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Evaluation of a PVT Air Collector
Dalarna University, School of Technology and Business Studies, Electrical Engineering.
2015 (English)Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE creditsStudent thesisAlternative title
Evaluation of a PVT Air Collector (English)
Abstract [en]

Hybrid Photovoltaic Thermal (PVT) collectors are an emerging technology that

combines PV and solar thermal systems in a single solar collector producing heat and

electricity simultaneously. The focus of this thesis work is to evaluate the performance of

unglazed open loop PVT air system integrated on a garage roof in Borlänge. As it is

thought to have a significant potential for preheating ventilation of the building and

improving the PV modules electrical efficiency. The performance evaluation is important

to optimize the cooling strategy of the collector in order to enhance its electrical efficiency

and maximize the production of thermal energy. The evaluation process involves

monitoring the electrical and thermal energies for a certain period of time and investigating

the cooling effect on the performance through controlling the air mass flow provided by a

variable speed fan connected to the collector by an air distribution duct. The distribution

duct transfers the heated outlet air from the collector to inside the building.

The PVT air collector consists of 34 Solibro CIGS type PV modules (115 Wp for each

module) which are roof integrated and have replaced the traditional roof material. The

collector is oriented toward the south-west with a tilt of 29 ᵒ. The collector consists of 17

parallel air ducts formed between the PV modules and the insulated roof surface. Each air

duct has a depth of 0.05 m, length of 2.38 m and width of 2.38 m. The air ducts are

connected to each other through holes. The monitoring system is based on using T-type

thermocouples to measure the relevant temperatures, air sensor to measure the air mass

flow. These parameters are needed to calculate the thermal energy. The monitoring system

contains also voltage dividers to measure the PV modules voltage and shunt resistance to

measure the PV current, and AC energy meters which are needed to calculate the

produced electrical energy. All signals recorded from the thermocouples, voltage dividers

and shunt resistances are connected to data loggers. The strategy of cooling in this work

was based on switching the fan on, only when the difference between the air duct

temperature (under the middle of top of PV column) and the room temperature becomes

higher than 5 °C. This strategy was effective in term of avoiding high electrical

consumption by the fan, and it is recommended for further development. The temperature

difference of 5 °C is the minimum value to compensate the heat losses in the collecting

duct and distribution duct.

The PVT air collector has an area of (Ac=32 m2), and air mass flow of 0.002 kg/s m2.

The nominal output power of the collector is 4 kWppv (34 CIGS modules with 115

Wppvfor each module). The collector produces thermal output energy of 6.88 kWth/day

(0.21 kWth/m2 day) and an electrical output energy of 13.46 kWhel/day (0.42 kWhel/m2

day) with cooling case. The PVT air collector has a daily thermal energy yield of 1.72

kWhth/kWppv, and a daily PV electrical energy yield of 3.36 kWhel /kWppv. The fan energy

requirement in this case was 0.18 kWh/day which is very small compared to the electrical

energy generated by the PV collector. The obtained thermal efficiency was 8 % which is

small compared to the results reported in literature for PVT air collectors. The small

thermal efficiency was due to small operating air mass flow. Therefore, the study suggests

increasing the air mass flow by a factor of 25. The electrical efficiency was fluctuating

around 14 %, which is higher than the theoretical efficiency of the PV modules, and this

discrepancy was due to the poor method of recording the solar irradiance in the location.

Due to shading effect, it was better to use more than one pyranometer.

Place, publisher, year, edition, pages
National Category
Energy Engineering
URN: urn:nbn:se:du-19831OAI: diva2:865382
Available from: 2015-10-28 Created: 2015-10-28

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