3 ms·

How big of a tank on your roof do you need to replace a box of lead acid batteries?

• msandford 11y ago
  Is your house 100 feet tall or taller, and I hope your whole house is made out of structural steel.
• mhandley 11y ago
  A 12V deep-discharge lead-acid battery is typically 120amp-hours. That's 1.4kWh. Suppose you only 50% discharge it for longevity, that's 700Wh. I'll assume your box of batteries has ten of them, so a usable capacity of 7kWh. 1kWh = 3.6MJ, so 7kWh = 25MJ How high is your roof? Lets say 10 metres. Potential energy U = mgh. (m=mass in kg). h=10, g~=10, so U=100*m. So, to equal those batteries, assuming 100% efficiency, the mass of water needs to be 250000 kg, or 250 tonnes. Probably going to need to reinforce the loft.
  • Dylan16807 11y ago
    So 'roof' is clearly out of the question. Now let's look at basement. I install a 4x4x2 meter tank, then drill down 100 meters to create another such tank. 32 tonnes lifted 100 meters gives me 32MJ, perfect. Now how expensive is it to build a water storage area underground? Is this a 50 thousand dollar project or a 50 million dollar project? If the ground water is at the right depth, you would only need to drill a well. So this should be practical somewhere, at least.
    • debacle 11y ago
      Your 100 meter channel is going to get flooded.
      • Dylan16807 11y ago
        That's your biggest objection to the idea? A 100 meter waterproof pipe is the easiest problem to solve here.