Solving the power problem

[iFred]

Lately I have been thinking of the problem of power conversion. The problem it seems lies in the conversion of low voltage. This produces inefficiencies in power conversion.

The problem is the 1:10 ratio of power conversion in a typical 12vdc inverter. 1 (one) amp of ac requires 10 (ten) amps of dc current to be converted to boost the voltage from 12 vdc to 120 vac. It takes the current and converts it directly to voltage. This also does not include the additional 1-3 % efficiency loss by the inverter doing the conversion, which brings the ratio of power conversion up to 1:11 to 1:13 approx. I have done tests to confirm this. Low voltage inverters are inefficient, the losses sustained are to great, but the cost of such devices and the fact that wind is free and the availability due to mass market distribution means this is what we are stuck with, or are we?

Most wind generators produced on this web site and even most of the commercial units produce 12 to 24vdc, for the -primary- reason to charge batteries, the current is then used to run a standard 12 or 24 volt inverter. A 24 volt system is far more efficient then a 12 volt system because of the voltage. This is approx one quarter of 120 v and therefore more efficient, but there is more.

Most large wind generators have no problem in producing currents in the 10 to 20 amp or even some in the 40 amp range in a large wind condition, but let's just say that you wanted to run larger loads? The obvious solution is building more generators to produce more current without realizing where the problem is, or how to correct it. Sometimes these things can get you thinking in new ways.

A standard load at 10 amps AC will require 120 amps DC to be converted. This took a bit of time to sink in and fathom what was wrong with this picture... And herein lays the problem, to build a generator to produce heavy currents in this range, or produce a lot of generators or do we even need to? Can we correct the situation and if so how?

It seems that fate is not without it's sense of humor at times. About a year ago I wrote an article regarding the building of higher voltage generators, but at the time I had many issues to solve and put it momentary to the side to figure out other things. But the solution to the above problem was already solved though I didn't realize it. Only lately when I was thinking of the inefficiencies of inverters did the high voltage generator idea pop up again and this time sunk in and totally made sense.

This chart (chart 1a) shows that 24 volts is only a 5 step process instead of a 10 step process of conversion and shows why 24 volts would be more efficient. It is already at the half way point. Notice all the smaller steps of small voltages required for conversion.

The closer we get to a one to one ratio the better the efficiency.

This chart (chart 2b) shows that at 1200 watts conversion, 100 Amps of DC would be required from both battery and generator, however the closer to a one to one ratio the less amps is required to be produced and the higher the voltage is needed. This means that a generator producing higher voltage is more efficient then when it produces current.  A generator producing 120 volts at 10 amps can take a load at 1200 watts, impressive.

The nice part is that generators are voltage producers primarily. In the essence of their function they are a voltage device more then they are a current device. The production of voltage is their primary essence; the production of current is actually secondary and in some cases a hindrance.

So what does all this mean? Build higher voltage generators, hook up batteries in series but charge in parallel, build inverters for voltages less then 120 volts and thus increase efficiencies. Design generators around voltage rather then current.

Not all will agree with what is said in this article, granted. I await to hear your comments and see what you have to say about the subject. Let the debate begin, only then can we find the problems and find solutions.

Having fun!

www.internetfred.com

[finnsawyer]

I think your idea merits consideration.  I'm not sure about your numbers, though.  Powerwise 12 volts at 10 amps is equivalent to 120 volts at 1 amp.  I also doubt any inverter is 97% efficient overall.  Batteries are basically low voltage high current devices and expensive.  If you stack them to get 24 volts you halve the current, but also double the voltage needed for charging.  Since the inverter needs to handle half the current it may be possible to use less robust components and save money, a plus.  A higher efficiency design may also be possible.  As far as the alternators are concerned, you need twice the output voltage or twice the number of windings.  The current is halved, though, so thinner wire will work.  Result: Same amount of copper on same cores.  Pretty much a zero sum game, (twice the resistance per foot x twice the length x (half the current)^2), as far as internal alternator losses.  The regulators must handle the higher voltages also.  

[TomW]

GeoM;

Good points that dovetail well with what I am thinking on this. I think it all comes down to ohms law and its derivatives and without a major breakthrough like superconducting it is a damned if you do and damned if you don't situation. But, it never hurts to question the way things are done. In the end 100 watts is 100 watts regardless of the voltage, I think.

I am locked in to a 12 volt system because of my inverters but if I had it to do over I would go for a higher bank voltage perhaps even up to 96 volts which would be fairly dangerous DC levels to fool with but wire size would be smaller in the whole system.

Cheers.

TomW

[windstuffnow]

  Interesting discussion...  I've given alot of thought to similar situations but as Tom said 100 watts is 100watts no matter how you look at it.  It is, however, much cheaper to set up a system with higher voltage.  Unfortunately, I've been with a 12V system for many years and until my inverter pops and the repairs are high I'm stuck with it.   Can't see tossing good money out the door.

   In any case, no matter what you do, its a "give and take" situation.  I had envisioned a basement type structure for the batteries, inverter and all the other goodies at the bottom of the tower then simply run the 120V directly into a breaker box.  About as efficient as you could get using off the shelf components.  But after costing it out, its cheaper to run cables for the 12V system and keep everything inside.

   It would seem, at least at this point and using off the shelf components, we have to take what we can get.   Since the wind is free anyway anything you get, efficient or not, is only the cost of components.  So overall the most efficient way would be the least expensive way to capture the "free" wind energy.  If it cost say 500.00 to bang together a reliable 600 watt system that only achieved a 50% overall efficiency as opposed to spending 2500+ for the same system achieving 75% overall efficiency I would say the cheap system is the most efficient and the payback is far quicker and we have 2000 left over to play with and build 4 more 50% systems... or not.

   I became a bit obsessed with efficiency at one point, I'm guilty, then realized it really wasn't that important.  What was important was the money I was spending to achieve the efficiency.... and how much I saved by putting together quickie mills to basically do the same thing...  Isn't what were doing supposed to "save" us money as well as become a bit more independant?

Most important over all is Having fun doing it!!

Windstuff Ed

[arc]

iFred,

Great, inspirational, article illustrating the advantages/disadvantages of various voltage/current relationships. I've bookmarked it for the charts as well as a seed for thought.

I would agree that building more efficient wind machines and making better use of the power produced is not only needed, but essential if we plan to wage the war on carbon.

I would like to add, however, that in terms of winning this (carbon) war, we must burn the candle at both ends - in other words concentrate equally, if not more, on power consumption. The largest gains will be, by far, are in changing the way we adapt to using such things as natural & LED lighing where possible, passive solar heating, alternative water heating etc. to reduce the demands.

Thanks for the article,

Dave (arc)

[Oso]

I think that you are overcomplicating the subject, and you are thinking in the wrong terms.

First and foremost, generators are not voltage producers, they are wattage producers. That is why they are rated at 500 watts, 1.5 kilowatts, 110 megawatts, etc. Yes, they select a voltage to do it at, but this is done to reduce the winding size (the amount of copper) while keeping insulation levels down to reasonable levels.  

Electrical loads are also rated in watts. 25 watts, 100 watts, 1200 watts (or 1.2 kilowatts), or 25 megawatts.

Current (expressed in amps) is a mathematical ratio between watts and volts. 1200 watts is 10 amps at 120V, and 100 amps at 12V. It is extremely important for wire sizing, but is the wrong unit to think in, in a system of mixed voltages. This is why your power company bills you in watt hours or kilowatt hours, and not amp hours.

Your statement that low voltage inverters are inefficient is wrong, because you are thinking in amps, not watts. Consider the following:

System 1 12vdc/120vac, 200 watts on the 12 volt side, 10% loss delivers 180 watts on the 120 vac. You are saying 16.6 amps dc, 9 amps ac.

System 2 24vdc/120vac, 200 watts on the 24 volt side, 10% loss delivers 180 watts on the 120 vac. You are saying 8.3 amps dc, 9 amps ac. So, you think the 24v system is more efficient.

Wrong, they are equally efficient because they only lost 20 watts (heat loss) in the power conversion.

Unfortunately, we are stuck with primarily 12vdc appliances and equipment due to the automotive, marine, and RV industries. 24 or 48 vdc blenders are not common.

Our other choice of readily available appliances is 115vac (or 120vac if you prefer).

So, yes, when you try to combine the two most commonly available equipment and appliances, it can be complicated. If your 1200 watt load is a hairdryer, get rid of it and use a towel. If it is 12 100watt light bulbs, go florescent and reduce the load to about 175-200 watts for the same amount of light. Apply real energy efficiency /conservation methods to reduce the amount of generation/storage that you need.  Then, when you know what your average and peak consumption is, you can design the system that you need.

For some, a 12v system is fine. With higher loads, 24 or 48 volts may be desirable and they may be more cost effective. (Smaller wire is cheaper than larger wire). But that does not mean that the higher voltage system is more efficient.

[BT Humble]

I would like to add, however, that in terms of winning this (carbon) war, we must burn the candle at both ends...

But wouldn't burning a candle produce more carbon?  ;-)

BTH

(Sorry!)

[BT Humble]

For some, a 12v system is fine. With higher loads, 24 or 48 volts may be desirable and they may be more cost effective. (Smaller wire is cheaper than larger wire). But that does not mean that the higher voltage system is more efficient.

While I was researching my system, I repeatedly came across comments like "If I had my time over, I'd have gone with a higher voltage system", or "12V systems are fine for cabins, but for a house 24V is a lot better".

...so I went with a 24V system.  However I have a separate small 12V/20W solar system for the lights in my caravan (trailer).  The benefits that I see from the higher system voltage are:

• You can use smaller (cheaper) cable;
  
• A 1V drop over a cable run is far less of a problem in a 24V system than a 12V one;
  
• Your mill can be quite a bit further away from your battery bank without incurring significant losses;
  
• Lighter cable is easier to work with if you're fitting low-voltage throughout a building.
  
  

On the downside:

- Lights, accessories and inverters are more expensive and can be difficult to find.

If you're planning to run all of your loads via an inverter, and your windmills/solar panels are close to where your battery bank will be located, then I don't think it makes any significant difference what system voltage you use.  

In fact, I suspect that it's a bit of a holy war of the "PC Vs Macintosh" variety. ;-)

BTH

[Oso]

I do not know how I typed the 9amps for the ac side in the two examples above. I do know that I coumpounded the error with a copy/paste.  The AC side should be for both examples 180 watts at 120vac equals 1.5amps

[nack]

On the contrary, it would consume carbon faster.

nack

(very sorry)

[River Goat]

Hello All,

I have lived here, off grid, for 29+ yrs. The first 10 I had a 12vdc system then I went to a 120vdc system. Where the difference in efficiency shows up is in the resistance of the wire and connections. 120watts at 12vdc=10amps, and at 120vdc=1amp. The voltage drop across a run of wire or a connection will be 10 times greater for 12vdc than for 120vdc, also a 1.2volt drop in a 12vdc system is a 10% loss, in a 120vdc system it is a 1% loss. The loss in a 12vdc system is 100 times greater than in a 120vdc system for a given resistance.

My system voltage is actually 132vdc because it works better with my electronic loads. Resistive loads and dc motors like 120vdc and I have a way to supply that from the 132vdc mains. 99% of my stuff is common off the shelf equipment and runs on 132 or 120vdc.

Jerry

[Chagrin]

Flourescent lighting is efficient. LEDs are only efficient if the color of light required would force the use of a color filter with a different type of lighting.

[iFred]

Wow, I didn't expect all the varied comments that where posted. much to absorb. I suspect I opened pandora's box. I guess what I was attempting to say was that it seems easier to build and design a higher voltage system with lower current and reduce the losses initially then it is in building a low voltage system with higher current. Most small wind generators produce small currents, and many people have been asking the question of running larger loads.

We all know that conservation of energy consumption is important but in reality we do have loads that consume large currents no matter what. Large appliances are one of those things and we all have them.  I was looking at what it would take to run these loads and how it could be done in the most efficient manner possible. Cost was a secondary issue. What I found was that the closer one gets to the "one to one ratio" the less current is required. I was looking at efficiency only because of loss of the low voltage system.

Many stated that watts is watts no matter what, but when your generator needs to put out 100 amps of continues current it seems to become ridiculous. When do we change over to a better system and find a better alternative? We have great minds in this chat room that seem to be able to solve problems, which is what this chat board is designed to do.

There are pro's and con's to both arguments, on the one side are those that have established low voltage systems that cannot be changed nor do they want to, on the other side of the argument are those that see this as too large a hurdle due partly to cost and on the other side it comes down to the knowledge required to build a better system.

This is no easy task, but I believe the rewards in designing such systems will easily overcome any of the above arguments. I have given this a great deal of thought...Consider all the losses suffered in low voltage systems and I believe you will find that the higher voltage system and the closer you get to a one to one ratio system the better the system would be. It will take effort and thought but the outcome and rewards are greater as well.

To answer one of the questions posted; Contrary to popular believe, it is not voltage that kills it's current, or more accurately a penetrating voltage with a much higher current, and it's only going to do that if you allow it to and if it races through your heart from hand to hand. But that's another subject. Just remember to keep one hand in your pocket at all times.

Always having fun!