Hot water from PV?

[s/v Jedi]

You should stop and make sure that the water becomes hot enough before buildings these systems. A water heater sitting between 20-50 deg C is the recipe for legionnaires disease.

https://en.wikipedia.org/wiki/Legionnaires'_disease

[fxykty]

Originally Posted by s/v Jedi

You should stop and make sure that the water becomes hot enough before buildings these systems. A water heater sitting between 20-50 deg C is the recipe for legionnaires disease.



https://en.wikipedia.org/wiki/Legionnaires'_disease

But doesn’t that mean that every time our tank temperature decreases after being heated (through engine use or electric) we risk legionnaires? That doesn’t seem right.

[KWISPEL]

https://www.green-yachting.online/solarwaterheating

[s/v Jedi]

Originally Posted by fxykty

But doesn’t that mean that every time our tank temperature decreases after being heated (through engine use or electric) we risk legionnaires? That doesn’t seem right.

It doesn’t. It means that every heating cycle should bring it to 80 deg. C to kill any bacteria. There is code for this as well.

[noelex 77]

Originally Posted by goeasy123

I can only fit somewhere between 300 and 400w on the side rails. I have 420Ah of AGM.

If you have 300-400w of solar (and no option to fit more), water heating via these panels is not likely to be very productive. Water heating takes a lot of energy and after running normal house loads (even if you are frugal) there will not be enough energy left over to make much of an impact on water temperature.

If you can fit more solar it is a worthwhile goal. The traditional engine heated calorifier does not work well for many full time cruisers who do not spend much time in marinas and often have several days in the same anchorage. The options of tolerating cold showers or running the engine just to heat shower water are not appealing.

Unfortunately, diverting excess solar into water heating automatically is not easy. It needs a reasonably smart control system. The simple solution of powering an element when the battery voltage is above a certain level sounds appealing, but in practice does not work well. As the voltage reaches the level the solar controller will power the element but this will very rapidly drop the voltage and the cycle restarts. This not great for the batteries and the rapid switching is hard on the relay contacts.

The above problems are solvable with smart systems, but there are few commercial products that are suitable. Homemade solutions are possible, but they require some expertise and it hard to make something reliable in a marine environment. Ideally a solar controller that can operate a variable diversion load, like a wind generator controller would be perfect, but this is not the way solar controllers work. It is possible with some controllers. Plasmatronics and Midnite controllers can be wired to function in this way, but the resulting system is complex, with other drawbacks.

The popular Victron controllers have a reasonably programmable output with variable start and stop voltages combined with a two minute hysteresis that could be made to work with a simple on/off system (not a variable load), although I have never seen it done.

A simple KISS solution has a great deal of appeal. This can be done in several ways, but if you have a calorifier the easiest is a simple switch (with a relay to handle the high current) that can be activated to turn on the hot water element. This is not an automatic system but humans, with our large brain capacity (usually ) are in a good position to judge if enough solar power is available to allow the power draw to take place without unduly compromising the batteries. If you feel there is any danger of forgetting to turn the system off then a timer can be added.

The actual heating element used is not very important. The existing 120 or 240v element powered by an inverter will work with the above system. Slightly better and more efficient is a lower wattage DC element that can run directly from the house battery bank. These are not difficult to install although they do add some cost, especially if you want to retain the ability to heat water via shore power.

Personally, our shower system is very different using a dedicated water tank where the water is premixed to the correct temperature. This has many advantages. One of these is water heated in an electric kettle (via solar) can be used to shower. We can do this on most reasonable solar days, but when this is not possible a mix of solar, diesel water heating (via our Reflex) or propane/butane (via the stove) can be used depending on what is most suitable. I hate cold showers.

[Simi 60]

Originally Posted by s/v Jedi

It doesn’t. It means that every heating cycle should bring it to 80 deg. C to kill any bacteria. There is code for this as well.

In Australia.........

70 degrees celsius
Under Australian law the internal temperature of a hot water heater must be set at 70 degrees celsius. This temperature kills harmful bacteria and preserves a safe operating temperature for your hot water system.Feb 20, 2017

https://australianhotwater.com.au/hot-water-safety/

[Simi 60]

Originally Posted by noelex 77

If you have 300-400w of solar (and no option to fit more), water heating via these panels is not likely to be very productive. Water heating takes a lot of energy and after running normal house loads (even if you are frugal) there will not be enough energy left over to make much of an impact on water temperature.

We have 2.2kW of solar and that is enough.......just, for a 240v hot water system
On a good day we do have + amps coming in during the heating cycle

[Pete7]

Sailing ABC used a magic widget from France to switch the solar at a set point to a 12v water heater. Didn't quite go to plan and the widget had to be repaired. However, they have 600w of solar to manage the boats needs then heat the water.

Given your location in N Spain, a solar water heater might be easier from Spring to late Autumn.

Originally Posted by goeasy123

I can only fit somewhere between 300 and 400w on the side rails. .

We have 300w and when it sunny, great. When its heavy cloud and rain we are down to 60w as the rain trickles into the bucket.

Pete

https://www.youtube.com/watch?v=JxuA...l=SailingABSea

[noelex 77]

Originally Posted by Simi 60

We have 2.2kW of solar and that is enough.......just, for a 240v hot water system
On a good day we do have + amps coming in during the heating cycle

I am not surprised .

We have just over 1000w and except in the colder months in more northern latitudes we have enough solar power for electric cooking and hot water, including showering.

There are signifant variations between different boats, but the amount of electrical energy available for these optional type of functions is not linear with solar array size. It takes a certain base level to run basic necessities such as lights, pumps, fridge, navigation, electronics, entertainment etc so a boat with, for example, a 500w solar array does not typically have half the available power for water heating that a boat with 1000w may have.

Solar energy is fantastic. Reliable, trouble free, silent etc, but it is important to be realistic about the power available, particularly the power that can be used consistently. Unless you have a very large solar array, have alternative means for accomplishing high energy tasks such as cooking and water heating, especially if you want the ability to cruise areas or in seasons with lower solar insolation.

[AndyEss]

At the risk of starting another thread war, if you have propane for cooking, small, instant water heaters are available at about or less than $100 (US). They take up little space, and vent thru the cabin top.
I’ve maxed out my area for solar panels at about 500 watts. When my cranial capacity is available to chose a load when my batteries are full, I turn on my watermaker. It’s rare to have too much freshwater when there’s water, water everywhere - but none to drink.
Another hot water option might be to use the bottom of the panels to transmit heat to a water system. This would also cool the panels, increasing electrical generation efficiencies. One outfit was selling these integrated panels last time I looked about two years ago, but they might be a bit of a pain to plumb.

[skenn_ie]

Get a heating element that runs on your DC rail voltage. Connect a relay that kicks in at just under battery-full votage. If you have a turbine, use the same element as the braking load.

[zstine]

Originally Posted by noelex 77

I am not surprised .

We have just over 1000w and except in the colder months in more northern latitudes we have enough solar power for electric cooking and hot water, including showering.

There are signifant variations between different boats, but the amount of electrical energy available for these optional type of functions is not linear with solar array size. It takes a certain base level to run basic necessities such as lights, pumps, fridge, navigation, electronics, entertainment etc so a boat with, for example, a 500w solar array does not typically have half the available power for water heating that a boat with 1000w may have.

Solar energy is fantastic. Reliable, trouble free, silent etc, but it is important to be realistic about the power available, particularly the power that can be used consistently. Unless you have a very large solar array, have alternative means for accomplishing high energy tasks such as cooking and water heating, especially if you want the ability to cruise areas or in seasons with lower solar insolation.

According to the calculator linked below, It takes 3 hours to heat 6 gallons of water from 75F (24C) to 175F (80C) at 500W input.


I have 530W solar and typically reach 100% SOC before noon. Giving me maybe 3 hours of 500W wasted power. This is sufficient to heat my 6 gal tank to scalding hot temps!

If the OP is not going to have this much heat (110F is warm enough for a shower) and is concerned about Legionnaires disease, Then he can add some bleach to his water and have no worries!

https://bloglocation.com/art/water-h...e-energy-power

[zstine]

Originally Posted by skenn_ie

Get a heating element that runs on your DC rail voltage. Connect a relay that kicks in at just under battery-full votage. If you have a turbine, use the same element as the braking load.

As has been said before, this setup is not desired because the water heat will turn on as soon as Absorption phase is reached in the battery charge cycle. The redirection of power away from charging batteries may result in chronic under-charging of the batteries.


He can wire a switch and flip it manually when his batteries are at 100% SOC or purchase one of the charge controllers that have relay outputs that switch at 100% SOC. I think many of the Victron MPPT charges have this.

[Talbot]

An alternative approach, that I have seen is to construct a direct solar heating system for your water. - relatively straight forward if you already have a calorifier. Just tap into the feeds and divert through a thermostatically driven pump to copper coils on the deck. Paint the copper black and you have a free heat source.

[s/v Jedi]

Originally Posted by zstine

According to the calculator linked below, It takes 3 hours to heat 6 gallons of water from 75F (24C) to 175F (80C) at 500W input.


I have 530W solar and typically reach 100% SOC before noon. Giving me maybe 3 hours of 500W wasted power. This is sufficient to heat my 6 gal tank to scalding hot temps!

If the OP is not going to have this much heat (110F is warm enough for a shower) and is concerned about Legionnaires disease, Then he can add some bleach to his water and have no worries!

https://bloglocation.com/art/water-h...e-energy-power

You can not rely on bleach for preventing Legionnaires disease for hot water systems because heat evaporate chlorine before it can do it’s work. See https://www.cdc.gov/legionella/about/prevention.html for more info.