SaurEnergy Explains- AC & DC Capacity of Solar Projects

As Solar PV penetration hits new highs each year, the numbers are just adding up. 2023 saw at least 29 countries installing more than 1 GW, up from 25 countries in 2022. Nineteen countries (not including the EU) now have more than 10 GW of total cumulative capacity and five have more than 40 GW. With the surge of solar PV market, however, the complexity in solar reporting has also increased. That is why you will frequently see disparities in total numbers. Most of these are caused by reporting in AC or DC capacity, which can lead to significant variations.

For instance, IEA PVPS now counts all solar panel setups, whether they’re connected to the main power grid or not, estimating unreported installations. Some countries have a growing gap between shipped/imported panels and actual installations due to factors like AC to DC conversion, replacements, and decommissioning. Converting AC to DC power, especially in large areas like China, is uncertain; China reports utility-scale power in AC, but experts use different conversion ratios. Limited data means these ratios rely on surveys and standard practices.

SaurEnergyExplains demystifies this confusion of AC versus DC capacity of solar projects.

What are AC & DC Capacities?

In a PV system, the rated capacity can be reported based on either all its modules or all its inverters. PV modules are rated under standard conditions and generate DC energy, while inverters convert DC to AC energy. So, the PV system’s capacity is measured either in MWDC by adding up all module capacities or in MWAC by adding up all inverter capacities. The ratio between these capacities is called the inverter loading ratio (ILR).

When we figure out the capacity factor of a system, we can express it using only AC units or mix AC units for electricity with DC units for capacity. Both ways give the same cost for energy, as long as other factors use the same capacity rating. For example, if we use AC and DC units for capacity factor, then the cost for equipment should use the same units. Hence, if capacity factor is calculated in kWhAC/kWhDC, then CAPEX should use the units of Rs/kWDC. Also, both ways will show the same amount of energy produced if we use consistent units.

The ILR is also relevant when planning a solar array, as it makes sense to oversize it so that that the DC-to-AC ratio is greater than 1. This allows for a greater energy harvest when production is below the inverter’s rating, the status for most of the day.

Which One is Higher Amongst AC and DC?

A PV system’s DC-rated capacity is typically higher than its AC-rated capacity.

Capacity factor is the key metric for evaluating the effectiveness and performance of a solar plant, or for that matter, any energy plant. It is expressed as a ratio, measuring the annual average energy production of a solar PV system relative to its theoretical maximum annual energy production.

For PV systems, the rated capacity is typically aggregated either in terms of all modules’ capacities or all inverters’ capacities. The ratio between these capacities, known as the inverter loading ratio (ILR), profoundly influences the calculation of the capacity factor.

Thus, a PV capacity factor calculated using a DC-rated capacity has a higher denominator and, thus, a lower ratio than a PV capacity factor calculated using an AC-rated capacity. To translate between the two capacity factors, simply multiply or divide by the ILR.

Is solar power AC or DC?

Solar panels produce direct current, that is the incident sun energy on the panels stimulates the flow of electrons in a single direction, creating a direct current (DC). Because solar panels generate DC, solar PV systems need inverters to power multiple needs. The inverter converts DC energy into AC energy so that electricity can be used in the home or sent back to the electric grid.

It’s crucial to note that industries, offices, and most appliances operate on AC power. Likewise, the solar systems available in the market are designed to work with AC appliances like lights, fans, and other electrical devices.

What are AC solar panels?

Technically, all solar panels produce DC energy which needs to be converted to AC power by the inverter. So, what are AC solar panels? Simply, AC solar panels have microinverters integrated into them. This eliminates the need to buy and attach the microinverters separately.

Pros and Cons: DC Solar Panels

DC voltage is generally considered safer due to its lower risk of electrocution. Additionally, DC solar panels offer greater affordability and variety compared to AC panels. Moreover, DC-coupled battery storage systems are more efficient as they involve only one conversion from DC to AC, enhancing overall battery performance.

However, DC solar panels also are disadvantageous in some aspects which include the need for an extra conversion step, requiring a separate inverter to convert DC energy to AC for household use. Additionally, DC electricity has a restricted range compared to AC, resulting in voltage drops over longer distances. Moreover, installing DC-coupled battery systems for solar storage can be more intricate, potentially increasing installation expenses.+

Pros and Cons: AC Solar Panels

Advantages of AC solar panels include simplified installation processes, as they eliminate the need for separate DC wiring and standalone inverters, reducing material requirements and installation time. Additionally, integrating battery storage with an existing AC solar system is straightforward, resulting in cost-effective and time-saving battery installations. Furthermore, expanding an AC solar setup is hassle-free compared to traditional DC systems, as AC panels do not require a central inverter, allowing for seamless addition without the need for additional equipment.

Needless to say, AC solar panels cost higher due to the inclusion of microinverters, making them generally more expensive than DC panels. Additionally, the inverters in AC panels are integrated into the back of each panel, exposing them to outdoor elements and increasing the risk of damage compared to traditional DC setups where inverters are typically located in more protected areas. Moreover, maintenance can be more challenging with AC panels as identifying and addressing issues with individual panel inverters may be more complex than diagnosing problems with a central inverter in DC systems.