how many gallons for dump?

[cardamon]

I have a 1000 W turbine and 240 watts of solar which will be charged controlled with diversion to a hot water tank for domestic use.  Just wondering if anyone has advice on how large a tank I should use.  My place is small so I am leaning toward something in the 12 gallon range.  I will use the hot/warm water for dishes, maybe light bathing. According to my calculations, It will take about three hours with everything at max warp to bring 12 gallons of water to a boil from 70 degrees, then about a gallon will be evaporated every 40 minutes.  The system will not be pressurized so the water will not be replentished automatically.  I would like to not worry about the system drying up and frying if I go away for a week.  

I plan on using an actual 12 gallon water heater and replacing the 120v element with a 12v, and sticking a second element in somewhere, either by welding on a nipple or adapting to a larger sized nipple and mounting the element in that sticking out of the heater (all the accesory holes are 3/4 inch and the elements are 1 inch).

 I know the theoretical with all this, just looking for some advice from the practacle side from those who have lived with dump-heated hot water.  Thanks

[Warren]

Hello,

I have a hydro turbine producing about 690 watts of continuous power. The excess power is diverted to a 40 gallon domestic hot water tank with two 12 volt heater elements. If we do not use any water the safety relief valve will blow after about two days and this is with our water starting out at a lot colder than 70 degrees.

We initially set up an unpressurized 20 gallon galvanized tank with the two heater elements. After a couple of days you could not keep your hand on the tank. We only ran this tank for less than a week before we switched over to the domestic hot water tank.

I imagine the size of your tank will depend upon how much wind you get at your site. The worst case is you could have better than 1200 watts to get rid of.

Warren

[Gary D]

You may want to brake the wind generator if you will be gone for extended times. The solar can fill your battery bank and you will most likely come home to warm/hot water. Just a passing thought, water elements don't last long in open air...

[Ungrounded Lightning Rod]

Just a passing thought, water elements don't last long in open air...

Yeah.  Like seconds.

Don't believe it?  Get a teacup water heater, put it in your fireplace, and plug it in...

[cardamon]

Thanks for the replies and real life experiences.  I agree that braking the turbine if I go away for an extended period would be a good idea.  Due to the variablness of wind and uncertainty of my site, I'll just have to let her rip and see how it works.  Maybe a 20 gal tank wouldnt hurt.  The 28 gallon is the smallest size that has two stock element holes, but that is really big for my place so I dont want to go quite that big.

[richhagen]

If you were only using this as a dump load, I would suggest stripping the insulation off of the tank to aid in heat transfer from the tank to the surrounding environment.  That additional heat transfer would reduce the amount of energy available towards the latent heat of vaporization of the water, and reduce the rate at which the water boils off.  Rich

[nothing to lose]

I would suggest a reflux condenser above your tank like used on an alky still.

 If your gone awhile, not using power, and your dumping to the tank allot you don't want it to boil dry. With a reflux condenser the boiled water steam will raise to leave the tank, it gets cooled to under boiling temps and condenses back to water running back into your tank. Since your running an open system, no pressure, I think you could maybe get by with a large pipe or copper tubbing packed loosely with stainless steel wool. Make it long so there is lots of length for cooling before the steam escapes the open end.

Also since water seeks it's own level, if your worried about running dry you could also have a second tank beside the heater to store extra water. This way your only heating what you need in the 12gal tank, not trying to heat too much all at once. When the level falls in the heater more water will flow in to replace it from the other second tank. Kept mounted at the same levels you could have all the water available you want, like 35-70gal but only have to heat 12gal at a time with the dumpload.

Since you want the hot water and making it with dumpload, cooling the tank itself or using a larger tank may not work that well wgen you are home using it.

Your part

"According to my calculations, It will take about three hours with everything at max warp to bring 12 gallons of water to a boil from 70 degrees, then about a gallon will be evaporated every 40 minutes.  The system will not be pressurized so the water will not be replentished automatically."

The reflux condenser should reduce or stop that "gallon will be evaporated every 40 minutes" part. Extra storage in a side tank should not increase your heat up times.

If you figured correct, 3 hours is a long time to heat water when it's needed, and that's only if your batteries are full charged and your dumping power at full blast as you say, so I dought you would want a larger water tank which would take even more time to heat up more water.

If you have the room, I would lay a 35gal barrel on it's side beside the water heater then pipe from near the bottom of the barrel to the heater. Fill barrel to even with top of your water heater. Leave an air hole or mount an open fitting on top of barrel so water flows freely.

 Not sure how you plan to fill your heater now, but this way you could also just fill the barrel as needed and always have extra water ready for use as needed.