Feb23

## AC vs DC Breakers

AC vs. DC Breakers Most of us are familiar with AC breakers found in the typical residential service panel.  Every once in a while we need to work on the wiring in the house, so we make a trip out to the side of the house to manually open (trip) the breaker to kill the power to that circuit, allowing us to safely perform our work.  Though AC and DC breakers appear similar in form and function, they are very different internally. The function of a breaker (AC or DC) is to detect when too much current (amps) is flowing through the circuit, then disconnect the circuit from the main power source to protect the wiring from overheating.  During the act of disconnecting, the internal contacts separate.  As they pull apart from each other, an arc will form as the current jumps across the air gap.  (You have experienced this on a smaller scale with a static electric shock.)  If this arc continues to jump the air gap, the current will continue to flow through the circuit, defeating the purpose of the breaker.  This arc must be extinguished.  The AC and DC breakers extinguish this arc differently.  This design difference is why AC and DC breakers are not interchangeable. AC Breakers In North America, the grid alternates at 60 Hz, or 60 cycles per second; hence the name “Alternating Current”.  The voltage alternates between +V and –V, 60 times a second.  That means there is a point at which the voltage is 0v, 60 times a second.  It is at this 0v point that the AC breaker will “break” the connection, extinguish the arc, and protect the wiring from too much current. DC Breakers In contrast, a DC circuit does NOT alternate.  It stays at a constant voltage.   Since there is no 0v point, the AC breaker design will NOT work in a DC circuit.  The DC breaker uses a magnet to attract the arc, pulling it from the air gap, and extinguishes it.  The AC breaker is NOT equiped with a magnet, and cannot extinguish a DC arc. Moral of the strory, use AC-rated breakers for AC circuits, and DC-rated breakers for DC circuits. Only breakers that are labeled as DC-rated should be used for DC applications.  NEVER attempt to use an AC-rated breaker in a DC circuit!  Why?  It will fail to extinguish the arc, the wires will overheat and cause a fire.  If a breaker is DC rated, it will state so.  NEVER assume an AC breaker is DC rated just because the amps and volts match what you need.  Conversely, don’t use a DC rated...

Jul21

## What Upfront Rebates for Residential Solar Are Left Around the States?

It used to be that homeowners could receive some very generous upfront rebates that could offset 30% or more of the cost of installing a solar system. But as the price of installing solar PV has dramatically dropped over the last three years, so has the upfront rebates offered by states and utilities. In addition to the wide spread decrease in rebate funding and amounts, many programs have switched from upfront payments that defer the cost of installing to performance based incentives that pay you a certain amount for every kilowatt-hour (kWh) produced by your solar system. But that doesn’t mean there aren’t any upfront rebate programs left. In fact, there are many, but they’re just not as generous as they used to be, but then again, installed prices have significantly fallen too. (Also, keep in mind that all solar owners are eligible to receive the 30% solar investment tax credit until 2016 for even more savings and ROI!) With the above in mind, the following is a random sampling of upfront solar rebates that we found on the Database of State Incentives for Renewables and Efficiencies (DSIRE). The links for each program are to the updated information from the actual utility or state authority, so we assume that this information is accurate as of this writing in mid July, 2014. California Upfront Solar Rebates Most of California has exhausted the funds for the state’s California Solar Initiative (CSI) program for home solar, but the good news is that many of California’s municipal utilities are still offering some type of upfront cash rebate. City of Santa Clara’s Silicon Valley Power utility is offering \$1.75/W AC for up to 10 kW. For a 5 kW system, that’s \$8,750 off the price of installation. However, the amount is actively stepping down as systems go online, so the sooner you install, the higher your rebate. City of Palo Alto’s electric utility is on its last rebate step, so get it while it lasts. Its program gives solar homeowners \$.80/Watt AC for solar systems as large as 30 kW. For a 5 kW average system size, that’s \$4000 off the price of solar. City of Pasadena has its own Pasadena Solar Initiative (PSI) program that’s now offering an upfront residential solar rebate of \$.85/Watt AC up to a 30 kW system size, which pencils out to \$4250 in decreased solar install costs for a typical 5 kW home system. Los Angeles’ LADWP municipal utility is offering just \$.40/Watt AC for its solar rebate, up to the average 5 kW system size. So, the maximum rebate amount is now just \$2,000 and continues to...

Jun19

## The U.S.-China Trade Case Determination and What It Means for Solar Installers and Consumers

A few months back, we published a post on All You Need to Know About the US-China Solar Trade Dispute and how it might affect solar installers and consumers if the case isn’t settled. Well, a preliminary decision is in. The Department of Commerce (DOC) has made a preliminary determination on June 10th in favor of SolarWorld, the German/U.S. solar panel manufacturer who filed the suit. Before we get into the penalties being proposed and finalized, we should remind readers that there are two parts to this case: Part 1: The DOC Decision The first part, now in the preliminary determination stage, has to do with SolarWorld accusing China of illegally subsidizing its solar panel manufacturers with low interest loans and other cash-related subsidies that allowed Chinese manufacturers to manufacture solar panels and export them to the U.S. (and the rest of the world) at below their actual cost. The 2012 DOC decision determined that was the case and imposed over 23% to 254% in countervailing duties (CVD) on various solar cells made in China. However, Chinese manufacturers got around these tariffs by manufacturing their solar cells in Taiwan and other nearby countries, then assembling the rest of the panel in China. Consequently, this new 2014 DOC preliminary determination now includes solar cells and other basic solar panel materials being made in Taiwan and shipped back to China for assembly and export. So, how much in duties will be tacked on to the price of imported Chinese solar panels? The preliminary CVD varies and depends on the brand: For Suntech solar panels, the tariff is 35.21%. For Trina SolarEnergy, the tariff is 18.56%. For all other Chinese brands, the tariff is 26.89%. That means that the wholesale price of all Chinese-made solar panels coming into the U.S. may be increased by as much as 35.21%, and at the very least, by 26.89%! The DOC will make its final determination by August 18, 2014. But wait, there’s more: Part II: The ITC Decision Remember, we said that there were two parts. Now that the DOC has ruled, their evidence has been handed over to the International Trade Commission (ITC). The ITC is deciding whether China is intentionally overproducing (“dumping”) their artificially inexpensive Chinese solar panels on the U.S. market in order to flood the U.S. solar market, forcing SolarWorld to lower their prices to compete. The ITC previously said this was the case in the earlier 2012 decision, so most industry analysts think they’ll do so again, but now include solar panels and cells from Taiwan. Should the ITC rule in favor of SolarWorld again, then additional antidumping duties may...

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...

Mar04