## TI Tech Days

Join Texas Instruments for a day packed with technical design seminars.

How does solar power work?

Solar power is possible through something called the photovoltaic effect. This effect takes place in solar cells when sun hits them, creating electricity. Solar cells consist of a conductive front grid, semiconductor material, and a conductive backplate. When light hits the front of a solar cell, light particles, called photons, travel through the semiconductor material. Electrons in the semiconductor material are given enough energy by the photons to move through the semiconductor and collect along one side. Since electrons are negatively charged, the area they move to becomes more negative, and the area they leave becomes more positive. This produces a potential difference (or voltage difference) between one side of the cell and the other - just like the potential difference in a battery - enabling the cell to produce electricity.

What makes up a solar panel?

A solar panel, or module, consists of multiple solar cells placed in series - the potential of each cell adds to the available output voltage and current of the entire panel. In the same manner, an underperforming cell in the panel detracts from the output voltage and current of the entire panel.

Solar modules are then placed in series strings. A solar array is made up of some number of strings determined by the required output power of the array and the inverter voltage range.

How much light does a solar panel need to work?

The amount of direct current (DC) power a solar panel produces depends upon the amount of irradiance. Irradiance refers to the amount of power the sun provides per area of the solar panel (See "What is insolation?"). Under ideal conditions, the sun provides around 1000 Watt hours per square meter. Real-world conditions, like shade and aging, can significantly decrease this number, reducing the effectiveness of a solar array.

What is Insolation?

Insolation is a measure of (solar) radiation on a particular surface or area, and is expressed in W/m2. In other words, it can be a measure of how h2 the sun is in a particular geographic area. Insolation is h2est when the angle of incidence (of the sunlight) to the panel is 90 degrees. Insolation becomes lower with decreasing angle of incidence - this is because the light rays are spread across a wider area and are more diffuse. Less radiation is incident on the panel per square meter, meaning less power will be produced. Insolation is also called irradiance.

How efficient are solar panels?

The efficiency of a solar panel depends upon the technology used to manufacture the panel. The energy conversion efficiency (sunlight to DC energy) of photovoltaic (PV) cells in production today range from about six percent for a thin layer cell made of amorphous silicon to 23 percent for high-quality single-crystal silicon cells. Some very special manufacturing techniques have produced cells in the high 30 percent range. Today's typical single crystal silicon cells usually average around 14 percent, thereby giving module efficiencies of 11 to 12 percent.

## What are the real-world conditions that affect the performance of a solar array?

What does temperature do to panel performance?

Solar panels become less efficient and produce less power as temperature increases. A significant drop-off in performance is seen at between 40 and 50 degrees C.

Why is panel mismatch a big deal?

Traditional solar arrays comprise one or more strings of solar modules. Because the panels in the strings are series connected, the performance of the entire string is limited by the worst performing panel in the string. This behooves system designers to ensure each panel's performance is as close to its neighbors' as possible and to maximize the design's efficiency.

If a mismatch causes one panel in the string to underperform other panels, the entire string's performance is degraded. If a mismatch causes a panel to outperform other panels, the benefits of that performance cannot be gleaned by the system.

Examples of mismatch

Mismatch can be caused by many things. Some are listed here:

• Differences in array orientation and plane of array
• Dirt, dust and debris
• Shade from clouds, trees and other obstructions
• Varied panel aging
• Design challenges (panel-to-panel variation, different string lengths, etc.)

What is MPP (maximum power point)?

Solar arrays are designed to produce power. Power, measured in Watts, can be calculated by multiplying voltage by current. At any given moment, there is a point in a panel's characteristic curve that will give the maximum possible output power. This is the maximum power point.

What is the difference between SolarMagic power optimizers and microinverters?

Solar arrays produce DC power that must be converted into AC (alternating current) power. A traditional array will have one large inverter to do the job. SolarMagic power optimizers operate in the DC domain, prior to the system's inverter. Microinverters convert DC power to AC power at the panel and does away with the need of a central inverter in the system, as it converts the energy output of each module directly from DC to AC. SolarMagic power optimizers provide flexibility in both existing and future installations.

Micro-inverters have been introduced mainly into the residential PV market and adoption has been steady, largely because of the ease of installation and flexibility of installation (e.g. no string sizing is required, arrays can be as small as the system owner desires). Another advantage is that it micro-inverters do away with the need for a central or string inverter, which is oftentimes one of the weakest points within an installation of the central inverter. Another advantage of the micro-inverter approach is that an installer can avoid high voltage DC wires, which often are the source of arcing. However power optimizers provide the advantage of smaller size for module integration, easier retrofitting of older applications, and longer warranty coverage due to simpler architecture designs with less components.

When retrofitting existing installations, SolarMagic power optimizers are simple to install - no rewiring or redesign is required. Simply de-energize the system, mount and plug in the SolarMagic power optimizers using existing wiring, and re-energize! Microinverters require system redesign and rewiring in retrofits - making the retrofit far more time consuming and costly.

SolarMagic power optimizers provide flexibility in newly designed and built systems. Effects of real-world conditions are easy to design for, using SolarMagic power optimizers. Where once a chimney might present a significant challenge in designing an effective solar array for a customer, SolarMagic power optimizers provide an easy solution. Trees that once precluded a solar array installation - or required lopping - can now live in harmony with an effective solar array with SolarMagic power optimizers.

And while microinverters must be used on every panel in an array, only strings impacted by real world conditions require SolarMagic power optimizers. SolarMagic power optimization technology provides flexibility in newly designed and built systems offering power optimization at both the module and string level.

## Power Optimization

What is power optimization?

Traditional solar arrays comprise one or more strings of solar modules. Because the panels in the strings are series connected, the performance of the entire string is limited by the worst performing panel in the string. This behooves system designers to ensure each panel's performance is as close to its neighbors' as possible, and to maximize the design's efficiency.

If a mismatch causes one panel in the string to underperform other panels, the entire string's performance is degraded. If a mismatch causes a panel to outperform other panels, the benefits of that performance cannot be gleaned by the system. This demonstrates the need for power optimization technology that ensures the MPP or maximum possible output power is achieved on each and every panel within an array.

Why do I need power optimization?

Power optimization increases system energy harvest and maximizes ROI by correcting hidden imbalance and extending system life. This imbalance occurs due to current or voltage mismatch (and can prevent the system from meeting performance expectations. SolarMagic optimization technology improves system output regardless of environmental conditions, weather, or layout. Independent studies have shown that SolarMagic optimization technology recaptures up to 75% of energy lost to mismatch.