We have finally completed our water well-drilling adventure. Everything that could went wrong – amounting to a 2 month delay – but the bottom line is that we have a 4 inch-bore well that we estimate is giving us 1000 gallons of water per day based on the pumping that we have done so far. We have yet to see whether the well dries up in late summer heat. See our second Factor e Live video (forthcoming by tomorrow) for more documentation on the well.
This means that we are at a great transition at Factor e. The next step is full time work on LifeTrac – and we aim to have it driving in 2 weeks and fully operational with loader, rototiller, and other implements, in 1 month. Our primary attention will go to this – as it is the backbone of the infrastructure for CEB construction – to start on July 15. That’s when the great promise of quality, dirt-cheap building will be tested in practice – as the first example of high-caliber, appropriate technology equipment developed at Factor e Farm. We will then be able to tell if our CEB machine, The Liberator, is worthy of its name.
The next point to mention is the solar turbine– we’re planning ground-breaking on August 15. Our design specification is an affordable, kilowatt-scale, scalable, solar concentrator electric system based on a linear (scalable) reflector Fresnel design of 16-fold solar concentration:
(source). Based on proven techniques, we are predicting exciting results. The bottom line prediction – using overall 8% efficiency (nothing spectacular) from solar input to electric power – is 3 kW of electricity from a 4×10 foot array of mirrors. If we succeed at this, then we will have a breakthrough in solar power generation. What I mean is that none of the ideas utilized are in any way original – but we are putting them together from the systems design perspective – and resulting costs are 2-10 times lower than any system that we are aware of, at any scale of operation. Our calculations show a materials cost of $2000 for the reflectors and collector – plus another $500-$7000 for the turbine, generator, and balance of system. We are talking of costs for solar electricity at 80 cents – $1.30 per installed watt. This is cheaper than coal power plants. Add the labor costs on top of that if you are doing this for outside markets – and we may be talking of replicable power systems that bring about the promise of solar economies.
The trouble is, we’ve heard predictions of cheap solar for many years – but solar cells are still at $5/watt and $10+ for installed costs – and no better alternatives are emerging, except at large scales. How are we any different? We’ll see – but we do have open source methods working for us here. Please continue reading below about our quest for the world’s first replicable, open source solar turbine package. Here we discuss heat engine choices – the universal missing link in such projects.
The solar concentrator part does not appear to pose any serious design or deployment challenges. The working engine choice is our present challenge. We have considered the Tesla turbine, the standard bladed turbine, a piston steam engine, and off-shelf turbines/rotors taken from other applications. We need your help to evaluate these choices or suggest others. Be part of helping to make an open source solar turbine a reality. Here is our evaluation of different options:
Tesla turbine – See link. Proven results show a performance about half as good as that of standard bladed turbines (reference 1 below). Warren Rice shows in a peer-reviewed paper that the best results (1.5 hp for a 5 lb/min flow rate of air) appear to be at least 4 times worse than low-performance piston steam engines (1 hp for 0.6 lb/min steam) such as this off-shelf model. Note that Tesla turbine efficiencies are reported around 20% – but one must be careful about the definition of efficiency used. Advantages: low cost and simplicity of fabrication, scalability – <$1k for a 5 kW turbine. Disadvantages: poor efficiency. Summary: If proven efficiencies are at least 4x worse than standard piston steam engines, then the Tesla turbine should be eliminated as a feasible engine choice.
Bladed turbine – See link. Proven parameters indicate performance (mass flow of 3 lb/min for 5 hp power output for the T-500 turbine) similar to low-performance piston steam engines. Advantages: good performance. Disadvantages: high RPM requires gear reduction. Difficult to fabricate and balance the turbine. No small-scale off-shelf versions are available. Summary: if piston steam engines show similar performance, then it is more effective to utilize a piston engine due to its higher simplicity and lower cost.
Steam engine – the standard piston steam engine appears to be a winner based on performance. Off-shelf, low-performance models produce 3.5 kW of electric power from a steam flow rate of 5 lb/min – which is the theoretical solar steam output from our 10×40 foot array. Advantages: Adequate performance; off-shelf availability. Disadvantages: off-shelf model of 3 kW electric capacity production is $4k. Summary: The piston steam engine could be a proven test bed for OSE’s solar turbine, and other options should be evaluated. Simplification, optimization, and in-house fabrication of said engine will result in <$1k steam engines of interest.
Other turbines – turbine pumps, turbos charger from diesel cars, and tractor centrifugal water pumps (for engine cooling) are good off-shelf candidates for a steam turbine system.
Turbine pumps – these are centrifugal pumps with turbine-shaped propellers. When operating in reverse, they function like a turbine. Advantage: off-shelf, possible low cost. Disadvantage: must be tested for steam operation; efficiency is questionable. Summary: should be evaluated.
Turbo charger – the MIT Solar Turbine is using a turbo charger from a car as the winning engine choice in their 1000 Watt solar thermal electric system (not steam-based). Advantages: a turbo from a car has the turbine shape that we are trying to build – and it is available off-shelf, and on-the-cheap from salvage. Readily testable. Disadvantages: Turbo pump may have to be modified for steam compatibility; are there turbo pumps that can produce a suitable power range? Summary: Should be investigated immediately for feasibility.
Tractor water pump – another option worth exploring. Advantage – readily available from salvage. Should be compatible with steam if it’s designed for near-boiling water temperatures. Disadvantage – what is the efficiency?
Please comment on the above and help us narrow down our choices.
(1) “The turbine efficiency of the test model was over 20%, which is fairly good when one considers that it was not in a high state of development. Turbine efficiency for conventional turbines of this size run between 40-50%.” – from Elroy William Beans, Ph.D. thesis, Pennsylvania State University, Department of Mechanical Engineering, June 1961.