Moving Toward a Carbon-Balanced Economy
Solar power is clean, silent safe energy. As the entire world becomes more aware of the need for energy free from fossil fuels that create carbon dioxide and other greenhouse gasses, solar power has become the fastest growing worldwide energy source. During 2006, photovoltaic solar power production increased by 36%, with about 90% of the capacity in Germany, the United States and Japan.
 A growing number of large-scale commercial and residential solar projects are connected to the power grid, in the planning stage or under construction. In California, for example, search-engine colossus Google has constructed the largest commercial solar system in the U.S., using 9,212 Sharp polycrystalline panels (larger versions of the Sharp panels we offer) to provide 1.6 megawatts, 30% of the electricity Google uses, or enough to power 1000 California homes. Their system uses all available roof space on eight office buildings where it is installed, as well as two carports where employees can recharge their hybrid cars. With incentives from PG&E, Google’s system will pay for itself in 7 1/2 years.
As part of our company Mission Statement to reduce our impact on the environment, West Marine has embraced photovoltaic technology. We constructed our own sizable 57,600kW array on the roof of our Santa Cruz, CA, store (with 480 panels of 120W each, connected to 24 inverters, rated at 2,100W each, producing enough electricity to meet 70% of the store's electrical needs). According to the EPA, a 57.6kW solar power system like West Marine's can eliminate 4.4 million pounds of carbon dioxide that would otherwise be produced by a power plant over 30 years. As a clean, renewable energy source, it can save more than 400 million cubic feet of natural gas over the same 30-year period. More information about this project can be found at www.westmarinesolar.com.
What Solar Panels Do
Solar panels, or photovoltaic panels, produce electricity when exposed to the sun. This electricity is used to charge batteries, which can power DC loads, or panels can be connected to inverters to produce AC power. Two types of panels use either silicon crystals or thin chemical films to generate electricity. In crystalline panels, silicon, the primary material in quartz sand, is grown into crystals, refined, purified (by an expensive process), sliced into thin wafers and “doped” with the addition of chemicals. This process alters the wafer so that, when exposed to light photons, one side produces a surplus of electrons and the other side has a deficit. A voltage difference between the two sides of slightly less than 1/2 volt is created. Acting like an “electron pump,” solar cells create electrical current, the quantity determined by the size and efficiency of the cell and the amount of light. Solar modules are created by connecting cells in parallel to increase amperage and in series to increase voltage. Typical solar modules have 30 or 36 cells (generating between 14 and 18V DC).
Types of Solar Cells and Arrays
Types of panels most commonly used in boating applications contain either multicrystalline or amorphous thin-film cells. Single crystalline and multicrystalline (c-Si) panels are the oldest technology and also the most powerful. When sized correctly and matched to appropriate batteries, these are the panels to use for running large DC loads such as lights, a TV, radio or VCR. In our catalog, they’re represented by the Sunsei panels, the Sharp solar panels, and the BP solar panels in the Solar Stik array.
Amorphous thin film Silicon (a-Si) panels are only about 50% as efficient as multicrystalline panels, but can be manufactured in flexible forms so they can roll or fold, or conform to the shape of a cabintop. They are more efficient in low or diffused light conditions and are less subject to voltage drops when they heat up. These are the panels most often used for low amperage charging and battery maintenance. They don't generally have enough output for serious energy replenishment, but can be used to “float” or trickle charge a battery. The Sunsei solar powered battery chargers represent this type of economical solar cell. So-called “Single Junction” panels of this variety have the fewest number of layers of chemical coatings deposited on their metal plates.
The most advanced thin-film panels (and the type represented by the SunForce folding panels and Sunsei Flex flexible panels) are constructed from copper, indium, gallium and selenium (CIGS), a new blend of semiconductor materials. Unlike crystal silicon panels, so-called “Heterojunction” A-si and CIGS thin film panels feature multiple layers deposited on a metal surface, like a chemical layer-cake, with each layer responding to different light frequencies. Thin film panels, of either the Single Junction or Heterojunction variety, require lower manufacturing costs than c-Si panels like the bigger Sunsei, BP and Sharp panels (with 45% of multicrystalline panel cost coming from making the raw silicon crystal structure).
How Much Power Do Solar Cells Make?
Generally, we measure a solar array’s power output in watts or kilowatts of energy, and in watt-hours or kilowatt-hours per day (when estimating energy needs of a given application). Unless you are familiar with various formulas derived from Ohm’s Law (Watts = Volts x Amps) and can use this formula backward and forward, watts are not a useful method of determining power output. Since we use amps when discussing our boat electrical systems, we rate solar modules used onboard boats by their estimated electrical output, measured in Amp Hours per day. The model numbers of the Sunsei panels indicate their output (in mili-amps), so the SE-500, for example, is a 500mA charger. It is much easier to estimate what to do with 400mA than with a 6-watt panel.
We arrive at these values by averaging the number of hours the panel spends in full sun (defined as 1000 watts of energy per square meter). Full sun means enough light so you see fairly sharp-edged shadows, and most locations get no more than 80 to 85% of full sun. In most of the Continental U. S. the amount of time a panel spends in full sun averages 4 or 5 hours per day.
Shadows covering even a tiny fraction of the panel have a dramatic impact on power output. All the individual cells are arrayed in series, and shaded cells show a large voltage drop that acts as a barrier to useful power production. Shading a single cell on a panel can cut its output by 20% or more. Shading two or more cells effectively turns off the panel until the shadow is removed. This defect is corrected somewhat by the use of bypass diodes across each cell, which allow the module to produce power even when partially shaded.
Pointing the array squarely with the panels perpendicular to the sun makes a large difference in efficiency as well. That is the reason we like the new Solar Stik, because it makes the adjustment for the height and angle of the array simple and convenient so the maximum amount of useful energy reaches the module. Temperature also changes the efficiency of a solar panel. The colder the temperature at the panel surface, the higher the output. Performance on a clear, cold winter morning can be 30 to 40% over rated specs.
When Do Panels Require Regulation?
As a general rule panels that produce less than 1.5% of a battery’s rated capacity in amp hours do not require regulation. This means that a 1.5 amp panel is the largest you should use without a regulator on a 100-amp-hour battery. Regulators should generally be used any time you have two or more large panels connected to your batteries. One caveat to the general rule applies to cruising boats that run an "energy deficit". That is, when your boat removes more energy from the batteries than the panels replace. In this case, regulation might not be required. If you think you might fall into this category, it would be helpful to develop an "electrical budget" for your boat. You will find a helpful guide to this in the You Can Do It project section here at westmarine.com. Frequent checks of your system voltage can alert you to possible over-voltage situations. Remember, a simple On/Off switch can remedy this problem by taking the panels off-line.
Matching Solar Modules With Your Needs
Many boat owners are disappointed when they learn the real-life energy economics; the size of the panels needed, the effect of partial shading, temperature, and the hours of available sunlight. Our Technical Sales staff at 1-800-BOATING are often asked to help size a solar system, and they find that boaters usually overestimate what solar panels can produce and underestimate their electrical needs. Make a list of the appliances on your boat, get the amperage (Amps = Watts ÷ Voltage) and estimate the operating hours to get weekly amp hours for each device. You can then create an estimate of your “electrical budget” and size your system correctly.
Conclusion
The rapid increase in oil prices and the need to replace greenhouse gas-producing fossil fuels have made photovoltaic solar energy an increasingly realistic alternative for generating electrical power. Replacing a gas or diesel generator with a clean and properly sized solar module, which has no moving parts and requires no fuel or maintenance, is a great investment in making boating both cleaner and more affordable. |
