Solar Energy Advocacy for San Francisco and the Bay Area  
 

September 11, 2007

  INTRO      ECONOMICS      IS SOLAR FOR ME      BLOG/NEWS      RESOURCES      ABOUT US      HOME     

GET A SOLAR EVALUATION  

 

Is Solar For Me?

The most critical requirement for solar electricity is a roof with an unobstructed view of the sun. South facing roofs are best, although east and west facing roofs are good candidates (west facing is preferred due to higher costs of electricity in the afternoon). Your roof (or wherever you intend to mount the panels) should be free of shade, especially during peak production hours between 10am and 2pm. Flat roofs and pitched roofs can both be accommodated - flat roofs are easier for installation and may offer more flexibility on angle adjustment.

As longtime San Francisco residents we just assumed that with our foggy weather, solar electricity simply wouldn't make sense. Most people are surprised to learn San Francisco and the Bay Area are ideal for solar electricity. Fog does reduce the efficiency and output of solar panels, however light colored fog (or "bright" fog) may only cause a 10-15% reduction in efficiency. Dark fog, or heavy clouds, will significantly reduce efficiency, by 75% or more.

In general, Bay Area homes benefit from very high numbers of sunny days, averaging over 300 per year. Also, the relatively temperate climate reduces the stress on the panels - they operate more efficiently at cooler temperatures. And you certainly never have to worry about panels getting covered with snow!

Factors Affecting Solar Output

Shade Shadows prevent the PV panels from collecting and converting solar energy to electricity. Your site should be relatively free of obstructions, especially during peak hours between 10am and 2pm.
Weather The key measure here is how many days of sunshine you have per year. Summer months have the highest solar intensity, so you especially want sunny days during this time of year.
Surface obstructions Panels lose efficiency if the surface is obstructed. Leaves, snow and dirt can reduce your output significantly. While solar panels do not need much maintenance, you do need to keep them clean.
Panel inclination To achieve maximum output, solar panels should be positioned at an angle as close to perpendicular to the sun's rays. This angle cycles from the sun's highest point on June 21 to the lowest point on December 21. Your installer can recommend the best angle.
Panel orientation Southern panel orientation offers the highest output. If you don't have a south-facing roof, you can get excellent results with east- or west-facing roofs. Also, PG&E pays you more for afternoon energy production so a west or southwest orientation may be best.

How Big a System do I Need?

The first thing to assess is what your goals are for solar electricity. Here are some common goals:

  • Eliminate all my high-rate electricity usage (i.e., cover my usage above PG&E's base rate tier). This may require a system that can produce 50% of your total energy usage.
  • Eliminate my annual electricity bill. Thanks to Time-of-Use rate difference, you may be able to accomplish this with a system that produces 60-70% of your annual usage. Note, no matter what, you'll still have a small PG&E bill. They charge $5-8/month just to be connected to the grid.
  • Eliminate my total electricity usage. To achieve this you'll need a system that produces 100% of your annual energy requirements.

Review your Electricity Usage

Next, take a look at your electricity usage for the past 12 months. Don't worry if you haven't kept all your PG&E bills. You can call (800-743-5000) and request this information, or better yet, get it all online. If you don't already have a PG&E online account, follow these steps:

  • https://www.pge.com and login to "My Account"
    If you don't have an online account setup, click "Sign Up" - you'll need your PG&E account number and the phone number on record.
  • Click on "Billing > Usage History" on the blue menu on the left.
  • This will provide you the past 12 months KWH, electric charges.
  • Add these up and divide by 12 to get your average monthly usage

For guidance, here are some ballpark estimates of system sizes and costs. In San Francisco, almost all installations are 2-5 KW, with the majority in the 2-3 KW range. If you live outside the city and have a larger home, you might consider something larger than 5KW.
 

Average Monthly Electric Bill Estimated Solar Panel Size Estimated Total Cost*
$80 2KW $15,000-$17,000
$125 3KW $22,000-$24,000
$200 4KW $30,000-$32,000
$300 5KW $37,000-$39,000

* Cost estimate includes equipment, materials, installation, permits, and is net of rebates.

One last thing to consider is your future expected electricity usage. Future household purchases may be made with solar in mind. For example, you might replace a gas dryer or stove/oven with electric, or buy an plug-in car or electric scooter for transportation. If you know this is likely, you should factor this into how large a solar panel system you need.

Get a Solar Evaluation
Tell a Friend about Solar4SF.org 

Sponsored Links

 
Copyright 2007 Solar4SF.org - Privacy - Blog