Courtesy of DOE/NREL

Part 5 – Cost-of-System

Welcome back. The holiday season has past and I’m finally getting some time to continue the series. This is Part 5 in the “PV Solar – Homeowner Analysis” series, comparing the cost of fossil fuel generated electricity used in my home with the cost of electricity generated by a theoretical photovoltaic system. In this segment I’ll go over the component and installation costs along with the Federal and State tax incentives and rebates to come up with a fixed cost for the life of the system.

Component Costs
I’ll be using a retail price for solar modules, 125 Watts and Higher, of $4.30/peak watt for this analysis (for more information concerning the panel pricing see the following article from solarbuzz.com “Solar Module Price Highlights: January 20109″). The size of the system for this analysis, which was calculated in part 1 and revised in part 4 to give a more real-world estimate, is 5.55 kW or 5550 watts of solar panels. Therefore the component price for the solar modules will be approximately (5550 watt x 4.30/watt = 23,865) $23,865. Advertised solar power system packages of this size also include mounts, Wiring, disconnects and the other required small electrical components in the cost.

Inverters for this size of system were priced anywhere from $3600-$4400, using an approximate cost of $4,000.

• Component Cost= $23,865 + $4,000 = $27,865
• Transportation Cost= (2% of component cost) = $558
• State sales Tax (California)= (8.25% of component cost) = $2299
• Total Component Cost= $27,865 + $558 + $2299 = $30,722

Installation Cost
Without an estimate from a licensed contractor the installation cost is only approximate. The actual cost for installation is harder to determine because of all the variables involved, which includes labor, ground versus roof mount, panel configuration, utility service upgrade, roof type, permits and inspections, etc. Therefore, for this analysis I’ve used a fixed cost per module watt of $2.00, which calculates out as (5550 watts x 2.0/watt = 11,100) $11,100.

Total Installed Cost= Total Component Cost + Installation Cost = $30, 722 + $11,100 = $41,822


As I’ve stated before, a battery based system will cost around 20-30% more.


Renewable Energy Rebates and Incentives

• Federal Incentives – Residential Renewable Energy Tax Credit
  A taxpayer may claim a credit of 30% of qualified expenditures for a system that serves a dwelling unit located in the United States and used as a residence by the taxpayer. Expenditures include labor costs for on-site preparation, assembly or original system installation, and for piping or wiring to interconnect a system to the home. If the federal tax credit exceeds tax liability, the excess amount may be carried forward to the succeeding taxable year. The excess credit can be carried forward until 2016, but it is unclear whether the unused tax credit can be carried forward after then. There is no maximum credit for systems
  placed in service after 2008. The maximum credit is $2,000 for systems placed in service before January 1, 2009.

  Federal Tax Credit= $41,822 x 30% = $12,546

• State Incentives – State Rebate Program (California)
  • Equipment Requirements:
    System components must be on the California Energy Commission’s (CEC) list of eligible equipment.
    Systems must be grid-connected.
    Inverters and modules must each carry a 10-year warranty.
    PV modules must be UL 1703-certified.
    Inverters must be UL 1741-certified, and tested by the Energy Commission.

  
  

  • Installation Requirements:
    Systems must be installed by licensed California solar contractors. An installer certified by NABCEP is recommended.

  California Solar Incentive payments are currently disbursed in one of two ways:

  1. Expected Performance Based Buy-down (EPBB): The applicant receives the entire incentive payment at the time the system is installed, and the payment is based on expected electrical output of the system.
  2. Performance Based Incentive (PBI): The applicant receives a portion of the incentive payment every month over a period of five years, and the payment is based on the actual metered output of the system.

  The California Solar Initiative is structured so that the incentive payments decline as the market grows. Therefore, the incentive step levels decline as more applicants apply for the program. The area of California used in this analysis is currently in step 6 of the program which provides an EPBB payment of only $1.10 per watt.

  State Rebate= $1.10 per watt x 5550 watts = $6105
  
  

• Total Federal & State Incentives= $12,546 + $6105 = $18,651.




• Visit the DSIRE website for more information on State and Federal Incentives.

Courtesy of DOE/NREL

System Cost After Applying Federal Tax Credit and State Rebate= $41,822 – $18,651 = $23,171.

This is the approximate cost of a solar electric system sized to provide the same amount of electricity I now use in my home. In the next and closing post (Part 6) I’ll spread this cost over the estimated life of the system, at least 30 years, and compare it to the amount I’m paying for my electricity (fossil fuel generated). Hopefully this will provide a real-world cost comparison between fossil fuel generated electricity and solar generated electricity. Hopefully this comparison will also indicate how viable PV solar is as a renewable energy source at this time. As I stated before, this is a learning experience and I may be missing some important points, so if you see any errors or omissions, please feel free to share and leave a comment.

Part 4 – Balance-of-System

This is Part 4 in the “PV Solar – Homeowner Analysis” series, comparing the cost of fossil fuel generated electricity used in my home with the cost of electricity generated by a theoretical photovoltaic system. In part one we went through the process of sizing a system, in part two we continued by examining how this type of system would work with the existing utility grid and in part three we covered solar panels (modules), which make up approximately 50-60% of the installed cost of the system. In this fourth segment I’ll cover the remaining elements making up a grid tied residential solar electric system.

The remaining elements of a solar electric system are called Balance-of-System (BOS) components. The major BOS elements include such items as the grid Tie inverter, the combiner box, the AC & DC disconnects, the module mounting system and the cable and wiring. There are other optional parts, but these elements make up the major BOS components of a residential grid tie system.

• Grid Tie Inverter
  The solar inverter converts the variable DC output of the photovoltaic cells into AC current. The grid tie inverter is a pure sine wave inverter that synchronizes with and feeds power back to the grid. A grid tie inverter connects directly to the utility grid without the use of batteries. One important thing to consider when purchasing the inverter is the efficiency. Even though you may have purchased solar panels with a very high PTC wattage rating, a low efficiency rated inverter can negatively effect the system’s performance.




• Combiner Box
  The Combiner box is where all the wires from the Solar Panels are routed and allows multiple solar panels to be combined in parallel. A combiner box is basically an electrical box that connects the input panels in parallel to produce one circuit. The breakers and fuses for the solar panels will also be placed here as well. The box is typically made to go outside near the solar panels.




• AC & DC Disconnects
  The DC disconnect is used to isolate the PV array from the inverter and an AC disconnect is used to isolate the inverter from the AC panel or load center. The AC disconnect (switch), installed on the inverter output, allows the system to be disconnected from the grid by utility personnel.




• Module Mounting System
  After you’ve establish the number of panels and the array arrangement, the mounting location is determined. Although module mounting systems are available for ground and roof installation, roof mount installation is the most common and cost effective method. The roof mounted panels are attached to a mounting system typically consisting of an aluminum or steel support structure which attaches the panels to the roof. If the roof space is limited, shaded or unsatisfactory for any reason, the array can be mounted on the ground. The most common type of ground mount is a wedge shaped steel structure anchored in concrete. Another type of ground mounted system is the pole mount, in which the panel array is mounted on top of a single steel pole. There are numerous variations of these installation types, including rail mounts, tilt adjustment, automatic tracking, etc.




• Cables and Wiring
  This includes the Wiring that connects the components of the PV system together. Most solar panels are now manufactured with multi-contact connectors (MC) which makes series and parallel connections a snap. The panels are wired together as needed and then routed into the combiner box paying special attention to safety and grounding requirements.

That’s it for the Balance-of-System components. In the next post I’ll go over the component and installation costs along with the Federal and State tax incentives and rebates to come up with a fixed cost for the estimated life of the system. As I stated before, this is a learning experience, so if you see any errors or omissions, please feel free to share and leave a comment.

Before I end this segment, I want to refer back to part 1 and revise the calculated system size. The last step used in determining the size was to multiply by a real-world factor of 1.2. Further study suggests that a factor of 1.3 is actually closer to a real-world situation. Due to module and inverter inefficiencies along with other power losses, the calculated system size of the 4.271 kW system is multiplied by a factor of 1.3 to give a more real-world estimate (4.27 kW x 1.3 = 5.55 kW) of 5.55 kW.


Recommended Site
Pennsylvania Solar Course
This is an online solar training course from the state of Pennsylvania designed for residential applications and specifically includes the siting, sizing and installation of solar electric (PV) and solar water heating.

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”