LPG for generator in semi-underground building

stephendv
stephendv Solar Expert Posts: 1,571 ✭✭
in Off Grid Solar & Battery Systems #1
Hi all,

Well generator season is creeping up on us, and I'm considering converting the Honda gen to use LPG to save on gasoline costs (converted it costs 6.8 USD/US Gallon here). The trouble is that I have a semi-underground power bunker for all the off-grid kit, so I'm worried that if there's a leak in the system there's no where for the gas to go. Are these gas conversiones generally safe enough to risk this? or are there other ways to make the system safer?

The bunker is about 1.5m underground and 80cm above ground.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #2
    Re: LPG for generator in semi-underground building

    Is your net cost of LPG really any cheaper in the EU than Petrol? I would be pretty wary of putting LP into an under ground system, unless I provided some sort of positive drain. I suppose it would depend on what else (who else?) is in the bunker. If y can provide some positive venting for vapor, and a positive drain for liquid that would be a different matter IMHO.

    Tony
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  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    #3
    Re: LPG for generator in semi-underground building

    Many sailors use compressed natural gas on sailboats as the vapors are lighter than air while propane is heavier than air. Similar situation to yours, they dont want vapors to build up in the bottom of the boat.

    I expect that most life safety codes would require positive ventilation of the space. Usually there is some sort of requirement that prior to startup of the engine that the space has to be ventilated for a set period of time to evacuate the entire volume of the space. It can be a simple as blower ducted down to the floor so it sweeps out any vapors with a outlet on the other end of the building. Even if the LPG is "safe", there is a still a potential for carbon monoxide.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #4
    Re: LPG for generator in semi-underground building
    icarus wrote: »
    Is your net cost of LPG really any cheaper in the EU than Petrol? I would be pretty wary of putting LP into an under ground system, unless I provided some sort of positive drain. I suppose it would depend on what else (who else?) is in the bunker. If y can provide some positive venting for vapor, and a positive drain for liquid that would be a different matter IMHO.

    I'm told about a 40% saving in fuel costs with LPG. Who else is in the bunker? All my most precious inverters,batteries and charge controllers! What do you mean by positive venting? I have a type of ventilation system in place at the moment for the generator exhaust, which is a large vent in the lower part of the door and a strong (I think about 300W) AC fan in the roof which vents outside. The roof fan is connected to the gen output, so when the gen goes on, so does the fan. There are 2 more 20cm diameter holes in the roof for venting battery gases. Not sure if this is enough for an LPG leak though, as I can imagine the gas pooling up on the floor and as soon as the gen starts I'll get to see a pretty fireball through my tears.

    I had a problem with flooding a while back, and since then have a small DC pump to get rid of any water pooling at the entrance. A gravity drain is not really practical because I'd have to dig a monster trench.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #5
    Re: LPG for generator in semi-underground building

    I'd say that you might want to do what we do in the Marine World with Generators in the hull. Put a 5 Minute delay in the start sequence that allows the bilge Blower to come on and evacuate any explosive fumes. There lot's of off the shelf controllers available to do it, the AGS may have it already built in. Like you , I have a blower connected to the Generator output, but that does not help with fumes already built up.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
    Re: LPG for generator in semi-underground building

    Venting vapor (like as been suggested like they do in boats) is pretty easy, and would cover a small leak. A large leak, big enough to pool liquid gas in the bottom of the bunker is the bigger issue. Imagine a scenario where for some reason the regulator or valve fails and allows unlimited fuel to flow at high rate from the tank. It could flow long enough, and with enough volume to put a ton of liquid in the vault.

    I suppose you could install a pump system, but you would have to e very careful about accidental ignition.

    It does come under the issue of, how much re you concerned about a leak.

    I have installed propane appliances in the lower parts of houses before, which is technically illegal, but my h istory with LP is that I have very little fear of a big enough leak to fear liquid build up. You could simply wire a LP detctor to alarm you if there is gas in the vault, and I suppose if you really wanted to protect, you could engineer a solenoid valve to kill the flow in the event of a gas build up.

    As for the economics of propane, my guess is that (especially in the case of EU) the big price difference is between what y pay for the fuel relative to the road tax. Gasoline is much cheaper to produce (as you get more gallons of gasoline out of a barrel of oil than propane) but it is typically road taxed at a high rate. Can you figure out a way to buy gasoline without road tax?

    In many places you can apply for a rebate for legitimate uses of fuel (gasoline, diesel etc) for off road use, which can save a considerable amount of money.

    Tony
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #7
    Re: LPG for generator in semi-underground building

    Another thought would be a LP gas/fume detector like they put in a RV or Boat. I don't know about a massive leak, seems like that would be a bad situation no matter what. They are less than $100 good insurance I guess.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #8
    Re: LPG for generator in semi-underground building

    Only problem with LPG detectors is they are often too sensitive. Any other fumes that may be considered normal can set it off. You may get a lot of false positives.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #9
    Re: LPG for generator in semi-underground building

    Thanks guys, quite a lot to consider. The CNG option seems the safest, but is not easy to get around here, will have to ask around to find a supplier. For LPG even with the venting I'd still be a bit nervous about a leak especially since the generator use will be quite sporadic so there would be a lot of time for gas to accumulate between generator runs. Guess I could do daily venting during winter just in case...

    Lots to think about :)

    Tony, we can get cheap agricultural diesel for heating and farming, but not gasoline. And even this diesel is not that cheap at 5 USD/Gallon.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #10
    Re: LPG for generator in semi-underground building

    You may be correct on the LP gas detector and it's sensitivity. Another thought would be a solenoid valve in the gas line wired into the generator control. I have seen them used before. I don't know what he's trying to do.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #11
    Re: LPG for generator in semi-underground building

    LPG leak detectors have a whole host of issues--there are many different types.. Many that will read accurately until the oxygen is displaced--then they will read low (they are really combustion sensors, not propane concentrations). And many can be "poisoned" by stuff in the air (silicon spray lube, etc.)...

    I don't know what the answer should be--Perhaps just an at ground level building for the genset--Everything else could be in the "bunker".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • papa
    papa Solar Expert Posts: 51 ✭✭
    #12
    Re: LPG for generator in semi-underground building
    Blackcherry04 wrote: »
    Another thought would be a solenoid valve in the gas line wired into the generator control. I have seen them used before. I don't know what he's trying to do.
    Most engine related LPG installs (especially vehicles) have a either a 12v solenoid lockoff valve or engine vacuum actuated lockoff. This is installed on the high pressure side (input side) of the regulator/heat exchanger. Impco's VFF-30 is probably the most common, but there are many others. Reality is, all you need to do is leave the bottle valve OFF when not in use. In use, the lockoff is relied on when the engine isn't running and the bottle valve is open. I've not experienced or heard of any failures with Impco's VFF-30.
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  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    #13
    Re: LPG for generator in semi-underground building

    If you could take the generator out of that building and put it in it's own little above ground shed, your problem would be solved.
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #14
    Re: LPG for generator in semi-underground building

    Or better yet, put it in its own below-ground hole with enough room for service access.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #15
    Re: LPG for generator in semi-underground building

    Thanks for the suggestions, I've been mulling it over and if I have spend any significant money on the solution I'd rather put it into more solar. The bunker is an isolated building in the corner of a field so it's not possible to locate anything outside it without building another structure. It's also 300m away from the house so an alarm might not be heard. Will still try to find CNG locally and if that's not feasible then it'll be more PV instead. Was generating minimums of 5% of rated power in the rain yesterday, with double the solar that would be enough for our base loads.
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