Did I miss something?

[ambervalley]

G'day Guys,

Like many I have been trawling the forum, websites and books researching our alternative power options.
I am in the planning stages for building a new home off the grid and have been advised that we will need to run a 48v system to meet the demands we are likely to have.
My question is, most information leans towards setting up 48v windmills due to the improved performance over 12 & 24v, but don't I need higher performance to be able to charge a 48v battery bank to start with?
 
Cheers
Chris

[wpowokal]

Chris short answer what you need is good wind with a clear site (no turbulence).

If you are planning a large (relatively high load) system and have the ability to recharge the batteries then 48V is the way to go, I use it, most arguments for higher voltage systems revolve around efficiency and cable costs. If you double the voltage you halve the amps for equivalent watts (volts x Amps) transfer, losses are current squared x resistance (I2 x A) so within a wind turbine there is less heating in the windings, depending on how it has been wound (wire size) and therefore greater efficiency.

You have planned for energy efficient equipment, load scheduling etc, haven't you?

I personally I like to keep my batteries in the top 15-20% of charge each day, when I have poor input days coming up I economize even further like swapping the big plasma television for the smaller LCD unit which can save a lot of power. Most sales people and books will go on about 3 days autonomy, which is needed to not discharge the batteries too deeply, however that is assuming you will have a large amount of incoming on day four. If this is not expected to be the case or your system power source is sized close to your requirements (not recommended) then it is smarter to back them up sooner.

I see no logic in taking 30Kw out of the batteries and thus running them down to 50% then having to run a generator for 8 hours, smarter to run that generator for a short period each day when you have the heaviest loads, the batteries are there to be used but be kind to them and they will last a long time.

Allan of the jungle

[ambervalley]

Hi Allan,

Thanks for that - yes we are planning low use/liited appliances. I guess the main question is, does a 48v turbine put out enough to charge a 48v bank?
There will be a large solar array, solar hot water and a back up diesel generator to help as well.

Cheers
Chris

[DanG]

To stay healthy a flooded lead-acid twelve volt battery needs greater charging voltage than it holds in capacity.

The numbers vary from battery make to another, but recharging and equalizing may use 13.5 - 14.7 Volts to reverse the chemical reactions 99.98% (always some irreversible chemistry has occurred) - So a twenty-four volt system might need to see 29.4, and a 48V 58.8V to stay healthy but they are still called 24V and 48V systems.

[Flux]

Hi Allan,

Thanks for that - yes we are planning low use/liited appliances. I guess the main question is, does a 48v turbine put out enough to charge a 48v bank?
There will be a large solar array, solar hot water and a back up diesel generator to help as well.

Cheers
Chris

The battery sets the system voltage. There is no such thing as a 48v turbine, it is just one whose characteristics match a 48v battery system as well as possible. The turbine volts will vary from zero to something over 150v if you don't connect to a battery.

Any time the turbine volts are lower than the battery it won't charge so you need more wind to charge a full battery than a flat one. It takes little wind increase to deal with the battery voltage variation from nominal to gassing volts so a suitably chosen wind turbine will be able to charge the battery even when it is up near 60v, it is not inherently a voltage limited system like a solar panel where you must have a certain minimum number of cells in series to charge a battery.

Flux

[Ungrounded Lightning Rod]

If you are planning a large (relatively high load) system and have the ability to recharge the batteries then 48V is the way to go, I use it, most arguments for higher voltage systems revolve around efficiency and cable costs. If you double the voltage you halve the amps for equivalent watts (volts x Amps) transfer, losses are current squared x resistance (I2 x A) so within a wind turbine there is less heating in the windings, depending on how it has been wound (wire size) and therefore greater efficiency.

A nit:

Mills wound for higher voltage have more turns of thinner wire.  Given both tend to be optimized to fill a given area with copper, if the rest of the genny is unchanged you get the same percentage loss at the same wattage of generation from the same amount of copper, regardless of the voltage for which it is wound.

The efficiency differences of different voltages shows up primarily in the wiring hooking things together (especially the line between the genny and the powerhouse) and also in the efficiency of the electronics in things like inverters.  Doubling the voltage halves the current and quarters the resistive losses in a given size of wire.  So you can cut your costs by half by downsizing the wire, or cut your losses by a quarter by leaving the wire the same size.  For a factor of 4 in voltage (48V vs 12V) the factors are four in copper savings or 16 in loss reduction.

Small systems tend to be 12V due to automotive technology driving the economy of scale for equipment, upping availability and squeezing price.  Equipment is easily available for currents up to about 100A, after which it gets harder to find and more expensive.  So 12V systems, as a rule of thumb, go up to design targets of roughly a kilowatt, 24V to two KW, and 48V above that.  (48V also has an economy of scale going for it due to its use in networking central offices.)  Going over nominal operating voltage of 50V puts you into a more stringent part of the electrical code, so 48V systems often bite the bullet on higher currents - or use multiple loads separately hooked to the batteries - to go beyond 4 KW.  REALLY big systems may bite the bullet on voltage, code, and specialized equipment and raise the voltage still farther.  But 4ish KW is adequate capacity for an energy-conscious family's residence (without electric heating {except as dump loads}, with limited air conditioning, and with special provisions for heavy motor loads such as workshops).

[ghurd]

A less tech related reply may help?

but don't I need higher performance to be able to charge a 48v battery bank to start with?

No.  You need a 48V windmill.

A 12V windmill in a 12V system will do its intended job.
A 48V windmill in a 48V system will do its intended job.


Two 100W light bulbs.  They both make the same amount of light.
One is 12V, the other is 48V.
You would not buy a 12V bulb for the 48V system, or vice versa.
The same thing applies to windmills.
G-

[ambervalley]

Hi Ghurd,

Thanks for that (and everyone else that repsonded)

I guess what i was asking was will a 48v windmill put out a charge rate higher than 48v to charge the battery bank.
I was surprised to see comment that there is no such thing as a 48v turbine and its the batteries that set the level. If this is the case, why do the recognised 'experts' like Hugh P refer to them in their books and sites? Are they just dumming some stuff down for people like me?

Nevertheless, I will wire my F&P to suit 48v, that or buy a complete washer and get a really big hamster.

Cheers
Chris

[ghurd]

"I guess what i was asking was will a 48v windmill put out a charge rate higher than 48v to charge the battery bank."
Yes.   (unless you bought it on ebay!  LOL)

You are (quite understandably) getting a bit lost in the terminology.

Do not take this as a terse/bad/evil/cold/mean reply... although I hear I am often terse/bad/evil/cold/mean.
Being American, I never learned to speak Austrailian.  Bear with me.   

I would suggest reading through the FAQs.
Read them while thinking about what they are talking about.
No need to understand every word or term, as long as you can grasp the concept of the problem.
The terms will begin to fall into place. 
As the terms fall into place so will the problems and solutions.

FAQs
http://fieldlines.com/board/index.php/board,27.0.html

In your situation, pay extra attention to:
http://fieldlines.com/board/index.php/topic,143908.0.html
http://fieldlines.com/board/index.php/topic,143642.0.html
http://fieldlines.com/board/index.php/topic,143574.0.html

and
http://fieldlines.com/board/index.php/topic,143592.0.html
(if someone smart and honest has tried 8463 different wiring methods and determined how your version of an F&P should be wired for 48V with a certain type of blades, believe them!)

and do not make the newbie mistake of believing high open circuit voltage means high power output.
I fell for it, wasted a lot of time and money, and I know better now.

Here is a terminology glossary.
If you only speak Aussie, it will help about as much as a Greek to Latin dictionary.
I hope it will help as you read through the FAQs.
http://fieldlines.com/board/index.php/topic,144541.0.html

ECM is electrically similar to F&P.
One is insideout from the other.  The concepts are the same.
G-

[SparWeb]

Did I miss something?

I always miss something.  Like this thread.  A week late (hopefully not a dollar short).

Battery system voltage is one of those "secondary" questions that you really only have to deal with after you answer the main questions.

Will I be off grid?  Should I have the grid available?  What is my target energy consumption in life?  Where will I live?  Family/kids around?

These are the things to consider before diving into the residential RE way of living.  Once you know you will do it, and how, you're better prepared to pick the details, such as battery system voltage.  You may find, at the end of answering the big questions, that the right solution for you involves NO batteries at all!

[Flux]

I made that statement so I think I should explain it.

If you take a 48v turbine and connect it to a 24v battery the system volts will now be 24v.the turbine will now charge but not as well as before, it will start charging in very low winds but will match badly and give far less power. Similarly a 24 v turbine connected to a 48v battery will be a 48v system and again it will perform badly and need a lot of wind before it starts charging.

What we call a 48v turbine is one designed to work best at 48v, Hugh Piggott publishes designs intended to work best for each nominal voltage. His 12v design works best at 12v and so on, so it is just logical to call it a 12v turbine. It's just not dumbing things down it's a logical convention that everyone follows. It is not absolute and possibly you could get the case where a 12 turbine could give better results in a very windy area than a nominal 24v one designed for best results in a low wind area for a 24v battery. Unless you have a detailed knowledge of these things you just choose one nominally rated for your system voltage. The point I was trying to make was that a 48v turbine will have enough spare voltage to fully charge a 48v battery even when it is gassing at near 60v ( the point I thought you were originally asking).

Flux

[ambervalley]

Hey Guys,

My question was answered, thankyou. All I wanted to know initially was whether a 48v turbine would have the guts to charge a 48v bank, that's what we've been told we'll need based on our estimated demands.

I will have grid power up at the road, already connected to the existing farmhouse. We are going to build a new house further from the road and therefore power - the temptation to connect up to it, of course is there, but guestimations suggest the cost of doing so is up towards $60-$75k.
My biggest motivation is to 'stick it up' the power companies - we have always had reasonably priced power here, but recent changes have seen MASSIVE cost increases. Add in that our none too popular Prime Minister wants to add a carbon tax and our retailers want to pass on the cost of bush fire damage repairs to the grid infrastructure for the next 12 years (bare in mind neglected power lines caused several of the fires, including the worst that killed dozens), you may get an idea why I want to go this way.

All a steep learning curve - I appreciate all your responses

Cheers
Chris

[shawn valpy]

Just one thing I might be able to help you with is the output of the F&p windmill (I fly one) A single stattor is only good for around 400 watts max (unmodified) with neo upgrade and the right blades you could get around 900 only reason I point this out is unless there are comercial wind turbines all around you (good wind site) its proberly not going to keep up with your power demands!!! If you want to go off grid you will need a bigger turbine to give more kwh year round just my thoughts .

[WindriderNM]

It is hard to get enough power from wind alone. I use solar and wind. When I first started i bought a modified car alt mill on ebay that was rated at 800 watts. The most i got out of it was about 150watts then the blades flew off. From reading the claims about wind I thought it would be cheaper then solar. (how could I have been so wrong. The 14g wire to the connector on the generator should have been a clue.). I now have 9 solar panels and 4 wind mills.