Kickstarter project for $100 - 1 kW - stirling engine | Hacker News Reader

Kickstarter project for $100 - 1 kW - stirling engine

kickstarter.com

68 pointsmeow61 comments

Yes gas is near $4 - what does that have to do with utility prices, since there aren't any gasoline powered plants in the USA since the 70s ?

I would have to assume the way the utility company produces power is far more efficient than a town with thousands of mini-engines. Only stuff like solar cells work better in distribution.

Not sure how this would work either - what fuel are you going to use to power it for 24 hours without maintaining it? Will it drive an alternator to power an inverter? How stable would the feed be?

Unlike other engines, a Stirling engine (like other external combustion engines) is more suited for using alternative power sources like solar energy. You can heat the end using a Fresnel lens or a solar concentrator (http://en.wikipedia.org/wiki/Solar_power_in_Spain). But more importantly, with a $100 price tag, it will be an affordable engine to experiment for hobbyists.

Hi, thanks for the question - The fuel source intended for the Volo Engine is some type of biomass - for the biomass the plan is to use a gassifier to get the heat out of the biomass. Solar is a good possibility, but not enough solar in the northern part of the US to make enough heat.

I would put it on heating stove.

Compared to your local big-city nuclear plant, no this thing doesn't compete.

But if you are off-grid or have unreliable power it is better than a Honda gasoline generator, especially because they can pretty much burn anything - from wood chips to pig manure.

Although you do need a big cold sink for it to work well - a river/stream is ideal.

A huge amount of the generated electricity is lost on resistance of the power lines on the way to your house. So having it in your basement and going 30 feet to a lamp/outlet would be more efficient.

According to wikipedia, the average loss on the power lines is 7%. Source:

https://en.wikipedia.org/wiki/Electric_power_transmission#Lo...

That's not what I'd call "huge".

The goal of the project is to spark infrastructure independent energy solutions - the stirling engine is flexible enough to run off of any type of heat (gas, wood, solar, etc). Stirlings can be very efficient, but, on top of that you're eliminating the transmission loss. You'd need both, some type of alternator, and some type of heat capacitor (fire box) to get the steady feed your talking about, but the first step is to complete the engine development.

Looks like a cool project.

One note to entrepreneurs using Kickstarter, or creating any slide presentation for potential investors: Take the time to spell check your slides.

Tim Sefton (creator of this project), if you happen to be reading this, here are some notes that may help you make your presentation more professional...

"One thing.. The Sterling engine is about 10% more efficent then the gasoline engine, but strugles with changes in suden acceleration - like what is needed for cars."

If you are the author of the presentation, you may want to correct the four errors: efficient, than, struggles, and sudden. Also misspelled is "temperature" (on the previous slide),

Not a big deal to me, but some potential investors will absolutely be turned off by that.

Not to mention it's "Stirling", and not "Sterling".

This. Maybe it's just because I am a web designer and lover of the English language, but when a company's blog URL looks like this: http://volodesigns-sterlingproject.blogspot.com/

a) free site b) a dash? c) mispelled stirling?

I get just a tad anxious.

Appreciate the feedback. I'm going to have to give that typist a tough tongue lashing !

One of the first things you learn when you run a company is that you own your mistakes in public. In other words, it doesn't matter who f'd up, you own it and you can't pass the buck.

Regardless of who did it, you should have proofread it, or you should have had someone else proofread it.

And even after that any mistakes would still be yours to own in public.

If it was in jest and you were the typist then apologies for responding in a serious way.

Yes, I'm the typist - just trying to lighten the mood a bit.

"Well the average US household uses about 8,900KWH of electricity per year - that comes down to 24 KWH per day and so our goal is to have a minimum engine output of 1KW so that it can produce close to the average home use of electrical power per day (24 hours of 1 KW output give you 24KWH)."

This math isn't taking into account that the power use isn't consistent, batteries will be needed to handle the variances in consumption. You'll never get 100% efficiency from power storage so the amount needed per day is much higher.

I also didn't see anything about the temperature required to make this run. Does this go on a roof or do they expect me to keep this in the fireplace the whole time.

with this kind of device you just need smart plugs so that your dishwasher/dryer/washinmachine run at night.

That wouldn't work either since this power isn't clean and steady. Same goes for SV and wind. All these solutions need batteries to even the flow of power.

You'll never get 100% efficiency from power storage so the amount needed per day is much higher.

Lead acid batteries are 85-95% efficient for getting power in and back out. It doesn't change your sizing much.

That said, until a significant percentage of the utility's customers are using these devices, it makes no sense to use batteries. Just sell surpluses to the grid and buy back to handle peaks.

If you have no grid, then about $1000 of batteries will cover you, and need replacing every 5-10 years. Either way, your inverter is probably around $2000.

I'd have already clicked to buy in, except there is a missing chunk of the efficiency. Assuming I don't have a small lava flow next to a stream in my basement, what is the total projected efficiency of these units from fuel to electrical energy? They don't seem to be addressing burner efficiency. How will it compare to a small gasoline powered generator? (You can't buy a diesel genset this small.)

If you have no grid, then about $1000 of batteries will cover you, and need replacing every 5-10 years.

This is wishful thinking, both on lifespan and cost of a household battery bank sufficient to run average household appliances like air conditioning and electric water heater and such. Even deep cycle batteries in this sort of working environment will need replacing every 3-5 years (and past 3 years, you'll probably be working with maybe half the capacity of what you started with). The workload of a household running off of batteries during periods when power usage far outstrips power generation is really hard on batteries. There are very expensive batteries that are rated for 5 years or more of use, but they cost two or three times what regular deep cycle lead acid batteries cost, making the total cost much higher. You'll also need more than $1000 worth of batteries for an average American household that uses air conditioning and electric heating devices.

I live in a motorhome with a $300 battery bank (a motorhome has far fewer energy users than a standard home, and I don't run AC, microwave, or electric heaters off of the batteries; I have to crank the generator to use those), and solar on the roof. I'm very familiar with the limitations of batteries, and lead acid battery technology is extremely unforgiving of discharging beyond 50% (even beyond 75% leads to degradation, but most people in RVs accept that because the weight of carrying more batteries to be able to run at 75+% charge at all times is more costly than replacing batteries more frequently).

But, I agree with you that selling back to the grid is the way to deal with this problem in a home on the grid. It's more cost-effective and more environmentally responsible.

Your right, there would need to be a storage device in the system - this is just the first piece that coverts the heat to work - The temperature range we are designing to is about 420 degrees F hot to 100 degrees F cold. Think of it as a small outdoor appliance. It would need some type of fire box for heat generation - we are outlining a small gassifier for bio mass but that will come latter.

It's possible to buy something like this.

A WhisperGen which generates electricity (1kW) and makes hot water using a four-piston Stirling Engine: http://www.ehe.eu/ehe/dm/whispergen.asp?nombre=2401

They do both because they get cooling by transfering the heat to the domestic hot water supply getting hot water and electricity at the same time. They are powered by natural gas. The gas company E.ON in the UK did a study on them (they also provide them I believe): http://www.microchap.info/Carbon%20Trust%20field%20trial.pdf

To quote that report: "For typical family homes, carbon savings of up to 20% are realistically attainable with economic payback of around 3 years."

WhisperGen is also only available in Europe and costs two orders of magnitude more than this device would last time I checked.

But this device is vaporware, and its price is a pipe dream.

Lets hope not - we did complete a working prototype, proving out the mechanics, linkages, and feasibility. We are pretty close to budget on the full sized model - bearings may take us slightly over the $100 mark.

What would be useful is an apples-to-apples comparison. The WhisperGen is about £3,000 in the UK but that's a complete installable unit in the home that burns natural gas and hooks up to the electricity and water supply.

It sounds like your $100 is for just the motion part of the engine (perhaps I'm wrong about that). Do you have a sense for what it would cost me to go from having nothing to a working system in my home generating electricity?

That's the device, cool. Then there's the infrastructure as others have commented.

Another compelling issue is, will it work uninterrupted for 10 years? Like other household appliances e.g. water heater, furnace, softener, dryer, roof.

Building it cheap may preclude building it to last. Thats where Engineering comes into play.

Variant idea: a small portable version for camping. Stick one end in a fire, USB plug for power connector at the other. 2.5W shouldn't be hard to get under conditions where "unreliable" is normal.

It will be kind of heavy though. For simple charging of appliances, other projects are very interesting:

http://www.kickstarter.com/projects/ryochijiiwa/bootstrapsol...

http://www.kickstarter.com/projects/davefoster/lilypad-using...

I have a solar charger/battery. Surprising how often you can't get enough sun to matter, as you need many hours of continuous direct bright light to collect anywhere close to enough.

I'm imagining a sort of pencil-sized Sterling; stick one end in the fire and the other in a cup of cold water. Not reliant on ambient/weather conditions for power.

aah, that's very interesting.. though I'm skeptical a pencil sized one will be able to output that much of power :). The problem with Stirling engines is that power output is kind of low when compared with a similar sized IC engine.

I've got a miniature Stirling on my shelf. It's a two cylinder setup that runs off of two small alcohol lamps (about the equivalent of two candles), and is air cooled. It weighs about a pound (but could probably be lighter). I don't know exactly how much power it puts out, but it's not much - you can stop the flywheel with light finger pressure.

More heat would produce more power, but I think pencil sized may be a bit optimistic. I like the idea though.

Although the goals are clearly different, Dean Kamen (inventor of Segway) has been working on optimizing Stirling engines for years with seemingly great results:

http://www.nextenergynews.com/news1/next-energy-news4.24.08d...

One particular design that I'm very interested in is a quasiturbine based stirling engine. It seem to have a lot better power/volume ratio than other stirling designs. Unfortunately, I haven't seen even a single running model yet :(

What sort of performance could you expect by just sticking this in the wall of your house? In the winter, you've got cold air outside and you're already heating the inside. In summer, you've got hot air outside and you're cooling the inside. Does it matter which side is hot/cold?

And waste the energy you used (via a furnace or air conditioner) to create that temperature gradient in the first place?

I like that idea - can anyone commment further? Up here in the Yukon it's regularly -30C and below for long stretches and we all have our wood stoves burning 24x7 for 4+ months.... It would not be hard to have one end touching the wood stove (200-400C) and the other end outside (-30C - -40C). Will this work?

It depends on what your power requirement is. For a 200C difference, you should be able to get around 500W to 600W with a properly built stirling engine.

Sounds nice for all the people running off-grid up here who get so little precious sunshine in the winter. Can you provide more information on where I might be able to buy such a Sterling engine? Are there any companies actively making them?

Unfortunately, there are not many companies building these engines commercially (at least at these power outputs). Most of the engines I have seen are built by hobbyists (either too tiny or crude :( ). That's changing in recent years with increased focus on solar power.

Thats what we saw and why we started the project - just not enough solutions for real world requirements. The engine itself is somewhat simple, its the thermodynamics that are tricky - There are only a few moving parts, no spark plugs, no oil, no valves and works off of any kind of heat.

An interesting side note: You can build one of these that will run off a candle and fit in the palm of your hand. I've got one in my office. It's a pretty neat technology.

Can you give us more details please - did you build it? buy it?

I suppose he is referring to this - http://www.thinkgeek.com/gadgets/9e84/

It was a kit like one of these: http://www.ministeam.com/acatalog/Bohm_Stirling_Engines_and_...

I also tried to build one from scratch once, but only got a few parts in before I sold my lathe and mill. The kit was much easier...

Also look up flame eater or vacuum engines. Pretty neat.

>The second difference is the Stirling engine is more efficient then the gasoline driven engine.

Gotta proofread this stuff.

Anyway, I was thinking recently about how a stirling engine could be powered by solar energy, and discovered that this is actually done. From wikipedia:

>Placed at the focus of a parabolic mirror, a Stirling engine can convert solar energy to electricity with an efficiency better than non-concentrated photovoltaic cells, and comparable to Concentrated Photo Voltaics.

That's cool, and I'm startled that it isn't mentioned at all on this kickstarter page, especially considering the first paragraph of the pitch.

Problem is, CPV only works with clear sun. i.e. it's best for deserts. My hunch is this is targeted at off-grid homesteaders, who tend to live where there's vegetation (and thus clouds).

Seems like a huge long shot. Even if you wanted to get one now, it's $250.

I guess I've never seen this yet, but what happens when they can't' deliver you the working product? Do you get your money back?

Also, there has to be some sort of mechanism for heat, and then something to actually generate it. All this is going to be is the engine to turn it I believe...

Sterlings are normally run on solar heat.

I don't know why you're being downvoted. One of the primary uses of Stirling engines, especially for off-grid homesteaders (at whom I'm sure this is aimed) is concentrated solar. All you need are a giant Fresnel lens (~$100), some black metal to act as a collector, and heat transfer compound to attach that to your Stirling engine and you're off to the races.

Yep, also somewhat common on boats, especially sailboats, for the same reasons.

Not a downvoter, but maybe it was the "normally". The cool part of a Stirling is that it is indifferent to fuel.

That's true, but in the real world it's fairly uncommon to see actual burners in use, outside of machine shop projects and the like.

Correct - this is just the piece that turns heat into work. The rest electrical system and fire box / solar concentrator comes latter.

There is no money back guarantee, it is a gamble, although we feel its a pretty good gamble.

Can you point me in a direction where I can buy one now for $250? It's something I'd love to experiment with in my off-grid cabin

I don't know of anyone providing a working engine for $250 at this time - you can find desktop models that run off of coffee cups but don't do real work. The industrial models cost in the tens of thousands. Give the Volo a shot - we hope to have it completed by spring.

Hmm. I see a few practical issues with this. I need to keep a fire burning the whole time? Not practical for many (most) homes and also will result in a lot of wasted heat.

We've given some thought to this - one idea we are kicking around is embedding a heat capacitor in the engine, kind of like a battery for heat so that we can even out the heat input to the engine - The heat capacitor coule be a type of insulated molten salt bath.

Great, if I had enough space I would build one.

Robotics.

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