Used off grid solar system for sale

The impact of Haze on Solar PV Systems

Haze reduces the intensity of light falling on the solar panels thus, reducing the energy yield.

However, reduced light intensity also results in lower operating temperature of the PV cells.

With a cooler temperature, the PV cells operate more efficiently, resulting in less thermal/heat energy losses.

Although the haze reduced the energy output of the panels, less energy is lost thanks to cooler temperatures (The Performance Ratio* improves).

Prolonged incident of haze may result in formation of dust on the panels, temporarily reducing energy yield. It is recommended to perform more frequent cleaning to maintain optimal energy yield.

Performance Ratio* is a measure of how well a PV system is producing energy for a given system capacity. 

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

Will the inverters generate significant harmonics that might affect sensitive equipment connected to the electrical network?

All inverters are vetted and approved by PowerGrid to ensure that they meet the power quality technical specifications, in terms of harmonics, flicker, DC injection, etc. Most reputable grid tie inverters comply with EN61000 (electromagnetic compatibility).

In addition, for PV systems of more than 1 MW ac, PowerGrid would require monitoring of the power quality at the 22 kV intake feeders 7 days before and 7 days after the commissioning of the PV system. This will serve as a record of the impact of the PV system on the network harmonics. 

From our experience so far, PV systems have not been known to cause significant harmonics that impact the operation of the building’s loads..

Will the solar panels cause any glare to nearby residents ?

Solar panels are made to absorb light rather than to reflect light. This is achieved by means of an anti reflective coating on the top glass of the solar panels. The average reflectance of solar panels is only about 5 to 6%, as against the maximum reflectance of 20% permitted by BCA.

For solar projects located in the vicinity of airports, glare analysis simulation studies need to be submitted to CAAS and RSAF for prior approval. In most cases, only minor tweaks to the layout and tilt angle is necessary to clear CAAS and RSAF requirements.

How is the Building LEW involved in the PV installation?

The Building LEW will need to be informed of the proposed grid tied PV installation as it is to be connected to the existing electrical network in the premises, which is under his charge. 

The PV System Integrator's LEW (PV LEW) will be responsible for the design and installation of the PV system in compliance with CP5 and he will make all necessary applications and metering requirements and seek approval from Singapore Power. 

Upon completion of the PV system, the PV LEW will apply to PG for inspection and turn on. During the turn on, the Building LEW must be present to witness the turn on as the system is to be connected to the building’s electrical network under his charge.

What is kWp?

Watt-peak or Wp is the DC name plate rating of solar panels.

It is the rated peak DC output under standard test conditions (commonly known as STC) of 1000 W/m2 irradiance, cell temperature of 25 deg C and air mass of 1.5. Solar irradiance of 1000W/m2 occurs at about noon time and hence most of the time, the irradiance will be lower than 1000 W/m2 and as such the net output of the solar panel will drop below the STC value.

Also the cell temperature may rise to as high as 65 deg C on a hot day and hence the output of the solar panel will also drop from the STC value.

The name plate rating at STC is ideal condition and in actual operation, the net output will be reduced. Most established System Integrators should have taken these derating into consideration when computing the estimated energy yield of the PV system.

1 kWp = 1000 Wp. If one solar panel is rated 350Wp, a system of 100 solar panels = 100 x 350 = 35,000 Wp = 35 kWp.

Does cloud affect performance of solar panels?

Clouds reduce the intensity of irradiance falling on the solar panels. However, the average annual irradiation in Singapore of between 1580 to 1620 kWh/m2 has already factored the effects of clouds throughout the year. This worked out to an average irradiation of about 4.32 to 4.44 kWh/m2 per day (i.e 4.32 to 4.44 peak sun hours per day). However,  the daily irradiation may range from 1 to 6.5 kWh/m2 (i.e 1 to 6.5 peak sun hours) on a very wet and/or cloudy day to a very sunny day. The average figure is used to estimate the energy yield of the solar panels.

Why is it not recommended to install off-grid solar system with batteries in Singapore?

In rural countries where there are no grid supply, the PV system will be an off grid system which must be supported by batteries to overcome the intermittency of solar irradiation.

In Singapore where we have a stable and reliable grid supply, the PV system should be connected to the grid without batteries. In this way, whatever PV energy generated will be consumed by the loads (appliances) and the balance drawn from the grid. There is no concern of the intermittency of the PV supply as the system is tied to or connected in parallel to the grid and hence the loads will always receive a constant supply either from the PV or grid or combination of both. 

For any installation with a reliable grid supply, it is pointless to go for off grid system as the batteries will drive up the first cost and operating cost. The battery maintenance and replacement costs are much more than the savings in grid electricity charges.

Can I get paid for excess PV energy exported to the grid?

Yes, all customers whether contestable or non-contestable can enjoy net settlement (i.e rebate) for export of excess solar PV energy exported to the grid. The PV System Integrator will arrange for the application and installation of dual register meters and advise you on all the required PV generation meters, licences and applications.

Caveat: For consumers under the master and sub-metering scheme, currently Singapore Power does not grant any export rebate to both the master and sub-account holders.

What are the compliance requirements mandated by SCDF and how do they impact the PV system?

SCDF has issued a circular FSR-13 on 31 December 2015 that spells out fire safety requirements to enhance fire safety for rooftop PV installations.  You can view a copy of the circular here -  https://www.corenet.gov.#2B11DD2

Basically, the requirements include mandatory provision of staircase access,  2.5 m (1.5 m if there’s a 900mm railing or parapet wall) perimeter aisle, 1.5 m accessway between each 40 x 40 m array, product listing scheme, emergency shut down switches, signages, etc.

Building plans showing the PV Installation must also be submitted to SCDF for approval.

The appointed System Integrator has to ensure that the PV system design and installation complies with the SCDF requirements and that he engages a QP to undertake the plan submission to SCDF. He has to highlight to the Client if certain aspects of the fire safety requirements are excluded from his offer.

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