Costs: LPG vs Electricity.

Discussion in 'Motorhome Chat' started by scotjimland, May 28, 2009.

  1. scotjimland

    scotjimland Funster Life Member

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    Being on metered electric I wanted to calculate if it was cheaper to run appliances on LPG rather than electric, fridge, water heater, etc.

    I used this info for the calculation:
    1 Gallon of LPG = 27 kWh (Kilowatt Hours) of electricity

    LPG costs ~ 50p lt.
    1 lt equal to 6 kw
    so 1kw costs 8.3p

    Electric costs 16p kw

    So LPG is ~ half the cost of electricity (assuming appliances are equally efficient on either fuel.)

    Have I calculated correctly.. ?
    if so then LPG wins hands down until it reaches £1 per lt.
     
  2. Snowbird

    Snowbird Funster Life Member

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    Hi,dont know if this is any help with your calculations but when overwintering in Spain I found it much cheaper to run the fridge freezer on gas.I also put a switch on my charger so that I can switch it off when not neaded to charge batteries,I never had to switch it on yet,with the solars.If your RV is a UK conversion I was told the converter uses quite a lot of power,but I dont know cos I dont have a converter becouse mine was imported new with no 110 volts in it.I do know that the US fridge freezer uses a lot of electric and seems to be more efficient on gas.Hope this helps,Dave.
     
  3. scotjimland

    scotjimland Funster Life Member

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    Hi Dave

    Indeed it does, the 230/110v tranny uses power even when not in use , I did a post about this some time ago ..

    http://www.motorhomefun.co.uk/american-rv/11300-230-110-transformer-power-losses-costs.html

    cheers

    Jim
     
    Last edited: May 28, 2009
  4. Braunston

    Braunston Read Only Funster

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    Hi, Jim

    I think your end result is true that LPG is cheaper to use than Electricity at the rates you are paying, but i think you need to add a few items into your equation

    Delete:- LPG i would suggest on the fridge is at best 70% efficient, so on your calculations the kW rate goes from 8.3p to nearer 11.8p xxxxxxxxxxxx

    You also need to factor in transport costs for the LPG i.e. road fuel costs to and from the LPG filling station.

    hope that helps

    Edit
    Hi, Sorry messed that up forget the 70% etc as that has no bearing on your calculation as i would think you were correct that the efficiencies are very similar, the only part of my thread that bears any point is the transport costs




     
    Last edited: May 28, 2009
  5. Geo

    Geo Trader - Funster

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    Your calcs as ever seem correct
    You have won me over Jim
    Your next mission should you choose to except it is
    where can I buy gas mantles for the lights, and a LPG 26" tft Telly:Laughing::thumb:
    Geo
     
  6. scotjimland

    scotjimland Funster Life Member

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    Hi

    Thanks.. your probably correct about the efficiency, but I couldn't find any figures on that .. still quite a saving even at 70%
    but on electric I have the losses of the 230/110 tranny to consider .. which probably puts it about even again..

    re transportation, I have 2 x 19kg bottles and fill up just down the road using the toad.. so no significant cost there :BigGrin:

    Jim
     
    Last edited: May 28, 2009
  7. scotjimland

    scotjimland Funster Life Member

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    Funny you should mention gas mantles.. :Wink:
    was just talking about them other day.. had them in an old van, lovely and cosy ..

    TV.. and water pump are more of a challenge :Laughing::Laughing:
     
  8. olley

    olley Funster

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    Hi none of that will be a problem if they ever get an LPG fuel cell sorted out at a realistic price just for motorhomers.

    Olley
     
  9. Braunston

    Braunston Read Only Funster

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    Hi,

    I don't know what type of bulbs you are using for lighting, but if you want to reduce your fuel?? consumption its really worth looking at the low energy bulbs and now the LED alternatives,

    If we could get the unit costs down on the LED bulbs there could be some very real energy savings. I am still looking at trying to make my own

    Interesting subject you have started, thanks
     
  10. hilldweller

    hilldweller Funster Life Member

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    You are going to make LEDs - respect !

    But I guess you mean building your own modules. You'll not do it if you buy the parts from RS, that's for sure.
     
  11. Braunston

    Braunston Read Only Funster

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    Hi, Brian

    As I wrote' if we could get the unit costs down on the LED bulbs there could be some very real energy savings. I am still looking at trying to make my own (LED bulbs)

    I have found a number of places that will sell the small plastic dome type LED's at reasonable prices, but i still can't find anywhere that sells the small flat yellow coloured LED's that were being used on the made up bulb replacements at the Peterborough show, anyone know where i can purchase them from would be a help,

     
  12. hilldweller

    hilldweller Funster Life Member

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    Wander round RS and you'll find about 3000 LED hits.

    OSRAM Opto Semiconductors | Optoelectronics and Displays | Optoelectronics | LED | Chip LEDs

    NOTE: this is just to get you into RS, it's not powerful enough for illumination.

    This is but look at the price:
    http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0539870

    But don't overlook the switchmode regulator that you need to engineer.
     
    Last edited: May 28, 2009
  13. pappajohn

    pappajohn Funster Life Member

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    im probably totally wrong here....
    but my leds look like SMT components (surface mount technology) and are usually assembled by machine as a regular soldering iron is just too damn big.

    i bought a load at newark to replace ALL my halogens....£8-ish per unit.....50,000hrs average lifespan.
    thats 0.016p per hour purchase cost per unit.
    hardly worth the effort involved in making 'em.
     
  14. Braunston

    Braunston Read Only Funster

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    Hi,

    I take your point about the cost/lifespan and it makes sense, but the chaps who were selling them were making them up from components, as in one particular case they didn't have the ones a friend wanted and said they would make them up overnight for him, which they did and he purchased them the next morning

    If i had the money I would probably buy them as you did but as I don't that's why I have been asking the question as i would like to know where to purchase the components and see if i can make them within my budget.

    As for your suggestion of SMT, I don't know anything about them and you may be correct, however from those LED bulbs that were on sale there did appear to be quiet a number of configurations albeit they were/did appear to all be mounted on minute sized circuit boards.

    Can they be purchased ready mounted on differnt sized circuit boards ???




     
  15. scotjimland

    scotjimland Funster Life Member

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    Hi Olley

    Information from Truma would suggest that the leccy would be more expensive than off the grid

    Market launch of Truma’s LPG-operated fuel cell for recreational vehicles


    So 22lt LPG @ 50p = £11 produces 30 kw
    Cost per kwh = 11/30 = 36.6p :Sad:
     
    Last edited: May 28, 2009
  16. Braunston

    Braunston Read Only Funster

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    Just out of interest do you know why the "W" in kWh is capitalised ??

    answers on a £20 note to the originator please :Rofl1::Rofl1::Rofl1:


     
  17. scotjimland

    scotjimland Funster Life Member

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    :Wink:

     
  18. Braunston

    Braunston Read Only Funster

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    Hi, Jim

    Using your original figures it appears that the Truma unit will need to use nearly the equivalent of 4.5kW of LPG to produce 1kW of electricity. that dosen't sound right as if its correct that's an awful lot of fossil based fuel to use to produce just 1 kW of electricity

    what do you think ?



     
    Last edited: May 28, 2009
  19. scotjimland

    scotjimland Funster Life Member

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    Don't sound right to me either ..

    Can someone else double check ?

    I got my original info from here Propane Vs. Electricity - A Comparison
     
  20. scotjimland

    scotjimland Funster Life Member

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    I've checked again:

    To generate 1kW of electricity, the Truma uses 0.73 lt LPG, equivalent to 4.38 kW electric.

    if these figures are correct that makes it only 22.8% efficient.

    Information about fuel cell efficiencies is hard to find ..

    Not much use .. says little , nor does this ..

    but I did find this chart comparing the efficiency of fuel cells with diesel and gasoline engines.. rather disappointing I think ..

    [​IMG]
     
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