P.V. Solar Hot Water System. D.I.Y.

[Jing Joe]

Noticed in a recent article about "last power bill ever" some are using solar water panels at ground level for hot water systems, the temps are probably not great, and tanks need mounting at a higher level to prevent reverse cycling at night.

This suggestion below is definately D.I.Y. whereby 6 x 250Watt second hand off grid 30V P.V. panels can be on the roof out of the way, and a 200 litre tank (max) can be anywhere. Diversification and increased thermal storage is the theme.    Similar commercial designs are on the market.

Screw in a 48v DC element (typically 1.6kw) into the tank with the usual 2 small links rearranged in series to make it a 96V element. Matching of the 90V panel config to that element voltage appears best.

Install 2 strings of 3 P.V. panels each, to give 90V at about 16A combined, and feed that current via a 25A? safety isolation C/B, to a typical 30A 300V? D.C. Solid State Relay on a matching heat sink, to the element.

Connect a very small 12v solar panel (100/200ma) via a small on/off switch, via the system's thermostat to turn the SSR on/off, and adjust the temperature up to 95 degrees if you choose, BUT then must have a tempering valve near the tank outlet to mix cold water, adjusted to give about 50 degrees, or to suit the regulations. 40 is ok for showers if the insulated feed line length doesn't lose much heat. Absorbtion type tank or low pressure design? you can work around that.

If the tank has good insulation, the increased stored thermal energy can with care last many more days at 95 derees during cloudy weather, compared to the typical lower maximum temperatures of the old hot water pipe plate absorbers.     Want better tank insulation? dismantle the outer skin and replace with better stuff.  Need an sacrificial anode because of acidic water? Your decide.

Skeptics dont bother.   My system has worked amazingy for 5 years now.

 

 

 

 

 

[Bandersnatch]

40 minutes ago, Jing Joe said:

Noticed in a recent article about "last power bill ever" some are using solar water panels at ground level for hot water systems, the temps are probably not great, and tanks need mounting at a higher level to prevent reverse cycling at night.

 

I was the poster in the  "last power bill ever" 

 

I just want to correct something you said in case people get the wrong impression about solar thermal.

 

"the temps are probably not great" 

 

Unless ambient temperatures drop to low teens I always have to add cold water as the hot water is scalding hot on it's own.

 

"some are using solar water panels at ground level for hot water systems" - yes that's me again

 

 

"and tanks need mounting at a higher level to prevent reverse cycling at night."

 

I am not sure what you mean by "reverse cycling at night" I assume you mean the daytime convection system working in reverse at night, but that doesn't happen with my setup.

 

On the right side of the tank (the side you can see) fresh cold water is added to the bottom of the tank as hot water is used (blue pipe)

Hot water leaves the top of panel (green pipe) and enters the top of the insulated 200L tank 

 

The side of the tank you can't see 

 

Hot water leaves the top of the tank (green pipe) to go to the bathrooms

The coldest water in the tank is most dense (convection) sinks to the bottom of tank and follows another green pipe to enter bottom of the panel to be reheated by the sun.

 

During the day water is constantly moving via convection as water gets heated in the panel rises and displaces the coolest water in the tank.

 

At night the tank is insulated so stays hot, the panel is not insulated so the water is cooler and no water moves between the panel and the tank unless hot water is sent to the bathroom.

 

My system has an emersion heater with various settings like time to start and stop heating; minimum temperature to maintain, but I have never used it.

 

 My system has also worked amazingly for over 5 years now.

 

One criticism I would acknowledge about solar thermal is that it is expensive. My system cost ฿30,000 6 years ago, but I have heard people paying more than twice that more recently.

 

The system is pressurized with pressure release valves so no pump is required  

 

 

 

 

 

 

 

 

 

 

[radiochaser]

11 hours ago, Bandersnatch said:

 

I was the poster in the  "last power bill ever" 

 

I just want to correct something you said in case people get the wrong impression about solar thermal.

 

"the temps are probably not great" 

 

Unless ambient temperatures drop to low teens I always have to add cold water as the hot water is scalding hot on it's own.

 

"some are using solar water panels at ground level for hot water systems" - yes that's me again

 

 

"and tanks need mounting at a higher level to prevent reverse cycling at night."

 

I am not sure what you mean by "reverse cycling at night" I assume you mean the daytime convection system working in reverse at night, but that doesn't happen with my setup.

 

On the right side of the tank (the side you can see) fresh cold water is added to the bottom of the tank as hot water is used (blue pipe)

Hot water leaves the top of panel (green pipe) and enters the top of the insulated 200L tank 

 

The side of the tank you can't see 

 

Hot water leaves the top of the tank (green pipe) to go to the bathrooms

The coldest water in the tank is most dense (convection) sinks to the bottom of tank and follows another green pipe to enter bottom of the panel to be reheated by the sun.

 

During the day water is constantly moving via convection as water gets heated in the panel rises and displaces the coolest water in the tank.

 

At night the tank is insulated so stays hot, the panel is not insulated so the water is cooler and no water moves between the panel and the tank unless hot water is sent to the bathroom.

 

My system has an emersion heater with various settings like time to start and stop heating; minimum temperature to maintain, but I have never used it.

 

 My system has also worked amazingly for over 5 years now.

 

One criticism I would acknowledge about solar thermal is that it is expensive. My system cost ฿30,000 6 years ago, but I have heard people paying more than twice that more recently.

 

The system is pressurized with pressure release valves so no pump is required  

 

 

How hot does the water get with that system?

 

 

 

 

 

 

 

 

[Muhendis]

12 hours ago, Bandersnatch said:

I assume you mean the daytime convection system working in reverse at night, but that doesn't happen with my setup.

I also think that is what the OP means.

If the storage tank is higher than the heat collector panel then there can be no reverse convection at night.

With my system, the 200 litre storage tank is lower so there is no natural convection circulation. I use a small 7W pump to do that.

To get around the reverse nighttime circulation I have an NRV (non-reverse valve or check valve).

The system also has a small expansion tank. Total cost in the order of 10k baht and has been in service for over ten years now and always gives hot to scolding hot water.

I would not be atall happy with the idea of making electricity to heat water when we can do it more directly from that big fusion power station in the sky.

[Crossy]

Direct solar water heating will convert about 80% of the arriving sunshine into heat in the water.

 

Going via PV panels is closer to 20% or less.

 

But going PV is more flexible as to layout and cable is easier to route from where the sun is to where the hot water is needed.

 

Horses for courses.

[Muhendis]

3 minutes ago, Crossy said:

Direct solar water heating will convert about 80% of the arriving sunshine into heat in the water.

 

Going via PV panels is closer to 20% or less.

 

But going PV is more flexible as to layout and cable is easier to route from where the sun is to where the hot water is needed.

 

Horses for courses.

Horses for courses indeed.

It depends how much space is available. I have a "well house" which contains a surface water well, lots of filters and a couple of big storage tanks as well as the hot water storage and automatic house water pump. The heat exchanger for the hot water is on the roof of the well house. 

I am fortunate in that I have plenty of space to do what I have done. All my hot water bits are easily located relative to each other.

There is a down side.

The hot water needs to travel 30 Metres in an underground gulley so a minute of patience is in order and a few litres of cold water is wasted.

 

I would imagine that living in a townhouse, one may not necessarily have things in such a convenient arrangement so routeing cables would generally be easier than plumbing pipes.

[Bandersnatch]

My supplier is no longer selling solar thermal. I have a friend who bought one recently, it was quite expensive, but he is very happy with it.

 

 

 

 

 

 

[Jing Joe]

Sorry guys. Couldnt locate the A/N page for my "brilliant" invention some 5 years ago. 😇 after which I discovered was commercially available anyway.🫢

 

Ever since originally designed by Aussie? guy, about 100?  years ago, many newer desig features got temps up, better back-insulation in water plates, vacuum tubes, curved focussing mirrors etc, all to raise temp and improve efficiency. Farms till then had slow combustion stoves with a water filled back plate in the fire box.

Bander you are very neat, and lucky you copied Solarhart brand design whereby the low profile tank is easy to establish that critical distance above the uppermost plate level being below the cold tank input to prevent reverse cycle at night. Older mug shaped tanks protruded high above the plates.

Conversly my orig thermal plates were 3 metres above tank so needed special consids. Briefly:- a sensor in top of plate also top of tank, comparator, small circ pump for daytime. Leave it. Sure a low push-n-flow NRV and/or pump can prevent reverses cycling. Leave it.

Should have tablated design reasons in the long body of orig text:-

1. A much higher tank temp of 95 is a  higher stored thermal mass over many days of following clouds. Tempering vale? OH YES.    Greater Delta T suggests good "r" factor of insulation to take advantage of.  Much higher tank temp is possible. Even boils if bypassing the thermostat, not so with thermal plates.  

      No plate frost danger.    In L.O.S.? ha ha.

2. Total flex location design of both Solar P.V. and tank.

3. Negates water leakage mtnce.

4. Low Press water supply negates need for steam release.

5. S/H solar P.V. panels made it very cheap.

6.  Independent of A/C power avoids my home battery accidental drain.

7. Back up energy source for shorter days? or more clouds?   up to your

    imigination/needs.

Cheers guys, and seems like the badgering non-experienced skeptics bowed out this time and noticing how Bander and others are now respectfully "up there" where they belong.

Dont ya just love the Thai boots beside the neat but vulnerable  H.W.S.😚 in Banders pic.

 

 

On 2/15/2024 at 3:44 PM, Bandersnatch said:

My supplier is no longer selling solar thermal. I have a friend who bought one recently, it was quite expensive, but he is very happy with it.

 

 

 

 

 

 

 

 

 

 

 

 

 

[Jing Joe]

On 2/15/2024 at 11:36 AM, Crossy said:

Direct solar water heating will convert about 80% of the arriving sunshine into heat in the water.

 

Going via PV panels is closer to 20% or less.

 

But going PV is more flexible as to layout and cable is easier to route from where the sun is to where the hot water is needed.

 

Horses for courses.

Yes Crossy, of the typical 1000W/sq metre of solar insolation, the water panels might gain 80% of that energy compared to the 25% per square m of P.V. panels,(that work best in cold weather) but the max temp of the former is limited to the protected ambient air temps of water panels and "r" factor of back-of-plate insulation and maybe double glazing etc. then vacuum and mirror tubes later became state of art. 

Again.. my aim was high levels of stored thermal energy (because of 95water temps) for following cloudy weather.   Like you say:- horses for courses.  i.e. clouds and family usage. 

Are you into stored heat in "sand batteries" heated by P.V.?  My next project. Similar principle i.e.  higher thermal energy stored at phenominal temperatures like 1000 degrees?? for winter heating houses.  Happening in Europe at council level.      L

[Jing Joe]

Cant quite make out what it is exactly in Banders picture (no glass?) but did anyone see a possibility of what could be "heat tube" design?  Very old and amazingly efficient technique where evaporation, transfer of energy, then condesation is used and has comparative conduction to gold bar transfer efficiencies.