15.07.2015   EuroSun2008-3

Electric/Thermal power ratio in Solar8

Knowing that the beam fraction of the global irradiation increases when we move closer to the equator, conclusions can be taken on Solar8 electrical/thermal output ratio depending on its location (Table 5).

Table 5. Solar8 electric and thermal annual outputs per square meter of total glazed area, on a N-S tracking axis and 50°C average working temperature. The total glazed are on Solar8 is 4.6m2.

Solar8 annual outputs per glazed area

(A Solar8= 4-6 m)

Stockholm

(lat=59.2°N)

Lisbon

(lat=38.7°N)

Lusaka

(lat=15.4°S)

Solar8 electric annual output per glazed area (kWh/m2,yr)

47.7

86.8

105.7

Solar8 thermal annual output per glazed area (kWh/m2,yr)

159.7

434.9

605.3

Ratio Electric/Thermal

0.30

0.20

0.17

The ratio between electric and thermal outputs decreases when Solar8 is moved closer to the equator where the beam irradiation values are higher. The electric output is proportional to the irradiation thus, a PV module as constant efficiency for the same working temperature. A solar collector as higher efficiencies for higher irradiances since the thermal output increases more than proportional when the irradiation increases.

4.3. Solar8 vs. traditional side-by-side system based on glazed area

There are many ways and factors to take in account when comparing the performance of a concentrating hybrid with a traditional side-by-side system composed by a PV module and a solar collector working separately. The following tables feature Solar8 comparison with the traditional side — by-side system based on their power outputs and total glazed area (Table 6 to Table 8).

Table 6. Solar8 electric and thermal outputs with a N-S tracking axis at 50°C average working temperature.

Solar8 annual outputs

(A Solar8= 4-6 m2)

Stockholm

(lat=59.2°N)

Lisbon

(lat=38.7°N)

Lusaka

(lat=15.4°S)

Solar8 total electric annual output (kWh, yr)

219.2

399.0

486.1

Solar8 total thermal annual output (kWh, yr)

733.9

1998.9

2782.1

Table 7. Traditional side-by-side-system electric and thermal outputs per square meter of glazed area. The PV module n0b=16% at 25°C. The flat plate collector q0b=80%, ai=3.5 W/m2oC and operates at 50oC average

working temperature.

Traditional side-by-side system

Stockholm (lat=59.2°N) Fixed tilt=40°

Lisbon (lat=38.7°N) Fixed tilt=30°

Lusaka (lat= 15.4°S) Fixed tilt=20°

PV module output per glazed area (kWh/m2,yr)

173.2

278.7

324.5

Flat plate collector output per glazed area (kWh/m2,yr)

478.7

999.7

1266.0

PV area needed to equal Solar8 electric annual output (m2)

1.3

1.4

1.5

Collector area needed to equal Solar8 thermal annual output (m2)

1.5

2.0

2.2

Table 8. Traditional side-by-side-system and Solar8 comparison based on total glazed area.

Side-by-side system vs. Solar8

(A Solar8=4-6m2)

Stockholm (lat=59.2°N) Fixed tilt=40°

Lisbon (lat=38.7°N) Fixed tilt=30°

Lusaka (lat= 15.4°S) Fixed tilt=20°

PV module area / Solar8 total glazed area (%)

27.5

31.1

32.6

Thermal collector area / Solar8 total glazed area (%)

33.4

43.5

47.8

Side-by-side system area / Solar8 total glazed area (%)

60.9

74.6

80.4

The traditional side-by-side system uses less area than Solar8 for the same electric and thermal outputs. This difference decreases when the systems are moved closer to the equator since Solar8 is exposed to higher beam irradiation values. In Lisbon, for instance, Solar8 can be replaced by 1.4m2 of PV module and 2m2 of thermal collector for the same outputs. Hence, it would use 74% of Solar8 total glazed area (4.6m2). Practically, two components require more space than one component.