The amount of solar energy that hits a square mile every year is equal to 4 million barrels of oil. So how does a photovoltaic system turn the planet's most abundant source of energy into usable AC electricity?
Grouped together in a "solar array," solar panels collect electrons from the sun's light. Still in the form of direct current (DC) electricity, these electrons must be sent through an to be converted into AC electricity- the kind you use on a daily basis
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When you're producing more electricity than you're consuming, you're sending electricity back into the utility grid. Your electric meter spins backwards, saving you money on your electric bill.
When you're not using the solar energy that your system is harvesting during the daytime, you're giving it back to the utility company as a credit towards your electric bill.
The utility grid is kind of like your "battery," because you use electricity from the utility company to power your home at night when it's dark.
The overwhelming majority of solar panels are composed of cells made of either monocrystalline or polycrystalline silicon. Though there are subtle differences between the two, neither one is necessary better than the other.
A monocrystalline solar cell is composed of a single crystal of silicon, a purity that can be identified by a dark, even coloring.
Monocrystalline solar panel panels will typically have higher efficiency rates (15-20%), converting energy particularly well in low-light and lab conditions.
Because monocrystalline solar cells usually have higher efficiency, these solar panels will make good use of limited roof space.
Because the output of monocrystalline cells can be significantly affected by shading and soiling (i.e. dirt, dust), microinverters often pair well with these solar panels.
Monocrystalline is an older technology, but these solar panels are still usually more expensive than polycrystalline solar panels.
• High efficiency
• Performs well in low-light conditions
• Usually more expensive
• Sensitive to soiling and shade
• More silicon is wasted in the manufacturing process
When would I use monocrystalline solar panels?
Example: You live in a location that’s prone to low-light conditions and you have limited space to work with.
Polycrystalline solar panels are easily identified by their solar cells that have a textured look that resembles a granite countertop.
Because polycrystalline solar cells are composed of multiple silicon crystals, the manufacturing process is more efficient and wastes less silicon in the process.
Because of this, “poly” solar panels are more cost-effective than “mono” solar panels because they are less expensive to manufacture than monocrystalline cells.
The silicon in polycrystalline solar panels is technically lower in purity.
Efficiency rates are usually between 13% and 16%. Polycrystalline performance has improved to the point that monocrystalline is not necessarily better.
• Manufacturing produces less waste
• Doesn't perform as well in low-light conditions
• Aesthetics? You can be the judge of this.
• Lower efficiency
When would I use polycrystalline solar panels?
Example: You’re located in an area that doesn’t have particularly low-light conditions and you want the most cost-effective PV system.
In the past, monocrystalline panels were considered better because they are made from single crystals of silicon and they’ve also traditionally had higher peak efficiency. Polycrystalline technology has improved to the point that monocrystalline cells do not necessarily mean a better solar panel.
The more important concern when choosing a solar panel for your application is the quality of the manufacturer and the warranty offered on the product.
The decision between poly and mono can hinge on a number of factors including your geographical location and solar insolation. Talk with a qualified solar installer about the best choice for your specific application.
For every grid-tied solar system, the electricity produced by your solar panels must be converted from direct current (DC) to alternating current (AC) by a grid-tie inverter. The AC power that isn’t used by your home is back-fed into the utility grid.
String inverters are the most common choice for residential solar applications.
Because string inverters have been for decades, there is much more field data that has been collected.
It is for this reason that string inverters are still the most trusted solution, regardless of the advantages microinverters hold.
A string inverter will convert DC electricity from multiple solar panels into usable AC electricity at ground level by your service panel. Consequently, central inverters will be high voltage.
String inverters are recommended for larger photovoltaic systems with no shading concerns, ground-mounted systems, and non-residential applications.
The down side to string inverters is that an entire string of solar panels is affected if one solar panel is shaded. Fire hazard and electrocution risk is higher when you have string-based systems with no built-in power control within the array.
• Proven Technology
• Not optimized for shading
• Difficult to expand
• No monitoring
When would I use a string inverter?
Example: You’re designing an 8kW grid-tied solar system.
You either have the roof space available to fit the entire array or you will install a ground-mounted system.
You also have no shading concerns and you do not plan on expanding this system.
Microinverters are mounted directly behind each solar panel, turning the DC electricity from each solar panel into usable AC electricity.
Because each this conversion is happening at the modular level, you're maximizing the potential output of your system. If one solar panel is shaded by a tree, it won't affect the output of any other solar panels because there is no single point of failure.
Microinverters also eliminate potentially hazardous high voltage DC wiring and make your solar system much easier to expand.
Maximum power point tracking (MPPT) is a technology used in microinverters that optimizes the electricity output by responding to the varying levels of light every couple of minutes.
Every microinverter also has its own IP address so it can be monitored remotely with web-based software.
• Easy design, installation, & scalability
• Optimized for shading
• Remote monitoring capability
• More expensive
• Relatively new technology
When would I use microinverters?
Example: You’re designing a 2.5kW grid-tied system for your home. At this point, you’re not sure whether you’ll want to expand the system later on.
Without a large roof space to fit the entire solar array, the system will have to be segmented into 3 smaller arrays on different parts of the roof and on top of the garage.
There is also large oak tree next to the home, which will occasionally cover part of one array.
Different applications are going to determine whether it's best to use a string inverter or microinverters. If you have any doubts, give us a call at (586) 883-2991.
If you're using a string inverter, you can use solar panel maximizers to optimize the harvest more from each solar panel while getting module-level data for operational management and performance monitoring.
Get up to 20% more energy from your string inverter system by integrating power maximizers like the Tigo Energy® Maximizer™ system. Designed for residential, commercial and utility scale photovoltaic solar arrays, the Tigo Energy® Maximizer™not only maximizes the power output of individual modules, but it also allows for online monitoring feature that's most commonly elusive to microinverter systems.
How do solar panels stay on the roof?
Attaching solar panels to your roof is not as simple as buying a pack of nails and hammering away until the panels feel secure.
No, solar panels are classified in the building code as “Components & Cladding,” and consequently, must be fully integrated with the building’s structure.
This means the products used to mount solar panels are attached to rafters and are engineered to handle the same forces and environment as the roof.
Factors to consider in solar mounting
Over the last decade, a number of products have been designed to attach solar panels to a building. But selecting the correct product is going to depend on local and site-specific factors, such as weather and roof style.
For example, homeowners in coastal California do not need a solar array that can handle snow loads or hurricane-force winds. However, they do need to deal with the corrosive effects of sea salt in the air.
Conversely, people in the Northeast must account for both hurricane-force winds and snow loads, as well as the corrosive effects of high humidity and near-marine environments.
What’s in a mounting system?
Solar mounting systems are composed of three parts: (1) roof attachments, (2) mounting rails, and (3) module clamps.
Each of these components can vary in size, weight, and material, so manufacturers typically provide detailed information to aid in component selection and system design.
Some manufacturers even offer free online design tools to help with planning.
For every roof, there’s an attachment
Roof attachments are the base or foundation of any solar array. There are a number of different types and style of solar attachment, each designed for specific roofing materials.
Composition asphalt shingles are the most common roofing material in the US. A number of attachment products for composition shingle roofs are designed to be both a structural anchor and a waterproof flashings. These “integrated” products help reduce the time and cost associated with installing roof attachments.
Tile and slate roofs, on the other hand, require more complex products with more labor-intensive installation procedures. These challenges are compounded by the fact that tiles are fragile and can crack if not handled carefully.
Homeowners with these roof types should expect to pay slightly higher costs when receiving bids from solar installers. As well, it’s a good idea to discuss ahead of time how the installer plans to avoid damage to the tiles or replace them if damage does occur.
Rails of all shapes and colors
Solar mounting rails are typically made of aluminum. Aluminum is strong, lightweight, and corrosion resistant, making it a great material for rooftop construction.
Most rails have an “anodized” finish, which means they have a protective layer on their surface to prevent damage or surface corrosion. This feature ensures a clean appearance long into the future by preventing buildup of oxides on the surface of the aluminum. Preventing this buildup is also key to ensuring any future maintenance of the solar array is easy and hassle-free.
Anodization is available in “clear” (silver) or “black,” depending on the customer’s aesthetic preferences. Rails with a “mill finish” are not anodized, and are best suited for dry, non-marine, non-industrial regions, such as the desert Southwest.
In addition to anodization options, manufacturers frequently offer more than one size of mounting rail. Different sizes are engineered to handle different wind and snow loads.
A large, heavy-duty rail will always provide sufficient structural strength, but it may be more expensive than is necessary. Often, a mid-range or lightweight rail is going to provide more than enough structural strength for mild climates, while also minimizing the cost and weight of material on the roof.
Clamps that “bite,” literally…
The final component of the mounting system is the clamps.
Most clamps are known as “top-down” clamps because they secure the top surface of the solar module to a slot in the mounting rail, which is supporting the module from below. These clamps are very secure, while also being quick to install and making any future maintenance easy to perform.
Newer designs of top-down clamps incorporate “teeth” that bite into the module frame. These teeth are actually making a grounding connection to the module, which provides an additional measure of electrical safety for the solar installation.
Clamps with this capability are all certified to the Underwriters Laboratory test standard 2703.
And luckily, the teeth are small and remain hidden beneath the clamp, avoiding any unsightly “bite marks”.
Always select a trusted supplier
The final and most important component of any solar installation is trust.
Solar installations are designed to operate for decades without major repair. This requires a high degree of confidence in the products and the workmanship, backed by years of experience.
Often, the difference between a reputable company and a low-cost competitor can be difficult to discern. Homeowners should discuss the product and warranty options with their installer in detail. Warranties should be at least ten years, and ideally twenty or more.
Also, make sure that the installer has experience working with the product manufacturer. A trusted supplier will be one that has proven the value of their warranty through years of collaborating with their installation partners.
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Michigan Solar Energy LLC 2015