Wednesday, March 3, 2010

Solar Electric Basics, Solar Photo-Voltaics

March 2nd, 2010

Crystalline Silicon PV Panel:
100 sq.ft. can create 1 kW, efficiency 15% to 22%

Thin film PV (like tiles):
200 sq.ft. can create 1 kW, efficiency 7% to 15%

Monocrystalline (single crystal): 75W, Polycrystalline (multi crystal): 80W,
Amorphous (Thin Film): 43W

PV Output drops with higher temperatures, say above 70 F / 20 C
- Percentage amount of drop with temperature increase is called Temperature Coefficient of Power. This number is less in thin film PV.

- converts DC electricity to AC electricity
- should locate in a cool area

PV Panels can last 25+ years – used in space program

Net Metering – Electrical meter sins both ways, net amount is measured. Also, Net Time of Use Metering applies to time of day you are making electricity and when you are taking from the grid

On-grid vs. off-grid (off-grid requires battery)

On-grid requires electric grid. Electric grid goes down, on-grid system goes down too.

However, buying electricity is cheaper at night. Also, the less energy one uses, the less susceptible one will be to higher-charged electric rate upper tiers.

PG&E of California estimates that a proper figure for approximating costs to install PV systems is $9 per Watt installed (note this is per Watt, not kilowatt).

Payback on PV electric systems should be 8 to 18 years, according to PG&E.

Other Factors:

Solar Resource Potential (kWhours / sq. meter / day)
Monitoring Hardware Required?

PV Panel and mounting:

Shading (Trees, Buildings, etc., 2:1, two feet of horizontal distance to every
one foot above panel height of any potential shading element)

Southern Exposure (True south, not magnetic south)

Orientation of Panel (True south by southwest, SSW, is probably best)

Tilt of Panel (depends on your latitude, normal roof pitch is generally okay)

Cleanliness of Panel (dust, etc.)

Solar Window (when sun is best, usually 9 AM to 3 PM)

Adequate Roof Area (100 to 300 sq. ft. of roof area per kW, depending on type of
PV panels installed)

Roof Condition (shingle conditions and weight on roof)

Tracking Systems (to follow the sun through the sky and through the day)

Excessive Wind Loading Possible?


Solar Pathfinder
Solmetric SunEye

Incentive calculator (for California):

Nationally, 30% Tax rebate on Federal Returns

National Rebate Information for Homeowners:

California Residential Systems must be OG-300 Certified to qualify for rebates.

California Commercial/Non-Residential/Multifamily Panels (only) must be OG-100 Certified to qualify for rebates.

Compare AC Watts with AC Watts, not AC with DC

Panel DC wattage X number of panels X inverter efficiency = number AC watts

Be suspicious if only given DC output of designed/installed PV system?

Normalize to price per AC watt or price per AC kilowatt

Adam Trotter, P.E. / AVT

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