FAQS

The short-circuit current and the open-circuit voltage are the maximum current and voltage respectively from a solar cell. However, at both of these operating points, the power from the solar cell is zero. The "fill factor (FF) is a parameter which, in conjunction with V_oc and I_sc, determines the maximum power from a solar cell. The FF is defined as the ratio of the maximum power from the solar cell to the product of V_oc and I_sc. Graphically, the FF is the area of the largest rectangle which will fit in the IV curve as illustrated below:

Examples of FF of various solar panels:

Solar Frontier CIS – 64.9%

Stion 150W CIGS – 68.2%

SolarWorld 325W Mono – 74.8%

Trina 315W Polt – 76.9%

Sunpower 327W – 76.5%

Panasonic 245W HTI – 79%

Crystalline modules usually have higher FF and the power curves drop steeply before and after the maximum power point. 

Thin film (CIGS) solar cells tend to have lower FF as shown on the graph on the right, but the power curves are less steep before and after the maximum power point. This explains why thin film modules experience less mismatch and hence less susceptible to severe power drop due to partial shading.

 

Solar panels, including the mounting structures, should be bonded to the building’s lightning protection system. This is known as equipotential bonding. It has to be ensured that all metal parts of the entire solar array and structure are made electrically continuous and effectively bonded to the building’s lightning protection  system.

The payback period depends largely on the size of the system and the prevailing and future grid tariff. For systems of 100 kWp and above, the straight payback period can range from 7 to 9 years, without considering interest on investment. Maintenance of PV system is very minimal and if this is taken into account, the payback period may increase to say 8 to 10 years.

 PV systems require very little maintenance. Just basic spot cleaning of the panels once or twice a year

depending on the environmental conditions, inspection of electrical connections and mounting structures.

Most systems have online monitoring which will show the live performance of the system and give warnings

in the event of any malfunction or shortfall in performance.

Where the solar panels are clamped direct onto metal roofs, the loading of the panels and mounting rails is approximately 0.15 kN/m2 (approx 15 kg/m2). Most metal roofs are required under the BCA regulations to be designed

for a live load of not less than 0.5 kN/m2 (approx 50 kg/m2).

For panels installed on concrete roofs using ballasted system, the loading will largely depend on the wind uplift. Thus the loading of the panels and mounting system could be between 0.5 to 1.5 kN/m2.

Performance ratio is a measure of how well a PV system is producing energy for a given system capacity. It is the ratio of actual energy produced over the ideal energy that could be produced by the system. The formula is: 

Performance Ratio = Actual Energy / (System Capacity x Irradiation)

Irradiation is the measure of sunlight energy over a period of time. For example, the typical average daily irradiation in Singapore is about 4.38 kWh/m2. This is equivalent to a peak intensity of 1000 W/m2 or 1 kW/m2 for a duration of 4.38 hours or simply 4.38 peak sun hours (PSH).

The annual irradiation in Singapore was observed to range between 1580 to 1620 kWh/m2. This is 4.32 to 4.44 kWh/m2 per day.

Irradiance is a measure of the instantaneous sunlight intensity in W/ m2 . The peak irradiance occurs at solar noon at about 1 pm. On a sunny day, the peak irradiance is about 1000 to 1200 W/ m2

The annual irradiation recorded in Singapore is between 1580 to 1620 kWh/ m2. Hence on average the daily irradiation is between 4.32 to 4.44 kWh/ m2. On a very sunny day, the irradiation can be up to 6.7 kWh/ m2 while on a rainy day, it could be as low as 0.8 kWh/ m2.

Since Singapore’s latitude is only about 1 deg north of the equator, the panels just have to face flat and horizontal to receive incident sunlight. However, it’s good practice to tilt them at an angle of about 5 to 10 degree to promote self-washing by rain.