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”

Part 2 – Grid Inter-tie and Net Metering

In the last segment I determined the size of the residential (PV) solar electric system I want to install as a minimum of 5.13 kW. The system was sized to produce approximately the same amount of electricity I use on a daily basis and would hopefully eliminate my electric bill. I was going to begin this segment by starting to price a system, but before we do that, I need to go over a few things that effect how this solar electric system will work with the current electric utility infrastructure.

Because your solar electric system will produce more power than you need at some times and less than you need at others, you’ll need a way to store the power that’s generated so you can use it at night and at times when you need more power than the system is generating. Net Energy Metering laws allow owners of solar power generators to use the electricity grid as a battery to store power from their system when they are not using it and to withdraw the power later when they need it.

Grid inter-tie (interconnection) is basically connecting an alternative electricity generator to the power grid. Net Energy Metering is a billing system that works similar to the banking system and allows the inter-tie to work successfully. When your solar electric system is inter-tied/connected to the utility grid, the grid will accept excess electricity generated by your system. If your system generates more electricity than you need at the moment, that extra electricity is deposited into the local utility grid to supply other customers. The deposit is made through your electric meter, turning it backwards, lowering the meter reading. The electric meter keeps track of how much excess electricity is generated by your renewable energy system and sent back into the grid,  and how much grid electricity you consume. If for any reason you need additional power above what is generated by your system or at a time when your system is not generating, it can be withdrawn from the utility grid without cost up to the amount you’ve deposited earlier. Any electricity withdrawn from the grid, above the amount deposited, will be billed at your fixed billing rate. Most utility companies presently, will not pay for the electricity you deposit into the grid above what you consume, instead they will credit your account for the next billing period.

Net metering policies continue to change, a few states now require the utility company to pay the homeowner retail cost for the additional energy. Net Metering is currently offered in more than 35 states, with polices varying from state to state. For a detailed description of each states net metering policies see the DSIRE database for Net Metering. For a detailed description of each states Interconnection Standards see the DSIRE database of Interconnection Standards.

Net metering also helps to respond to today’s stressed power grids by adding additional energy during the peak demand period of the day. The solar powered systems generate electricity during daylight hours when there is a high demand for power and shut down during the lower demand hours of the night. You’ve made your deposit during daylight hours and can withdraw at off-peak periods during the night.

Before we get back to pricing a system I’ll also need to decide whether or not to have a battery backup or to go battery-less. Although both options will allow a grid inter-tie, there is cost and efficiency differences between the two systems. If your not going to be connected to the utility grid you’ll definitely need a bank of batteries and even if you’re connected to the grid, the battery backup system could be handy when the utility grid is down, at which time the the battery backup provides power to appliances and electrical devices. The battery-less system would shut down during a utility power failure and you would not have electricity available to your home until the utility company restored their power. The battery backup system is obviously going to to be more expensive, with the cost of the charge controller, batteries and replacements every 5 to 8 years. Another thing to consider is that the overall efficiency of a battery backup system is less than that of an equally sized battery-less system, which means you won’t get as much energy out of the system as with battery-less. Because of the added cost (about 20% to the cost of the system) and 30% less efficiency with the battery backup system I’ll opt for the battery-less system. I’m not really concerned as much about the possible utility power failures right now.

I didn’t get to pricing a system in this segment like I wanted to, but I felt it was important to cover the concepts of grid inter-tie and net metering before we went any further. I also decided that the solar electric system in this analysis will be connected to the grid and will not have a battery backup for now. In the next segment I’ll start out by introducing the two ratings given solar panel (module) output (DC Watts), determine the roof area (ft2) required to hold the panels and go from there.

Again, this is a learning experience for me, so if you see any errors or omissions, please feel free to share and leave a comment.