Digivation Hack Central » Solar

Optimal String Sizing for PV Systems

mark — Fri, 23 Apr 2010 02:44:59 +0000

Optimal string sizing for a given inverter can improve your return on investment.

As an example, I will use my system as an example. The PVI-5000-OUTD-AU efficiency plot is given below.

Aurora Efficiency Plot

The important panel parameters are:

Panel: TH175M24
Pmax: 175watts
Vmp: 36.2V
Imp: 4.85A
Voc: 43.9V
Isc: 5.30A

It can be seen from the inverter efficiency diagram that the sweet spot is at 50% full power and 345V string voltage. Note that it has 2 MPPTs. These may be independently specified.

Now the 28 panels for 4.9kW need to be split between the MPPTs such that the Pmax string voltages are near the optimal 345V. This gives us 2 optimal and a symterical choices:

2 x 9 Panels in parallel + 1 x 10 panels. This gives string voltages of 325.8V and 362V.
2 x 10 panels in parallel + 1 x 8 panels. This gives string voltages of 362V and 289.6V.
2 x 7 panels in parallel + 2 x 7 panels in parallel. This gives string voltages of 253.4V

The open circuit string voltage for this inverter must be less than 600V. This is 439V for 10 panels, so this parameter is ok.

By inspection of the efficiency plot, configuration 1 is the best. In fact is it 0.3% better than the symmetrical configuration, which would result in about $10 per year more income/power at 68c/kWh.

The MPPT which has 2 strings in parallel has a greater weight attributed when choosing panel configuration as it supplies more power.

Refs:
Aurora PVI-5000-OUTD-AU Datasheet
TH175M24 specs

PV System Install Phase1

mark — Fri, 23 Apr 2010 00:01:33 +0000

The panels are up but the Aurora inverter is still coming due to supply issues in mid May.
I have opted not to obtain an alternative GCI due to the excellent efficiency of the powerone aurora. It is generally 2% or more better than others currently able to be supplied at short notice so worth waiting. 2% is worth 98W at full power, and derated, works out to about $100 per year.

All things going well, we should be generating power and income in June some time, fingers crossed. Hopefully AGL wont stuff us around like others I know when we apply for the premium rate tarrif too.

4.9kW PV Panel Install with 28 x 175W Mono

PV Panel Orientation Effectiveness

mark — Thu, 04 Mar 2010 13:44:55 +0000

This site has a nice image showing PV panel orientation and the expected output as a percentage of optimal orientation at latitude 35°S.

A fully west or east facing panel will still achieve over 80% of the output of an optimally north facing system. This indicates orientation, whilst critical is not a reason to not install them if no available north facing roof space is available.

Watts Clever First Impressions

mark — Fri, 05 Feb 2010 21:44:47 +0000

I got my watts clever / currentcost envi the other day and have had a play.

Fairly basic display. Very easy to setup.

I measured the power consumption of the display with my plug in power meter from jaycar and it read 0W. Which means the display is fairly well designed.

Haven’t got the USB cable yet, so I haven’t implemented logging, which is why I got it.

It looks like the dynamic range is variable with more sensitivity at lower power levels than higher ones. Because the transmitter uses a PIC 16F689, which has a 10bit A/D, it has only so much accuracy. So what they must have done is to use one of the PWM outputs to generate the reference, and vary this to provide the dynamic ranging capability. This is all done in the transmitter. It also means that the 288W bug mentioned in http://blog.technicaone.net/post/2010/01/26/Current-Cost-5c-Watts-Clever-The-144-Bug.aspx is also fixable in the transmitter.

Since there is a programming header on the transmitter (visible from the battery compartment), I wonder if they forgot to blow the security bits, allowing the program to be read? But that’s for later.

Useful solar links

mark — Fri, 05 Feb 2010 12:36:44 +0000

http://yourhome.gov.au/technical/fs67.html

Solar Sites on the Web

mark — Tue, 02 Feb 2010 02:59:01 +0000

Curt Blank has written an Aurora GCI data interfacing program and written a web interface around it.

http://www.curtronics.com/Solar/

I’ll be using this one.

I just need to get a linux supported USB to RS485 interface (ebay) and run some cable up the wall from the server patch panel.

soon…

Grid Connect PV Solar System

mark — Tue, 02 Feb 2010 01:27:15 +0000

Ever since the Victorian government introduced the NET premium rate tariff of 60c/kWh exported, I decided that a PV system was economically viable. Green issues were not considered.

Using various methods, I found a 5kW with our daily usage of 20kWh system should return about $3500 per year using AGL’s generous 68c PFIT.

As per usual, got many quotations and settled on one with Glen Clark and Co. I decided to keep the REC’s.

Specs are

28 * 175 watt Solar Panels (Mono Crystalline) TH175M
1 * Aurora PVI-5000-OUTD-AU Solar Inverter

I did want thin film amorphous but it came out at $5k more, so even though they have better performance in low light and higher temperatures (PV panel temperature derating) which works out to about 10%.

This gives 4.9kW for A$25k without RECs. Ill have to recover the RECs later when hopefully the price will be a bit more than they are now. More on this later.

This should pay back in about 5 years, with a return of about 20% on investment after the RECs have been accounted for.