How to heat a fish tank

[force9BOAT]

I am getting ready to raise my first Wind turbine.  I plan to use the power from it and one or two solar panels to heat a 100 gallon saltwater reef tank.  The tank currently depends on a 100W heater running off household (grid) power.  Today the solution finally occurred to me to the problem I posted a couple months ago.  Namely the heater must work 100% of the time in order to keep the reef animals from dieing.  I think 100W provided 24/7 is a significant amount of power.  My wind turbine alone would not be able to meet that and in the great Pacific North West there is not much solar energy available either.  Here is the idea I came up with today.  Use two heaters, one connected to my RE system and one connected to my household power supply.  Set the thermostat of the grid powered heater a few degrees lower than the RE powered heater.  As long as my RE system has adequate power the RE heater will hold the water temperature at 80 degrees F.  When the voltage controller cuts the RE system out then the water will cool to about 77 deg. F where the household powered heater thermostat will kick-in and hold the water temperature at that level.  When the RE system comes back on line then the water temp will rise back to 80F.  

I think using the above method will reduce grid consumption by the amount equal to what my RE system can produce.  And I can do this without any expensive hardware and it will be fully automated.  During the summer months when there is lots of solar power and my house is naturally warm anyway grid consumption for the heater should drop to zero.  

[henjulfox]

Sounds like it would work during the winter, but what about a spring day with lots of wind and solar available? Do you have a battery, charge controller and dump load in the system, or are those components the expensive hardware you're trying to avoid?

If you have a thermostat on the RE heater I can see it kicking the heater off and your turbine would be free wheeling with no load, hitting some amazing speeds. If no thermostat, I believe the heater would either burn out or cook the fish.

What size wind generator/PV panels are you planning? If the capacity of both were less than 100 watts (pretty small) you might get away with it.

Sorry, but you probably have a lot of time and money invested in your tank and wind generator. Think of the expensive hardware as insurance to protect your investment.

-Henry

[Flux]

Yes Henry has a point, your idea is simple and will work but you need a dump load to take any power over what the tank needs.

It would seem better but more complicated to dump the excess power into another tank that is well lagged then when there is no wind you can circulate the hot water through a heat exchanger and thermostatically controlled pump to maintain the fish tank.

Flux

[Kwazai]

I'm not an electronics wiz, but it seems like it would be simpler to just put a couple transistors and relays in an OR circuit configuration with relays to operate the actual heaters--kindof a go no go circuit based on the incoming voltage....

L8r

Mike

[mlz]

Put a battery on the system, sell the second heater and get a load diverter (or build one).  Put a battery charger on the battery during low power months. I'm sure someone can design you a circuit to turn on the charger when the battery is flat and no power is coming in from the solar or wind.

I'm curious tho', have you checked the actual consumption of the heater, if it's a 100W of heat, it may be pulling considerably more.  Our fish tank heater is 25w but if you put a kill-a-watt on it, it's pulling nearly 50w of electricity.  (I believe the rating on it is the heat supplied, not the power used.)

[wooferhound]

>  I think 100W provided 24/7 is a significant amount of power.

Of course you understand that it is not 100watts all the time. The thermostat will turn the heater off and on depending on the temperature. What you want to find out is how many Kilowatt Hours it pulls and size your batteries to that.

Or I kinda like the idea above, about a second holding tank for the hot water and a thermostat on a circulating pump

[nothing to lose]

I think he has the better idea of 2 heaters than using a battery charger which I think may have been sugested in his older thread also. Battery and charger will have power losses in both, so when there is not enough RE power he would actaully be using alot more grid power than the tank heater would by iteslf on the grid power.

Over charging  batteries when there may be too much RE power would be the main thing to worry about I think. So batteries on the RE system and inverter to run the RE heater set to a higher temp makes use of the wind and solar power. Might as well run a second heater set lower directly from the grid though. Less power loss and also a second fish tank heater probably costs less to buy than a battery charger would cost.

[GaryGary]

Hi,

Have you thought about using a solar water heating panel?

You need (100 watts)(24hrs) = 2.4KWH per day.

If you built a 4ftX8ft solar water heating panel (3 sq meters) with some storage, it could meet all your heating needs (and then some) in 3 seasons, and a good fraction in winter.  For example:

Feb -- Seattle sun on 1 meter square panel = 2.5 KWH per day

Feb output = (2.5KWH/day-m^2)(3 m^2)(0.5 efic) = 3.75 KWH   (150% of 2.4KWH)

July(best) -- Seattle sun on 1 meter square panel = 5.7 KWH per day

July output = (5.7KWH/day-m^2)(3 m^2)(0.5 efic) = 8.6 KWH  (350% of 2.4 KWH)

Dec(worst) -- Seattle sun on 1 meter square panel = 1.4 KWH per day

Dec output = (1.4KWH/day-m^2)(3 m^2)(0.5 efic) = 2.1 KWH  (80% of 2.4 KWH)

During the summer, you could use the excess hot water for domestic hot water (or the hot tub).

The sun values come from the NREL site  http://rredc.nrel.gov/solar/pubs/redbook/  they include the effect of clouds -- they have other NW cities if you are not in Seattle.

The 4X8 panel might cost about $225 ($7 per sqft) with the absorber plate already made from SunRay ($4.50 per sqft), and $1 per sqft corrugated polycarbonate glazing from Home Depot.  You would also need a storage tank of some kind, a pump, controller, ...

If you are interested, there is some design info here:

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm

Just a thought :-)

Gary

[force9BOAT]

Yes, I guess I was not clear enough about my description.  I will have a battery bank to take up excess power from RE and provide power at night and when there is little wind.  During spring and summer months if RE provides too much power (very possible since the fish tank can keep warm just from ambient heat) then I can also switch one or more of the four small water pumps and/or the lights the aquarium uses into the RE system.  I would be thrilled if that turns out to be the case since I am trying to see how much grid power I can stop using.  My ultimate goal is to completely remove the aquarium from the grid.  If I could do that during summer that would be great, especially since the grid is under the greatest load in the summer.

During the California power shortage a couple years ago I remember a news story about how consumer electronics had greatly increased power demands.  Fifty years ago people had very little stuff in the house that needed power.  Now everybody's house is full of power sucking gadgets.  Aquariums were specifically listed as one of the culprits.

Thanks all,

Rob

[hydrosun]

Am I the only one here who thinks about reducing the load first? Wrap that tank with some kind of insulation! By reducing the heat loss you could save much more power with a lot less complication and cost.  Put the tank on a piece of styrofoam, put bubble wrap on the side of the tank toward the window if the plants need natural light. Cover the whole thing with a blanket or sleeping bag at night or whenever you're away.  As I stress in classes the key to efficiency is insulation, insulation , insulation to keep the temperature in the location, location, location it belongs. I use some of the power I produce to cook all our food . It is only possible by the use of insulated rice cookers. I even added a layer of aluminum foil between the cover of my bread machine to reduce the baking time substationally. I tend to modify everthing to make it more efficient.

So use the power you  produce  to heat the much smaller load needed.

Chris

[Don Cackleberrycreations]

The covering of the tank could  sufficate the fish .

C02 and 02 are exchanged on the surface.

being a reef tank I doubt he using a protien scimmer more likely  a sand bed and live rock with a dump gate wave maker. Possibly even a wet/dry sump.

  My personal preference is a macro algi system though they are power hungry.

[scottsAI]

Yes, I put 1 inch foam on the bottom and back of my tank, later on two sides.

Left the front and top open.  Had foam for the front never used it.

Have fun,

Scott.

[craig110]

Hi force9BOAT,

I like your idea of putting your extra energy into an RE heater to your tank, but I'm concerned that what you are thinking might cause your fish more harm than good.  Skipping all the AE aspects of this thread, I think you need a much bigger heater.

(Momentary digression: Ok, in deference to the previous discussion you can also put on lots of insulation.  Personally, though, I think saltwater tanks are far too gorgeous to hide in insulation.  Either you worry about energy or you shell out the big bucks to outfit a 100 gallon saltwater tank.  Doing both reminds me of people who pay lots of money for cars that are so fancy that they become afraid to drive them.  Ok, the flameproof suit is now on and yes, I'm sure someone out there has done a pretty job of insulating their tank.  I just haven't seen one yet. ;-)

Saltwater fish, the corals, and all those other beautiful invertebrates are notoriously finicky about the temperature needing to be constant.  Unless the room your tank is in is consistently very warm -- such as 75-78 degrees -- a 100w heater is far below the recommendation for a saltwater tank of your size.  Even if it was a freshwater tank, where the fish don't mind temperature fluctuations as much, the normal recommendations would have you using about a 200-250w heater.  (I have a 75w heater on my comparatively small 29 gallon freshwater.)  Since salts are more finicky, most recommendations are for near double that power, 2.5 to 5w per real gallon, to make sure that the temperature doesn't fluctuate.  Presuming that you have around 90 real gallons of water after the gravel volume is subtracted out, a heater in the 250 to 450w range would keep the tank at the nice consistent temperature needed to have a healthy saltwater setup.  A heater of this size won't be on 7x24, and yours being on 7x24 shows that it is too small, but it will have the ability to keep the water temp at a nice steady temperature.

Ok, so back to my original statement that adding an RE heater set a few degrees higher could be problematic for your fish.  Having a heater setup designed to allow the tank to vary from 77 to 80 degrees and back depending upon the current wind is a temperature variance far beyond what I've ever seen recommended for a saltwater setup.  Besides adding a more powerful heater on your grid-based side, what I'd suggest is that you set the RE heater just a tiny bit (half degree?) above the grid-heater setting.  As long as you have a very good filtration flow in the tank to distribute the heat from the RE-heater, even with that little temperature gap I'd venture that the grid-heater would rarely turn on while the wind is blowing.  This will, admittedly, not absorb as much RE as a 3-degree swing would.

One more comment -- be careful about the notion of the heaters never needing to turn on during the summer months.  "Heater never turning on" = "water above the target temperature" so make sure that you aren't accidentally cooking the fish.  One family I know that has a beatiful saltwater tank in their bedroom (100 or 120 gallon) has a window AC that is on 12 months out of the year to make sure that the room never gets warm enough to cause the tank to heat up.  (The AC doesn't cycle many times during a New Hampshire winter, but it is on just in case a sunny day overheats the room.)  They want the tank's heater to occasionally come on to hold it at the right temperature.  That might be a little bit of overkill (and potential heresy on this board ;-), but it does show how concerned some saltwater owners are about the temperature.

Craig

[inframan]

go with the cabinet/box insulation or styrofoam.

also maybe work with 55 gallon water storage/heating medium.

powered by solar collector on roof.

use a waterline under rocks or sand for exchanger.

or/and use candle from veggie oil to heat water/tank/smaller heat tank.

suitable pump for transfer. temp controlled relay.

backup by grid heater.

some solutions are getting to tech for purpose.

capture heat from light if used and transfer to cabinet so heat rises to tank.

ductwork and really small fan.

this may also need to be tried. apparently stirring water may create some heat.

get some fighting fish, free heat.

electric eel?

personally i would like to try the veggie burner. just heat the 1 gallon? secondary tank the temp controller would the n circulate as needed. you could even automate the veggie candle to light as needed. think solenoid and electric lighter.

if the candle isnt enough then super small veggie burner.