Planning the system

[sven]

Planning the power system


I've decided I want a wind turbine, a hydro plant and some solar panels.  I also need a complete power storage and distribution system.
I made a "nice" little diagram about it (well I like it anyway).





This is the process as I see it at this time, I'll change this view step by step in other sections.




These are the steps I'm going to take to make the power system.  This is the initial planning, and it will without any doubt change later.

 
• Calculate how much power we need

 
• How much power can we harvest from different systems

 
• How can we mold the power to charge batteries

 
• What kind of batteries are we going to use

 
• How can we make an inverter

 
• How can we do all this safe

How much power do we need


More important then trying to generate a lot of power, is to conserve a lot of power, so we begin by investigating our power needs.


In the cottage in France we need lights, a refrigerator, use of a portable computer, charging of a cell phone, a stereo, maybe a microwave oven
and maybe a water heater to have some hot water to do the washing up.


I looked for all power consumptions of these appliances:

 
• Refrigerator
   
  
     
  • Power: 25 W
  
     
  • Amount: 1
  
     
  • Hours/day: 24
  
     
  • Total Power: 25 W
  
     
  • Wh/day: 600 Wh
  
     
  • Amph/day (12V): 50.00 Amph
  
   

 
• Lamps
   
  
     
  • Power: 10 W
  
     
  • Amount: 6
  
     
  • Hours/day: 6
  
     
  • Total Power: 60 W
  
     
  • Wh/day: 360 Wh
  
     
  • Amph/day (12V): 30.00 Amph
  
   

 
• Portable
   
  
     
  • Power: 100 W
  
     
  • Amount: 1
  
     
  • Hours/day: 10
  
     
  • Total Power: 100 W
  
     
  • Wh/day: 1000 Wh
  
     
  • Amph/day (12V): 83.33 Amph
  
   

 
• Cellphone
   
  
     
  • Power: 60 W
  
     
  • Amount: 1
  
     
  • Hours/day: 2
  
     
  • Total Power: 60 W
  
     
  • Wh/day: 120 Wh
  
     
  • Amph/day (12V): 10.00 Amph
  
   

 
• Microwave
   
  
     
  • Power: 750 W
  
     
  • Amount: 1
  
     
  • Hours/day: 0.25
  
     
  • Total Power: 750 W
  
     
  • Wh/day: 188 Wh
  
     
  • Amph/day (12V): 15.63 Amph
  
   

 
• Stereo
   
  
     
  • Power: 50 W
  
     
  • Amount: 1
  
     
  • Hours/day: 4
  
     
  • Total Power: 50 W
  
     
  • Wh/day: 200 Wh
  
     
  • Amph/day (12V): 16.67 Amph
  
   

 
• Total
   
  
     
  • Peak Power: 1045 W
  
     
  • Wh/day: 2468 Wh
  
     
  • Amph/day (12V): 205.63 Amph
  
   

Assuming we have the batteries to store enough, we need to generate 2468 Wh a day,  let's round it to 2400Wh a day, since I rounded up on the appliances.
If we assume the the power generation is constant, we need 100W to be generated all the time.
For wind or water power, we are going to assume this, for solar power I am going to assume 8 hours a day sun exposure, I'll check the correctness of that later.
So if we are going to do it all with sun power, we would need 300W solar panels.






One at the time


Since it is no use getting ahead of myself, I will start with windpower since there seems to be such a high rate of success in that area.  First I want to see if it is feasible to extract enough from the wind to power everything.  I like diversity in sources of electricity, but a working system with 1 source of power is better then no system with a diversity of sources.







Getting the needed data


First we need to know how much wind is on our location, that can start all calculations.  
For our location, I checked the Meteorological institute of France
but I plan on taking my own readings on the site myself at a later date.


It tells me average wind speeds for that region are 20km/h (5.5m/s, 12.5mph) and with extreme winds up to 120km/h (33.3m/s, 75.5mph), so safety will be crucial when building this windmill.


To really start designing the windmill, I will need more accurate data, but for now I will calculate everything for 5.5m/s winds.




We need about a 100W from he wind in our initial calculations.







How much power has the wind



The power of the wind can be calculated using the following formula:




WPD (Wind Power Density) = 0.5 * Air Density * V (Windspeed) * V * V




The windspeed should be in m/s and the Air density in kg/m3.  The air density should in fact be calculated with temperature, air pressure and elevation,
but since my wind speed is so inaccurate, I'll just take 1.225 kg/m3 for the air density (sea level, 25 degrees celcius).


The result is in Watt/m2.


This comes to the following formula:




WPD = 0.6125 * V * V * V




If we take our average wind of 5.5 m/s, we can easily calculate that the power of the wind is:




102 Watt/m2




So if we had a windturbine with a circumference of 1m2 we would have what we need?


No, not really, we can't extract all of that energy.






How much power can we extract


We can't extract all of the power of the wind, if you extract power from the wind, you effectively slow the wind down.
and if the wind slows down, less wind power will be available.  If you slow down the wind too much, less power can be extracted.  
There is a limit to how much power you can extract from the wind, this is called the Betz limit.
I haven't fully understood the calculus behind Betz limit, well certainly not enough to explain it here, but in short the Betz limit says you can never exract more than 59.3%




Pex = Ptot * 0.593




So if we had a windturbine with a circumference of 1.70m2 (1m2/0.593) we would have what we need?


No, not really, we would have if we made a windturbine that is 100% efficient, but that's not possible.







How efficient can we make our turbine


The blades of your windmill are designed to work optimal for a certain windspeed, windspeeds are not constant however.
You have friction of the moving parts, your generater has some efficiency loss.  In short, you loose a whole lot of energy,
luckily the windenergy is free.


All of these factors are addressed later, and one at the time.  The highest observed efficiency is 45% windpower captured (with the Betz limit of 59%, this is extremly good).
An efficiency between 20% and 30% is what most systems get.


I'm feeling undeservingly confident I'll be able to get 25%
(well not really, but I'm gonna use this for my initial calculations, I'll figure part out further on, and the other part must be observed)




Pex = Ptot * 0.25




So if we had a windturbine with a circumference of 4m2 (1m2/0.25) we would have what we need?


Yes! Well, if the design is sound, this should about do it.


Transforming this into a diameter will give you about 2.55m (2*sqrt(4m2/PI))


That's not to bad, I expected a lot more.  In fact, it looks so small to me, that I am sure I made a calculation error somewhere, or on more then 1 place.


I'll probably see my error(s) appear later on, or this is really too good to be true. :-)

[troy]

I'm sure you've either accounted for this, or will at some point.  But I don't see any reference to battery and inverter efficiency.  For a well managed wet lead acid system, most authorities quote overall efficiencies of 70-80%.  Under ideal circumstances, the inverter might do a bit better than that, but in the real world, I also figure around 80% on the inverter. So overall system efficiencies hover around 0.8 x 0.7 = 56%

And if history has anything to recommend, it is that power requirement virtually never go down and almost always go up, so expandability should also be considered.

Have fun on the quest,

troy

[Gary D]

Sven, unless you have a very effecient refrigerator, I think 25 watts is quite a bit low. Sunfrost has a model that uses about .9kwh per day, however most effecient ones in the U.S. use 75 to 100 watts per hour.

  I noticed that no waterpump is included, so hopefully the spring is uphill from the cabin for gravity feed? Great start in planning! Will be interesting to see the mix of power choices you eventually decide on.

  Hugh Piggott has plans (in a book format) that is worth every penny to build a 6' and a 12' windjenny. Most if not all is on his website for free, however it is nice to have a hard copy.

 Wishing you all the best, and have fun! Gary D.

[Gary D]

My apologies, the two turbines by Hugh Piggott are 8' and 4' (or 2.4 meter and 1.2 meter). Just got my book out- the average output at 5 m/s or 11mph is 2kwh per day/.05kwh per day respectively. Sorry for my mistake. Gary D.

[ghurd]

Hello Sven,

You made a very nice diagram.

Make the most of the water available.  Water power is easy and not expensive to maintain.

Solar power and wind power are often oposite in a season.

Making more power than needed is a good design.

Excess power is good for hot water.

Also consider some devices run with battery power, and no inverter.  Items like 12vdc or 24vdc CFLs (compact fluorescent lights).  Bad 12vdc items in the US can be coffee pots, blenders, mixers.

G-

[sven]

I did know there was some efficiency loss, but I had no idea it was so steep.  I will better try to run everything in 12V, and only have an inverter for occasional stuff.
In any case I am planning on trying to produce more than needed.

Thanks for the input.

Sven

[sven]

You are probably right for the refrigerator, I seem to have bought some salespitch too easily, it's indeed more 60W for the more expensive low-energy refrigerators.  After some consulting on the IRC channel, I decided it would probably be better to run the fridge with gas.  More certainty of a continuous running fridge, and more power available for the rest.  




The spring is indeed uphill.




For the book of Hugh Pigott, I bought it, it arrived 2 days ago.  I was planning on designing my own windmill eventually, but I feel it better to first try and build a time-proven design, which was well thought out.  I plan on starting to build Hugh's windmill in the coming weeks.




Thanks, and I am certain I will have loads of fun.




Sven

[sven]

I was planning to first make a windmill, then get solar panels, but you are right, I might be better of trying to harvest the waterpower before spending big $$ on solarpanels (it is more fun to build a waterwheel anyway :-) ).




After talking to people on the IRC channel, I am also more convinced I should be planning to run more on 12Vdc, you're absolutely right.  I'm still planning on having an inverter, but only for occasional stuff.




Sven

[juiced]

Im not sure if i understand. The diagram says "waste" not water.

      If waste is the case, you would be wise to run a pump off batteries/PV or direct wind-drive.  (IMO)

      So dedicate one system to support your 'main' and use the other for a laid-out set of tasks. Not all of life is electronic and realistically a PC is almost all you need to get radio/phone/tv/vcr/etc. Then you have to deal with the appliances. From what i understand, fridges work (most) by compressing gas to make it cold. Why cant the water wheel do that directly?

   The more you convert, the more you lose. If this wasnt the case, we could all have miniature mills linked by hydraulic/air trannys.

 Think of it like this. You have an apple orchard and want to get wine. You might go sell your apples and then buy wine, or you could just settle with cider; which in my opinon is much more rewarding.

  If this sounds out to lunch, i must apologise. The others are much more experianced! :p

[juiced]

I thought it said waste... i went back and looked at it again and realised it doesnt. sorry.

[sven]

I absolutely agree that as little as possible conversion should take place.  However I do not see myself making my own refrigerator.  More so, a refrigerator one makes himself will far lack in efficiency compared to one from the store, so I fear efficiency loss will be greater.
I think it is best to find a balance between all things, and for the moment I would set up a system that can be changed in the future, but is functional anyway.

Sven

[ghurd]

Have you considered a propane or kerosene powered refrigerator?

They don't use much fuel.

G-