Using low-voltage water heating elements as a diversion load.

[jtsailjt]

Originally Posted by foggysail

YEAH! And I ran the numbers using a 40 degree water temperature change in a 6 gallon, 400 watt heater. Try 1.4 hours!

Yes, a 400 watt element will take quite awhile to heat the water for a shower, but that’s ok because its primary purpose is to be your dump load for your solar and wind generator during the very rare condition when all your batteries are full and more power is being generated. It’s enough so it should safely exceed the amount of excess power your setup is generating on a windy, sunny day but not so large so it will boil the water in your hot water heater even during best case energy production conditions.

The interesting part of the Torrid tank that was mentioned is that the AC element is 1500 Watts, which is what most small hot water tanks come with so you lose nothing but gain a dump load that on rare occasions will contribute to heating water rather than that energy being wasted. That sounds like the ideal setup to me. But from reading the post that mentioned it, I was unclear whether it’s 2 elements combined that can be easily screwed into any hot water tank or if it’s 2 separate elements that would require replacing the existing hot water tank. If it’s the former, it’s almost a no-brainer to buy one of these and use it as a dump load, but if it’s the latter and requires replacing the whole hot water tank, the cost probably exceeds any benefit that will be gained unless your old water heater needs replacing anyway. I say “almost” a no brainer only because of the case where you have drained your water system for some reason such as during a haul out or work being done on your plumbing and your wind generator is left on I would worry about the DC element not being immersed in water would overheat and burn itself out so you’d be left with no dump load.

[skipgundlach]

The dual element one I got from svhotwire.com was 1500/500w, and screwed in as a direct replacement. The one which came out looked like the typical home hot water heater element...

[foggysail]

Originally Posted by jtsailjt

Yes, a 400 watt element will take quite awhile to heat the water for a shower, but that’s ok because its primary purpose is to be your dump load for your solar and wind generator during the very rare condition when all your batteries are full and more power is being generated. It’s enough so it should safely exceed the amount of excess power your setup is generating on a windy, sunny day but not so large so it will boil the water in your hot water heater even during best case energy production conditions.

The interesting part of the Torrid tank that was mentioned is that the AC element is 1500 Watts, which is what most small hot water tanks come with so you lose nothing but gain a dump load that on rare occasions will contribute to heating water rather than that energy being wasted. That sounds like the ideal setup to me. But from reading the post that mentioned it, I was unclear whether it’s 2 elements combined that can be easily screwed into any hot water tank or if it’s 2 separate elements that would require replacing the existing hot water tank. If it’s the former, it’s almost a no-brainer to buy one of these and use it as a dump load, but if it’s the latter and requires replacing the whole hot water tank, the cost probably exceeds any benefit that will be gained unless your old water heater needs replacing anyway. I say “almost” a no brainer only because of the case where you have drained your water system for some reason such as during a haul out or work being done on your plumbing and your wind generator is left on I would worry about the DC element not being immersed in water would overheat and burn itself out so you’d be left with no dump load.

AHhhh—-solar! Absolutely but I thought someone wanted to use batteries and even at 400 watt load, that is 33 amperes. Now getting back to solar. I have just shy of 1200 watts of solar installed on my boat along with about 800AHs of batteries. My panels are 32vmp rated which are connected with two pairs of parallel in series for an operational voltage of 64vmp.

I think a properly designed system could use something similar but with the panels in series. Not only would such an arrangement be able to function with light gage wiring but it could switch directly to a standard marine water heater that operates at 120v.

And yeah......there are those who believe series connected panels suffer devastating power loss with shading which is another topic and I believe is bull poop!

You mentioned boiling. Heaters have temperature limited thermostats that will prevent that from occurring.

[jtsailjt]

Originally Posted by foggysail

You mentioned boiling. Heaters have temperature limited thermostats that will prevent that from occurring.

On my dual element for my hot water tank, there was a thermostat for the AC element but not for the DC element. Also, if you are using the DC element for a dump load and it is equipped with a thermostat that shuts it off, you just lost your dump load, so you really wouldn't want to equip your DC element with a thermostat.

[jtsailjt]

Originally Posted by skipgundlach

The dual element one I got from svhotwire.com was 1500/500w, and screwed in as a direct replacement. The one which came out looked like the typical home hot water heater element...

Do you have a link to that 1500W/500W element? The one I had that came from them was 500AC/300DC and that's still the one they are advertising at the link to them that you posted earlier in this thread.

[foggysail]

Originally Posted by jtsailjt

On my dual element for my hot water tank, there was a thermostat for the AC element but not for the DC element. Also, if you are using the DC element for a dump load and it is equipped with a thermostat that shuts it off, you just lost your dump load, so you really wouldn't want to equip your DC element with a thermostat.

I cannot think of a reason why you cannot connect directly to the AC element IF your DC voltage is 120+ as I suggested with solar panels in series. Now if your DC elements are rated for 12V, that is different and sure enough, one could boil the contents if powered long enough

[skipgundlach]

Originally Posted by jtsailjt

Do you have a link to that 1500W/500W element? The one I had that came from them was 500AC/300DC and that's still the one they are advertising at the link to them that you posted earlier in this thread.

Sorry, I don't - that was over 10 years ago.

But drop John a line; I'm sure he knows what's available if he doesn't have it (he's retired and selling off his remaining stock, but will gladly help you find what you need if he doesn't have it)...

[mako]

What’s wrong with just buying a cheap modified sine wave inverter from Harbor Freight and hard wiring it in? Keep things simple.

[Cadence]

Originally Posted by Stumble

If you batteries are already full, which is the only time you need a diversion load, having more batteries would actually make the problem worse not better.

Note this is not an argument for smaller battery banks...

A larger bank is inherently more efficient because it suffers less from the effects of Peukert's law. Basically there is less resistance from pulling power out of the batteries and less resistance putting it back in. So if you had a larger bank you would have lost less power to resistance while pulling power out, and lost less power as you put power back in. So under the same draw a large battery bank actually has less power taken out of it, and also needs less to put it back in.

In this specific, and rare, case a large battery bank just means you would need the diversion load sooner and for longer than with a smaller bank.

If so, you still have more usable power on demand and not relying on peak times. I think I'd rather have that and maybe not use some solar output than try to heat water with it?

[rom]

I may have missed it .. Anyone came up with an answer to OP's question ? I would be interested in doing the same modification.

[jtsailjt]

Originally Posted by rom

I may have missed it .. Anyone came up with an answer to OP's question ? I would be interested in doing the same modification.

The short answer is yes, but there have been quite a few important considerations discussed over the last 3 pages that it would be a good idea to read over before proceeding.

[SV FlyingSpirit]

There's a lot to chew on in these replies. I'm now looking at using both a dual voltage 120VAC/12 VDC element and wiring through an inverter. I'm at 13N lat (Guam) and a shunt isn't less desirable simply because I'd like to lessen heat generation inside the boat. Diversion to the water heater seems an alternative which will send excess energy to an insulated container, the water heater. I was thinking just wiring bank 3 of the MPPT to the water heater but i like the simplicity of wiring the inverter to the heater as well. I expect to be in the tropics for the next 2 years, the end which should find me in Capetown late 2020 so I maybe a little preoccupied with removing heat from inside the boat as I reconfigure solar and wind generation. Thanks all.

[OldBawley]

I have asked around in forums dedicated to wind energy.


In winter our two 85 watt solar panels bring almost nothing although wintering in Greece and orienting the panels. Since we winter on the hook we have two wind generators, one of them a big geared whopper for low winds. Solar and wind brings us trough winter, nothing to spare.


In summer we don't need the windgens so the big one is stowed away. Our boat is small, low tech.
All led lighting, my 17” Dell laptop uses only one Ah and the phones, I don't even know.
Long keel so even the autopilot uses minimal. Fridge 24 Ah/ day.


In summer at 11 h the battery's are full, and the Mppt regulator starts wasting energy.
I was asking around what could be useful NOT to waste energy.


Bigger batterys is nonsense if you cant use the energy.


Hot water is not needed. Greece is hot, why do you need hot water ? We have hot water from the solar heated shower barrel ( a fake plastic imitation olive oil barrel 35 l )


So we came up with a few possibilities for using lots of energy.


Brooding chicks.
Cultivating weed.
Distilling moonshine.


Water maker. Best solution

[jtsailjt]

Originally Posted by SV FlyingSpirit

There's a lot to chew on in these replies. I'm now looking at using both a dual voltage 120VAC/12 VDC element and wiring through an inverter. I'm at 13N lat (Guam) and a shunt isn't less desirable simply because I'd like to lessen heat generation inside the boat. Diversion to the water heater seems an alternative which will send excess energy to an insulated container, the water heater. I was thinking just wiring bank 3 of the MPPT to the water heater but i like the simplicity of wiring the inverter to the heater as well. I expect to be in the tropics for the next 2 years, the end which should find me in Capetown late 2020 so I maybe a little preoccupied with removing heat from inside the boat as I reconfigure solar and wind generation. Thanks all.

I don’t understand what’s to be gained by heating water via an inverter if you’re going to have a DC element too. Why change your DC power into AC to make hot water rather than just sending it right to your DC element? You’ll have to get a pretty big inverter unless you have a small AC element. Are you thinking of using both elements at the same time so it’s OK if they both are small? If you don’t have a genset or spend much time on shore power so can’t use a big AC element anyway I guess that could make sense. Just curious about the logic you used to arrive at your plan.

[foggysail]

Originally Posted by SV FlyingSpirit

There's a lot to chew on in these replies. I'm now looking at using both a dual voltage 120VAC/12 VDC element and wiring through an inverter. I'm at 13N lat (Guam) and a shunt isn't less desirable simply because I'd like to lessen heat generation inside the boat. Diversion to the water heater seems an alternative which will send excess energy to an insulated container, the water heater. I was thinking just wiring bank 3 of the MPPT to the water heater but i like the simplicity of wiring the inverter to the heater as well. I expect to be in the tropics for the next 2 years, the end which should find me in Capetown late 2020 so I maybe a little preoccupied with removing heat from inside the boat as I reconfigure solar and wind generation. Thanks all.

There are things to consider if your plan is to attempt connecting solar directly to a water heater. For example, a battery will try to output constant voltage whereas a panel will try to output constant current, they are current sources.

So for a 400W heater, it requires about 33 amperes at 12V. A battery will attempt to do that for as long as it can with it's available charge. Not so with a solar panel. Lets run some numbers.... using a 400 watt load.

The dc resistance and yes, I know the resistance will change as a function of heat but lets ignore that for this example the resistance R=V^2/P or 144/400 =0.36 ohms. So if a solar panel has a maximum current of say 15 amperes, the voltage across the 0.36 ohm load is only 5.4V which means you will only have 15X5.4= 81watts of heat being delivered. Not going to heat much water! Think about it.