An enlightened look at photovoltaic cost

By John Mills, P.E., LEED AP, Principal, Goetting & Assocs.,
    San Antonio Consulting-Specifying Engineer, September 2007

Given the double digit growth in the photovoltaic industry, PV conversion of sunlight is quickly making economic sense.

There are two basic types of PV systems: grid-connected and remote-storage. Grid-connected systems are connected directly to the building power system to supplement the power delivered by the local utility. Remote systems often are deployed in areas where the cost to extend utilities is prohibitive.

Three types of commercially viable modules are monocrystalline silicon, polycrystalline silicon and amorphous silicon. The relatively new amorphous-silicon thin-film technologies often are deployed as integrated roof, building skin or canopy systems, called building integrated photovoltaic systems (BIPVs). BIPVs offer the advantage of multiple use, as both solar shade and electrical generation.

One should consider relative solar angles and siting issues to site an array properly. In our hemisphere, the sun tracks along a southerly route due to the earth’s inclination to the sun. This makes it important to orient the array to the south. Ideally, a zero azimuth is the optimal orientation, but a 10-degree variation one way or the other won’t affect a cost-effective output of the system. Select a tilted angle close to the array’s latitude.

One can expect the present cost to be in the range of $5 to $8 per peak watt (Wp), including installation costs and any burdens, though I have seen estimates as low as $4 to $5 per Wp. The final cost of a 20-kilowatt peak (kWp) fixed-grid system should be about $160,000.

A good benchmark is the USGBC LEED credit available with a 5% system—one that supplies no less that 5% of a facility’s demands. Smaller systems are equally viable.

It is important to select a design team with an intimate knowledge of simulation and modeling techniques. A baseline calculation using an energy modeling tool will be required.

A typical system produces about 9 Wp to 10 Wp per sq. ft. and about 10 kWh to 12 kWh per sq. ft. per year, depending on the geographic siting of the array. These numbers are improving by significant margins based on improved modules, but they should hold for budget purposes over the next year or so.

Let’s look at a 100,000-sq.-ft. office building. Given 6 Wp per sq. ft. (use demand, not connected load) this value becomes 600 kWp:

600 kWp X 5% = 30 kWp

30 kWp X $8 per Wp = $240,000

These numbers are conservative, but should get budgeting in the ballpark. For a reality check, consider that if the office building is constructed for $90 per sq. ft., it would cost $9 million. The $240,000 represents about a 2.6% increase in construction cost. In San Antonio, Texas, for example, one can expect a payback in 10 to 15 years. Payback could be half that time in areas with higher energy rates. Utilities are offering help in capitalizing PV projects because it improves their adherent to renewable portfolio standards. Considering that a systems offer a 25 year or more useful life, it will be generating free electricity for half or more of its useful life.

Editor’s note: A longer, more detailed version of this article can be found in the Electrical Community at www.csemag.com.

Considerations in PV design Building integrated photovoltaic systems (BIPVs) function as both solar shade and electrical generation Federal, state and local jurisdictions offer tax rebates for PV use Utilities are stepping up to the plate by offering help in capitalizing PV USGBC LEED credit offers a benchmark for the percentage of power PV provides