Walk, Crawl or Run with Solar

Wed, 2011-06-01 11:51

Not necessarily “Plug and Play”
So, solar seems like a great way to supply environmentally friendly, cost-effective power, right? Right. But despite its seeming simplicity (sun’s rays = electricity), installing an effective and sustainable solar system involves more than sliding a solar panel into a rooftop rack.

Before installing a solar system on a residential home (or small business), it is important to consider the power needs of the structure, electric storage needs, and the availability of solar radiation. As a solar installer, you should be ready to assist homeowners in determining these needs.

What Does Your Client Want To Do?
Some people want to generate enough power to ‘watch their meters spin backwards’ and sell the power that they generate back to their utility company. This is called net metering and requires a licensed installation as well as a final on-site inspection by the utility company.

To install a solar system that will sell power back to the power company, first check:

  • That your system can connect to the utility company’s grid and have the company send you information about their solar requirements.
  • Obtain independent verification of the utility company’s costs, rates charges, and credits.
  • Keep in mind that most state, city, or utility offers rebates, tax credits, or other incentives. Visit dsireusa.org to find out about financial incentives in your area.

Other folks want to install solar systems to use as a backup in case the power goes out. Still, others want to run their entire homes “off the grid” and use solar systems to power every electrical appliance in their home.

Preparing To Go Solar
Follow these easy steps when working with a homeowner to install a solar system on their property.

First Determine How Much Sun A Client’s Home Gets: Remember that the power supplied by a single solar cell is largely dependent upon how much solar radiation the client’s property receives. Thus, this determines what size solar installation you will need. Keep in mind that all areas in the United States (including stereotypically cloudy places like Seattle, the Great Lakes, and New England) receive as much, or more, solar radiation than Germany, the world’s current leader in solar installations.

When determining the property’s solar radiation levels, keep in mind that:

  • Solar arrays should be installed on South-facing rooftops to maximize solar radiation.
  • The sun’s angles vary drastically from summer to winter. Solar installations should be optimized for winter solar radiation levels.
  • Solar arrays should have an unobstructed “solar view” on the sky.

Websites like The University of Oregon Sun Chart provide solar radiation data based on your zip code, time frame, and time of year. The map below gives a basic idea of solar radiation in various areas of the country.

us solar pv map

Then, Determine The Electric Load: If your client wants to power some, or all, of the appliances with solar power, the first step is to make a list of appliances that they want to run. For each appliance, multiply the number of hours the appliance is used in a week, by the wattage of each appliance. If the homeowner doesn’t know the wattage information, it is usually available in manufacturer materials. Check out various appliances on www.solarhome.org.

And Finally Decide If They Need Battery Storage: If the client chooses to connect to the utility grid and use net metering, then the power company acts as a battery to store electrical power for the client for times when the sun doesn’t shine. If, however, the client wants to completely disconnect from the grid, it is necessary to install batteries or other storage units to enable continuous electric power even on cloudy days or at night. Most PV batteries use a combination of 6 and 12 VDC batteries.

Determine your cloudy-day and nighttime electrical appliance use. Many people allow for 4-6 nighttime hours and 2-4 cloudy days. Anything higher than this will add substantially to your battery size and cost.

Some things to keep in mind concerning batteries (adapted from solarhome.org):

  • Temperature: Batteries are sensitive to temperatures – hot and cold. Try to keep your batteries in a relatively warm and dry location.
  • Mix and match: It is important to purchase and install the same type batteries all at one time. Mixing different battery types, sizes, and especially different ages (states of discharge) will cause more problems than it is worth, as the battery bank will seek the state of its weakest link.
  • Type of battery: Only deep discharge batteries should be used on a stand-alone solar system. Some people use RV or marine type batteries, but you’re better off with industrial grade deep-discharge batteries for longer life. There are many different types of batteries. Contact your local battery distributor or the web for a review of these.
  • Amp-hours: All batteries have some # amp hour rating. A battery rated at 100 amp hours (20 hour reference) will deliver 5 amp hours for 20 hours before being discharged. The higher the amp hour rating, generally the more expensive, heavier, and longer the battery will hold a charge.

For more information on solar training and how you can become involved or NABCEP certified, visit our Solar PV Bootcamp page and register for a course today! Have questions? call us at 800-460-2575.

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