Tracking is a mechanism for panel mounting that allows panels to follow the sun as it moves across the sky. Single-axis trackers follow the sun as it moves from east to west during the day, while dual-axis trackers also follow the sun on its north-south journey over the course of a year.
Trackers can increase the power output of a PV plant but add significantly to both the initial cost of the plant and maintenance expenditure. So trackers should be used on a case-to-case basis after performing a cost-benefit analysis over the lifetime of the rooftop plant.
A battery pack can add 25-30 per cent to the initial cost of a rooftop PV solar system for one-day autonomy (storing an entire day’s output). Inverters with integrated charge controllers are preferred so that the inverter can direct grid power or solar power, based on the availability and demand, to charge batteries. This extends the battery life compared with standalone charge controllers that allow parallel charging between grid and solar power at different power levels, damaging the battery. If batteries are required, it is vital to perform a lifetime cost-benefit analysis to understand the impact on the cost of rooftop solar power.
Other miscellaneous items required include:
1. Power-conditioning unit
2. Array junction box (AJB)/DC distribution box array junction box/ DC distribution box
3. Common AC distribution box
4. Common AC distribution panel board
5. Cables; DC cables carry current from panels to inverters, while AC cables carry current from inverters to loads
7. Lightning protection
8. Earthing protection
9. Jet pump
Basics of rooftop solar PV
Solar PV panels (also known as solar PV modules) work by converting sunlight into electricity. These do not use the heat from the sun, and can, in fact, output reduced power in hot climates. The electricity generated by PV panels is direct current (DC), which needs to be converted into alternating current (AC) using an inverter.
Panels are mounted on the rooftop using special mounting structures. If solar power is required when sunlight is not enough for the panels to generate electricity (such as at night), battery backup is required.
Types of solar PV systems
Grid-tied systems are a combination of solar PV and grid. As these systems depend on the grid-supplied reference voltage for their operation, grid-tied systems do not work when the grid is down.
Grid-interactive systems work in conjunction with either battery backup or diesel generator to support loads even during power failure.
Off-grid systems operate independent of the grid. These systems sync with diesel generators and/or batteries. Battery-based systems were uncommon in the past due to their high costs. However, the situation is changing now, given the improved economics of battery technology.
Types of mount
Mounting systems for rooftop installations are available for both inclined and flat roofs.
A variety of mounting systems are available, the most common being railed, rail-less and shared rail. All these systems require some type of penetration or anchoring onto the roof, whether attached to rafters or directly to the decking. The standard residential systems use rails attached to the roof to support rows of solar panels. Each panel, usually positioned vertically/portrait-style, attaches to two rails with clamps. The rails secure to the roof by a type of bolt or screw, with flashing installed around/over the hole for a watertight seal.
Solar business models include:
1. Service-based operation. Types of services being solar rooftop power plant installation and maintenance
2. Operational model. Just-in-time sourcing of components and products as per the project requirement
3. Financial model. A low-cost model where investment is done for mainly fixed and variable cost heads. Raw material or tools are purchased after order confirmation by the customer, utilising the advance from the customer.
Fixed-cost items include:
1. Company registration
2. Solar installation training
4. Miscellaneous fixed assets (laptop, smartphone, etc as per requirement)
Variable-cost heads include:
1. Human resource
3. Office space
Detailed business economics, including estimated value against the above-mentioned cost heads and other probable cost heads, along with breakeven point (BEP) calculation can be worked out based on the scale of operation desired. However, an overview of solar rooftop power plant installation cost and relevant subsidies and incentives is given below.
Solar rooftop power plant installation cost
Rooftop solar power plant installation costs roughly ₹ 55-60 per watt depending on the quality of components selected. Costs of different rooftop power plant components are listed in Table I. The table does not include battery backup as its cost depends on the extent of backup opted for. Not only do batteries add to the initial cost, recurring maintenance and replacement expenditure, the energy loss on charging and drawing from the battery also add to the electricity cost.