Part 3 – PV Panels

As I noted in part one, the object of this analysis is to provide a simple comparison of the cost of the fossil fuel generated electricity used in my home with the cost of electricity generated by a theoretical photovoltaic electric system. In part one we went through the process of sizing a system and in part two we contiued by examing how this type of system would work with the existing utility grid. In this third segment I’ll give a brief overview of photovoltaic modules (solar panels) which make-up a major portion of the system and cost.

A solar panel or solar module (terms are interchangable) is a collection of solar cells wired together in a series/parallel configuration so as to produce a desired voltage and current. The panels are made of aluminum framed glass with the individual cells mounted to the inner surface of the top glass (tempered, low reflective, etc.) with the back of the panel protected by another sheet of glass or glass-like material.

The following ratings, warranties and certifications are provided by the manufacturer and independent testing agencies to provide information about the panels and help the consumer compare apples with apples when shopping for solar panels. Be sure to check the panels specification sheet for this information or have the dealer provide it.

Efficiency Ratings
Most panels today are manufactured using two of the most common types of cell technologies, monocrystalline silicon and polycrystalline silicon. Solar cells manufactured with the lower efficiency material (polycrystalline silicon) result in larger cells and panels than those manufactured with higher efficiency material. The higher the efficiency rating of the module, the more power you’ll get per square inch of panel surface. In other words, the higher the rating the less roof area will be required for installation.

Panel Output (Wattage) Ratings (STC Ratings vs PTC Ratings)
The individual modules are manufactured to provide a specific amount of power output. Manufacturers rate the nominal power output (wattage) using a set of standard testing conditions (STC). The STC rating is the wattage specified on the panel’s nameplate. The independent rating anency, PVUSA, provides the PTC (PVUSA Test Conditions) rating which provides a more realistic or real-world measure of a panel’s output. Because the PTC rating uses more real-world conditions than the STC rating, the PTC rating is lower. A module with a STC rating of 200-watts, for example, may have a PTC rating of only 180-watts. When determining a system’s cost, it’s important to know that the PTC rating is used by California and various other states as the basis for determining system rebates. Ratings are listed as DC (direct current) watts.

Minimum Power Ratings
This is the manufactuer’s guarantee that the panels’ actual power output, out of the box, will not fall below a specified amount. This is sometimes called minimum warranted power and negative tolerance rating. A 200-watt solar panel (STC rated) with a negative tolerance rating of 5% will only be warranted for 190-watts (Minumum warranted power) out of the box.

Certifications
IEC 61215 – This is the international design standard for crystalline silicon modules. Conforming to IEC 61215 only guarantees that a test batch of modules has passed the required tests. It is not a guarantee of a manufacturer’s quality control in production.

UL listing – In terms of solar panels, Underwriters Laboratories tests for various safety considerations. Modules that pass testing are given UL’s “UL 1703″ listing for Flat-Plate Photovoltaic Modules and Panels.

Warranties
Provide some type of guarantee against defective workmanship or materials, which covers failures or problems during a specified period of operation. The remedy may be replacement or repair of the defective product.

Provide a guarantee that the peak watts of a module will not reduce by more than a stated percentage over a certain number of years (limited power guarantee). For example, a manufacturer would warrant its modules to produce no less than 90% of their initial minimum stated power under Standard Test Conditions for a period of 10 years from the date of original purchase, and also to produce no less than 80% of their initial minimum stated power under Standard Test Conditions for a period of 25 years from the date of original purchase.

The life expectancy for newer crystalline panels is anticipated to exceed 40 years with manufacturer warranties varying anywhere from 20-35 years.

Module Pricing
Panel prices for polycrystalline and monocrystalline have continued to delcine to the $2.50/watt and $2.75/watt range respectively. Module price greatly effects the cost of the solar system, as they encompasses approximtely 50-60% of the total installed cost (pretax cost). For more details concerning panel pricing see the following article from solarbuzz.com “Solar Module Price Highlights: November 2009″.

Although the present economic conditions are not that great, this is good news for consumers who have the money to buy modules now.

Okay, we’ve covered what you should know when comparing solar modules and found out that they make up approximately 50-60% of the installed cost of the solar system. In the next post I’ll cover the remaining elements making up a grid tied solar electric system and and begin pricing the system sized in part one. As I stated before, this is a learning experience and I know I may have moved along too fast at times, so if you see any errors or omissions, please feel free to share and leave a comment.

Recommended Sites and Articles

• solarbuzz.com
• greeneconomypost.com “A Cloud Over Solar In 2009; What are the Near Term Prospects for the Solar PV Sector?”
• solar.calfinder.com “Solar Panel Ratings Breakdown”