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RoofTop Solar Energy for Home Electricity

RoofTop Solar Energy for Home Electricity

Category : technology , 2 years ago

Overview of Solar PV

Solar PV converts sunlight (not heat) to generate electricity through a photovoltaic process. A solar plant consists of Solar Panels and Mounting Structures.

Solar Panels: These are mounted on the roof and convert sunlight into DC power.

Mounting Structures: These secure the solar panels to the roof of your building.

Most mounting structures require your roof to be penetrated. If you are worried about water seepage, non-penetrating options are also available.

Mounting structures should be strong enough to hold your solar panels even at high wind speeds, such as during cyclones.

Inverter: This converts the generated DC power into the AC power that is required by your appliances. Through a charge CONTROLLER it also regulates battery charging if required.

Balance of Systems (BoS): All the other components of the solar plant, such as cables, junction boxes, fuses, etc.

The size of solar plant you require depends on your electrical load and the number of kWh (units) you consume. The size of solar plant you can INSTALL is limited by the extent of shade-free rooftop space available.  The expected lifetime of a solar PV plant is 25 years.

Kinds of Solar Plants

Grid-tied: The plant WORKS in conjunction with grid power. Such a solar plant will turn off if grid power is not available, and may not suit locations with frequent power failure.

Hybrid: In conjunction with a diesel generator or battery bank, the plant can deliver solar power even during a power failure.

Off-grid: The plant only works off-grid. It can sync with batteries or a diesel generator but not grid power. Such plants can be INSTALLED in areas where the grid is absent, but not recommended for areas where grid is present, even if grid power is only available intermittently.

The only difference between the two kinds of plants is in the type of inverter used. It should be noted that a solar PV plant must have another source of power (grid/DG/battery) to function – the other source is used to provide a reference voltage as solar power is continuously varying. In the absence of reference power, the solar plant will not generate electricity even in bright sunlight.

    ·        A grid-tied plant synchronises only with the grid and will shutdown in the absence of grid power.

    ·        A hybrid plant can synchronise with either gird or DG or battery and will shutdown if all three are absent.

    ·        An off-grid plant can synchronise with DG or battery and will shutdown if both are absent

What kind of a roof do I need for a solar plant?

Solar PV plants require a south-facing roof (in the northern hemisphere). The roof should also be free from shadows; portions of the roof that have shadows should be excluded while calculating the roof space available for the solar plant. Shadows falling on solar panels reduce power generation, and may also damage the panels.

The kind of roof determines if solar panels can be INSTALLED. Ability of the roof to support the weight of the panels and mounting structure even in strong winds is the critical parameter.

Concrete Roofs: Solar PV plants can be easily INSTALLED on flat concrete roofs. Inclined roofs may pose a challenge depending on the angle and direction of the inclination.

Metal Roofs: This will depend on the type of structure and the weight it can withstand.

Asbestos/Other Sheet Roofs: These are the least likely of the 3 to be able to support solar panels, though it is possible in some cases.

How much of roof space do I require?  Approximately 100 SF is required for 1 kW of solar plant.

Can a solar plant be installed only in individual homes, or also in residential apartments?

Solar PV plants can be installed on the rooftops of residential APARTMENT complexes. A few issues should be considered when evaluating rooftop plants for apartments.

Roof ownership: In many APARTMENT buildings the roof is considered common area. Therefore permission from the building society/association may be required before an individual can INSTALL the solar plant.

Distance from roof to apartment: Since APARTMENT complexes typically feature multi-storeyed buildings, the number of floors between the apartment where solar power is to be used and the roof where the power is generated may be an issue as DC power provided by the solar panels suffers a great deal of loss as distance increases.

   ·        Using thicker DC cables is a possible solution to minimise loss.

   ·     Another solution is to place the inverter on the roof as the AC power from the inverter does not suffer much loss over distances compared to DC power. Issues such as permission to INSTALL the inverter and location of inverter (it needs a well-ventilated room) need to be addressed.

Earthing: The solar plant generates both AC and DC power and both need to be earthed. While AC earthing can be combined with existing building earthing, DC will require separate earthing for which permission will be required as well.

It is also possible that rather than an individual apartment owner having a personal solar plant, the building association as a whole can INSTALL a solar plant to supply common facilities such as common area lighting.

Can I run my entire home on solar PV?

This will depend on the kind of loads you run, but usually running the entire load off solar PV is not recommended.

    ·     Solar power is only generated during daytime. With heavy rain or mist solar power may not be generated even during the day (30-60 days of generation may be lost in a year due to these factors).

     ·        The solar plant may not run loads with heavy starting current requirements, such as water pumps. Air conditioning also may not be supported It may be possible to run inverter air conditioners off your solar plant.

In such situations a solar plant can be used to support part of the load, similar to a home inverter/UPS.

How do I know my electrical load?

The sum of the wattage of individual appliances represents the load i.e., a 60 W fan and 40 W light represent a 100 W load. If these two appliances run continuously for an hour they consume 100 watt-hours. If they run 10 hours they will consume 1,000 watt-hours or 1 kilowatt hour (kWh), also known as one unit.

Dividing the Total Wattage and Energy by 1,000 gives us the load in kW and energy consumed in kWh.

Your electricity consumption is billed on the basis of number of kWh consumed. Since solar is only available during daytime, it is the load and energy consumption during daytime that will need to be ascertained to calculate the size of the plant. Residents are usually away from home during the day and most energy consumption is at night. It is therefore important to calculate the size of the plant based on daytime use to avoid oversizing the plant.

The above example gives a simple calculation to calculate the load and energy consumption. In real world situations it may be difficult to determine the number of hours that appliances are used during the day. We can instead ascertain the energy consumption by noting the electricity meter reading at 10 AM and 4 PM for a few days. The difference between the readings is the energy consumption (kWh) for that period. If the electricity meter is a digital meter it usually also provides the load in amperes and kW. This can be noted several times each day to determine the average load.

What is the cost of a solar PV plant?

The cost of a rooftop solar PV system depends on the function it serves (to feed power into the grid, to support the load during a power failure, etc.) and incentives/subsidies available. It should be noted that all solar PV systems function by matching the voltage from some other source. Therefore the system has to be integrated with the grid, a battery backup, or a diesel generator.

The approximate cost of a rooftop solar PV plant is INR 100,000 per kW, before considering incentives. This includes INSTALLATION and all components other than batteries. Batteries can add 30% or more to the cost of the plant, depending on the extent of backup required.

1 kW of solar plant will occupy 100 SF and generate 4 kWh of power per day on average over a year.

What are the operating/running costs?

Other than washing of solar panels once in every few weeks, solar plants require little by way of maintenance as there are no moving parts; operating and running costs are minimal. The inverter is the only major component that may need to be replaced during the 25-year lifetime of the plant.

Should I use a solar PV plant or a solar water heater to heat water? 

Using a solar water heater is a more cost-effective option than using solar PV to generate electricity which is then used to heat water. Solar water heaters are a different kind of solar technology where the heat from the sun, rather than the light, is collected to heat water.

Key Takeaway

    1.     A solar PV plant costs approximately INR 100,000 per kW with INSTALLATION without batteries or subsidies, and will last 25 years.

·        1 kW of solar plant generates about 4 kWh of electricity per day on average over a year.

·        The inverter is the only major component likely to need replacement.

    2.     If you are considering solar to save on your EB bills, we recommend evaluating solar only if your residential EB tariff is Rs. 5.00/kWh or greater, subject to state specific incentive schemes that can lower the cost of solar.

     3.     As solar plants generate power during the day when most residents are not at home, the plant has to sized carefully for daytime load rather than peak load which is usually experienced only at night.

    4.    Solar PV plants can be installed in apartment buildings provided INSTALLING solar panels on the common rooftop is permitted.

    5.     A solar water heater is a better choice for heating water than a solar PV plant.

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