Odd solar power?

[Polish_Silver]

CNG compressor

There isn't a hope in hell that anyone can fill a vehicle CNG tank in a few minutes from a household connection downstream of the gas meter.

I'll try to find out more about his compressor. Couldn't the compressor fill up a resorvoir overnight, which could then be put into the car quickly?

[thriftyandboringinohio]

Re: CNG compressor

I'll try to find out more about his compressor. Couldn't the compressor fill up a resorvoir overnight, which could then be put into the car quickly?

The basic concept you mention is at the heart of a fast fill CNG compressor. No practical, affordable compressor can deliver the required flow rate at pressures above 4,000 psi, so the fast fill surge of fuel always comes from storage tanks, with those tanks filled slowly over time by a compressor. By the time you work out the details, you end up with system costing over $100,000 with some pretty serious safety issues for fire and explosion (the class 1/division 1 explosion proof electrical components and the ASME pressure vessels certified to 5,000 psi are big cost drivers).

When you work out the details, you'll find that you can't afford a single tank big enough to completely fill your car to 3600 psi, and you'll find you prefer instead to have 3 or 4 tanks that switch in and out bringing a new fresh high pressure tank on-line as the last one dwindles down in pressure. That's the "cascade tanks" I mentioned.

The problem GRG55 mentioned is the pressure ratio of a compressor. Half pressure into such a pump gives you half pressure out, and the gas lines in your house operate at "inches of water" pressure levels, barely any pressure at all. The thermal issues he mentions are also pretty big.

Here's a great paper that gives further insight. It was written from the viewpoint of the compressor manufacturer,
http://www.scribd.com/doc/38601741/CNG-Compressors

None of this is new technology, it's all garden variety industrial process engineering and off the shelf equipment. Unfortunately, it's all at industrial scales and industrial quality which puts you at industrial prices, out of the reach of most home owners. When GRG55 puts together a petroleum processing facility, he doesn't blink at $300,000 for a little gas compression system if he needs one at his site.