Best Solar Panels

Choosing the Best Solar Panels / Solar Modules and Inverters

Sanyo Solar Panels

Solar cells produce direct current electricity from sun light, which can be used to power equipment or to recharge a battery. The first practical application of photovoltaics was to power orbiting satellites and other spacecraft, but today the majority of photovoltaic modules are used for grid connected power generation. In this case an inverter is required to convert the DC to AC.

• Monocrystalline solar panels are the most expensive as they have the highest

Monocrystalline Solar Panels

power output. These modules are made from a single large silicon crystal. Typically, a monocrystalline panel will begin producing electricity at about 5% of maximum sun energy while a polycrystalline panel will start producing power at about 10% maximum sun energy. This means that the monocrystalline panel will produce energy for more hours per day and in lower light conditions. Additionally, the monocrystalline panel will perform better and produce more energy in hot conditions.

• Polycrystalline solar panels are made by taking raw silicon and forming it into an ingot. This ingot is sliced into cells. Polycrystalline cells typically are less efficient than are monocrystalline panels as they require slightly more light to start up and they output less energy at higher temperatures. Typical Polycrystalline panels are the Sharp 208, 216 and 224, Solon and Trina.  
• Amorphous solar panels comes in a film that is deposited on a substrate. This substrate can vary and include glass, plastic or metal. This is often called thin film. While polycrystalline and monocrystalline panels will have efficiencies of 13% to 15%, amorphous silicon is typically around 8%-9%. Amorphous silicon is much less expensive. However, the cost of installation is typically much greater for residential installations due to the fact that it requires much more area, more material and more labor.
• Sanyo Hybrid solar panels incorporate the best of both worlds. Sanyo solar panels have a monocrystalline core with amorphous silicon deposited on the top and bottom. The Sanyo HIT panels will start up in very low light, thereby outperforming polycrystalline, will perform 10% better at high temperatures due to the very low temperature coefficients and have the highest efficiency (watts per square foot) available.

Solar Panels come in many varieties. All of the solar panels we carry are high output mono and polycrystalline with a 20-25 year warranty. The things to look for in a solar panel are:

1. Cost per watt
2. Warranty of 20-25 years
3. Output tolerance
4. Temperature Coefficient
4. CEC rating vs. STC rating
5. Availability

Solon Solar Panels

Every module has a trade-off. For example, some modules have a guaranteed output of -0% while others have a guaranteed output of +-9%. The tighter tolerance is usually a better buy. Some modules lose more power and others lose less when they get hot. It is quite often the case that a solar module will be 85 degrees or so hotter than the ambient air temperature. If you have a small roof, you may need to specify higher power density, higher output modules. In most situations, we recommend the Sunpower modules or the Sanyo modules which are the highest output modules we carry. If you decide that you would like a Modern Solar Home, make sure you get the right solar panels for your application.

Grid Tie Inverters

Inverters work by taking the DC power from the source, such as an array of photovoltaic modules (typically 250 to 600 volts DC) or micro hydroelectric turbines, and inverting it to AC power so it can be fed into the grid. The inverter must also synchronize its frequency with that of the grid (e.g. 60 Hz) using a local oscillator and limit the voltage to no higher than the grid voltage. Typical modern GTI’s have a fixed unity power factor, which means its output voltage and current are perfectly lined up, and its phase angle is within 1 degree of the AC power grid. The inverter has an on board computer which will sense the current AC grid waveform, and output a voltage to correspond with the grid.

Grid-tie inverters are also designed to quickly disconnect from the grid if the utility grid goes down. This is an NEC requirement that ensures that in the event of a blackout, the grid tie inverter will shut down to prevent the energy it produces from harming any line workers who are sent to fix the power grid.

Grid-tie inverters that are available on the market today use a number of different technologies. The inverters may use the newer high-frequency transformers, conventional low-frequency transformers, or even use no transformer. Instead of converting DC current directly to 120 or 240 volts AC, high-frequency transformers employ a computerized multi-step process that involves converting the power to high-frequency AC and then back to DC and then to the final AC output voltage.Transformerless inverters, which boast lighter weight and higher efficiencies than their counterparts with transformers, are popular in Europe. However, transformerless inverters have been slow to enter the US market. Until 2005, NEC code required all solar electric systems to be negative grounded, an electrical configuration that interferes with the operation of transformerless inverters. The issue at stake currently is that there are concerns about having transformerless electrical systems feed into the public utility grid since the lack of galvanic isolation between the DC and AC circuits could allow the passage of dangerous DC faults to be transmitted to the AC side.

Most solar grid-interactive inverters on the market include a maximum power point tracker that enables the inverter to extract an optimal amount of power from the solar array by tracking the array’s maximum power point.

Micro Inverters

A solar photovoltaic micro-inverter is a device that converts direct current (DC) from a single solar module (panel) to alternating current (AC).

Unlike a central or string inverter that aggregates and converts the power generated by the entire array of solar modules, a micro-inverter converts the DC power from a single solar module to AC. The concept of panels delivering AC power has appeal for small-scale home project applications at lower voltage levels.

Disadvantages of Micro Inverters

Inverters are generally acknowledged to fail at a higher rate than other components in a photovoltaic system. The warranty of an inverter is typically 10 years, whereas the rest of the system can be warranted for up to 20 years. Thus inverters are most-often rated for shorter warranties than other components. Detractors of micro-inverter technology claim it is not advisable to distribute the least reliable component of the PV system to every module, as the failure rate of an inverter at the module level multiplies failure points. Another issue is that the Micro Inverters would be located on the roof and daily temperature cycling would be detrimental to the long term reliability of the inverter.

Ground Mount Solar Panels

Solar Panels and Inverters–The Bottom Line

If you have decided that you want to put Solar Panels on your home, talk to one of the experts at Heritage Solar. There are so many solar panel choices available that it is hard to find the best modules and inverters. Contact us if you have any questions or would like a free site visit.

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