Table of Contents
PV System Configurations
PV system configurations refer to the various ways solar panels, inverters, and other components can be arranged and connected to capture and convert sunlight into electricity. The configuration of these systems plays a critical role in their efficiency, performance, and suitability for specific applications.
1. System Configurations
There are two main configurations of Solar PV systems: Grid-connected (or grid-tied) and Off-grid (or standalone) solar PV systems.
1.1 Grid Connected PV Systems
In a grid-connected PV system, the PV array is directly connected to the grid-connected inverter without a storage battery. If there is enough electricity flowing in from your PV system, no electricity will flow in from the utility company. If your system is generating more power than you are using, the excess will be exported to the energy utility grid, causing your meter to turn backward. During the times when the PV system isn’t producing electricity, such as at night, the power grid will supply all the building’s demand. The energy utility company will provide energy credit to providers based on the solar production. This is called “Net Metering”. In this process, energy goes in and out through a single meter.
Grid Connected System is the simplest and most cost-effective way to connect PV modules to regular utility power. If utility power is reliable and well maintained in your area, and energy storage is not a priority, you don’t necessarily need a battery. But if the utility power goes down, even if there is solar, the PV system will be off for the safety of the utility workers.
The main application of grid connected PV system is in cities, which are well covered by the national power grid. The PV systems are generally installed on buildings on the roof or integrated into the building. The latter is also known as Building Integrated Photovoltaics (“BIPV”). With BIPV, the PV module usually displaces another building component, e.g., window
glass or roof/wall cladding, thereby serving a dual purpose and offsetting some costs. The PV systems can be mounted on the ground if land is not a constraint.
1.1.1 Benefits of Grid Connected System
- A grid-connected system can be an effective way to reduce your dependence on utility power, increase renewable energy production, and improve the environment.
- The system doesn’t always require covering all electrical needs
- Requires less surface area for panels and no batteries
- Less expensive
1.1.2 Drawbacks of Grid Connected System
- Does not prevent grid power failures
- Can be dealt with by a small battery bank
1.2 Standalone PV Systems
Off-grid PV systems have no connection to an electricity grid. A simple standalone PV system is an automatic solar system that produces electrical power to charge banks of batteries during the day for use at night when the sun’s energy is unavailable. Deep cycle lead acid batteries are generally used to store the solar power generated by the PV panels, and then discharge the power when energy is required. Deep-cycle batteries are not only rechargeable, but they are designed to be repeatedly discharged almost all the way down to a very low charge.
A charge controller is connected between the solar panels and the batteries. The charge controller operates automatically and ensures that the maximum output of the solar panels is directed to charge the batteries without overcharging or damaging them.
An inverter is needed to convert the DC power generated into AC power for use in appliances.
Standalone PV systems are ideal for the electrification of rural areas or offshore sites that don’t have utility grid service or where it would be very costly to have power lines run to the isolated buildings. In these cases, it is more cost-effective to install a standalone PV system than pay the costs of having the local electricity company extend its power lines and cables directly to the home.
1.2.1 Benefits of Off-Grid Systems
- The system meets all the electrical needs of the building
- No connection to the conventional power grid
- Works in remote locations
- Protection against power failures
1.2.2 Drawbacks of Off-Grid Systems
- Requires a much more powerful system. It must produce more power than average consumption.
- Significantly more expensive
- Could run out of power
1.3 Grid-Tied with Battery Backup System
Including a battery bank in the system allows the utilization of energy produced from the PV system and stored in the batteries during a power outage. A grid-tied PV system with battery backup is ideal when living in areas with unreliable power from the grid or that experience power outages due to natural disasters.
1.5 Comparison
The design of a PV system should consider whether the building should be able to operate wholly independent of the electrical grid, which requires batteries or other on-site energy storage systems. Here is the comparison.
| Type | Stand Alone/ Off-Grid | Grid-Tied | Grid-Tied with Battery Backup |
|---|---|---|---|
| Complexity | Introduction of Batteries and a backup generator increases complexity | Fewer components in the system | The introduction of Batteries and a backup generator increases complexity. Requires a different inverter. |
| Maintenance | Batteries increase maintenance needs. More than Grid-Tied but less than Grid-Tied with battery back-up. | Less than the other systems. | Depending on batteries. More than other systems. |
| Life Span | Decreased due to batteries | Longer than other systems due to decreased complexity. | Decreased due to batteries |
| Energy/Economy | No utility bills. Increased cost of the system | Net metering allows financial gains from the energy utility if Feed-in tariffs are possible | Net metering allows financial gains from the energy utility if feed-in tariffs are possible. Increased cost of the system. |
| Autonomy | Autonomous System. If power from PV modules cannot produce enough power, batteries and a backup generator cover the critical loads. | Relies upon the grid. If the grid fails, the system shuts down, and the energy produced is wasted. | Larger autonomy. If the grid fails, backup power from batteries is used to cover critical loads. |
Recommendations
Is a Battery Bank Really Needed?
The simplest and least expensive configuration does not have battery backup. Without batteries, a grid-connected PV system will shut down when a utility power outage occurs. Battery back-up maintains power to some or all of the electric equipment, such as lighting, refrigeration, or fans, even when a utility power outage occurs. A grid-connected system may also have generator back-up if the facility cannot tolerate power outages.
With battery backup, power outages may not even be noticed. However, adding batteries to a system comes with several disadvantages that must be weighed against the advantages of power backup. These disadvantages are:
- Batteries consume energy during charging and discharging, reducing the efficiency and output of the PV system by about 10 percent for lead-acid batteries.
- Batteries increase the complexity of the system. Both the first cost and the installation costs are increased.
- Lower-cost batteries require more maintenance.
- Batteries will usually need to be replaced before other parts of the system, and at considerable expense.
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References:
A. Bhatia, Course No: R08-002, https://www.cedengineering.com
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