Swimmig Pool Submerged Photovoltaic Solar Panel
Swimming pools are rather expensive luxury equipments, requiring continuous maintenance, often used in zones strong solar radiation.
This projects aims at using the solar energy impinging on the swimming pool with two main goals:
- to produce electric power for the electric network.
- to take advantage of the available space available in a swimming pool with minimal modifications and esthetic impact.
This dual goal can be reached thanks to the SP2 patent by SIT. This patent suggests a new use for photovoltaic panels by submerging them in water. The experimentations already carried out demonstrate that the when submerged in a thin water layer, PV panels increase their efficiency of approximately 10% (with summer peaks of 20%). Panels submerged 1-2 meters deep, instead, have a comparable yield with the panels normally exposed to sunlight. It is also possible to record equivalent behaviors, or, at least, a 10-20% reduction depending on the PV active material.
For sake of simplicity we can assume a 50 m2 (5x10) swimming pool, 1.2 meter-deep, except the last two meters where the depth reaches 1,8 meters with a total water volume of 66 m3. Here are considered two systems:
Overflow swimming pool. An edge of the swimming pool is covered with a thin layer of water, or a small cascade in equilibrium with the pool surface.
Skimmer swimming pool. The edge of the pool is made of stone, and raises several centimeters above the pool. A skimmer takes water from the pool, and pumps it through a filtering system
In both cases, the PV panels are positioned on the pool edge. Both single-crystalline and poly- crystalline panels are suitable to this scope. Another group of PV panels is positioned on the pool floor. In such case amorphous silicon seems to be the best technical solution.
Overflow swimming pool
Figure 1 shows the optimal solution for overflow swimming pools.
Figure 1 Overflow swimming pool. with PV panels on the edge
Details are given in figure 2.
The water falling down the grating encircling the swimming pool skims over he PV panel. These panels can be of any PV type or material. Experimental tests have verified that the system works well, and its efficiency increase is around 10-20%. By increasing the surface touched by the water, a waterfall further improves the performance.
Figure 2 Detail of an Overflow swimming pool
A second series of panels is submerged into water and is embedded in the bottom of the swimming pool. The available surface is of 45 m2 and the suggested panels are amorphous silicon panels. This for two reasons:
- Amorphous silicon gives good yields of conversion up to a depth of 1.5 meters, while single and polycrystalline silicon loose up to 20% of efficiency at one meter depth.
- Today, amorphous silicon is produced in compact and cheap panels, suitable to be integrated with the swimming pool’s floor.
Figure 3 The panels on the bottom of the swimming pool
Figure 4 Underwater view of the bottom of the swimming pool.
Figure 4 shows the floor of the swimming pool in amorphous silicon. The structure of the panels is used to design the bottom swimming lanes.
Swimming pools are normally used during six months a year, from April to September.
The following table shows the expected yields in kWh/day for several months, at Rome’s latitude.
| Average radiation Watt/m2 |
Pv deep kWh/day |
PV edge kWh/day |
Total kWh/day |
|
|---|---|---|---|---|
| April | 269 | 29,1 | 18,4 | 47,5 |
| May | 325 | 35,1 | 22,3 | 57,4 |
| June | 359 | 38,8 | 24,6 | 63,4 |
| July | 363 | 39,2 | 24,9 | 64,1 |
| August | 338 | 36,5 | 23,2 | 59,7 |
| September | 289 | 31,2 | 19,8 | 51,0 |
| Total production kWh | 6295 | 3995 | 10291 | |
We assumed an available surface of 45 m2 for the panels in amorphous silicon on the bottom of the swimming pool (10% efficiency), and a surface of 13.6 m2 for the panels on the edge in silicon mono or polycrystalline (14% efficiency). The total costs are estimated in the table below, assuming a cost for the amorphous silicon of 200 €/m2, and of 300 €/m2 for the single crystalline silicon.
The annual return has been calculated assuming greens credits for 0,42 €/kWh, and 0,10 € for the sale of the current on the grid.
| Panel Cost Deep | 9000 |
| Panel Cost Edge | 4080 |
| Inverter | 3000 |
| Total cost | 16080 |
|---|---|
| Annual revenue | 5017 |
| Payback year | 3,21 |
Skimmer Swimming pools
If the swimming pool has a kerb with inner water circulation, then the design will necessarily change. However, this type of swimming pool will also have a better and more efficient potential.
Figure 5 illustrates today’s most widely used solution: it is the common solution for open air swimming pools since the overflow technique, although with better performances, is more expensive and anyway suitable for PV arrangement.
In such a case the proposed outline is the one in figure 6
Figure 5: Photos of a particular of a swimming pool with skimmer
Figure 6: outline of the panel edge for a skimmer swimming pool
In addition to the panels on the pool’s floor (as in figure 3-4), the panels are arranged along the edge, and are equipped with a cooling system obtained from the circulation of the water from the filtering system of the swimming pool.
