How to Power Up with Photovoltaics

Hotels have become increasingly effective at improving the efficiency of their operations and conserving energy, many realizing meaningful energy savings and improved profitability. Such changes can also provide an opportunity to generate renewable energy on site with a photovoltaic (PV) system, displacing electricity that would have otherwise been purchased from a utility. 

As solar electric PV technology continues to improve in efficiency, reliability, and become more accessible for various applications and situations, more hotels are considering adding a PV system to whittle away energy needs while showcasing their concern for the environment with their guests. Various tax incentives and rebates are also furthering the adoption of PV systems, especially by those hospitality companies eager to be ahead of the coming requirements related to accounting for their carbon emissions. PVs also count toward LEED certification, created by the U.S. Green Building Council.

For most hotel locations, there’s enough sunshine to make PV systems a viable option for generating at least some of their own renewable energy. From small bed & breakfasts to large resorts and hotels, photovoltaic systems, like solar thermal systems, have become a part of the energy plan for businesses seeking to control spiraling energy costs by generating their own renewable energy. For example, at the Hotel Carlton, a boutique Joie de Vivre hotel in San Francisco, their 18.5 kW photovoltaic system mounted on their roof meets more than nine percent of the hotel’s annual electricity needs. A digital readout in the lobby allows guests to monitor how well the hotel is generating on any given day.

WHAT IS A PV SYSTEM

Not to be confused with solar thermal systems that capture the heat of the sunlight warming the Earth. 

• A photovltaic (PV) system generate electricity directly from the sunlight without creating any water or air pollution. 
• A PV system is quiet, reliable and relatively easy to install by a growing number of professional installer-dealers. 
• PV systems are relatively maintenance-free and could last as long as 30 or 40 years.

For many hotels, adding photovoltaic systems offer a visible and practical way to demonstrate their commitment to preserving the environment in ways that go beyond organic linens, recycling, compact fluorescent bulbs and low-flow faucets. As a result, many of these hotels end up garnering more media interest, translating to more visible public relations opportunities.

HOW ELECTRICITY IS GENERATED

The PV modules, or panels, are composed of many individual solar cells and generate electricity when some of the photons from the sunlight are absorbed by the silicon-based semiconductor atoms, freeing the electrons to flow through an external circuit and back into the cell. This flow of electrons provides the electrical current. 

Solar cells are grouped together into a panel with a specified power, and the panels are then grouped together to form 12-, 24-, 36-, or 48-volt arrays. The number of panels in a PV array varies based on the desired output of the system and the power of the PV panels.

(180w solar panel)

There are several main components to a PV system: the PV panels, the rack on which the panels are placed, and the inverter which converts the direct current (DC) electricity coming from the panels into alternating current (AC), which is typically used in powering appliances. There are two basic types of PV modules, each with specific features: 

• crystalline or polycrystalline modules - More time-tested technology. However:
•  Modules are fragile and moderately heavy, requiring the PV panels to be mounted into an aluminum frame between a layer of glass and a stiff bottom material. 
• These panels loose efficiency
• Produce less electricity in hot temperatures 
• Stop producing any electricity if a small portion of the panel is shaded.
• Because of their properties, are typically mounted on a south facing roof, on a static frame on the ground, or on a tracker that rotates to follow the sun’s path across the sky. 

• Amorphous silicon modules - The newer thin-film amorphous silicon modules, resemble shingles and standing-seam roofing panels, and are often called building-integrated photovoltaics (BIPV), or more commonly, solar shingles:
•  These flexible shingles use a stainless steel foil and weatherproof elastomer plastic coating,
•  More durable, 
• Much lighter,
• Less expensive. 
• Diffused light, partial shade, and hot temperatures do not greatly diminish energy production when using solar shingles.
• Can be mounted in various ways, depending on the location and size of the system.
• Thin-film amorphous silicon PV cells are installed in a way that resembles a roofing job; the shingles can be installed directly over plywood. 
• Solar shingles often offer a standard 25-year warranty.

DESIGNS

There are three basic PV system designs: 

1. grid connected without battery backup, 
2. grid-connected with battery backup, and
3. stand-alone, independent or off-grid system. 

Most hotels will select a grid connected system without battery backup system due to ease of installation and greater availability of funding or incentives. Banks of batteries for the second and third options increase the cost, complexity and maintenance of the PV system. In USA most of the states and publicly traded utilities offer net-metering, which allows hotels to bank any excess electricity on the utility grid if a surplus is generated. Some utilities will even pay $.25 per kilowatt-hour of surplus energy generated.

WHAT MAKES A SITE FAVORABLE

The first step in developing a renewable energy system design—after the size of the system is determined based on electricity use and available funds—is a site assessment. The three key factors for a viable site for PV are 

1. southern exposure with the modules exposed to sun as much as possible, usually between the peak sun hours of 10 a.m. and 3 p.m., 
2. the southern exposure being free from obstructions that might shade the module, and 
3. appropriate and sufficient space for the PV system. 

To address possible obstructions that might shade the panels, a special tool called a pathfinder is often used to evaluate both summer and winter paths of the sun.

The installed per-watt cost of PV systems, while decreasing after tax credits and state incentives, make the investment in PV worthwhile only if you have a 10 to 20 year economic payback horizon and have exhausted energy conservation efforts. Until costs come down on the solar panels, they are more expensive on a per-watt installed cost basis when compared to other renewable energy systems such as wind turbines. Within the renewable energy industry, it’s commonly believed that each dollar spent on energy efficiency saves at least three dollars in PV system components.

For many hotels in areas that showcase scenic natural areas, social and environmental costs are often more important than economic payback windows when considering conventional energy sources, like coal-fired electrical power stations. According to the U.S. Department of Energy (DOE), electric power plants are the largest single-source contributor to global warming, and according to the EPA, electricity generation from power plants also causes emissions of sulfur dioxide, the leading component of acid rain; emissions of nitrogen oxides, a key contributor to high ozone levels and smog, acid rain and fine particulate; and are a source of heavy metals (such as mercury), which can contaminate rivers and lakes.

A basic net-metered grid-interconnected system can cost about $8 to $15 per installed watt, depending on the site, scale and location of the system. In some areas, federal or state financial incentives, low interest loans, and tax credits can help reduce the installed cost. According to SolarBuzz LLC, the solar modules account for as much as half of the total cost of an installed solar energy system.

CASE STUDY

John Ivanko and his family operate the award-winning Inn Serendipity B&B in southwestern Wisconsin. The Inn is completely powered by renewable energy and “climate negative” in how it operates. Also, as it has been doing so well, the bed and beakfast is among the “Top 10 Eco-Destinations in North America” and earned “5 Green Stars” from Eco Hotels of the World. The owners  like to think Apollo, the legendary Greek god of the sun, is smiling down on their business. 

"We use the sun to grow most of the organic foods we serve our guests. So it made sense to also generate at least some of our power from the sunlight. We also generate renewable energy from a 10kW Bergey wind turbine and have two solar thermal systems. On an annual basis, Inn Serendipity generates about 3,000 more kilowatt-hours of electricity than it uses, resulting in credit payments from our local utility of about $300 per year.

To minimize our per-watt installed cost, we attached our four 170-watt Suntech PV panels onto a Unirac, which we cantilevered off the south-facing wall of an equipment shed. We ran a short DC line through the wall into a SunnyBoy inverter, then tied it into the nearest breaker box in the shed. With respect to our grid intertie with our public utility, a simple contract, certificate of liability insurance in excess of $300,000, equipment specification sheets, and a lockable external AC disconnect (to allow our utility to isolate our system when needed) were necessary for the project.

For our small 680-watt grid-tied PV system, the installed cost was about $5,600, less a $1,315 Wisconsin Focus on Energy state-sponsored cash-back grant. This resulted in our PV system having a net $6 per watt installed cost. We generate about 900 kWh per year. For our business, we receive a federal renewable energy production credit of $18.90 along with taking all depreciation allowed. The development of a “hybrid” renewable energy system using both PV and wind energy generation has enabled us to produce an energy surplus and generate income to offset anticipated maintenance costs for the wind turbine system. As it turns out, days with the most sunlight have the least wind, and vice versa."

ELECTRICITY DEFINITIONS

Watts: A unit of power (i.e., 100-watt incandescent bulb). Power used by an appliance multiplied by the time it’s in use, expressed as watt-hours. For example, running a 100-watt light bulb for one hour uses 100 watt-hours. Power is the product of current (amperes, or amps) times voltage (or volts), i.e., 1 watt = 1 amp x 1 volt.

Kilowatt-hours: Often expressed as kWh, this is how most companies buy electricity; 1 kilowatt-hour is 1,000 watt-hours (i.e., 1 kWh = 1,000 Wh).

Alternating Current: Usually expressed as AC, this refers to the electrons vibrating back and forth in the wire. Due to its efficiency at moving electricity over long distances with less line loss, AC is the type of current going into most businesses from the power grid. It’s what most appliances are designed to run on.

Direct Current: Usually expressed as DC, this refers to the electrons moving in one direction which, while effective at providing power, tends to degrade quickly when moved over long distances. DC is the form of current that comes from PV panels, and needs to be converted to AC for use in appliances.

Frequency: Frequency refers to the number of cycles per second, measured in hertz (Hz). For AC in the United States, the standard frequency is 60 Hz.

Inverter: An inverter is used to convert DC to AC. Today’s technology can achieve up to 90 percent efficiency (10 percent energy loss).

Source: adapted from  Green Lodging news