Gas Storage in PVC Pipe

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Basics

  • As a simple cheap way to store gasses, PVC pipe can be used
  • This page explores that and possible applications of this gas storage method

Research

6" Pipe for Methane

Have you considered PVC pipe for gas storage? 6" costs $45 for a 20' section, caps are $15 (verify). Pipe + 2 caps is $75.

Each 20' section holds about 4 cubic feet of gas. So $750 gets us 40 cubic feet, or about 300 gallons equivalent. So comparable to new propane gas tanks.

At 10 atmospheres (note this PVC is rated only for 100 PSI, not 140), that is equivalent to 3000 gallons of gas at one atmosphere. About 600 moles of gas, if primarily methane then it is about 10 kg of methane, or about 3.5 gallons of gasoline equivalent. [1]

That is 14 kWhrs of electricity from a Honda EU1000 generator.

Comparison to 1" Pipe for Hydrogen

Medium pressure production of hydrogen occurs at 33ATM, without need for pumping.

  • If 6" pipe is $75 for 4 cubic feet - what is the price comparison for 1" pipe?
  • It is .785 cu in per inch of pipe, or 188 cu in per stick. of 1728 cu in per cu ft - 1/10 cu ft per pipe. 40 cubic feet would be 400 pipes.
  • What is 40 cubic feet at 33 atm in moles? 40*33*7.5=9900 gallons of equivalent STP volume. This is 1650 moles of hydrogen - or 1.7 kg.
  • At $5 per stick and $0.59 per cap, this is $2.5k for this storage. Couplings are 28 cents, so cost may be slightly lower.
  • 1.7 kg hydrogen - specific energy density of gasoline 1/3 that of hydrogen - that is about 5 kg of gasoline, at 6.3 lb/gal for gasoline -or 1.7 gallons of gasoline. That is more than enough for storage over night.
  • Note: Honda EU1000 burns 1 quart per hour to generate 1kWhr. Using such an efficient generator for electricity, we get about 6kWhr from the stored hydrogen.
  • This makes for approximately $400/kWhr storage cost
  • or 1.5x the cost achieved for high pressure storage (875 bar) [2]. Not bad.

This implies that if we could split water, we could store it effectively from a very small area of solar collection - if PV is 10% efficient, and biomass production is .1%, there is about a 100x efficiency increase in using PV for fuel storage compared to biomass.

Comparison to Batteries

The methane or hydrogen storage route are both comparable in cost for pressurized storage. Hydrogen is more energy efficient in terms of solar capture area compared to biomass-derived methane, by about 100x. Advantage of hydrogen is not needing a pressure pump. If the pressure vessel cost is $2.5k, that is a worthwhile investment for going off grid.

Note that PVC pipe lifetime is 100+ years. This qualifies for OSE's metric of lifetime design. This is also about 20 times cheaper than lead acid batteries, based on a 10 yr life of deep cycle batteries.

Battery Cost

  • Deep cycle lead acid batteries are $200-300/kWhr [3]
  • Let's see on ebay - $125 for about a 1kWhr Trojan (close to 200A at 6V). They look like deep cycle but these are more like 2 year at 80% DoD, if that.
  • Trojan T-1275 150AH [4] - $190 on Ebay [5]. 1.3kWhr at 80% DoD at 10 hour rate. 150A rating is at the 20 hour rate. Conclusion: if this battery really does 2000 discharges at this rate - then this is cheaper than Walmart motorcycle batteries. 10 motorcycle batteries at Walmart are $250. But, these graphs [6] indicate that the lifetime is still about 2 years for the 'deep discharge' batteries when then are taked down to 80% DoD. The motorcycle batteries still appear to be a contender.
  • This appears to be a real deep cycle - [7]. 4 kW at 80% DoD for $1k. Yes, about $250/kWhr, for 17 year lifetime batteries. But at 80% DoD, even the industrial batteries have only a 5 year lifetime. The 17 year is for 30% DoD.
  • This definitely makes a case for Nickel Iron batteries.
  • Nickel iron - 30 years at 80% DoD. $2000 for 2000W - 24V@100Ah, 30 year life. Cost is $1000/kW. this is 4x as much as the lead acid battery. If lifetime is considered, though, the price is lower for the NiFe at 30 year lifetime. At 50 year lifetime, the NiFe is over 2x as inexpensive.

Comparison to a 1000 Gallon Propane Tank

  • Tank is $2500 - if stored at 10 atomospheres - that is 10000 gallons of STP hydrogen. About 1.7 gallons of fuel equivalent.
  • We can get 1" PVC pipe (as above) for $2500 - 9900 gallons of STP hydrogen.
  • Thus, same price - but less work to install a propane tank, arguably, than 400 PVC pipes.
  • However, PVC pipe will probably last much longer than a propane tank, if buried from UV light.

Conclusion

At $500/kWe cost of pvc pipe storage, compared to $250/kWe for lead battery storage - note that the 80% DoD on batteries means a five-year lifetime. Thus for the Hundred Year lifetime analysis the PVC pipe route of storing equivalent electricity- is 10x cheaper than lead acid batteries.

Basic Design

IO

  • 1x 1-Way Fill Valve (Standard Quick Disconnect Pnuematic Possibly?)
  • 1x 1-Way Withdrawl Valve (Standard Quick Dissconnect Pnuematic Valve with a welding gas regulator possibly)
  •  ?x Sensor Ports (Temperature Probe, Pressure Sensor, etc)
  • 1x Emergency Pressure Release Valve

Pipe

  • 0.25, 0.5, and 1 meter sections of PVC Pipe depending on need?

End Cap

  • Either PVC and Sealant, or a Screw Endcap (Which one, this needs to be determined)

BOM

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