Energy efficiency analysis of Solar panels using nanofluids

Analysis of Energy efficiency and thermal performance of  Photovoltaic Thermal panel (PVT) manufactured by HRSolar using Alumina nano-coolants

HR Solar, established in 2002, is a PVT panel manufacturing and installation company located near Delft in The Netherlands. They have extensive experience in designing and manufacturing PV/T panels. They install solar collectors on the roof which provide both electricity and heated water. Their main aim is to reduce reliance on fossil fuels and gas for home heating and electricity purposes.

Synano and HR solar worked together on a project to test alumina nanofluids for PVT panel cooling and heat transfer from PVT panels to water used for domestic purposes. Capturing solar heat from PVT panels is a clean and environmentally friendly source of energy for residential and industrial heating and hot domestic water requirements, ultimately reducing gas consumption and CO₂ emissions. Using nano-coolants as heat transfer fluid will increase the energy captured from solar panels, thus further reducing gas usage and  CO₂ emissions.

At present, air and liquid cooling are the most common ways to cool PV panels. These are relatively very simple ways and materials to realize the cooling with limited heat transfer ability. With nano-coolants, Synano introduces high degree of innovation in the PVT market and enables companies to gain a clear advantage over their competitors.

The objective of the project was to build an experimental setup of the PVT system at HR Solar facility and experimentally analyze the thermal performance of the PVT system using nanofluids and compare it with base fluid.

The major issue with nanofluids is the stability of the suspension. Synano uses 100 nm Alumina nanoparticles which are surface modified keeping them suspended in water and prevents agglomeration. The size, type and shape of these nanoparticles along with their surface treatment enables Synano to develop highly stable nanofluids with desired thermal and physical properties.

In this project, the nanofluid consists of 70% water and 30% ethylene glycol with 3 vol% alumina nanoparticles. Additional chemicals are added to prevent growth of micro-organisms and corrosion on the surface of heat exchanger tubes. The chemicals are chosen so that they do not react with the nanoparticles or the base fluid and prevent coagulation. Formulated nano-coolants were characterised in the Synano lab and their thermo-physical properties such as thermal conductivity, density and viscosity were measured.

The experimental system consists of a panel connected to a pump through a series of pipes. The pump is maintained at a constant power by controlling the pump speed. K-type thermocouples were placed at different reference points to measure the temperatures as shown in figure-1. The temperature data was collected by a data logger.

Figure 1: Schematic of the experimental setup and table of symbols and their meaning

An infrared lamp of 1000 Watt was used to raise the panel temperature. The effective flux available at the panel is 300 W/m². The PV module is provided with a cooling system at the back, which is essentially a heat exchanger. It consists of 3 mm thick serpentine copper tube loop inserted in an aluminum frame that spans the length and width of the panel to increase the heat transfer surface area as shown in figure-2.

The system was exposed to the infrared lamp for 20-30 minutes. After being sufficiently heated, the cooling circuit was activated. Temperature readings were started after an interval of 300 seconds. After a while, the system achieves equilibrium with the surroundings and the incoming radiation from the lamp, and there is no further change in the panel temperature or the temperature of the fluids indicating steady state.

From the experimental and analytical data gathered from our work, it is clear that nanofluids have a thermal conductivity 8.5% higher on average as compared to the ethylene glycol + water mixture which forms the base fluid. The heat transfer coefficients are also larger for the nano fluid as compared to the base fluid for range of mass flow rates.

The panel temperatures are lower and panel efficiency is higher when PVT system is being cooled by nanofluids compared to base fluid.

Although the thermal conductivity increase was higher for nanofluids, the panel temperatures show small differences. This can be explained by the geometry and design of the PV/T system. On closer observation we noticed that 90% of the absorber plate area is exposed to the air and is not in contact with the cooling surfaces i.e. the tubes and thus the fluid. Despite having a greater heat transfer coefficient than the base fluid, the heat transfer ability of the nanofluid experiences a bottle neck in the form of the design of the heat transfer surface.

With these experimental reports, Synano also provided an analytical model to HR Solar to improve the cooling system design such that they can take full advantage of any coolant they choose to put in their systems. As part of the project, Synano also provided engineering consultancy for further improvement and economic benefit of the customer.