image so it is all lower case and has no spaces. I.e. powertrack.jpg, not "Power Track.JPG"
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Post by Tassie Mike » Mon, 14 Mar 2011, 13:29

Thanks 63Cortina, but It still gives the same error report! Image Image
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Post by Tassie Mike » Tue, 15 Mar 2011, 04:03

"All lies and jest, still a man sees what he wants to see and disregards the rest!"

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Post by Adverse Effects » Tue, 15 Mar 2011, 11:43

Tassie Mike wrote: Finally Gentlemen!! A way for you to see this amazing contraption!


i think this would be better

Image

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Post by EV2Go » Tue, 15 Mar 2011, 15:12

Why not build a tiny seperate device to do the same thing and have it position all the panels instead of having bits that will block some of the suns rays on all the panels?

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Post by Johny » Tue, 15 Mar 2011, 15:16

I rather like the way my panels sit snug down on the roof when it's a howling gale outside. I'll pass in the extra n%.

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Post by woody » Tue, 15 Mar 2011, 15:46

Cheaper in the long run to put an extra panel out?

(Extra cells cheaper than regen argument :-)
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Post by EV2Go » Tue, 15 Mar 2011, 16:03

Depends if you lived on a property where you had plenty of space and you could arrange the cells on rack (much like the roof in Gattica) you could chase the sun from the moment it came up to the time it went down.

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Post by a4x4kiwi » Tue, 15 Mar 2011, 19:09

I prefer no electronics at all. They use the thermal expansion of liquid to move a hydrolic actuator
Hydrasolar
http://www.ecostar.net.au/green_power_010.htm
The original web site looks to be down.

also http://zomeworks.com/products/pv-trackers/introduction
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Post by Mesuge » Wed, 16 Mar 2011, 05:23

woody wrote: Cheaper in the long run to put an extra panel out?
(Extra cells cheaper than regen argument :-)


Exactly, given relatively exceptional aussie insolation endowment thanks to it geo position the tracker is not worth it. The direct route of adding extra panels seems more plausible, exceptions might apply (small/partly shaded lot). Or in case of high eff. triple junction cells (ala SunCube), but here the tracker is of different design anyway.

Leave trackers (especially 2axis based) to us sunshine challenged living closer to the poles. Fortunately, the prices have somewhat dropped and there are more vendors than before in this segment. Image
Last edited by Mesuge on Tue, 15 Mar 2011, 18:29, edited 1 time in total.
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