Segway Inventor Dean Kamen Thinks New Stirling Engine Will Get You Off the Grid

An engine that could run off a wood-burning fire and was built to last a couple decades would strike me as really neat - this not so much. I suppose other places have more issues with the power grid reliability, but it's presumably more efficient to maintain the current infrastructure than to get one of these into every house.

Natural gas is also going to get much more expensive if they ever push fracking regulations through - the current pollution from gas leaks is actually worse than burning an equivalent amount of petroleum.

However in quite a few places the practicality of prepaid metal gas cylinders beats installing electric utility lines & meters, ensuring efficient transformers, preventing pilfering/meter tampering, etc.

Mind: gas delivery networks likely would crumble (hopefully not literally) under the increased demand.

Depending on system costs, this could be viable as a back-up power generation option (blackouts, etc.), where electrical service might fail but the gas supply would still work.

Capturing and making use of waste heat could indeed be useful. I see the possibility of full grid independence as very slim, and not particularly compelling (with distributed small, renewable, and intermittent generation, the grid is a useful way to move surpluses and deficits around). Though being somewhat immune to major grid disruptions is a possibility.

I'd also keep an eye on natural gas trends. Supplies aren't endless, though the US EIA's estimates suggest a reference resource case of increasing extraction through 2040 at least, the less optimistic low resource case suggesting a peak by 2030. With fracked oil extraction very likely to peak before 2020, a transfer of fuel and energy uses onto natural gas will change market dynamics considerably. I've got my doubts as to how long gas will remain cheap. And suspect that its increased use in transport (EIA sees a large role in trucking) other uses may be limited.

A nice thing with cogeneration is that it works best when photovoltaic panels work the least. My case isn't typical, I live on a boat in Europe. She has panels which could push 5-6kWh/day on average in summer (they don't because our batteries are full long before that), but only 1kWh/day in december. We need 2-3kWh/day to be comfortable. So, we need more than what PV panels provides exactly when we also need to heat the boat, so a cost-effective CHP solution would be great.

Also, I'd like this to run on wood pellets, or diesel fuel: replacing the electrical grid with the natural gaz one is a bad idea, especielly considering that the expected yield of non-conventional extraction methods is continuously and rapidly adjusted down.

http://gigaom.com/2013/11/18/apple-solar-farm-fuel-cell-farm...

In terms of volume, 1 ft^3 is about 1025 btu, a therm is 10,000 btu, so you're looking at 97.5, let's call it 100 ft^3 of natural gas consumption per day.

As for running a Stirling engine on solar energy, or another heat source, yes, you could do that. Again, you need 33 kW of input power, which means a 33m^3 collecter surface -- that's 5.8m on a side, or 19 feet.

Because the Stirling's hot end is a point, you'd need tracking systems or a working fluid to deliver heat to it from your mirrors.

Incidentally, you can answer a lot of these questions using GNU units, written by Adrian Mariano. The great thing about it is conversion between different units and relationships, e.g., energy per hour per unit area. I find it invaluable in looking at energy, renewable, and related issues.

The waste heat will be roughly 50% of the energy involved. The difference between the generators won't be that big. So each unit of fuel provides more energy to the end user (which is what I am calling efficiency, the energy utilized for something vs the energy consumed making it available).

A small local generator will certainly be behind what a big commercial generator will do, but if the waste heat is also being harnessed ("Combined Heat and Power," or CHP), combined efficiencies of 60%-80% are possible. Commercial electrical generation is typically around 40% efficient, so CHP really can offer very big benefits.

Of course, there's nothing fundamentally efficient about a single family living in a huge mansion with a 10KW energy demand and a big heated swimming pool.

I would have guessed these things would be most attractive to hotels, universities, airports, truck stops, apartments and condos, and other institutional-scale places that have a significant round-the-clock demand for electricity and hot water.

I wonder what it says about the device and the market that they're planning to sell to well-heeled homeowners first.

A Stirling engine in particular needs an explicit heat sink to cool some parts of the mechanism; shuttling a working fluid (and its heat) back and forth between a hot end and a cold end is how it works. In this case, the cold end is the swimming pool.

A sterling engine isn't the only type of generation that works for co-gen. Most of these micro generation proposals involve some form of waste heat recovery in the form of warm water.

The efficiency of any heat engine depends on the gradient between the input and output temperature. So if you have a constant supply of cold water the Stirling engine can operate very efficiently, and the cold water becomes hot water which you can use for other things.

Of course, like I said, this is true of any heat engine. You can do the same thing by heating a boiler and using the steam to drive a turbine, which also generates waste heat for other things.

I've seen German stirling engines that use a fresnel lens focusing sunlight to supply the heat - and the most expensive part is the sun-tracking software and equipment.