Spring 2009 Newsletter
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June 12, 2009

Some Fantastic Deals For Our Grid Tie Customers 

We have a whole new section on our web site devoted to our grid tie clients, www.apxsolar.com/grid-tie-solar-system-packages.htm. These are the best deals on the Internet for grid tie solar systems. We also launched the above new ad in home power magazine www.homepower.com.

The goal of these two new additions is to let folks know that solar does not have to be complicated or expensive. Grid tie systems are really quite simple with few components.

We realize that most areas of the country have few options when it comes to local installers. If there are just a few local installers in your area, they may charge more than you feel is fair. So we put a grid tie package together that any local electrician, general contractor or handyman can install. As with all our systems, we’re there to guide you through the entire process.

Choosing the right grid tie package is made easy with our zone map of the USA. Just click on your location and a table with average monthly kilowatt usages will guide you to the proper system size, components and prices. We hope the guide is easy to use, so please tell us what you think.

               
                  Websites to Check Out

Getting Cool With Sunshine

The Coolerado is new product www.coolerado.com that promises to be a revolution in the air conditioning world. This is a hybrid between a standard compressor-driven air conditioner and an evaporative cooler or swamp cooler, as they are also known. The claim is that it can deliver 65 degree conditioned air using around 600 watts of power. That’s 10 times less than an average home air conditioner. Although we have not had the chance to evaluate the Coolerado, these units look good and they are shipping them as fast as they are produced. They even have a unit that can operate directly from solar modules. Wow, now that’s cool.

The important thing to realize is that these units could make off grid systems much more affordable for those folks that live in areas that need full time air-conditioning. For grid tie applications this unit could reduce annual energy consumption up to 50%, which could translate to making the jump to solar power a reality. A smaller load equals a smaller solar array and lower install costs. We would really like to hear from anyone who has any experience with these units and we plan on doing an update in a future newsletter.

Helpful Tips and Stuff We’ve Learned Living Off Grid

Battery Maintenance

With summer sun and higher temperatures comes increased gassing of your flooded lead acid batteries. It’s time to do a little battery maintenance.
 
Here’s our recommendation for battery maintenance. First, make sure that your batteries are fully charged. Remember, as the charge of a battery goes down, so does the electrolyte level. The plates within the cells absorb the electrolyte as the battery is discharged. So a fully charged battery will be at its highest electrolyte level. This is important only because adding water to a discharged battery ends up with water overflowing out the cap when the battery gets fully charged. Not only do you end up with an acid spill, but also your battery is losing valuable electrolytes.
 
When it comes to adding distilled water there are numerous devices and watering cans to do the job. And what a job it can be. With three to six cells per battery, a large battery bank can have 48 cells and use 5 gallons of water. So here’s the cool tip we learned through experience. We buy the large 2.5-gallon containers of distilled water and use a 6-foot length of 3/8” clear plastic tube. Punch a hole in the top of the water container and set it above the battery bank. Place the tube in the water and using the good old siphoning trick, get the water flow started. Just pinch off the water flow as you work your way around to each battery cell. If a little water gets on the top of the batteries it’s ok. Just prevent foreign objects from getting in the cells. This technique works especially well because the tube can get into and around objects like battery cables and get to the hard to reach back cells. After all the cells have been filled, replace the caps and wash the tops of the batteries with a very mild soap solution and an old rag. Do not use baking soda. If the soda gets into the cells it will destroy your electrolyte.
 

Spotlight On New Products

Xantrex XW Inverter

We recently had the opportunity to install the new Xantrex XW inverter. The key feature that set this inverter apart from the rest is its ability to use multiple sources of power to keep energy flowing. In this application, the client wanted an inverter that could use solar panels to power their needs and back feed the grid. But a straight grid tied inverter would shut down when there is a grid failure. So our client wanted a battery backup in the event of a grid failure, but here’s the kicker. If the grid goes down and there is no sunlight for a number of days most grid tied systems with battery backup will fail as well. Not this inverter. It has a second input for power from a standby generator. So if all else fails, a generator can be auto started and brought on line. The XW inverter manages all these power sources. The difference in cost between this setup and other battery-based inverters is negligible and the extra features are well worth the extra cost. Some of the other features of the XW inverter are:

• 120/240-volt AC, split-phase, inverter/charger
  that incorporates a DC to AC inverter/ battery charge

• Integrated design to minimize external balance-of-system components

• Unprecedented surge capacity

• Applications up to 18 kilowatts (kW). Capable of being grid-interactive or grid-independent
   

An Off Grid Perspective

STC, PTC, CEC, CEC-AC What Does It All Mean?

If you’ve spent any time looking at solar panels or doing research on solar power, you’ve come up against many new acronyms. Some of the most confusing aspects of solar power are understanding how much power a solar panel, or more correctly the solar module, will produce. This is especially important when comparing systems and evaluating how much power a system will ultimately produce.
 

Standard Test Conditions (STC):

So let’s start with the manufacture. Below is a typical spec sheet for a 170,180 and 190-watt solarmodule. When the manufacturer sells this module, they list the maximum power that the module can produce. It’s listed in this table as maximum power or Pmax in watts. If you note under the title (Electrical Performance) they specify that this module be tested under STC or standard test conditions.This is 1,000 watts per square meter solar irradiance, 1.5 Air Mass and a 25 degrees C. cell temperature.

That’s all fine and dandy, but most modules don’t operate in a laboratory. The important wordin the STC rating to look at is cell temperature. It is tested at 25 degrees C. That’s 77 degreesF. Most module cells will operate around 20 degrees hotter than the ambient outside air temperature. That means that this test assumes that the outside temperature is 57 degrees F. So why do they want to test in such a cool environment? Simple, if you look down on the chart you’ll see that the temperature coefficient shows that for every degree above 25 C you’ll lose .45% off of the stated max power.

So let’s do the math: at a roof temperature of 100 degrees, not that uncommon in most of the USA,your 190 watt module is really only producing around 161 watts. That’s a 28% reduction, not so goodfor marketing.
 

PVUSA Test Conditions (PTC):

The solar industry needed a real world test of the modules so the PVUSA testing center in Davis, California, developed the PTC rating, which is typically 10-15% lower than the STC rating. The PTC rating represents a more real life condition based upon 1,000 Watt/m2 solar irradiance, 20 degree Celsius ambient temperature, and 1 meter/second wind speed. Note that this test is at 20 degrees C ambient which works out to a cell temp around 40 C or 104 degrees F. The facility in Davis takes modules from different manufacturers and puts them head to head and records the output data, an independent test of output. The PTC rating is great for consumers to look at when shopping for solar panels.
 

The CEC or CEC-AC watt rating:

The California Energy Commission (CEC) adopted the PTC rating to measure nominal output power of photovoltaic cells or modules to determine the system’s rating in order to calculate the appropriate incentive level. So you may see a module’s power output listed as a CEC rating which is really just the PTC method. The CSI (California Solar Initiative) program uses the CEC method as well. After all these ratings, is this the real measure of power coming from your system? No.
This is where CEC-AC comes into play. We still have to take into account the location of the array geographically, the tilt angle, azimuth of the array and the loss of efficiency going through the inverter. What comes out the other end of all the equipment and is fed into the AC grid power at the home is the CEC-AC wattage rating. The CEC uses this to determine the incentive or rebate a consumer can receive.

So in review, you start with the STC rating as a marketing number that the manufacturers use. Use this number as a general size of the module. The PTC rating will give you a more realistic amount of wattage that a given module will produce. Use this number when figuring out how much DC wattage an array will produce. And finally, because the rebates are predicated on the KW power going into the grid, the CEC-AC wattage is used for figuring out the rebate amount for grid tie customers. The CEC-AC KW can be used as a direct comparison against your utility bill’s daily KW usage. The expected annual CEC-AC KW production can be compared against your actual annual use.

Please feel free to make comments and suggestions for upcoming newsletters to farrel@apxsolar.com

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