Solar Energy

Renewable clean energy from the sun. What could be more perfect? In Missouri, we have average solar isolation values (the intensity of sunlight) from 4.75-5.02 kWh/m2/day.

That is truly excellent. Germany, which has the highest amount of photovoltaic solar installations in the world, has an average of 3.0 kWh/m2/day. We have equivalent values in Florida and many parts of California and Texas!

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Photovoltaic

First, let’s talk about using the sun’s energy through photovoltaic applications. Sunlight striking solar cells in a photovoltaic panel or module causes the flow of electrons from one material to another. By wiring the two materials, a circuit can be created allowing the flow of electrons to product electric voltage and current. Connecting a number of solar cells in a module provides usable power. Connecting a number of modules in an array really provides usable power.

To optimize the conversion of sunlight to usable power, a photovoltaic solar module needs:

Clear orientation to the southern sky. That is true south—not magnetic south.

On average, a mounted angle should equal your latitude. In Missouri this is approximately 37-39 degrees from the horizon. For ground mounts, it is advantageous to have an adjustable mount with 27 degrees for the summer and 47 degrees for the winter. This allows for the seasonal effect of the sun being higher or lower in the sky depending on what season it is.

No shading during the solar window (10 a.m.- 3 p.m.). any shading will greatly degrade the power output of a module--even if it is only shading a couple of cells in the module.

Photovoltaic Can you get by with less than an optimal installation? Sure. Your contractor can calculate the difference for you.

You can optimize your solar collection by using a dual access tracking system. These systems are ground mounted and move in line with the movement of the sun—always keeping your solar array in perfect orientation—both horizontally and vertically.

Solar Collectors

Second, solar collectors are another type of system used in commercial and industrial installations. Solar radiation is concentrated or focused on a tube that carries water. This water is intensely heated so that it flashes to steam. This steam then drives a steam turbine coupled to a generator. It is that generator that produces power. Steam also is used for heating. After the steam gives up its energy, it condenses to water.

Thermal Heating

A third solar application is thermal radiation, used to heat a building’s space or hot water. A thermal air system is pretty basic. A large, black solar radiant collector is mounted on the south side of a building or on the building’s roof. A hole in the bottom of the collector draws air from the space to be heated.

As the air passes through the collector, it absorbs heat from the collector. Then, using a small solar-powered fan, the warm air is blown out the top of the collector and into the space to be heated. The solar collector requires no external power supply, and maintenance is limited to an occasional cleaning of the collector’s glass.

A hydro thermal hot water heating system uses a collector to heat antifreeze, which is then pumped through a network of floor or wall radiant heating tubes. Poured cement floors are perfect for this as the mass retains the heat during the day and gives up its heat during cold winter nights.

A hydro thermal hot water heating system heats an antifreeze solution in the collector, then pumps the heated solution to a heat exchanger located on or near a hot water reservoir (hot water tank). The heat exchanger allows the antifreeze solution to give up its heat to the hot water system. It is recommended that this type of system be used in conjunction with a gas or electric demand hot water heater for use when solar heating does not keep up with the demand.

Grid-tied and Off-grid Solar Systems

Solar photovoltaic collectors are necessary for the two primary types of solar systems: grid tied and off-grid.

Grid-tied - In a grid-tied system, power is generated and consumed by the owner. Excess power is returned to the local utility through the electrical grid. This power is repurchased by the utility at an avoided cost (wholesale), retail rate or power credit, depending on what the utility offers. An agreement spells out the safety and sell-back terms for the owner and utility. This is called a net metering agreement. When the alternative energy system supplies insufficient power for the homeowner, the grid kicks in to supply the additional power and charges the owner a retail rate or uses any credits that have been earned.

A grid-tied system consists of a solar array, an inverter (to convert DC power produced by the modules to stable 120 or 240v AC power usable by the grid and your house). The system’s inverter will shut down in the event of a loss of power. This is a safety feature so that your alternative energy system, whether solar, wind or micro-hydro, will not back feed the grid during an outage. The net metering agreement is usually completed by the system’s installer. A licensed electrician will need to sign off on the agreement to certify the safety and correct wiring of the system.

There is little maintenance with a grid-tied system.

Off-grid - In an off-grid system, power is generated and consumed by the owner. Excess power is used to charge batteries or in some cases fuel cells. These batteries are used to supply power when the power supplied by the alternative energy source is insufficient to supply the owner’s needs.

In an off-grid system, an extra component called a controller insures that the batteries are not overcharged by modulating the rate of charge.

An off-grid system requires regular maintenance of the batteries to keep the system operating optimally and to improve the life of the batteries.