Using the underfloor heating pipes to harvest heat from underneath photovoltaic panels
Darko SavicNov 19, 2021
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Underfloor heating pipes laid underneath photovoltaic panels. The circulating water then transfers the heat into homes, swimming pools, etc. Cooled solar panels produce electricity more efficiently.
Increased efficiency of the cooled solar panels results in higher electricity production.
Bonus hot water to heat homes, swimming pools, etc.
How it works
Various types of pipes are available specifically for liquid-based underfloor heating and cooling systems. They are mainly made from polyethylene, including PEX, PEX-Al-PEX, and PERT. They are cheap, flexible, and durable.
Rigid plasticized welded wire mesh would be cut to fit underneath each panel. The underfloor heating pipe would be looped and zip-tied to the mesh. The mesh would then be mounted underneath the photovoltaic panels so that the pipe is sandwiched in between the panels and the mesh.
Each panel has a strong aluminium frame with universal mounting holes drilled into the bottom side of the frame. Some of those holes would be used to hold the mesh tightly pressed against the bottom side of the panel.
Heating the water while cooling the panel
On sunny days the water would continously circulate through the pipe and cool the panel. This increases the efficiency/output of electricity.
As a side effect, there would be warm/hot water available. It could be used to heat homes, swimming pools, provide hot water, etc.
The water needs to be circulated through a large enough body of water so that it takes a while before all the water is heated up.
For added efficiency the hot water could frist go through a heat exchange pump:
In our case, the heat exchanger is mounted underneath the photovoltaic panels.
Melting snow from the solar panels
Solar panles covered by snow produce no electricity. They are often not easily accessible for snow removal. The snow could be melted via the same underfloor heating pipe, by heating the panels from below. In this case, the water in the pipes would be heated by an external source. The water would need to be substituted by antifreeze, to prevent it from freezing, expanding, and damaging the system.
There is a business opportunity for a manufacturer to create easy mounting systems, compatible with various photovoltaic panel dimensions.
K.A. Moharram, M.S. Abd-Elhady, H.A. Kandil, H. El-Sherif,
Enhancing the performance of photovoltaic panels by water cooling,
Ain Shams Engineering Journal,
Volume 4, Issue 4,
Some existing solutions that could help create a more efficient system
J. NikolaNov 26, 2021
Hi Darko Savic!
The idea is really cool, so I decided to do a small research on it. I found these:
Passive and active water heating solar systems
These systems have 2 main parts: the collector surface and the water tank. Collector surfaces can be flat (conventional) or made of vacuum tubes that can harvest more energy due to better-angeled insolation (especially during winter) and are less prone to accumulation of dirt and other materials on the surface. More information can be found here.
The above-mentioned flat surface system would fit your story perfectly if the surface was used to produce and store electric energy, too. Also, I am not sure if vacuum tubes can be used for the same purpose, but it definitely sounds cool. A guy did a comparison of the efficiency of the solar photovoltage panels (heating water with electricity) vs solar thermal panels (mentioned in the paragraph above; heating water with sun). The results were that the PV panels perform better!
Therefore, I would suggest sticking to your solution to place flat surface PV solar panels and use them to produce electricity and heat water!
Hybrid solar panels
Now, you proposed a system where heating pipes are placed under the solar panels. These researchers did a nice job explaining the history, novel materials and methods used to combine these too technologies.
Since the 1980s, when the first idea of the photovoltage/thermal panels emerged, a lot has been done to find a more efficient solution. On the backside of the PV panel, tubes or a thermal collecting-container was placed. The tubes were either empty or filled with liquid, depending on the usage (heating air or water). The researchers from the linked paper suggested using the phase change materials (PCM) to increase the efficiency of these systems.
The first picture describes the front and the back of the hybrid panel. The heat pipes (HPs), green elements, are the heat pipes and are placed under the black perimeter of the panel surface. On the lower part of the picture, a cross-section of the panel is described.
What they managed to achieve is the local heat storage inside the panel (PCM), greater thermal homogeneity, higher PC efficiency, adjustable heat/electricity ratio (customizable), dual PCM heating and using less space. They stated that their system can be efficient in generating electricity as an average solar panels, while, at the same time, being used for low-temperature heating systems, such as the floor heating. With some adjustments, they promise higher temperature yield from the thermal component of the system!
Here is one more example of people combining these.
So, conclusions are:
put the pipes inside the panels somehow
use transparent solar panels or transparent pipes if possible
try to store the heat in a fluid that has great thermal properties and help heat distribution to boost the PV efficiency
try not to lose a lot of heat in the pipes between the collector and the tank
In the same manner, the heat to the pipes could be harvested from many other surfaces exposed to sunlight, not only photovoltaic panels. The main thing that comes to mind is tin-plated roofs, the heat in private houses covered with tin roofs could then be used to provide heating/warm water.
The proposed melting of the snow could also be useful to remove the snow from the roofs because snow and ice falling from rooftops in winter can harm passers-by. This is more relevant for city streets, but in general perhaps for every house which has at least two floors.
The snow in this manner could be removed in a matter of few hours or even sooner depending on the temperature of the water circulating underneath and the thickness of the snow layer, so closing the sidewalk for a few hours would be way more convenient than closing it for days due to falling snow and icicles.