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Herb Kneirman, P.E., LEED^® AP, Sacramento Principal

Glumac was asked to examine the possibilities and associated cost and payback for installing a Photovoltaic (PV) Generating System at Norman Glick Middle School. The system would be mounted on the roof of the new gymnasium and connect directly to the 120 VAC electrical system for that building. Excess power generated would be "sold" back to Modesto Irrigation District by use of "net" metering.

Two installation options were available for consideration. The first option would incorporate the PV crystals directly into the building materials. Roofing and skylights would be manufactured with latest technology incorporating the PV materials. The obvious advantage of this type of system is its "stealth" nature. The PV film would be virtually invisible to the public. The disadvantages are in the reduced generating capacity and a higher first cost.

The second option would be to install the PV arrays in more traditional stand-alone structures. This option has advantage of higher efficiencies and lower first costs. In addition, the stand-alone system, both alone and in conjunction with above system, would aid in teaching energy awareness to students and parents.

Both systems would be interconnected and wired to an inverter installed within the gymnasium. The system would be permanently connected to the electrical system to allow for generation whenever the sun is shining. The PV modules generate direct current (DC). The inverter converts the DC to 120/208 VAC. Controls are installed within the inverter to shut down when the utility shuts down to prevent back-feeding into the system and causing a hazard to the utility workers.

The power generated by PV ranges from about 5 watts per square foot for the "film" to about 10 watts per square foot for pure crystalline arrays. The actual power output depends on solar exposure (angle), which changes with the time of day and the season of the year. A 20 kW system would require approximately 2000 square feet of PV crystals.

The material costs for PV is approximately $2,500 per kilowatt for PV modules. This includes the cost of associated structures. The cost of the inverter is approximately $15,000. The total system cost, excluding labor, for a 20 kW system would be approximately $65,000. Many utilities have programs available for a first cost buy down for PV installations. For example, SMUD will buy down the cost of PV at $2 per watt, leaving a net cost of only $500 per kilowatt. The state also has programs available to pay for up to half the cost of a new PV system. The payback for a 20 kW system, operating an average of 8 hours per day, 365 days per year would be 7.5 years with no buy down assistance from MID. PV modules require little or no maintenance. The inverter, as with all electrical equipment, requires routine maintenance. Overall, the maintenance costs are minimal over the life of the system.

Example: assume 20 kW installed at a cost of $65,000. The savings due to energy generated is 20 kW X 2555 hrs. = 51.1 MWH x $.11 $/kW = $5,621.

Price of the system: 69 kW x 10,000 $/kW = $690,000 (Approx. initial investment)

Based on $0.11$/kW

Some loans are also available through the various utilities and the State of California. The loan is repaid over a period of ten years at a financing rate of 9.5% for the 60 or 48 module systems and 10.5% for the 32-module system.

As can be seen from this table, with a minimal utility buy down, the system very quickly pay’s for itself. Additionally, any future rate increases magnify this payback.

The state-of-the-art PV technology can be characterized as follows:

• PV modules are technically proven, with an expected service life of at least 30 years.
• PV systems have been used successfully in hundreds of applications, large and small.
• PV can be integrated into virtually every conceivable structure, from bus shelters to high-rise office buildings.

Recent energy problems within California have been well documented. As a result of the energy crises, electricity prices are inverted. That is, the cost of wholesale electricity is greater than the amount charged for retail. We do not anticipate the cost inversion to last long with the bottom line result of higher consumer costs for electricity.

In summary, photovoltaics harness solar energy. Solar energy is an immense resource that, if utilized for power, can aid in assisting in meeting societies energy needs. Every roof, commercial and residential, is available as a solar collection point. Use of this space for power generation can only reduce our reliance on traditional fuels. We believe significant PV generation can be achieved within the next decade. With the system’s first cost buy downs currently being offered by state and local municipal programs, the decision to install a PV system is the right decision for both economic and social reasons.