Hot water with electricity from solar panels

[valhalla360]

Originally Posted by senormechanico

The hot water tank is original with the original 120 volt, 1,000 watt tank element.
The 1500 watt sine wave inverter is used for our VitaMix, wife's hairdryer, and whatever other AC uses like power tools, soldering iron etc.
Cost me $199 and free shipping from ebay.

Tiger Claw 1500w/3000w Pure Sine WavePower Inverter DC-AC Power Converter | eBay

Oh, I almost forgot the cost of some wire and a big fuse with holder. $50 ?

All the above was already in place when I added a few bits to engage the hot water tank circuit.

I fail to see the validity of your point.

The OP was asking about installing. As I said, if you already have everything in place and the charging system and battery bank is already oversized and you already have the inverter , I wouldn't rip it out.

[BjarneK]

Originally Posted by mrm

See the resulting plots and tell me if you still think those panels are well matched to this use. Look at P_heater / 2 curve, as each panel has to supply half of the power.

Looking at the graph, you could get more output at 800 W / m2, but at 500 W / m2, the panels are close to optimal. Panels mounted on the bimini (like these are according to Seriously Slow) will probably often only have closer to 500 W / m2 of input. Another thing is that I would prefer optimal performance at 500 W / m2 rather than at 800 W / m2 when you have plenty of power available.

[Dockhead]

Originally Posted by valhalla360

I suggest you take your own advice.i never suggested fitting two elements.
I also never suggested pulling off the batteries.

You suggested fitting a 12v element. That would require either giving up the existing element, or fitting two, neither of which works for the OP.

Originally Posted by valhalla360

And the perkuet effect is not effected by the voltage selection. It is a function of the amperage at 12v. A 500w element at 120v, 240v or 200,000v will draw the same amps from the batteries (not sure what the efficiency of a 200,000v inverter is so that may not make as much sense)

Wrong. Now it's clear that you didn't understand even the first thing about what the OP is doing

By reducing the voltage from 230v to 110v, he reduced the WATTAGE of the element to one-fourth of its original rating. His 700 watt element becomes a 175 watt element because he reduced the voltage he is feeding it.

That reduces the amperage at 12v to one-fourth of what it was, reduces the load in excess of available solar power, reducing the amount of battery power used, and reduces the Peukert effect losses on whatever battery power is used.


Carrying this idea further -- one could make a single immersion element infinitely variable in power if you could regulate the voltage of the inverter. This could be really useful in matching the power of the inverter to the excess power which needs to be dumped.

[valhalla360]

Originally Posted by Dockhead

You suggested fitting a 12v element. That would require either giving up the existing element, or fitting two, neither of which works for the OP.

If you read my post, a single 12v element would work fine. Power is very limited when away from shorepower, so that is where you want to maximize efficiency. It's easy for the battery charger to keep up with the draw from a 175w heating element.

Wrong. Now it's clear that you didn't understand even the first thing about what the OP is doing

By reducing the voltage from 230v to 110v, he reduced the WATTAGE of the element to one-fourth of its original rating. His 700 watt element becomes a 175 watt element because he reduced the voltage he is feeding it.

That reduces the amperage at 12v to one-fourth of what it was, reduces the load in excess of available solar power, reducing the amount of battery power used, and reduces the Peukert effect losses on whatever battery power is used.

You still don't understand how voltage and amperage works. You keep confusing getting a different wattage element with a different voltage element. A 175w element will use roughly the same amperage from the batteries regardless of voltage. The Peukert effect will be identical.

Carrying this idea further -- one could make a single immersion element infinitely variable in power if you could regulate the voltage of the inverter. This could be really useful in matching the power of the inverter to the excess power which needs to be dumped.

Again, wattage is what controls, not voltage. Doing extra energy conversions when at anchor and energy supplies are limited doesn't make a lot of sense. Much better to use an element suited to the 12v power source and accept a loss of efficiency when you have near limitless power at dock.

[Dockhead]

Originally Posted by valhalla360

Again, wattage is what controls, not voltage.

Let me try to help you out here.

The very same 700 watt element (rated at 700 watts @ 230v) becomes a 175 watt element if you feed it with 110v. He is changing the WATTAGE of the element , by using 110v when he's on solar. If he plugs into shore power, he gets 700 watts again. Now do you see? All this information is in the very first post.


Sent from my D6633 using Cruisers Sailing Forum mobile app

[travellerw]

Originally Posted by Dockhead

Carrying this idea further -- one could make a single immersion element infinitely variable in power if you could regulate the voltage of the inverter. This could be really useful in matching the power of the inverter to the excess power which needs to be dumped.

Since MPPT solar controllers have become commodities these days, this would be a fantastic idea for a company to latch onto. An enterprising company could really differentiate themselves by adding this functionality into thier charge controllers.

[sailinglegend]

I think everyone should go back to the Ops original point.

Originally Posted by BjarneK

.....I run the water heater whenever I have excess power available or when I expect this to become the case during the day. .....This is using leftover power from 600 W of flat mounted solar panels in the tropics....

Many on here have argued repeatedly that most boats when they are sailing who say their batteries are fully charged by midday, will hardly ever be 100% fully charged. Those who believe that their batteries are fully charged when a little green light comes on, or as soon as their multi-stage controller says they are in “Float” mode, have been got by the “Charging Gotcha”. They may in fact be at 90% or less – that’s 20% down on your useable 100% battery capacity!

This is a problem with nearly all charging regulators because they don't know the capacity of the batteries, and they don’t know how much of the current they are supplying is actually going into the battery. They are all trying to charge the batteries without overcharging them. It takes a very long time to get from 90% to 100%.

If you are relying only on Solar to recharge your batteries, even with 600 watts of panels, then falling to float too early may mean that the batteries never get to 100% before the sun goes down, so there may be no excess power available to heat your water with.

There are lots of discussions on these forums about why 100% is important, and why Battery Monitors say the batteries are full when they are not.

[wiekeith]

Originally Posted by sailinglegend

I think everyone should go back to the Ops original point.


Many on here have argued repeatedly that most boats when they are sailing who say their batteries are fully charged by midday, will hardly ever be 100% fully charged. Those who believe that their batteries are fully charged when a little green light comes on, or as soon as their multi-stage controller says they are in “Float” mode, have been got by the “Charging Gotcha”. They may in fact be at 90% or less – that’s 20% down on your useable 100% battery capacity!

This is a problem with nearly all charging regulators because they don't know the capacity of the batteries, and they don’t know how much of the current they are supplying is actually going into the battery. They are all trying to charge the batteries without overcharging them. It takes a very long time to get from 90% to 100%.

If you are relying only on Solar to recharge your batteries, even with 600 watts of panels, then falling to float too early may mean that the batteries never get to 100% before the sun goes down, so there may be no excess power available to heat your water with.

There are lots of discussions on these forums about why 100% is important, and why Battery Monitors say the batteries are full when they are not.

But surely, if the charger is in float mode it will not be utilising all the potentially-available power from the solar, so there will be excess power available to use for other purposes?

[StuM]

Originally Posted by sailinglegend

If you are relying only on Solar to recharge your batteries, even with 600 watts of panels, then falling to float too early may mean that the batteries never get to 100% before the sun goes down, so there may be no excess power available to heat your water with.
.

That's a different issue.

The excess energy (not power) that is available is the difference between what the panels are putting out and what the batteries are able to accept (ignoring house loads). There is likely to be excess energy at any stage after the system has changed from bulk to absorption.

[sailinglegend]

Originally Posted by StuM

....There is likely to be excess energy at any stage after the system has changed from bulk to absorption.

Yes, but not enough to power a heavy load like an inverter and get the batteries back to 100%.

These are indeed different issues, but the belief that there is excess energy available when the batteries are in float misses the point that the batteries are still charging. If they stayed in absorption longer by reprogramming the charge controller, only then may they get to 100% before the sun goes down.

[noelex 77]

It is a shame to throw away solar power, so putting it to use is always sensible where it is possible.

Heating water is not an easy option. The power draw is high for most commercial solutions. Ideally what is needed is a variable heating element so the batteries could be kept in regulation, but the excess power dumped.

As Dockhead cleverly points out, this could be acieved with a simple element of fixed resistance fed by a variable voltage. A great solution. The hot water element can be kept as standard and still fed its nominal voltage when connected to shore power. Most high end solar regulators could be configured to control this.

All it needs is a commercial company to produce the box of tricks to interface between the element and the solar controller. With the cheap price of solar panels, solar installations are becoming larger and I think this could be a commercial success.

In the meantime, running a 230v element from 110v is a very simple solution and another clever idea. This sort of wattage while fixed is more likely to be a suitable load to allow the panels to at least supply the power without pushing the batteries into discharge. This is likely to be a better solution (unless the boat is equipped with a very large solar array) than running the element at its rated voltage.

[wiekeith]

Originally Posted by sailinglegend

Yes, but not enough to power a heavy load like an inverter and get the batteries back to 100%.

These are indeed different issues, but the belief that there is excess energy available when the batteries are in float misses the point that the batteries are still charging. If they stayed in absorption longer by reprogramming the charge controller, only then may they get to 100% before the sun goes down.

But isn't that precisely what this post is about? The OP's cleaver (IMHO) suggestion is a way of reducing the heavy load (heating element) in order to potentially utilise the excess energy without effecting the batteries state of charge.

[noelex 77]

Originally Posted by sailinglegend

This is a problem with nearly all charging regulators because they don't know the capacity of the batteries, and they don’t know how much of the current they are supplying is actually going into the battery. They are all trying to charge the batteries without overcharging them. It takes a very long time to get from 90% to 100%.

If you are relying only on Solar to recharge your batteries, even with 600 watts of panels, then falling to float too early may mean that the batteries never get to 100% before the sun goes down, so there may be no excess power available to heat your water with.

I don't see any evidence that most people are using charging programs with absorption times that are too short.

My controller is set up with an advanced system that adjusts the absorption time based on the battery return amps. As you suggest this provides the most appropiate termination of the absorption cycle. Typically this produces quite short absorption times. Less than 1/2 hour is not unusual.

Excess absorption time does not do much harm to flooded lead acid batteries. So if you have a fixed absorption time, setting it on the long side is sensible, but most are between 1.5 to 3 hours as a default.

[mrm]

Originally Posted by noelex 77

All it needs is a commercial company to produce the box of tricks to interface between the element and the solar controller. With the cheap price of solar panels, solar installations are becoming larger and I think this could be a commercial success.

Actually, there is no need to produce anything new. Switching mode power supplies with variable/adjustable output do exist. Varying output voltage accordingly to surplus energy available seems to be all that is needed..

[Dockhead]

Originally Posted by mrm

Actually, there is no need to produce anything new. Switching mode power supplies with variable/adjustable output do exist. Varying output voltage accordingly to surplus energy available seems to be all that is needed..

I wonder if you could feed them DC power? I don't really see why not.

In that case, you wouldn't need an inverter at all, and a variable power-dump load would be a cinch. You'd need a changeover switch, though.

The controller would be very simple -- just reduce output voltage from max until input voltage reaches the required float voltage, and if that is unachieveable, then zero. Switch it on manually after the charger is in float, or if you can get a signal from the solar controller indicating float status, you can use that to switch on the dump load automatically.