Floating Tracking Cooling Concentrator (FTCC)
Photovoltaic floating plant with tracking and cooling system
Photovoltaic panels are emerging as a robust, efficient, distributed energy source. The costs are decreasing and this justifies the effort to improve their use and to study the possibility of building large plants.
There are still three limitations: the thermal drift which lowers the efficiency of the system of 10-15%, the availability of spaces for photovoltaic fields, the high cost of tracking systems.
Floating Tracking Cooling Concentrator (FTCC) System allows to exploit small basins and natural and artificial lakes to install PV plants.
The FTCC system consists of a series of floating platforms with photovoltaic panels supported by a structure in polyethylene tubes. The power of a single module ranges from 20 to 200 kW, depending on the type of panel used. Cooling of the panel is ensured by a veil of water that is generated by a set of irrigators.
The FTCC system overcomes the limitations discussed above. In particular:
- Water veil keeps the PV panel at low temperatures with an average yearly energy gain of more than 10%.
- The floating platform allows a very efficient one axis tracking, so that reflectors can be easily oriented to increase radiation collected on the panels.
- The system exploits the unused areas of artificial reservoirs and has a very limited environmental impact.
Finally the cost of the system is limited. In practice the cost of tracking, cooling and reflectors (platform included) is less than € 800 for kWp. This further investment is limited compared to the one needed for PV part and it is offset by the increase of the yearly energy yield.
The platform and tracking system
The platform can be of arbitrary form (circular or rectangular) and is built with modular elements (rafts) each supporting 2 or more PV panels.
The tracking system works with motors which generate a small couple respect to a light under-water basis anchored to a mooring. Simulations and measurements of wind load and structural forces were made and the data are encouraging: the forces involved are very low, due to the system configuration.
Panels are equipped with reflectors; two solutions have been studied. Experimental tests are ongoing for both solutions.
The panels are inclined by an optimal angle (for example 40°) and the platform is oriented in such a way as to optimize the solar radiation on the panels. Shadows are unavoidable when the sun is low on the horizon but can be partially compensated by reflectors which increase the radiation when the sun is high on the horizon.
The main problem in this case seems to be the lack of homogeneity in solar radiation on the photovoltaic cells.
The unevenness of radiation can significantly reduce the efficiency of the panel and for this reason is required some distance between the rows of reflectors and those of the panels.
In order to overcome the mismatched radiation problem, a second solution was proposed: the panel is positioned between two reflectors tilted. In this case the solar panels are tilted by a very small angle and are oriented in such a way as to be always in line with the solar radiation.
Reflectors are positioned on both side of the panels and form a suitable angle with the horizon.
The limit of this approach lies in the efficiency of the reflectors and in their inability to focus diffuse radiation. The gain due to the concentration, adequately supported by panels cooling, is however remarkable and can reach values between 60 and 70% depending on the latitude.
The second solution (angle 60°) has been adopted in the pilot plant in Pisa which will be finished by the end of September 2011. This pilot plant will be used to measure the system performance and to test the tracking system efficiency.
The FTCC system proposes an innovative solution to exploit surfaces already equipped and available for industrial uses while at the same time improving the efficiency and annual yield of PV plants. Costs of the supporting platform and of cooling, tracking, reflector system are rather limited and compensated by the increase in the annual energy yield.
The Cheongju plant
Korean company, Techwin has built a floating photovoltaic plant in Cheongju, Korea using the FTCC technology, with the final project entirely developed by Scienza Industria Tecnologia and Koinè Multimedia.
The Suvereto plant
The Terra Moretti group has made at its winery Petra in Suvereto (Italy), a floating photovoltaic plant that allows the use of a irrigation reservoir and at the same time have a greater energy efficiency.
The plant, which implements the proposed technology and patents of SIT, will be fitted with a tracking system and reflectors in order to further increase the total harvest of energy.
This plant, with capacity of 200 kWp, is the first of its kind and paves the way for a line of development in PV technologies that points at the following goals:
- Enhancement of existing facilities and better integration
- Greater energy efficiency
- Lower environmental impact
Another benefit of using this solution in irrigation reservoirs is to reduce the effects of evaporation, which increases basins functionality.
Coupling of photovoltaic float technique with hydroelectric
Italy has many hydroelectric plants with an installed capacity of 21.5 GW . Hydroelectric plants have good conversion efficiency and even if the initial fixed investment is very high, the cost per kWh is highly competitive. The only limitation is the reduced availability due to the water cycle and on average they are exploited for about 1,800 hours per year to full power, that is just over 20%.