# Just picked up a 7.5 Kilowatt belt drive generator



## Dune (Sep 18, 2011)

Thinking about building a Tessla turbine to run it off parobolic trough collecters in the summer and a wood fired boiler in the winter. 

http://www.phoenixnavigation.com/ptbc/

Building the turbine is straight forward enough, but what kind of challanges are involved in building a boiler for a ten horsepower motor?

Moderators, I don't know which forum is best for this topic.

Should I forget the boiler and just use the trough collectors?


----------



## peakbagger (Sep 19, 2011)

The laws of thermodynaimcs still apply, even to equipment designed by Nicolas Tesla. Be aware that for $90 you are most likley are paying a lot of money for interesting infromation that really wont get you what you want. 

The Carnot Cycle is the theoretical best available efficiency to convert thermal energy to useful power. It is independent of equipment, its based on the laws of thermodynamics.

Using this formula you can determine the minimum energy you need to put in the device to get 10 HP out

Efficency of conversion of thermal to usefull work is 

equla to 1-(Absolute temperature of the heat sink/absolute temperature of the heat source) , add 460 to degrees F to get absolute temperature in degrees Rankine. The heat sink it most likely the air temperature plus 10 degrees F if its air cooled or the water temp plus 10 degrees F if its water cooled.

Convert your desired output HP to BTU/hr, divide by the carnot efficiency and the result is the minimum amount of energy you need to put into the turbine. At a minimum double it to compensate for real world inefficiency of the process and thats how much thermal input you need.

A small scale real world system would have a tough time exceeding 10 % thermal input to electric output. 

When you do the calculations on your own, you will find that its going to require a whole lot of evacuated tube collectors. The reason to go with a boiler is that you can use a higher input temperature. Of course anything over 15 PSI means that the boiler must be built to ASME boiler code whihc makes things real expensive and not many folks have M stamps.  

There are several small firms making Organic Rankine Cycle systems, these basically use a low boiling point working fluid in place of steam. Turboden/ Pratt and Whitney makes a 300 KW unit thats is about 19% efficient. Last thing I knew it was $300,000. GE just bouhgt a company in Florida that makes a 50 KW unit that is also about 18% efficient. Infinity turbines used to sell a small R&D system that may be of interest.

The reality is currently that no one has figured out a way of cost competitively making a small scale thermal electrical generator system. Dean Kamen was plugging his Sterling desing a few years back but I am not aware that it ever went into production. If and when it does, thats the best chance of a small system as it was desinged fromt he begining to be small.


----------



## Jags (Sep 19, 2011)

Dune, I don't have much for you, but I will be watching this thread.  I do know that if you keep a boiler pressure low enough that it doesn't require certification, 10HP = one big boiler.

I am not sure how it would fit in with your mix of home built power, but have you ever considered turning this genny with a lister engine.  I hear that they run quite well with bio-diesel or vegi power.


----------



## Dune (Sep 19, 2011)

I am aware that the laws of thermodynamics apply, but thanks.

I wasn't planning to use evacuated tube collectors. I want to build parabolic trough collecters.  

Parabolic troughThis type of collector is generally used in solar power plants. A trough-shaped parabolic reflector is used to concentrate sunlight on an insulated tube (Dewar tube) or heat pipe, placed at the focal point, containing coolant which transfers heat from the collectors to the boilers in the power station


Thanks for the suggestions of other heat engines. I have been wading through the options for years and even have a google group with a bunch of engineers researching the alternatives.
The Tessla turbine seems like the most likely candidate due to simplicity for the most part, although I did come up with a sterling cycle turbine design I would like to work on but I don't have time to experiment with it right now.

I there a reason you don't think the Tessla turbine is appropriate?

Are you aware of the installation of hundreds of 25 KW solar thermal sterling engine generaters in the South West? They cost $125K including the stand and parabolic dish.


----------



## Dune (Sep 19, 2011)

Jags said:
			
		

> Dune, I don't have much for you, but I will be watching this thread.  I do know that if you keep a boiler pressure low enough that it doesn't require certification, 10HP = one big boiler.
> 
> I am not sure how it would fit in with your mix of home built power, but have you ever considered turning this genny with a lister engine.  I hear that they run quite well with bio-diesel or vegi power.



I already have a 25 kw diesel set up for veggie. The demand for veggie is increasing every day. Solid fuel is the golden chalice looking a few years down the road.


----------



## peakbagger (Sep 19, 2011)

I havent spent alot of time with Tesla turbine technology as you appear to have, to comment on the relative merits of the tesla versus other turbine designs. I am aware of the SES techology for concentrating dish collectors, but to date I havent seen any true commercial installations. I realize they have a 1.5 MW prototype facility and a really good PR machine. 

Having been involved with equipment supplied by another Sterling Cycle manufacturer, STM, that went bust due to seal durability issues after they were commercial, I am very hesitant to consider Sterling engines as an option, but if SES pulls it off great. I did like the Sunpower wood fired generator but they never went commercial.

No matter what the collector design, the Suns incident radiation is 100 watts per square meter and unless you go with vacuum tube collectors, its hard to get high temperature and good collection efficiency. Ausra technology looked good but they walked away from their 100 MW project and the only installations they have were highly subsidized arguably prototype. Sure it can be done but there is a lot to be said for PV in the small scale. 

You may want to check out Eletratherm, they have a 50 KW output ORC unit that seems sorted out. GE recently bought a company in Florida that uses an eliot microturbine concept for ORC, I think they are 100 KW.


----------



## Dune (Sep 19, 2011)

I thought it was 1000 watts per meter2.


----------



## peakbagger (Sep 19, 2011)

You are right 1000 watts per meter standard value (not 100).


----------

