Solar PV panel Hot Water System

   / Solar PV panel Hot Water System #1  

FordnMassey

Silver Member
Joined
Jan 22, 2022
Messages
171
Tractor
ford 3000 and MF35
Hi,

Thought I'd share an experience of converting a gas storage hot water system to be solar panel powered, without the need for an inverter or getting involved in high voltage AC. Being in Australia, some of the terms may be different, so forgive any confusion.

The LPG (Propane) gas fired storage hot water system I have uses around 0.3kg of gas a day, which is enough to be a worthy target in reducing my carbon footprint. I bought 3000W of "thin film" panels for $100. They make 60V and around 110W each. Of the 28 panels, I used 9. The thin film panels are superior for my situation, where we have many overcast days, and thin film perform well in the overcast conditions. The 9 panels makes 1000W in full sun, or about 350W on a bright overcast day.

The heating element is a 60V DC 500W immersion heater (eBay) on a 1/2" BSP thread. It is around 18 cm long and 15mm diameter. It's installed using the spare ports provided on the tank, with a 1" galvo pipe now running between the top and bottom spare ports. Using a T at the bottom of this pipe, the heating element is screwed into one side of the T to be running up the pipe. Convection moves the hot water up the pipe and into the tank. Make a sheet metal cover to avoid heat losses.

A DC 10a 60V thermostat is available on eBay. Use the DC fuse holders and switches from the recovered solar panels to save money on those.

Online calculators show the requirements for cabling. Solar panel connections from eBay.

Panels come in different voltages, and so do the heating elements. Elements are available in different wattages as well.

500W is heating enough water in a warm climate for 2 people.

The gas system remains in place, inactive because of the thermostat setting, for use in winter.

Next project: DC water pump to header tank using the remaining panels.

Happy days
 
   / Solar PV panel Hot Water System #2  
Did directly heating the water in solar (water) panels ever enter into your plan?
Seems like you took the long way around to heat water.
I'm not being argumentative and know little about solar electric but have heated water in a bag (daily) on a rock for a whole summer for showering while we were building our home. That opened my eyes to this.
It's a purpose built "solar shower" I believe for camping. 👍
 
   / Solar PV panel Hot Water System #3  
Wouldn't it be more efficient to directly heat the water with a solar water heater?
 
   / Solar PV panel Hot Water System
  • Thread Starter
#4  
Hi,
Agree and understand the interest in heating the water directly in solar water panels. I've owned 2 solar HWS in my time, and installed one of them. Issues are the lack of second hand panels or the cost of materials to make them. Second hand solar electricity panels here are very cheap due to a regulatory change. There's also the issue with solar water heaters failure to perform on cold or windy days or days without direct sun. And I've had commercial panels corrode out. And you need the space for a convection setup or a pump. With this setup I'm making hot water on cool, windy, bright days without direct sun with no chance of a tank or panel leaking on my roof and no pump. And it only took 12 hours to assemble and AU$250.

I also had no suitable roof location or tank for solar hot water panels. I happen to have 2 old solar hot water panels stored, but went with solar electricity instead.
 
   / Solar PV panel Hot Water System #5  
Have you seen the 'solar' water heaters that use a coil of black PEX in a frame exposed to sunlight? Sometimes used as a 'poor man' pool/spa heater; the coil is plumbed in-line with the pool/spa pump.
 
   / Solar PV panel Hot Water System #6  
So your preheating the water before it goes into your water heater?

We cant use direct to water solar heaters in the northeast. Lack of sun and the freezing temps.
 
   / Solar PV panel Hot Water System
  • Thread Starter
#7  
Hi,
I plumbed the heating element into my existing propane fired tank. It heats the tank to around 60C/135F on a sunny day. I'm yet to experience winter with it, but I suspect it will be heating to around 30C/90F and then I'll finish the heating by turning the gas on each evening. A bit clumsy, but should reduce my propane use by around 150kg/300lb a year.

The appeal of this comes from access to PV panels cheaply. If you can get them cheaply, it's a good way of heating water on cold, windy sunny days.

Australia does a lot of pool and spa heating using plastic tubing on roofs, but I've not seen them enclosed. Do they work well?
 
   / Solar PV panel Hot Water System #8  
The sun heats my 20x40 indoor pool to as hot as I'd like. The previous owner installed FAFCO solar panels (5) on the roof and the pool stays 85 degrees controlled by a computer. We don't try to heat it throughout the winter (upstate NY), but we've had it that hot into early November before we shut it down for the winter. Snow and cloudy days eventually put a damper on things. I can only imagine how hot you could get a normal-sized hot water tank. To your point, the panels aren't cheap though and they are not something I'd buy secondhand. For 9 months out of the year, maybe a good combo direct and electric works.
 
   / Solar PV panel Hot Water System
  • Thread Starter
#9  
The sun heats my 20x40 indoor pool to as hot as I'd like. The previous owner installed FAFCO solar panels (5) on the roof and the pool stays 85 degrees controlled by a computer. We don't try to heat it throughout the winter (upstate NY), but we've had it that hot into early November before we shut it down for the winter. Snow and cloudy days eventually put a damper on things. I can only imagine how hot you could get a normal-sized hot water tank. To your point, the panels aren't cheap though and they are not something I'd buy secondhand. For 9 months out of the year, maybe a good combo direct and electric works.
That's an impressive amount of energy you're capturing, to heat a pool.
Panels here are "dumped" onto the second hand market as people upgrade their systems. I picked up 3000W of panels for Au$100~Us$66.
I only installed 1000W and am yet to see the winter performance.
 
   / Solar PV panel Hot Water System #10  
Electric is needed to run the pump that is sending the water for "free" heat. I guess the good news is that I'm not using both electricity and natural gas to make it happen. The cost you are getting for second hand solar panels I'd probably be trying the same thing :) That is great.
 
 
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