Using Excess Solar Power to heat water....

puiumeu

New member
Hi everyone,

As we will have an air cooled engine I have no residual hot water to share from the engine.

I would like to, after my electric system is charged to a set amount be able to route solar power to the electrical input of a Truma Combi D 6 E.

The idea is this would at least keep the water warm in the background and thus require less power to get it to full temp before use.

Does anyone have or know of such a solution or can offer any advice or any other solutions.

It is planned to have about 800w solar power and use Lithium or LiFePO4 batteries as our goal is not to be places with mains hook ups....

Thanks in advance.

Al.
 

WOODY2

Adventurer
Have you considered building some type of heat coil or exchanger centered around the exhaust system?
 

Bbasso

Expedition Leader
800watts?!?
What do you plan on powering?
And what size is the battery bank?

Maybe take one 100 w panel into a scc then into a med-size agm just for for the heater element? And that would be it's own system always active.
 

dwh

Tail-End Charlie
Use a Midnite Classic charge controller. Has dump load relay for wind, not needed for solar. Use that relay to switch on dedicated inverter for water heating element.
 

wanderer-rrorc

Explorer
Abs piping on the roof that absorbs sunlight direct and heats the water? Via solar shower..

Sent from my VS987 using Tapatalk
 

Factoid

Three criminal heroes
I have researched and tested a bunch of solutions to this issue. In my current build, I am targeting an off grid completely electric solution that relies on solar and battery storage while sitting and will charge the batteries via a separate alternator while the engine is running. Things to consider:

1. An on demand electric heater is the only way to go. They are more effficient and draw less current. The wattage demand is not your friend when trying to heat water with electricity.

2. Modify how you shower. Plan your shower to take advantage of times where you have the most wattage available (full sun at noon, fully charged batteries, etc.). Of course you will take what we called a sailor shower when I was in the navy. Water on to wet down, water off to lather up, water on to rinse off. This conserves both water and energy and irritates the wife, but such is the sacrifice of trying to live off grid for extended periods.

3. Consider how you store and convert energy. Energy can be stored in a variety of ways. For example, as hot water in a tank or an electrical charge in a battery. It could also be stored as both depending on how and when you want to use it. For example, you could use a tankless heater in recirculate mode (heats and reheats the same water until a set temperature is reached) with a tank to store the hot water once it reaches an effective temperature. This allows you to use a lower amperage heater, turn it on just prior to your shower and then shower once the tank is full of hot water.

4. Consider how you source and store fresh water. The higher the inlet temperature to the on demand heater, the faster and more efficient it heats the water. If you regularly travel in sub freezing environments, you have to keep your onboard water from freezing, but you also now need to keep it as close to room temperature as possible for maximum efficiency.

5. Consider how you wire your system. There is no reason to have a dedicated battery or energy source for hot water. There is however a good reason to be able to switch all power to the hot water heater when you need it and turn of other electricity consumers. Even tankless heaters are huge consumers of precious electricity and you do not want to overload your system. A dedicated switch from you inverter that either powers the hot water heater and water pump or everything else (including said water pump) is important. Overloads don't just trip breakers. They introduce heat that can cause longer term damage to wiring and loosen connections in a vehicle that moves and vibrates.

6. Select your components carefully. Here is one of the lowest consumption on demand electric heaters, that frankly is barely up to the task, but is reasonably priced and rugged. Ecosmart POU 3.5 Point of Use Electric Tankless Water Heater, 3.5KW@120-Volt https://www.amazon.com/dp/B0047RAQZG/ref=cm_sw_r_cp_tai_OV3OAbQ6EVMJ3

I say go for it and don't be afraid to try some different approaches until you figure out what works best for you. Oh, and then report back here on your success!
 

Joe917

Explorer
No problem. we have 630 watts on the roof, so similar to you. We have a 5 gal Isotemp Spa hot water heater with a 230 volt element. We keep an eye on the battery bank state of charge, when it is full or almost full we turn on the hot water tank. Pretty simple and effective. Water stays hot a long time in the tank.
There are two element options with that tank. 750 and 1500 watts. Choose the 750watt and the panels can almost handle the load alone in good sun.
 

Haf-E

Expedition Leader
Using the excess solar energy to heat water in a tank is a practical idea - it is also possible to power the same water heater from the engine's alternator as well.

If you have a built in electrical element in the tank - it can be powered by either an inverter (at 230VAC 50HZ in your case) or even 24VDC directly from the vehicle or batteries. If the element is 1500 Watts - then at 28V it will draw would only consume 24 watts - so a different water heating element would be needed to use the DC directly. (if that same 1500 Watt element was 115VAC - then it would use 95 Watts at 24VDC).

I would not use a point-of-use type tankless water heater as the better idea is to heat water once the battery is full or while the engine is running - therefore utilizing energy which would otherwise not be used. Going with a water heater element in the 500 watt range would probably be best - but it depends on the size of the inverter and engine alternator.

What inverter are you using? Many have the ability to power an external relay to control a diversion loads such as a water heater element.

Here is a good explanation of how you calculate water temp rise and the energy required: https://elementsofheating.wordpress.com/2012/09/26/how-to-calculate-the-kw-required-to-heat-a-volume-of-water-in-a-particular-time/

-------------------------------------------------------------------------------------------------------

The following formula is used to calculate the power of heating element needed to heat a specific volume of water by a given temperature rise in 1 hour.

volume in litres x 4 x temperature rise in degrees centigrade / 3412

(4 being a factor and 3412 being a given constant)

for example 100 litres of water, to be heated from 20ºC to 50ºC, giving a temperature rise of 30ºC would give –

100 x 4 x 30 / 3412 = 3.52

meaning that the water would be heated in 1 hour by 3.5kW of applied heat.

Also we can use this information to extrapolate both ways. To heat the same water volume in half the time (30 minutes) would need twice the heating power, ie, 7kW.

Converesely, if we only use half the heating power, 1.75kW, it will take twice as long to heat up to desired temperature, ie, 2 hours.

If we only have a 1kW element available, we will expect a heat up time in excess of 3 hours.
 
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rayra

Expedition Leader
Abs piping on the roof that absorbs sunlight direct and heats the water? Via solar shower..

Sent from my VS987 using Tapatalk

Yep and that way you just need a little power for a circulatory pump. There's a guy in the storage forum that did an awesome hot water tank in the back of his pickup, btu he used a radiator coolant loop and a heat exchanger. But he used a circulation pump to move his stored potable water thru the exchanger on the tank side.
 

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