# Go Solar at Home - Homework Assignment

February 2015

Decades ago, technology advancements enabled central air conditioning (A/C) to become a standard feature in homes. Now decades later, new innovations have brought solar photovoltaic(PV) technology to the point of being the next appliance for your home. And with it, finally the ability to offset that increased electricity usage brought on with A/C units with CLEAN LOCAL energy from the SUN!

As with any new technology deployment, it is best accompanied with education. Therefore, to participant in the project, you will need to understand and research these two initial concepts:

1. determine the orientation of your residence, and
2. determine for your home, three example solar PV system sizes - we will call them SMALL, MEDIUM, and LARGE.

1. Determine the orientation of your residence:

The ideal position to install solar panels is on a south-facing roof, however, even east-west roof surfaces can produce sufficient electricity to make it worth your while to go solar. Most installations in Plano will be roof mounted so understanding your home’s directional orientation and consideration for any surrounding structures or trees that could cause an undesirable amount of shading is important. A site survey performed by the solar installation company will ultimately determine the suitability of your home’s roof and shading impacts, but it is important for you to understand the basics of this concept.

It is recommended that you use Google Maps to input your home address and then look at the satellite (or earth) view to determine your home’s directional orientation and see how much desirable roof area you have. Normally, the top of the Google Maps page faces north.

2. Calculate three example PV solar system sizes for your specific energy usage:

This step is included to give you a basic understanding of the relationship of how your electricity usage relates to a few example sizes of solar PV systems. Knowing an estimate for how much electricity you use on an annual basis is a key step in determining what size of solar PV system would be most appropriate for your situation. Ultimately, a site survey from the solar installation company will be the final determination of your sizing options.

SMALL means a PV solar system size (measured in kW) that will provide approximately 33% of your total annual energy usage.

• This size might be appropriate if you have limited suitable roof space, or limited funds.

MEDIUM means a PV solar system size (measured in kW) that will provide approximately 50%  of your total annual energy usage.

• This size is generally appropriate if you have suitable roof space and available funds.

LARGE means a PV solar system size (measured in kW) that will provide approximately 67% of your total annual energy usage.

• This size might be appropriate if you have suitable roof space, available funds, and are comfortable with managing the process with your electric utility of larger amounts of excess electricity buy back.  (Note: The larger the solar PV system size, the greater the potential for larger amounts of excess electricity being put back onto the electric grid.)

Recall - the estimate for your annual electricity usage is determined by adding up the per month kWh usage for the last 12 months.  This information is available on your electricity bills, or possibly available when you log into your account on your electricity company's website.  (See the “note 2 ” below if you are having trouble locating this information.)

Knowing these three example systems sizes in kW for your specific home will better prepare you for discussions with solar companies and for reviewing their proposals.

The basic calculations to perform are shown in Note 1. Reading through these calculations will help your understand the basics of system sizing.  We have also provided a link that will let you download a simple spreadsheet that assists with the calculations. (See solar-PV-system-size-examples.xls) Be sure to have the results from your calculations available when you talk with the solar installation company.

Best Regards & Shine On!

Larry Howe & Bob Litwins, Plano Solar Advocates volunteers

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Note 1:

1. for the SMALL system size determination, multiply your total annual energy usage by 33%. Then take this number and divide it by 1400, which is the estimated annual production in kWh from a 1KW south facing PV system in North Texas.  As an example, assuming your annual energy usage is 15,000 kWh:

15,000 * 0.33 = 4,950

4,950 / 1,400 = 3.5 kW PV system

2. for the MEDIUM system size determination, multiply your total annual energy usage by 50%. Using the example from above.

15,000 * 0.50 = 7,500

7,500 / 1,400 = 5.4 kW PV system

3. for the LARGE system size determination, multiply your total annual energy usage by 67%. Using the example from above.

15,000 * 0.67 = 10,050

10,050 / 1,400 = 7.2 kW PV system

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Note 2:  If you are having trouble locating the last 12 months of energy consumption, you may also try contacting Oncor's Service Request line at 1.888.313.6862 (see http://www.oncor.com/EN/Pages/I-Need-To.aspx) and asking for consumption or usage history.  If you live in the CoServ service area, try calling the CoServ Customer Service number and inquiring about usage history for your address.

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