Some design input appreciated!!

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Some design input appreciated!!

Postby Dex » Wed May 21, 2014 10:46 am

Hi All

We have a place in Southern Tasmania that we've been working on for 18 years

Just getting ready to finalise the design and install our off grid system. Its had a few temporary iterations as a genset RAPS.

Main components we have on hand (on site) at present;

2 different 3kW solar arrays, 60A schneider xantrex C60 charge controller, GSL 60A mppt charge controller, a 1kW wind turbine (just got that running last weekend), 30kVa gas fired genset (ex ABC Sale standby unit with a total of 117 hours runtime from new and a v6 holden engine..sweeet!!), 6.5kVa honda sinewave generator, 3kW puresine 2 inverter (12V), 3kW puresine 2 inverter (24V), several chinese pure sine inverters between 1kW 12V and 6KW 48V, 60A 24V Mastervolt charger, 40A 12V xantrex true charge 2, a couple of 1kW hydro turbines that we are hoping to stitch into a pumped storage between our dams + numerous other PMA's and bits and pieces.

Looking for an elegant way to stitch all this together...hoping for some input from you all

We have just upgraded from a shack that kept the rain off for 15 years to a proper shed that is now complete and a house being built so the transition from collecting to installing this for real is upon me.

Few key factors;

1kW Wind turbine (3phase) is 80m from the house (and will probably get upgraded to a 3 or 5Kw unit if it makes enough powerover winter to justify that), solar array will be located 20m downhill from the turbine, 60m from the house. Shed is 150m from the house (ie 230 m from the turbine) and gensets needs to be located at the shed so it has stand alone power (and 3 phase power).

House is AC....12 - 15kWhr/day consumption

I intend to cable link the components underground

I understand the need to use AC for power transmission over distance due to line loss with DC/low voltage

Some of my key questions;

Is it better to locate the battery bank near the house (midway between the solar/turbine and the shed/genset) or elsewhere

Battery bank is scrappy and need upgrade. At the moment we are using 4 x 12V x 250Ahr ebay cheapies. Appreciate some input into that....How many A/hr? What Voltage? Best value for money?

No issue with acquiring a better inverter to tie all this together - been thinking about a SMA Sunny Island in the 5kW - 8kW range - any input appreciated

Some suggestions on suitable cable dimensions between locations...I have been squirrelling lengths (ie 50 - 100m runs) of SWA 1 and three phase for years..OMG....such a hoarder....;P but I will purchase the right stuff if my scraps are not large enough (cross sectional area)

Pumped storage is an option - we have ~500t of water that we can afford to pump uphill ~ 300m (~22m static head) from pond to pond as a means of using excess energy - I will need to aquire a 6" poly line for this...the 3" line we have is fine for irrigation but the line loss for moving 500t of warter fast enough to store/make electricity is too much - anybody have any experience with this? I realise its left field and may have fatal flaws - just brainstorming it atm.

Phew....time for a breath!!

Cheers

Dex
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Re: Some design input appreciated!!

Postby Tracker » Wed May 21, 2014 2:22 pm

..
Dex wrote:Looking for an elegant way to stitch all this together.


I can't help thinking that it's a guessing game for any reader.. to think how to put all that together

I think that you need to decide which way you plan to go with batteries..

You will read a deal on here about 48 Vs 24Vdc.. Clearly the higher the voltage, the better the efficiency of it all..

Three Phase WTG.. Do you plan to have three phase house power.. You may be able to just feed that 3Phase power to the battery house and rectify it and into the battery (LITHIUM would be BEST choice)

Likely, you either do a real jigsaw with all those bits, or you decide to base your system on a particular technology..

Eg. A Selectronic SPPro could be a good choice as a basic Inverter/controller, and then use one remote PV system with a Grid-Inverter to AC-Couple to the full network.. and then the other AC devices can be linked in..

An alternative and more DIY, might be to do what our friend of Flinders is doing, but that necessitates some practical electronics experience... ;)
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Re: Some design input appreciated!!

Postby Dex » Wed May 21, 2014 2:37 pm

Thanks for the prompt reply Tracker.

Agree that batteries is important and reading through some of the other posts I see that 2V cells are the go

Still not sure on 24V vs 48V...still not sure on gel vs AGM etc

The WTG is 3 phase because I wanted to test output before committing real cash and this was cheap

At the moment it is being rectified to DC and charging a 24V 250Ahr bank and does seem to be producing "ok"

In reality I put this "out there" to generate discussion and enable me to focus on the key issues

I intend to stitch the best "bits" of this together to produce a cohesive reliable RAPS

The rest will be used elsewhere on our property or sold.

Clearly batteries is a key issue and pretty close on my agenda

The selectronics SPpro is ac coupled...isnt it?

My understanding of this is that I can draw directly from this with my AC appliances and that excess energy charges the batteries/exzcess demand draws from the batteries

Is that close to the mark?

Dex
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Re: Some design input appreciated!!

Postby Gordon-Loomberah » Wed May 21, 2014 5:35 pm

Here are a couple of threads you might find useful in deciding what you want to do with panels and battery.

Lithium vs Lead
solar-wind-gear/topic5108.html

Virtual Tracker
solar-wind-gear/topic5064.html

Re 24V vs 48V, given your estimated usage, 24V may actually be more efficient that 48V, I'm sure Tracker has posted a graph showing just that ;) It depends somewhat on the particular inverters characteristics. Either way, using Lithium (actually ~ 26V or 52V) instead of Lead will have a much greater effect on overall system efficiency.
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Re: Some design input appreciated!!

Postby Dex » Wed May 21, 2014 5:35 pm

You may be able to just feed that 3Phase power to the battery house and rectify it and into the battery (LITHIUM would be BEST choice)

How many amp hours of these do I need?

What cell voltage for LiPo?

They look prohibitively expensive....perhaps I am looking in the wrong place?

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Re: Some design input appreciated!!

Postby davidg » Wed May 21, 2014 7:59 pm

Dex wrote:What cell voltage for LiPo?
They look prohibitively expensive....perhaps I am looking in the wrong place?


There not too bad considering......... for say 48V on an SP-pro you would use 16cells but it does depend on whether you get something like the SP-pro which can do fairly precise programmable charging voltages which nearly all of the cheap inverters cannot to do.

Selectronics Sp-pro can do both AC and DC coupled and at the same time if you want as can a number of other brands, SMA for one.

I'm setting up a 48V 700AH LiFePO4 pack with BMS at clients site next month, compared to PB it was no more expensive for the number kWh's able to be delivered on a lets say daily basis, with based on Gordon's observations around 10% higher efficiency in the charge to discharge ratio. That adds up to a lot of dollars saved overtime.
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Re: Some design input appreciated!!

Postby Smurf1976 » Wed May 21, 2014 8:39 pm

Dex wrote:still not sure on gel vs AGM


Advantages of AGM - higher maximum charge and discharge rate, moderately tolerant of over charging, can be charged straight from a car's alternator - not ideal but won't damage anything.

Advantages of Gel - much greater tolerance to deep discharges and otherwise not being kept fully charged. Longer lifespan if not abused.

At work we have around 650 completely separate, stand alone 12V solar systems. Let's just say that I've done the maths and there's more chance of me landing on Mars than of me buying AGM batteries. The reason is simply this. None of the "advantages" of AGM over Gel have any real world consequence in this application, as such they theoretical rather than practical. Gel lasts considerably longer, and is less likely to be damaged by a non-battery fault (given that such faults would almost always result in under charging rather than over charging).

If you refer to manufacturer's data then Gel has at least one third longer lifespan than AGM if everything is done properly.

And if you really press battery retailers on the subject, they'll eventually admit why they push AGM almost exclusively and stock little if any Gel. The reasons are simply that AGM (1) can be charged directly by a car's alternator and is thus an easy solution for camping, caravans and so on and (2) consumers are less likely to ruin the battery within the warranty period given that they're more tolerant of over charging and will withstand as many deep discharges as they're likely to get during 1 or 2 years of warranty. So AGM is a "safer" choice for the battery suppliers, it gives them less hassle given that a lot of what they sell is being bought by people with little or no knowledge on the subject. But push them and they'll eventually admit that Gel is a better deal from the consumer's perspective if they are used properly.

As for LiFePO4 (lithium), we're evaluating that but not willing to do a large scale deployment without further testing of our own. That comes down simply to risk management - with Gel we know exactly what we're getting and what's likely to happen but we don't have comparable knowledge with LiFePO4. Hence we aren't rushing into this one - in due course we'll probably be buying nothing but lithium batteries, but we're taking the cautious approach at this stage and Gel is a very "safe" option in that sense even if it's old tech.
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Re: Some design input appreciated!!

Postby Helipos » Sat May 24, 2014 12:16 pm

Dex wrote:How many amp hours of these do I need?

What cell voltage for LiPo?

They look prohibitively expensive....perhaps I am looking in the wrong place?

Dex


How many days of (not blowing a gale) or no sun do you want to get away without using the genset?
Nominal voltage of 3.2Vpc
They look expensive until you consider you can go for a much smaller bank using a greater DOD vs Pb
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Re: Some design input appreciated!!

Postby Dex » Sat May 24, 2014 10:16 pm

Thanks for all this input its much appreciated.
Whats the ballpark cost for LiPo 1000Ahr 48V?
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Re: Some design input appreciated!!

Postby davidg » Sun May 25, 2014 3:01 pm

Dex wrote:Thanks for all this input its much appreciated.
Whats the ballpark cost for LiPo 1000Ahr 48V?

The real question is do you really need 1000ah, that's quite a lot of storage in LiFePO4, not allowing for losses, gross it's 48kWh's of total storage so @ 70% DOD = 33.6kWh's and @ 80% DOD = 38.4kWh's. If however if you were to shave another roughly 10% off each number it would be close to thee actual number of kWh's capable of actually delivered, with good quality equipment involved. ;)
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