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Solar 101: What’s the difference between microinverters and string inverters?
Mar19

Solar 101: What’s the difference between microinverters and string inverters?

If you’re a homeowner or an installer doing residential or small scale commercial solar installations, you essentially have three choices for converting the solar system’s DC power into AC power: You can either go with new microinverters or with string inverters—with or without DC power optimizers. All will work, but there are differences, especially in certain situations. String Inverters: The solar industry standard With residential string inverters, all solar modules are connected in a series circuit to a DC electric cable, which is then connected to a single inverter box mounted on a wall by the home’s main AC panel (as well as to any required DC disconnects). So it’s a very centralized system with a limited amount of labor. Modern string inverters not only convert the power from DC to AC, but also use Maximum Point Power Tracking (MPPT) to deliver the maximum amount of power available. This is important, since each solar panel can produce different amounts of power due to manufacturing anomalies, intermittent shading, leaves, dirt, passing clouds, and/or other factors. While a string inverter’s MPPT works fairly well, especially in sunny areas with no obstructions, having all solar modules tied in a series circuit can still be a disadvantage for several reasons: 1)   MPPT technology is essentially drawing the average amount of power available, rather than the full amount available from each module. As a result, the entire solar array can lose 15% to 30% or more of its full potential output because one or more panels in the string are temporarily shaded or have debris. 2)   If you have limited roof space and need two arrays with different sun orientations, each array will need its own string inverter. 3)   Similarly, since module mismatch can cause efficiency issues, you’ll need to use the same brand and panel voltage within each string. 4)   String inverters don’t easily allow for expanding the system in the future unless you purposely oversize the inverter, wiring, and other BOS parts. 5)   While it’s common to have online monitoring with string inverters, the monitors only measure the performance of the entire array. So, if an array isn’t producing the expected power, installers will need to individually test each panel for malfunctions. 6)   String inverters are typically warrantied for 10 years and have an expected lifetime of 12 to 15 years, while solar panels typically last 25 years or longer. Thus, the string inverter will need to be replaced at least once. Adding DC Power Optimizers to String Inverters Adding DC power optimizers to a string inverter system can solve most of the above string inverter challenges. Power optimizers are relatively new...

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3 Ways Enphase M215 Just Got Better
Jan27

3 Ways Enphase M215 Just Got Better

Enphase Energy just revealed some key improvements to the Enphase M215, 215 Watt microinverter and their system as a whole. Take a look at the new features… 1. Enphase M215 with Integrated Ground Photovoltaic (PV) systems in North America have normally required bonding each microinverter together with continuous copper grounding wire.  The purpose of this standard is to prevent fires, protect workers from shocks, and comply with National Electrical Code (NEC).  Some changes to NEC have allowed Enphase to incorporate integrated (DC isolated) ground technology into their 4th generation line, which now includes the M215. Because the DC circuit is isolated and insulated from the ground, you can now safely install Enphase M215 microinverters without a Grounding Electrode Conductor (GEC) connected to each microinverter. Coming soon… the 4th generation M215. Download the new M215 Microinverter data sheet (PDF). As you can see in the image above, the M215 now has a flat lid with no grounding lug. Yes, this product meets U.S. National Electrical Code (NEC) requirements Ungrounded Photovoltaic (PV) Power Systems and it’s actually a safer product. Integrated Ground(IG) technology simplifies this cumbersome installation process, reducing materials and labor costs.  Installers and D.I.Y. customers already prefer to use Enphase for residential systems because of its straightforward installation.  The new M215 further simplifies the process because there’s no need to run copper wire between each microinverter. Sound familiar?  Last year, Enphase released their fourth generation model, the Enphase M250, which also features this new IG technology.  The Enphase M520, however, is optimized for solar panels all the way up to 300 Watts. The Enphase M215 is compatible with modules up to 270W, a lower wattage range where consumers are finding the best dollar per Watt on solar panels.  So basically, Enphase put all the benefits of the M250 into the M215. Oh yeah, the new Enphase M215 also has a CEC efficiency rating of 96.5% compared with the previous version’s 96%. For more information on the new M215’s integrated grounding feature, please see Enphase’s M215 white paper. 2.  Wi-Fi option for the Envoy Communications Gateway Now Available! The Envoy Communications Gateway is the hub connects your Enphase microinverter system to Enlighten, Enphase’s web-based monitoring software for PV systems. Instead of running an Ethernet cable from the Envoy hardware into a broadband router, you can now connect the Envoy Communications Gateway with the new wi-fi option (pictured top right). The new Wi-fi option simplifies connectivity and makes finding a location for the Envoy way easier. Connect up to 600 microinverters to one Envoy.   3. MyEnlighten & Enlighten Manager Software Customers who use the Enphase Envoy to monitor their systems get...

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How to make a light source out of plastic bottles.
Jan08

How to make a light source out of plastic bottles.

Well over a billion people on our planet don’t have access to electricity and this D.I.Y. solar light can brighten homes during the day and replace toxic kerosine lamps. Watch this video: 4 easy steps to light a room with a solar bottle lamp: 1. Add a couple teaspoons of bleach to keep the water clean. 2. Drill a hole in roofing to fit the circumference of the plastic bottle. 3. Push the bottle up through the hole in the roofing. 4.  Seal the the bottle with polyester resin to prevent a leaking roof. [i] It’s a stunningly simple lighting solution: sunlight passes through the water inside the bottle, refracting light, and brightening the room. Even though you might not insert a 2-liter bottle into your roof, this might also come in handy if you’re want to illuminate the inside of a tree-house. Check out the infographic below and “share” this page if you think this is cool!    ...

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Texas $2 per Watt Rebate?
Nov27

Texas $2 per Watt Rebate?

Coserv’s $2 per Watt Rebate If you’re one of the 141,000 member-owners of the  Coserv Electric Cooperative in Texas and you’re thinking about going solar, you’re smart. You might have heard that this co-op utility offers a $2 per DC Watt rebate on solar generation. $2 per Watt? This rebate means homeowners in Texas can get $2 per DC Watt installed.  Many solar rebates are based on the size of the solar system in AC Watts,  which is a measurement of the system after the electricity has been converted from DC to grid-quality AC power.  A $2/ AC Watt rebate would already be a very strong incentive, but this rebate is in DC, which means more money in your pocket. $2/W DC  >  $2/W AC For example:  you’re installing a 2kW (or 2,000W) grid-tied solar system.  That number “2kW” is based on the sum total of watts in your solar system – we’ll call it eight 250W solar panels. In this case, you would qualify for a rebate of $4,000, given that the funds allocated towards this rebate program haven’t yet been exhausted. Depending on the size of your system, this  rebate your 2 kW (or 2000 Watt) solar system will yield a couple hundred dollars more. This utility rebate program caps off at $5,000 for each system, which is equal to a 2.5kW solar system.  Contact us today for solar design help and while you’re at it, fill out the Coserv solar rebate application form.  All 2013 funds were reserved in early 2013.   Check their website at the beginning of 2014 for any changes to this rebate and get on the list so they can reserve funds for your project.   Rebates are paid out after your solar system is installed and inspected by a Coserv Auditor. On top of this rebate from Coserv, you’ll also qualify for the Federal Tax Credit.   After any state/local/utility rebates have been subtracted (including Coserv’s solar rebate), 30% of this net cost is returned to you in the form of a tax credit that directly reduces the dollar amount you pay on your taxes....

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No CA Rebate without Solar Panel Monitoring?
Nov15

No CA Rebate without Solar Panel Monitoring?

Homeowners using the Enphase Envoy to monitor their solar panel output can qualify for an upfront, lump-sum rebate through California’s Expected Performance-Based Buydown (EPBB). What’s the EPBB Rebate? The Expected Performance-Based Buydown (EPBB) is one of two incentive options offered by the California Solar Initiative (CSI). The EPBB is an upfront rebate for small businesses and homeowners with systems 30kW or less (as opposed to systems greater than 30kW, which would qualify for 5 years of monthly payments through a Performance-Based Incentive).  If you qualify for the EPBB rebate, you’ll get the entire payment at the time of installation. The EPBB rebate is determined mainly by the expected performance of a photovoltaic system, which is based on factors including CEC-AC rating, tilt, orientation, location, and shading. To qualify for the EPBB rebate, you need to get a monitoring system like the Enphase Envoy Communications Gateway to track the output of your solar panels.  With a reporting accuracy of ±5%, Enphase monitoring is sufficient for the EPBB rebate, whereas revenue-grade meters with ±2% would be required for PV systems of 30kW or greater under CSI’s Performance-Based incentive.   Enphase monitoring systems include: Enphase or Siemens Microinverters Envoy Communications GatewayTM Enlighten® web-based monitoring and analysis software For more information about monitoring requirements, visit the CSI Website.   How does Enphase work? The Enphase Envoy is designed for PV systems with Enphase Microinverters, which attach behind each solar panel, turning the DC electricity from each solar panel into usable AC electricity. With each microinverter working independently, Enphase systems are optimized for locations prone to shading from nearby trees and make it easy to add solar panels to your system in the future. Each mircoinverter is connected to the internet with it’s own IP address, so the web-based software Enlighten provides data about your system’s output – whether you’re at home on your PC or using your the Enlighten app your iPhone.   Each microinverter operating independently means you can see the output of individual panels in your array, making troubleshooting issues much easier than a string inverter would. Enphase microinverter systems are recommended for small grid-tied systems, systems with multiple arrays, and systems with potential shading concerns. Benefits of Enphase Systems: Easy installation Design flexibility & scalability Maximum Power Point Tracking (MPPT) Optimized for shading Remote monitoring capability...

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Quick Look at STC vs. PTC Ratings
Sep17

Quick Look at STC vs. PTC Ratings

What’s the differnce between STC & PTC? Looking at the specifications for a solar panel, you’re going to see two distinct ratings:  STC and PTC, both of which refer to DC (direct current) Watts of the solar panel. STC rating Standard Test Conditions, or STC ratings, are the solar panel’s name plate value.  This means that if it’s a Sharp ND-250QCS, 250 Watt solar panel, the STC rating is 250 Watts.   STC ratings reflect the solar panel’s production in ideal conditions, which is actually a flash of light shot at the solar panel in a lab environment. PTC rating When you’re looking to get an idea of PV output, PTC ratings are a more realistic number to look at.   PTC ratings, or PVUSA (Photovoltaics for Utility Systems Applications) Test Conditions, show the results from a test that more closely mimics real-world conditions.  PTC ratings are based on 1,000 Watts per square meter of solar irradiance at 10 meters above ground level, at 20 degrees Celsius, and with a wind speed of 1 meter per second. As seen in the image above, the Sharp ND-250QCS, 250W solar panel has a PTC rating of 223.6 Watts.  If you were using these solar panels for your photovoltaic system, using the PTC rating of 223.6W to estimate output would provide a more accurate, “real-world” number than the STC rating of 250W. Keep in mind that there are still other factors that will effect PV output.   There will usually be some energy loss via wires, inverters, etc.  There’s also normal degradation of solar panels over time and environmental factors such as soiling (dirt), heat, and shading....

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