Solar and Your Home

How Solar Works

Sunlight hits a solar cell, electrons start to move, and an electrical current is created.  Solar is simple relative to traditional sources of energy.

In traditional sources of electricity or thermoelectric power plants, an intense heat or force is used to turn a turbine.  Coal, natural gas, nuclear, wind, solar thermal, and hydro are all electricity sources that turn turbines to create electrical currents.  Ultimately, we have two basic ways to generate an electrical current, solar photovoltaic cells or spinning a turbine.

Here is a short video of how a Solar Cell works:

Reliability of Solar

Solar has no moving parts and is inherently more reliable than other power sources that require moving parts. Solar’s reliability means solar module manufacturers offer strong warranty coverage.

For example, San Jose based SunPower makes the best equipment on the market. The design, patents, and quality materials used to create a SunPower module give the module a 40-year usable life and the strongest warranty coverage available today; 25-year product and performance warranty.

I dive into warranty coverage in a later post. For now, just know that solar is reliable and comes with 25-year manufacturer warranties that cover performance too.

Solar on Your Home

In the first lesson, I went over how PG&E sells you electricity and addressed: rate tariffs, net energy metering, solar power production, climate zone, usage and how all of those affect your bill.

If you haven’t read that one yet, you should check it out.

Lesson 1: PG&E and Your Home

Now I will address how your home influences the solar design and the installation approach…


Your home consumes electricity. Many homes on the Central Coast of California use less electricity because major appliances are powered by natural gas and air conditioners are typically not needed in our temperate coastal climate zone.

Significant Electrical Loads:

  • Refrigerators
  • Air Conditioners
  • Hot tubs
  • Well or pool pumps
  • Clothes dryer
  • Space heaters
  • Kids glued to video games

These all require a lot of electricity and typically drive electricity bills up. If you are paying over $100 per month for electricity, you likely have two of these electricity loads in your home.

Usage and Solar

Solar companies use a home’s usage to target the amount of solar electricity to create. In California, a typical solar project offsets 70-90% of a home’s annual electrical demand. Buying a little of your electricity from PG&E and producing the rest with solar PV typically saves homeowners the most money.

Here are some typical scenarios using a SunPower 327 Watt Module and monthly bill amounts:

  • $100 Monthly Bill would be around 10 solar modules (3.27 kW)
  • $200 Monthly Bill would be around 16 solar modules (5.23 kW)
  • $300 Monthly Bill would be around 24 solar modules (7.85 kW)

Sunny Space

A typical solar module is around 3 feet wide and 5 feet long. Based on a home’s electrical usage a certain number of modules will be recommended for the best Return on Investment.

In 2013, Allterra’s average installed system size was 4,000 watts, or 4.0 kilowatts (kW). 4 kW of solar installed on a sunny roof will generate around 6,400 kWh in a year and would be good for bills around $175 per month.

There are two types of places where you can install solar:

Roof Space

Ideally, sunny roof space is available for use. Solar typically goes on roofs because it is easily mounted to the roof and can use the roof’s tilt to angle solar modules towards the sun. Roof space is the most cost-effective location to install solar. Building and Fire Codes will affect where modules can be installed.

Ground Space

No roof space or not enough sun hitting the roof? Not a problem. A ground-mount can be constructed. Ground mount solar systems perform great because we can point modules at the sun and optimize production. Ground mounts require more work and inspections so they cost more than roof mounts. Planning and Building Codes will affect where ground mounts can be installed.

Sunny Space and Solar

Solar modules can be installed in more than one area.  The more areas used the more wire and labor will be needed to complete the solar installation.  It is typical to break a roof mount solar system up into two areas or two arrays.

Roofing Material

There are many different roof materials in the Central Coast. Some are easier to work with than others. Homeowners with sunny composition shingle roofs are in luck, composition roofs are straightforward and typically cost the least.

Other roof materials work too. Some roof types require more time than others.  Here is a breakdown…

Ideal Roof Materials:

  • Composition Shingle
  • Standing seam metal roofs
  • Rolled composition

Challenging Roof Materials:

  • Tar and gravel
  • Wood shake
  • Membrane roofs

Allterra Solar is one of the few solar companies that can install on any roof type.

Roof Material and Solar

Composition shingle and standing seam metal roofs are the easiest to install on and will be less expensive than other roof types (typically).

Roof penetrations are a small portion of the design and installation process. It does not cost much to have roof experts seal off roof penetrations when needed.

Concerns about your roof should not affect who you hire for solar. Every solar company works on roofs daily and can handle any roof application.

We include roof leaks in our 10-year workmanship guarantee; something most solar companies do not offer.

Electrical Service

Solar PV generates electricity and needs to be interconnected to PG&E’s grid. A solar PV system is interconnected through your home’s electrical service.

Most homes were built when natural gas was cheap and homes did not use much electricity. Today’s average household uses more electricity and electrical services are often maxed out.  Consequently, many homes on the Central Coast will need a little electrical work as part of a solar project.

It is important that solar contractors have their own certified C-10 electricians on staff to address electrical service work.

Here are the local scenarios we see arise on the Central Coast:

  • Normal: The electrical service is relatively new and has existing space to add a breaker dedicated to solar. Most homes fall under the normal category and no additional time or effort is needed.

  • Lots of Work: Electrical service is older and extra work reorganizing breakers may be needed to interconnect the solar system.

  • Service Upgrade:  The home changed over time and the electrical service is undersized for the home’s current usage. There are creative ways to interconnect solar without a service upgrade but sometimes it is required. A service upgrade means we are working with PG&E and will need to upgrade the wires to the house. Sometimes service upgrades are a good idea if you plan to purchase an electrical vehicle and use more power.

Electrical Service and Solar

The amount of electricity going through your service panel is subject to building code requirements.

Your electrical service (# of amps) determines the amount of solar you can interconnect. You have one of the below:

  • 100 amp
  • 125 amp
  • 150 amp
  • 200 amp

Based on your electrical service, electrical use, and solar system size, additional electrical work may be needed to interconnect.


Solar is a mature reliable energy source that requires no fuel. Manufacturers offer strong warranty coverage because solar has a proven track record of reliable operation.

The specifics of your home determine the approach a solar company will use.

A home’s electrical usage, usable space, roofing material, and electrical service all affect how a solar company will install solar.

If your home has up-to-date electrical, a sunny roof with composition shingle or standing seam metal roofing, and usage over $100 you are a strong candidate for solar.