12 Volts water heater?

System

Does anyone know about a 12 volt, small (2 or 3 gallons) water heater?

I may be completely insane, but I was thinking that, perhaps, if there is such a heater I may be able to connect it to my mx60 auxiliary port and use it as a diversion load, to use all those watts that goes to waste when the battery bank is full; and have some extra warm water available.

Thanks.

BB.

Re: 12 Volts water heater?

Try this thread... More or less similar question.

Short answer, yes you can do it... Longer answer is that this does not usually give a great amount of heat for the cost of power.

-Bill

System2

Re: 12 Volts water heater?

I agree with Bill. Don't expect much from it. Unless your tank is super insulated on top of the factory insulation, it might mot even replace what's lost normally through the insulation. Now if you have a 10,000 watt PV system, it might be worth it. In most cases. you'd be far far ahead to use a water heating solar panel.
Wayne

crewzer

Re: 12 Volts water heater?

Amilkar,

What is the size (Watts STC) of your PV array?

Later,
Jim / crewzer

System2

Re: 12 Volts water heater?

Crewzer:

Sorry for the delay.

Solar array size is pretty small, just around 750 watts (six Kyoceras 130). However, since I am using the system mainly as a backup, that means that usually I have plenty of energy production that is not being used.

By the way, in addition to the Kyoceras I have the mx60, four 6 volts golf-cart batteries, and an Exceltech 1100 inverter.

Thanks

System2

Re: 12 Volts water heater?

Why not use an auto headlamp(s) and shine them on your exsisting water heater?

System2

Re: 12 Volts water heater?

Samkent:

Because there is no existent water heater!

Nevertheless, though I Do not think that your idea would work, the reasoning behind the idea is pretty good. Maybe I should start to "think outside the box" and look for unusual alternatives.

Thanks.

mike95490

Re: 12 Volts water heater?

Water heaters for boats (5 - 20 gallon range) have a heat exchanger for engine coolant, and electrical heaters (120 & 12V) installed, but they are pretty pricey, if you had space for a hot water panel, I'd go for that, and a heat exchanger wand for the existing tank
http://www.butlersunsolutions.com/bss-featprods.html Butler spiral wand.

BB.

Re: 12 Volts water heater?

If this is just for backup power... You may wish to look at a small grid tie inverter... Sunnyboy's start at 700 watts (good brand).

One of the problems is that the small inverters are based on their bigger brothers (many times, just derated by software to the smaller size)...

So, you end up paying ~$2 per watt for the inverter, when a larger inverter is closer to ~$0.50 per watt...

You can also design a battery backed, grid tied system (like the Xantrex XM 60)--however, from what I have seen, those are mostly for much larger systems.

Realistically, the amount of power you are "losing" is probably worth $0.10 to $0.20 per day (or $36-$72 per year)... Spending a $1,000+ to save that small amount of power through grid tie--is probably not worth it.

If you go back to using the excess electricity to heat some water--yea, you can probably make it work--but you have to be careful you do not cycle your batteries while doing this--you can shorten their life by quite a bit vs your standby use right now...

-Bill

crewzer

Re: 12 Volts water heater?

Does anyone know about a 12 volt, small (2 or 3 gallons) water heater? …I was thinking that, perhaps, if there is such a heater I may be able to connect it to my mx60 auxiliary port and use it as a diversion load, to use all those watts that goes to waste when the battery bank is full; and have some extra warm water available.

Solar array size is pretty small, just around 750 watts (six Kyoceras 130). However, since I am using the system mainly as a backup, that means that usually I have plenty of energy production that is not being used.

By the way, in addition to the Kyoceras I have the mx60, four 6 volts golf-cart batteries, and an Exceltech 1100 inverter.

Amilkar,

Using a diversion load (resistor) to heat water is a common application for PV energy that otherwise be wasted during the absorb, float, and/or EQ cycles. I’ll lay out some of the details for you, and hopefully you’ll then be able to decide whether this would make sense for you.

One issue is to estimate/calculate how much “wasted” energy is available for a diversion application. For example, a system that operates in bulk mode in the morning (~8 AM local Sun time to ~Noon local Sun time) and produces 2.5 kWh, and that operates in absorption and float modes in the afternoon and produces 1.5 kWh, may have 1 kWh of “wasted” energy available.

What to do with one kWh? Well, that’s 3,413 BTUs. Assuming 90% overall efficiency, 3,413 BTU’s will heat five gallons of water (41.65 lbs) from ~55 F to ~129 F, for a gain of ~74 F. If you have several kWh of otherwise “wasted” energy available each day, then you might want to consider a larger capacity water heater, or just replacing the bottom element in an existing household water heater (40 gallons?).

The MX60 can be easily configured for this application. The key is to use its AUX (12 VDC on-off) feature’s DIVERSION function to control a heatsink-mounted solid-state relay, or SSR, that connects/disconnects the diversion load to/from the battery bank. There’s limited discussion of this application the Rev C version of the MX manual (pgs. 28-31). See: http://www.outbackpower.com/pdfs_manuals/MX60_REV_%20C.pdf

Here’s a link to a source for SSR’s, heatsinks, assemblies, etc: http://www.power-io.com/products/hdd.htm
This SSR + heatsink assembly should work: [SIZE=-1]HDD-06V75-HS1.0 HDD-06V75 on a HEATSK-DIN-1.0 heat sink[/SIZE]

You’ll also need a water heater element, installed in an existing tank (typically the lower element), or in an add-on “pre-heater” tank”, with a power rating that meets or exceeds your PV array’s STC power spec. Configured in parallel and rated at 817 W, the 12/24 V heater element in the link below is the right size for your array.

See: http://www.solarseller.com/diversion_load_heating_air_water_wind_hydro_solar_loads.htm#back_to_water_heating_diversion_loads
And: http://www.solarseller.com/diversion_load_heating_air_water_wind_hydro_solar_loads.htm#water_heating_diversion_load_chart_

Another approach is to use a Morningstar TriStar controller (in addition to the MX60 controller, but without the SSR) configured for a diversion application. See Tristar manual page 7, and all of Section 6, which is a quite good primer on diversion control applications.

See: http://www.morningstarcorp.com/products/TriStar/info/TS_Manual.pdf

FWIW, the new FM80 controller includes a more elegant solution for this particular application. Its AUX/Diversion function includes a new SSR setting that features low-frequency (~200 Hz) dynamic duty-cycle PWM control of the AUX 12 VDC output to divert excess energy while maintaining a fairly steady battery voltage. :cool:

The info above will provide you with much of the technical info you need. Whether this is cost effective or not is another issue entirely.

HTH,
Jim / crewzer