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Originally Posted by dog_and_ape
Thanks MarkyDee.
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You're welcome! I've learned a lot from everyone here. Just want to give back....
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Originally Posted by dog_and_ape
Apologies for how I phrased some of that. The only water that will be up on the roof will be the 4" PVC at length (12-16'?). That should only be 6-10 gallons and won't be more than 100 pounds max (probably closer to 75 pounds I think)- I can't see that being an issue, right? My fresh and grey water tanks will sit at low points inside, insulated from the elements-gravity fed just meant no pumps needed to fill them.
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Ah, ok. I was having flashbacks to a bus I saw that had huge tanks on the roof and was cringing.... ;)
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Originally Posted by dog_and_ape
Are you referencing the water heater or the heater I identified for climate? The one for climate will be last resort (very cold nights). I'm not planning on doing large amounts of driving at any given time- idea is to meander around slowly and without plan or purpose in between living sites. I wouldn't think I would drive more than 2-3 hours at a time so I'd be able to heat the bus with the wood-stove before I moved out, put the fire out and then let the insulation work with some augmentation from engine heat.
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I was referencing climate, but the hot water is an issue as well. Any heating with a resistance element from electricity is very inefficient - period. I'd sooner put thermal tubes on the roof than heat with resistance elements.
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Originally Posted by dog_and_ape
As for hot water, I don't use much- no showers (off the water heater) so it would really only be to clean my dishes in the evening. Do you think the 1500W, 4 gallon heater is still too much draw? I'll have the wood-stove if I run out of battery in a storm or some similar situation.
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Well, lets see ... 1500W will draw approximately 125 Amps from a 12V source. If you are using a 200Ah battery, that battery will be 50% exhausted in less than an hour.
To raise one gallon of water one degree F takes 8.33 BTUs.
Assuming 100% efficiency, that 4 gallons will take 33.32 BTUs to raise it 1 degree F.
1kW of electricity has 3412 BTUs.
A 200Ah battery has 2.4kWh of energy. Assuming a draw-out of 1hour (i.e. the battery is dead in one hour), that battery will deliver 2.4kW, giving us 8189 BTUs. That means that you can heat your water tank up 246 degrees F before your battery is dead. Factor in inefficiencies and you'll be lucky to get 150-200 degrees of heating before your battery is dead (oh, and if your water hits 212F, its starts to boil, taking energy that would otherwise go to heating).
Now, consider the BTU content of 1 pound of propane: 21800 BTUs. 1 Gallon of propane: 91000 BTUs. 1 Gallon of #1 Diesel: 136000 BTUs. Compare that to a 200Ah battery: 8200 BTUs.
So, to answer your question, yes, you will find it very hard to live with just a 200Ah battery if you are trying to heat with it for any significant amount of time (whether it is your food, water, or yourself). If you are in a "significant weather event" such as a blizzard, you could find yourself in a life-threatening situation rather quickly without a reliable source of heat. I want at least two for redundancy. Three is even better if you are going to be trusting your equipment with your life.
That's why I really like SomewhereInUSA's three-loop system. It gives a large amount of redundancy, allows for directing the heat where you need it, and it uses the various forms of energy in the modes that they are good at (propane/diesel for heat, electricity for pushing that heat around). If you can figure out how to add a water jacket to your wood stove, you could add that to the loops.
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Originally Posted by dog_and_ape
I'm really trying to avoid using petroleum products and by-products if possible- they just become a recurring cost. The propane stove is a redundant feature. Most cooking would be done in rice cooker, solar oven, induction top or wood stove/camp fire. I'd like to only think about filling a 5 gallon tank once a year or so and not have to worry about running propane lines.
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Oh, I understand, but electricity will only go so far. Batteries are the most
inefficient way of storing energy, period, full stop. If you want heat, electricity into a resistance element is
not the optimum way to do it (no matter what it is you are trying to heat). We have a lot of electric-powered gadgets because electricity is plentiful in a sticks-and-bricks. Electricity is
not plentiful in a disconnected, mobile environment like a skoolie. In a mobile environment, petroleum products make lots of sense because they are much more energy-dense. Unless, that is, you desire a return to a pre-modern skillset. If so, you have more constitution than I do (at least at this point in my life).
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Originally Posted by dog_and_ape
Thanks again!
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I wish you good fortune! I hope I've helped at least a little. The real take-away here is that batteries are absolutely terrible in terms of how much energy you can carry for the mass/weight of the batteries. Petroleum products and even wood has better energy-density than batteries. The real balance would be to use the different forms of energy for what they are good at. Wood and Petroleum are great for heat and motive power. Electricity is great at little gadgets to gently push the other forms of energy around (unless you're tied to the grid...). Even with new battery chemistries that "calculus" isn't going to change for some time yet.