Exploring DC and AC Coupled PV Configurations in Residential Solar Systems
As the adoption of solar photovoltaic (PV) systems with on-site battery storage continues to grow, homeowners and installers are considering various configurations to optimize system performance and costs. Two common configurations are DC coupled and AC coupled PV systems. This article examines these configurations and their impact on cost, using a 7.9-kWdc PV system coupled with a 5-kWdc/12.5-kWhdc storage system as an example.
DC and AC Coupled PV Configurations
A typical DC coupled PV system connects the solar panels and the battery storage directly through a common DC bus, using a single inverter to convert DC power to AC power for use in the home or export to the grid. This configuration is often more efficient as the energy from the solar panels is directly stored in the battery without multiple conversions.
On the other hand, an AC coupled PV system connects the solar panels and the battery storage through separate inverters. The solar panels have their dedicated inverter to convert the generated DC power to AC power, while the battery storage has its inverter to convert the stored DC power to AC power when needed. This configuration allows for more flexibility in system design and is often used in retrofit applications where the PV system is already installed.
Changes to Residential PV and Storage Models When PV and Storage Are Combined
When combining PV and storage systems, certain cost adjustments can be made, as shown in Table 8:
- Electrical BOS: The balance of system (BOS) costs for the combined PV and storage system is 90% of the standalone costs. This reduction accounts for the removal of duplicative parts.
- Installation labor: The combined installation labor costs are 90% of the standalone costs for PV and battery systems, as duplicative work is removed.
- PII (Permitting, Inspection, and Interconnection): The combined system only includes PII associated with the standalone PV system, as duplicative work is removed.
- Profit: The profit markup is assumed to be 15% on PV modules, battery, PV and battery inverter, BOS material, and installation labor. The cost of the combined system is lower than the cost of separate systems, resulting in a lower profit markup.
When considering residential PV systems with on-site battery storage, it is essential to understand the differences between DC coupled and AC coupled configurations. The following table compares the advantages and disadvantages of these configurations:
Table: Advantages and Disadvantages of AC and DC Coupled Systems
| Configuration | Advantages | Disadvantages |
|---|---|---|
| DC Coupled | 1. Higher overall efficiency | 1. Less flexibility in system design |
| 2. Simpler design with a single inverter | 2. May require a larger, more expensive inverter |
| 3. Direct energy transfer between PV and battery | 3. Less suitable for retrofit applications | |
|---|---|---|
| AC Coupled | 1. Greater flexibility in system design | 1. Lower overall efficiency |
| 2. Suitable for retrofit applications | 2. Multiple inverters required | |
| 3. Independent operation of PV and battery systems | 3. More complex design and installation |
While DC coupled systems are generally more efficient, AC coupled systems offer greater flexibility, especially in retrofit applications. By understanding the advantages and disadvantages of each configuration, homeowners and installers can make informed decisions and optimize the costs and performance of their solar energy systems, making solar energy more accessible and affordable for a wider range of consumers.
Table: Manufacturers of AC and DC Coupled System Inverters
| AC Coupled Inverter Manufacturers | DC Coupled Inverter Manufacturers |
|---|---|
| 1. Enphase Energy | 1. SolarEdge |
| 2. SMA | 2. Schneider Electric |
| 3. Fronius | 3. OutBack Power |
| 4. ABB (now FIMER) | 4. Morningstar |
| 5. Victron Energy | 5. Delta Electronics |
Note: The mentioned manufacturers produce a variety of inverters for both AC and DC coupled systems. The classification in this table is based on some of their popular products in each category.
When considering residential PV systems with on-site battery storage, it is essential to understand the differences between DC coupled and AC coupled configurations. While DC coupled systems are generally more efficient, AC coupled systems offer greater flexibility, especially in retrofit applications. By combining PV and storage systems, homeowners and installers can optimize costs and performance, making solar energy more accessible and affordable for a wider range of consumers.