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Maximizing Power Production with High-Efficiency Solar Panels

Posted by AllEarth Renewables on June 7, 2016 in Maximizing Power Production, Power Production, Types of Solar, Future of Solar, Solar System Design, Small Commercial Solar, Dealers, Consumer

Fosters-688114-edited.jpgReturn on investment is key for any solar project, but especially small commercial solar. In these projects, every dollar matters. As a result, savvy investors and installers today are focusing more attention on the production capacity of a system and the dollar-per-kilowatt-hour generated, rather than simply the installed cost of a system, to ascertain a more accurate picture of the project's long-term value.

Maximizing the power production of a project is thus very important, and there are a number of ways to accomplish this. One of the easiest ways is by choosing a high quality, higher-efficiency panel, which can deliver a tremendous increase in energy output compared to a conventional solar panel.

Not All Rated Watts Are the Same

All panels are rated on output of watts (W), at 25 degrees Celsius (77 degrees Farenheit) at noon on a clear summer day (1000 W/m2 of sun). The problem is that people don't really care about watts, because the electric company charges based on energy generated, or kilowatt hours (kWh), not the installed watts.

Watts are an inaccurate measure of performance--just take the lightbulb, as an example. When comparing two incandescent bulbs, both rated at 60W, you know that they'll perform about the same. But what if you have two different technologies? Now, a 7W LED bulb can give you the same amount of light as a 60W bulb. You can no longer use the measurement in Watts to figure out how much light you'll get out of a bulb--you need to look at the amount of light generated to create an accurate comparison. It's the same with solar panels: if all you had to choose from were conventional panels, rated watts would be a fine way to measure how much energy you'd get each year. With higher-efficiency panels on the market, such as SunPower panels, you'll get a very different energy output for the same rated watts, resulting in more kWh than conventional panels of the same size and wattage.

High-Power Panel Technology vs. Conventional Panels

High-efficiency solar panels are proven to maximize power production, deliver long-term performance, and are readily available. SunPower is an industry leader, with unique, differentiated technology that sets its solar panels apart from the competition. Their panels have a fundamentally different cell architecture than conventional panels, and yield superior performance, with 7-10% more energy delivery per rated watt. High-power, high-quality panels are more reliable and deliver a better performance than conventional panels, especially in a few key areas.

Corrosion

The process of making conventional solar cells is the same as screen-printing a design on a T-shirt: you create a template, paint it, and then remove the template to leave the paint where you want it on the fabric. The T-shirt is then baked to adhere the paint onto the fabric. In a conventional solar cell, a similar process occurs with thin lines of metal paste, which are printed and baked onto the silicon cells. These lines, which carry the electricity into the cell, are problematic, as they actually block light from hitting the silicon and making electricity. For a better power output, the lines need to be as thin as possible, and just large enough to carry the electricity. Over time, water corrodes these lines, and the resistance of the panel goes up, making it harder to pass electricity through and ultimately reducing power output.

SunPower solar cells designed with no metal on the front, and the entire back surface is covered with a thick copper foundation. The copper foundation adds massive strength and makes the cells almost impervious to corrosion, enabling the cells to offer unmatched reliability.

Transmission of Electricity

Another benefit of a SunPower solar panel is that electricity is transported to every part of the solar cell from the copper foundation. In contrast, a conventional solar cell has a much more challenging task, as electricity is carried to the silicon through two thin, fragile copper ribbons.

This makes conventional solar cells susceptible to being compromised by thermal expansion. When you mount a panel, it goes from being cold at night to hot during the day, which can be as large of a swing as 50 degrees F to 150 degrees F. The conventional thin copper ribbon expands when it's hot, and contracts when it's cold. However, the silicon cells that the copper ribbon is soldered onto hardly change in size as the temperature changes, creating a daily push-and-pull cycle which places tremendous stress on the solder connection between the copper ribbon and the silicon cells. Over time, the solder bond can break, or the silicon can crack, resulting in electricity being unable to flow through the conventional solar cells, and a sharp reduction in power production.

Cell-to-Cell Connections

A solar panel is like a stack of batteries: the electricity, which is also referred to as the current, goes from cell to cell, and each cell contributes about half a volt. By wiring a string of several solar panels together, you're essentially creating a stack of 600-1000 solar cells, which creates the electricity your system generates. It is essential for every single cell to have electricity pass through it for the system to work, meaning the connection between cells is critical. A conventional solar cell has two narrow copper ribbons that carry electricity from the top of one cell to the bottom of the next, and all the stress from cell-to-cell movement is concentrated in those copper ribbons. When one breaks, part of the cell will no longer be able to pass electricity.

SunPower panels establish a robust connection between their cells with the "dog-bone," a solid copper bar that connects two cells and uses multiple solder connections to send electricity from one cell to the next. This type of connection is the most common connection in the electronics industry, known for its robustness. It also offers double-redundancy, meaning if one solder connection is broken, electricity can still flow through the others.

Silicon Cracking

Silicon is a brittle material, and cells are essentially extremely thin glass wafers, so they crack easily from the stresses of temperature cycling, shipping and installation, and heavy weather conditions. Because SunPower solar cells are entirely covered on the back with a copper foundation, cracks in the silicon have very little effect. Other than the area right around the crack, the rest of the silicon in the cell remains a part of the electrical path, since it's connected to the foundation, meaning cracks result in almost no power loss.

In contrast, in a conventional solar cell, cracked silicon can cause large areas of silicon to disconnect from the electrical circuit. Any time an area of silicon is not connected through a line of metal paste to the copper ribbons, that area of silicon is no longer part of the circuit--it's essentially dead. This happens frequently when a cell is cracked, because the metal paste offers little strength to hold cracked pieces of silicon together. When the broken part of the silicon separates even slightly, the electrical connection through the metal past is lost, and the cell has dead areas. This results in significant power loss.

Maximizing Power

With a higher-efficiency panel, you'll get more power for your money. Compared to a conventional panel, a SunPower panel produces 60% more energy in the same space over the first 25 years.

Not only will these panels produce more energy, their high-quality, durable design means you don't have to worry about failures that will impact power production and cost you money. According to NREL, cell or interconnect breakage and corrosion are the leading cause of solar panel degradation and failure, at 40.7% and 45.3% respectively. By designing out failure modes and ensuring long-term durability, these high-efficiency panels will consistently produce at a high level. SunPower has the industry's lowest average degradation rate at 0.25%, meaning more energy over the total life of the panel.

By choosing a solar panel that produces more power and has been designed for durability and performance, you're ensuring that your small commercial project will get the most bang for its buck, resulting in a higher return on investment for your team. 

Interested in learning more about maximizing power production? Watch a recording of our recent webinar on Maximizing Power Production for Small Commercial Projects.

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