Solar water heater

A place to discuss all things involving power and technology (including cameras). Generator tips, alternative energy, lighting your camp/bike/art/self, sound systems and more.
Post Reply
nixiebunny
Posts: 90
Joined: Mon Jul 23, 2007 10:27 pm
Location: Tucson
Contact:

Solar water heater

Post by nixiebunny » Sat Aug 16, 2014 1:03 am

I hope that plumbing and electricity are closely enough related hat this thread makes sense in this forum.

I'm modifying my 1977 Starcraft popup trailer for use at Burning Man. So far, I've installed a 12V solar power system with a couple 18AH sealed lead acid batteries, and three pumps to move water from a 10 gallon fresh water tank to two faucets (inside, outside) and through a solar water heater.

I'm currently pondering the water heater itself. I've made similar things in years past that circulate water from a 5 gallon bottle through 50 feet of 1/2" black poly irrigation tubing. I plan to do the same this time, but put the tubing on the roof of the trailer and use the freshwater tank as the hot water storage tank. (We will have separate drinking water!) I also want to have an automatic controller to circulate water during the day until the tank is at a nice 100 degree "hot water" temperature, then hold it there.

I'm an electrical engineer, so the circuitry (old school analog) is the easy part. The tricky part is the control parameters. I used a 555 timer in the past to give me a variable duty cycle pump sequence, so the water would cook in the tubing for 10 minutes, then be cycled out with different water in a half-minute pulse of pumping (The tubing holds 3/4 gallon). But it wouldn't turn itself on and off for the diurnal cycle, so I'd go away and forget it. you know how the playa is.

I have installed an auto engine thermistor on the tank's outlet fitting, and I have some thermistors to sense the temperature of the heater on the roof. I figure that I'll run the pump when the water at the outlet of the heater is some number of degrees above tank temperature. It will also stop the pump when the tank is hot enough. This should make the system automatically shut down at night, or when it's too hot outside.

Am I missing something?
--David Forbes

User avatar
BBadger
Posts: 5798
Joined: Wed Jan 19, 2011 10:37 am
Burning Since: 2010
Location: (near) Portland, OR, USA

Re: Solar water heater

Post by BBadger » Sat Aug 16, 2014 1:30 am

You could get a solar powered pump so that you don't have to worry about leaving it on all the time, and then just use that thermostat or some other feedback controller for temperature regulation. You could also make a thermosiphon and avoid the pump; just tap at a specific height on the tank for a certain temperature.
"The essence of tyranny is not iron law. It is capricious law." -- Christopher Hitchens

Hate reading my replies? Click here to add me to your plonk (foe) list.

User avatar
Popeye
Posts: 635
Joined: Thu Aug 15, 2013 10:39 pm
Burning Since: 2013
Camp Name: Beaverton
Location: Where the east wind blows

Re: Solar water heater

Post by Popeye » Sat Aug 16, 2014 2:28 am

It will work fine but a little overengineered. :) It would be a lot simpler with two thermostats. One that closes on temp rise on the poly tubing. I would cut the poly and put a short piece of copper in as copper is a better heat conducter. Attach the bulb to thecopper and insulate the thermostat bulb. Second thermostat in the tank, closes on temp fall. Wire the thermostats in series and play with the settings and differential to avoid short cycling.
A timer needs to be adjusted for a sunny day, readjusted for a cloudy day, etc. etc. This way the pump only comes on when the water in the tubing is hot and the tank needs hot water.
If you can come across an old electric hot water heater you could swap the tank out and have an insulated tank with one of the tstats already installed. I realize I don't know your space requirements.
nobody wants to live in a world with only one flavor...

nixiebunny
Posts: 90
Joined: Mon Jul 23, 2007 10:27 pm
Location: Tucson
Contact:

Re: Solar water heater

Post by nixiebunny » Sat Aug 16, 2014 7:21 am

Thanks for the suggestions. I'm already pretty far along in the build and the water tank is part of the trailer, so I don't see a reason to change the basic setup.

I forgot to mention that the purpose of the water heater is to make delightful showers available to my camp mates and myself. I've been doing this since 2007. It's gratifying when a camp mate says "That's the best shower I've had in my entire life". This is why I want the water temperature to be just ever so. I provide a nice shower head with a long hose, and a pushbutton to make water spray from it. Just like home, but with a push-to-talk switch.

I will effectively have two thermostats - each are made of thermistor and a comparator, so they are adjustable. Like I said, that stuff is easy for me. I might build the controller circuit on a solderless breadboard and play with it during the week. One thing is for certain - it WON'T be an Arduino!
--David Forbes

User avatar
FIGJAM
Posts: 10063
Joined: Thu Mar 25, 2010 10:39 am
Location: apache junction az.

Re: Solar water heater

Post by FIGJAM » Sat Aug 16, 2014 7:47 am

You know more about this than I do, so let me give you a uninformed opinion.

It seems to me that 50' of black irrigation hose sitting in the sun is going to make the water too hot simply getting from one end to the other. :?
"Don't buy ur Burn...........Build ur Burn!"

"If I can't find an answer, I'll create one!!!"

Fuck Im Good Just Ask Me

User avatar
some seeing eye
Posts: 2815
Joined: Tue Sep 09, 2008 12:06 pm
Burning Since: 1999
Camp Name: Woo
Location: The Oregon

Re: Solar water heater

Post by some seeing eye » Sat Aug 16, 2014 8:52 am

I understand what you are proposing and am an engineer. Suggest looking at the user experience elements. What time showers, how many gallons per shower, feedback to showeree on gallons and temperature in F/ even with your push to shower.

Thermal technical: insulated hot water tank and copper or steel tubing if available are something to consider. Sounds like your design has the tubing dry after the water is heated. That may be a problem for black plastic tubing, People are often selling/freeing 1980's solar thermal water collectors with metal tubing on Craigslist.

And of course, suggest sharing experiences with the Alternative Energy Zone village! Hey maybe you camp with them already!
increasing the signal to noise ratio with compassion

User avatar
Captain Goddammit
Posts: 8235
Joined: Sat Sep 06, 2003 9:34 am
Burning Since: 2000
Camp Name: First Camp
Location: Seattle, WA

Re: Solar water heater

Post by Captain Goddammit » Sat Aug 16, 2014 8:59 am

Or you could just get a propane hot water heater from an old camper.
Compact, works on cloudy days and at night/morning, and already has a thermostat.
Unless that's too easy and works too well...
GreyCoyote: "At this rate it wont be long before he is Admiral Fukkit."

User avatar
BBadger
Posts: 5798
Joined: Wed Jan 19, 2011 10:37 am
Burning Since: 2010
Location: (near) Portland, OR, USA

Re: Solar water heater

Post by BBadger » Sat Aug 16, 2014 4:30 pm

But... but... renewables.
"The essence of tyranny is not iron law. It is capricious law." -- Christopher Hitchens

Hate reading my replies? Click here to add me to your plonk (foe) list.

Elliot
Posts: 7706
Joined: Sun Dec 18, 2005 8:41 pm
Burning Since: 2006

Re: Solar water heater

Post by Elliot » Sat Aug 16, 2014 8:46 pm

nixiebunny wrote:... I provide a nice shower head with a long hose, and a pushbutton to make water spray from it. Just like home, but with a push-to-talk switch.
...
Can you tell me about this shower head with push-to-talk valve? I think I want one.

nixiebunny
Posts: 90
Joined: Mon Jul 23, 2007 10:27 pm
Location: Tucson
Contact:

Re: Solar water heater

Post by nixiebunny » Sun Aug 17, 2014 12:15 am

The solar heater is nicer than propane mainly because it's much less invasive and licensed-contractor requiring... no gas to worry about exploding the trailer. If my popup was originally plumbed with hot water, my decision may have been different.

My shower sprayer setup is a Oxygenics X-stream low-flow shower head mounted to a handle made of 1/2" PVC pipe. I use a doorbell button mounted to the PVC pipe as a pump actuation switch. A standard little water pump pushes water into the shower pipe when the button is pushed, completing the power circuit to the pump. It's the best way to save water, by not letting it run unless you are pushing a button.

You can do the same thing for a handwashing station, but with a foot pedal to run the pump switch.

I'll post photos once I get the solar heater installed.
--David Forbes

User avatar
Captain Goddammit
Posts: 8235
Joined: Sat Sep 06, 2003 9:34 am
Burning Since: 2000
Camp Name: First Camp
Location: Seattle, WA

Re: Solar water heater

Post by Captain Goddammit » Sun Aug 17, 2014 12:47 am

Licensed contractor requiring? If you're afraid of gas appliances in your trailer you could just toss it on the ground and use flexible water hose to it, and a propane bottle, regulator and hose just like a regular gas barbeque grill has.

Elliot, pretty much every camper/RV has a shower head with a super convenient on/off water switch right on it. The pump stays on, but since RV water pumps have a built-in pressure switch, as soon as you turn the water off the pump stops. No wires, and your temp setting doesn't get messed up.
GreyCoyote: "At this rate it wont be long before he is Admiral Fukkit."

Elliot
Posts: 7706
Joined: Sun Dec 18, 2005 8:41 pm
Burning Since: 2006

Re: Solar water heater

Post by Elliot » Sun Aug 17, 2014 3:40 am

OK, I already have a standard RV water pump system installed, so all I'm missing is the RV shower wand. Thanks, both!

Oh... I like the idea of the black hose on the roof. I'm still using a small black barrel, which I carry in and out of the bus. :lol:

krly
Posts: 79
Joined: Fri Dec 13, 2013 4:10 pm
Burning Since: 2018

Re: Solar water heater

Post by krly » Sun Aug 17, 2014 4:53 pm

There's always another alternative......http://www.duckworksbbs.com/gear/shower/
krly

nixiebunny
Posts: 90
Joined: Mon Jul 23, 2007 10:27 pm
Location: Tucson
Contact:

Re: Solar water heater

Post by nixiebunny » Mon Aug 18, 2014 11:42 pm

Did someone say "overengineered"? Because yes.

Building a deluxe shower is my Burning Man art project.

Image
--David Forbes

Post Reply

Return to “Power & Electronics”