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DIY 12v / 24v solar thermal HW system on a barge

FloaterBoater

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Aug 28, 2022
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Hi there, first time posting so apologies if I'm going over old ground. I'm looking to install a solar thermal system on my liveaboard Dutch barge and was hoping for some thoughts/feedback on my ideas.


I've recently had the central heating onboard updated. The primary heat source is a 15 kw diesel boiler. As part of that retrofit, i had a 3 coil unvented tank (calorifier) installed. 1 coil is for the boiler, one for the engine, and one is spare with the intention of using for solar thermal. The tank volume is 90-100 litres. The tank also has a 1000w, 240v immersion heater. We are two people onboard and rarely get through a tank to the point of cold water, with heating cycles in the morning and evening. The barge is located on the Thames in London, UK.

Ideally I would like the system to be self supporting, meaning it would be powered by its own PV panel connected to an independent 12v battery. The domestic systems onboard are 24v and 240v shore line. Ideally i would rather not have a draw on either of those systems for a variety of reasons.

The barge is fairly large, with a good amount of roof space, though I separately have plans for a fairly powerful PV system in future which would likely also include a solar dump to the immersion.

General questions I have.

- Any recommendations for equipment in terms of control units, pumps, etc?
- Thoughts on how large the collector would need to be / how many? I don't really know how to size these.
- The tank does not have inbuilt locations for temperature sensors. I'm assuming that thermistors on the tank body and possibly HW output would be ok? I can't find any real online resources that explain how this works.
- Is this even a road worth going down with a relatively small tank compared to what I've seen in my research?
- Any other words of wisdom/products to recommend/resources to look at?

Thanks so much,
Rob
 
"The tank volume is 90-100 litres. The tank also has a 1000w, 240v immersion heater."

Disregarding AC/DC, let's say to heat 100 liters of water one degree C, you need:
Kilowatt hours = (4.2 × 100 × 1 ) ÷ 3600 = .1166kwh.

If you were delivering a full 1K watts to the tank for one hour you'd heat the water by about 8.6°c.

Have you considered just powering that heating element directly with a panel (or one with a lower, DC appropriate resistance screwed in it's place)?
You could dump extra energy/heat into your tank basically any time the sun was out. You'd want to leave a secondary system in place with a lower setpoint to help overnight or on cloudy days and you'd also want a way to dump some heat if it gets too hot. But otherwise you could achieve a lot without anything that gets wear and tear like a battery...
 
Your water tank capacity is too large for a dc element to be fitted.
If you have the roof space 4 x 300watts + half cut cell 35-40 volts solar panels and 600ah + battery storage as a 24 volt system
you can run almost everything dc to dc without a dc to ac inverter so less items to go wrong, including a dc 15 ltr hot water heating system enough for a couple of showers/washing dishes.
You can use a split charge relay to use wasted pv energy to power the water heater as a dump load so the leisure batteries are not discharged.
Step down adjustable dc to dc buck converters can be used to power 19 volt dc laptops/tv/satellite and 12 volt dc items and you can use a a dc to ac inverter to heat the larger hot water tank in the summer.
If you have roof space for 6 plus solar panels in series you could fit a hybrid high voltage battery less system that converts dc to ac directly with grid/generator battery charging back up for a battery bank.
 
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