Grid Connect PV systems

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acmotor
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Post by acmotor » Fri, 02 Apr 2010, 04:58

Under the existing Renewable Energy Buyback Scheme Horizon power allow 10kVA/phase or 30kVA on 3 phase (subject to netwrok assesment) North West Interconnected grid.

Synergy only allow 5kW (not 5kVA although should be same) on their Renewable Energy Buyback Scheme.

Neither specify kWh/day limit just max system feed rate to grid, so 24 x 5 = 120kW per day. Now just need wind and solar (and batteries or pedal generator)

The FIT is still not confirmed.


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Post by antiscab » Fri, 02 Apr 2010, 05:17

so they might be a bit suspect if i pump 20kw (25kva) onto the grid at 5pm when i capacity test a battery?

i still wonder how they're going to measure it over the long term.

a certain battery and inverter only combo from over east comes to mind Image

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Post by amnonholland » Fri, 02 Apr 2010, 14:54

If your roof faces north at an inclination of between 5-30 degreess you can expect about 1500kWh/year per kW capacity installed. The goventment figure geerally used i Sydney for calculating RECs is 1382kWhkWh/year per kW capacity installed. Our 3.6kW system can get up to about 1700kWh/year. This does depend on inverter efficiency, and cable losses etc.

SMA inverters are good(we run 2 of them for 4 years now)
Panels- most on the market(that can be used in grid connect systems) are generally good due to australian standards. some good brands; schott, kyocera, suntech, evergreen, BP ok. Go for mono or poly crytsal, all typical efficiencies of around 12-18% or wait till soon suntech release a mass produced 20% eff. panel.

With the FIT in NSW PV systems are cost effective(if you consider a payback period of 4-5 years against free power for 20 Years as worthwhile) for anything up to 10kW

I like the idea of charging battery pack from offpeak power and getting 60c/kWh on discharge. I suppose the energy utility will be sus if the see an x rated kW system generating twice or 3 times the expected kWh output, but then again are the energy utilities going to spend the time looking over piles of energy data to see whose generating more than they should.

You need a new smart gross meter to take advantage of FIT which records 30min or hourly data i think. So yes if they suspected anything they would be able to check. You could always just say you were using NASA's tripple junction cells that have efficiency of 45% on your roof. They may not belive you.
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$ payback = kWh generated = kW x hrs generation. So you could extend hrs of operation, for example pump out battery power 2 hrs before and after the PV system comes online and finishes for the day. Energy provider could really argue that on data. Just say you got optimally inclined panels with high efficiency at part load(part light) performance.

Also these grid connect inverters require typically dc voltage input in the range of 300-600VDC, so thats alot of batteries. Wouldnt it be cheaper to use lead acid batteries. we dont care about weight right?
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Post by photomac » Fri, 02 Apr 2010, 18:19

I did the calcs on sucking power off peak to a battery bank and feeding back at peak - lithium batteries - cost recovery 10 to 12 years. battery life - 5 to 8 years   Image Perhaps lead Acid?

None the less - the concept is to store solar. That's where an AUSRA solar thermal domestic unit could be a goer Image
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Post by acmotor » Fri, 02 Apr 2010, 19:50

Probably if you push 20kW into the grid then you'd want everything turned off in your house unless it is 300V rated. Image

Efficiency of the panel is rather less important (unless you are space limit on the roof) ?
More important is the thermal coefficient, $/W and life expectancy ?
Also the light angle incidence factor (must be a jargon for it ?). i.e. for non tracking systems, how well does the panel perform off angle ?

The idea of some stored energy in the system is tantilising, even if not economic at present.
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Post by antiscab » Fri, 02 Apr 2010, 22:03

i would not have thought an extra ~30A on each phase would cause the voltage to rise by so much :S

the 1378kwh/kwp number would take all the panel off angle and other (oppurutnity) losses into account.

i once ran the number for carnarvon, and came up with ~2700kwh/kwp.
the rebate there happened to be around 55% up front aswell (diesel fired grid)

lead acid batteries have a round trip energy efficiency of ~70% where as LiFePO4 has a round trip efficiency of ~95% (both charged and recharged slowly).

so unless you were only thinking short term (until they wised up to you) go lithium, or any other high efficiency chemistry


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Post by amnonholland » Fri, 02 Apr 2010, 22:11

excuse my ignorance, but why would the voltage rise? Most GC inverters output 230V +-10V.
Ive seen inverters in my local area where the external grid voltage was 250V which caused the inverter to shutdown(overvoltage safety).
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Post by antiscab » Fri, 02 Apr 2010, 22:17

because i wasn't planning on using an inverter.

i was planning on using an induction generator mechanically coupled to a shunt motor.

the induction generator has no smarts Image

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Post by amnonholland » Fri, 02 Apr 2010, 22:22

ohh ok, but how would you match the frequency and phase(so the generated wave in phase with the grid) ? Image
thats a good idea, Inverters are expensive
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Post by antiscab » Fri, 02 Apr 2010, 22:45

an induction generator does that for you.

you start it direct online as a motor, then used the dc motor to speed it up past synchronous to be a generator.

an induction generator also requires the grid to be present for its reactive power, so if the grid goes down, so does the generator.

they won't island with a grid tie inverter as a grid tie inverter wont supply any reactive power (if its code compliant).

up front an induction generator is cheap (any induction motor can act just as well as a generator).
they aren't quite as efficient, and power factor is no where near as good.

if going from DC into a DC motor to go into a induction generator, the efficiency is *really* bad.
in that case, if the object of he game is to put energy onto the grid, use an inverter.


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Post by acmotor » Sat, 03 Apr 2010, 00:02

Voltage rise...
Just a example, thinking out loud ...
I measure at the meter box with 20.3A draw, 231VAC and 243V with everything off.
Source impedance of mains as viewed at the meter box is then R=V/I =12/20.3 = 0.59ohm I think this would be typical ?
This is hardly the grid impedance ( much lower ) but does represent the feed in line/fuses/meter/cbs etc.

If I were to push 20kW as matt suggested then at say 90A the voltage would need to be 243 + 53VAC (296VAC) with no house load.
Though not actually possible, since the Oz standard on max V on GCIs is some 250VAC ?
If fact from this exercise it seems logical that without special attention then only some 5kW could be exported before GCI would reach max allowed line voltage anyway.


Non Islaning and IM generators....
I'm not certain a driven IM would shut down if there continues to be a non resistive (pf<>1) load. It would continue to generate until load is disconnected or the pf of load approaches 1. ??
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Post by lithbattboss » Sat, 03 Apr 2010, 00:46

We (LiFeTech Energy) are about to release a "Solar and Wind Energy Bank". This is a grid connect unit we have developed for some housing development customers in the USA. All of the solar/wind/grid power data is available at the LCD touch screen at the top of the unit and LiFePO4 battery storage is underneath.
I might look at bringing a few of these units into Australia. Councils might like them since they are such a "green" product.
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Post by lithbattboss » Sat, 03 Apr 2010, 00:48

The complete cabinet with lithium battery storage underneath.

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Post by acmotor » Sat, 03 Apr 2010, 04:18

Yeah ! there are some goodies on the market.
Here's another push the power around box...
supercombi

LBB, any specs on your box ?


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Post by lithbattboss » Sat, 03 Apr 2010, 22:19

No, specs as yet. The pics are "hot off the press". The power unit hasn't been officially released yet. The official launch is at a major renewable energy trade show to be held in Taiwan later this month.

You heard the latest news here first on the AEVA forum! Image
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Post by acmotor » Sun, 04 Apr 2010, 00:00

Thanks for the heads up then.
All we need now are some free samples for evaluation !! Image

"Energy bank" , I like it. It will be one of the techology items that make zero emission pwer sources more able to tackle the base load issue.
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Post by acmotor » Sun, 04 Apr 2010, 04:00

A question for grid connect gurus....

Does a GCI self limit the power fed to grid even if the solar/wind source can supply more, or do you have to size the GCI to be less than the source ?
If GCI has this active limit then what happens about the MPPT logic ?
(Maximum power point transfer as used in most modern solar/wind systems)

The thing is, can I connect my EV to charge off the PV DC and have the GCI convert/export when excess power is available with a PV>GCI rating rather than having to go via 50Hz mains and back through charger to EV battery ?
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Post by amnonholland » Sun, 04 Apr 2010, 13:59

Re-"excess power is available with a PV>GCI rating rather than having to go via 50Hz mains and back through charger to EV battery ?"

You dont want to go from GCI back to DC again. round trip could be as bad as 75-80% eff.

The inverter needs to be sized at the PVpeak capacity rating. If voltage is higher than the MPPT range then inverter disconnects from DC(could possibly happen on a bright winters day for a poorly designed system). If current is higher than MPPT max then there is usually a current derating element(definitely in Wind inverter), thats how optimal blade speed is controlled in windy conditions. Some wind turbine inverters have an external dump load for this reason which you could ideally use to charge the EV.

In your situation id go for a multi-string inverter ( i.e. has a few PV series strings in parrallel) then have an electrician install a transfer switch and a DC outlet with a special plug so the when you need to charge you can redirect maybe half of the inverters strings from the inverter to your DC charge point.

The inverters efficiency at part load will be poorer. Also you would need to check the minimum number of strings or amperage the inverter could run off and a few other specific things.

GC inverters run off high voltage. what is your EV charge voltage?
GCI are expensive! Its almost worth it just ordering a few cheap panels(that dont have to meet high voltage GC standards) for battery charging to get the volateg you want. The excess power could be used to charge a small battery backup for you home, dump power into your HW system if you dont have solar HW, etc.


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Post by photomac » Sun, 04 Apr 2010, 15:10

Another Advantage of thin film PVs is their robustness.
Unfortunately, the recent hail storms in Perth have caused many mono/poly panels to fail. I understand from colleagues at work who have suffered, that while the glass panel hasn't broken the impact has flexxed the cells beneath sufficient to "shatter" them. Minute hairline fractures being enough to render them useless. I don't know of any thin film issues post the hail storms.

There is a story of a traveller losing his Uni-Sola (thin-film) panel off his Landcruiser while travelling the Alice Springs/Darwin highway. It bounced, rolled and flew. The frame mangled was removed and the panel plugged in, working!

When my Kaneka system was installed I witnessed an installer lose his balance and counter from the middle of a panel. It bent radically. No concern about it's strength. While a hail stone the size of a tennis ball will incur a probable projectile puncture I understand the panel will work - although the broken seal will diminish the panel's life.


(edited adding 'ball' and "(thin-film)" )
Last edited by photomac on Sun, 04 Apr 2010, 05:15, edited 1 time in total.
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Post by acmotor » Sun, 04 Apr 2010, 16:18

amnonholland wrote:....
GC inverters run off high voltage. what is your EV charge voltage? ....


13.8 x 48V = 662.4V fully charged. Image
or 48V parallel mode (13.8 x 4 = 55.2V fully charged) refer red suzi's posts.
My work in progress Rodeo will be 800V charged or 80V parallel modules.

Re thin films vs mono/poly and the Perth hail storm.
There are a number of organisations looking into this WASEA for instance and I will be interested to hear the outcome.
I have a lot of time for TF panels.
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Post by gttool » Tue, 13 Apr 2010, 01:44

paid for my panels today installed on the weekend hopfully ended up with 70 Kaneka panels 60w and 2 2500 SMA inverters 4.2kw 70sqm of panel fits verrry well on one side of the carport, just hope i dont need to get to one in the middle 10 wide 7 high

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Post by Johny » Sat, 05 Jun 2010, 05:03

Can someone in the know about Solar PV systems please answer a question about tarrifs and selling electricity to the grid?

I am in Victoria and have been told that the 60c/kwh electricity generation tarrif only applies to the monthly average power out of the house - after power used has been deducted.

I thought that we got 60c/kwr for anything sent out to the grid (assuming the house doesn't draw much during the day) and that we paid 20c/kwr (say at night).
I.E. There is an advantage to no-one being home during the day.

Does this question make sense - anyone know an answer?

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Post by acmotor » Sat, 05 Jun 2010, 05:59

There are different systems around Oz.
Vic has a 5 kW max system size 60c/kWh Net feed in tarrif of 15 years scheme duration. There is a scheme cap of 100MWh. AFAIK

As I have mentioned already, a Net FIT is a safe, potentially no cost option for Govt as the 60c is paid only on what you don't use (and so export to the grid). Truth is not many households will get to export much (if anything) e.g. a 1.5kW system producing maybe 6kWh/day in a house that uses 15kWh/day = no export = no cost for Govt.

A gross FIT (everything you generate)(ACT and NSW ?) is far more of an incentive but actually costs a lot more !

Yep, sell PV power at peak rates (up to 27c/kWh normal smart meter peak rate anyway in some states) or at the 60c/kWh peak rate and buy back at the off peak rate nights/weekends. (Be thankful, FIT is only 40c/kWh rate in WA Image )

Someone will say if the numbers aren't current. Image
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Post by Johny » Sat, 05 Jun 2010, 22:16

Sorry - still not clear.
So power generated during the day when house is not using much is paid at 60c/kwr?

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Post by coulomb » Sun, 06 Jun 2010, 03:25

Johny wrote: So power generated during the day when house is not using much is paid at 60c/kWh?

Yes, I believe so. You get paid on what's on the meter, which is the accumulation of instantaneous outgoing energy only.

So the "average" thing is a furfy; it's just that, on average, many homes that don't change their habits are unlikely to export much. If you arrange your power usage appropriately, then you can get much more energy exported, and get paid for all of it.

Yes, such systems reward users that don't use much during the day when there is energy to sell.
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