How simple it was for Captain Kirk-he asked for energy, and he received it. “More power, Mr.Scott!”
Alas, the world is ruled by physics, not fantasy. With more onboard demand for electronics and creature comforts, daily power usage keeps creeping up. Many of us rely solely on a diesel or gasoline engine to charge batteries, but today many are using other options either to supplement or even replace the engine/alternator combination for battery charging.
Solar panels have been springing up everywhere for supplying power and charging batteries. On land, we have solar-powered flashing lights at school crossings, construction warning signs, and pedestrian call boxes. On boats, we’ve seen solar panels mounted on outboard engines, on top of dodgers, biminis, and cabin tops, on radar arches, on stanchions, draped over booms, hoisted in the rigging, and reclining on the deck. We’ve even heard rumors of folks putting them across their dinghy and floating them away from boat shadows.
Background
Even though solar panels have become commonplace, the original discoveries go back to 1839. That year, French physicist, Edmund Becquerel found that certain materials would produce an electric current when exposed to light. The effect wasn’t explained until 1905, when Albert Einstein published his paper on the photoelectric effect, which won him his only Nobel Prize in physics in 1921.
In 1941, Russel Ohl at Bell Labs invented the silicon solar cell. However, it wasn’t until the advent of the space program, with their need for power generation without burning fuels, that solar cells came into use. Today, the cost per watt of power from solar panels has come down enough that cruisers and racers alike are buying panels to provide electrical power. Uses range from occasional to full dependence: A small panel will keep a battery or batteries trickle-charged during the days and possibly weeks that an owner leaves a boat idle. One or two powerful panels, on the other hand, can supply much or all of the battery energy for a crew that is parsimonious in their demands, or a goodly chunk of supplemental energy for crews that need lots of juice.
In simple terms, and leaving out the quantum nature of light, solar panels work by converting the energy in sunlight (or any light) to an electric current. The sunlight striking the silicon material in the panel causes the material to give up electrons, which then can be used to power something, or for storage in a battery. The amount of power potentially available from the panel is related to the light intensity, the angle of the light to the panel, the panel’s temperature, and the cell material.
Light intensity. The greater the amount of light falling on the panel, the more power available from the panel. The output of a panel is comprised of two measurable quantities, voltage and current. While solar panel voltages are fairly insensitive to light levels, the output current will double for each doubling of the light intensity. Since power is the product of voltage times current (P = V x I), and since the voltage is pretty constant, the power output is directly proportional to the current. Monitoring the current will be a close analog of the panel’s output power.
Angle. The angle of the solar panel to the sun will have a fairly large impact on the panel’s power output. For the best results, the light should hit the panel perpendicularly to its surface. As the sun’s angle moves away from perpendicular, the light intensity falls off as the cosine of the angle. One simple way to demonstrate this effect is with a pad of paper and a desk lamp. Hold the pad so that its surface is perpendicular to the light and then notice the size of the pad’s shadow. Now, change the pad’s angle away from perpendicular and watch the effect on the shadow. At increasing angles, the shadow will get smaller. The smaller the shadow, the less light hitting the pad (solar panel). Additionally, below a certain angle, which is not shown in Figure 1, below left, the sunlight will just reflect off the panel’s surface without producing electricity.
Temperature. The silicon material used in the production of the solar panels is sensitive to variations in temperature. As the panel temperature increases, the power output goes down. As a rule of thumb, the power output goes down 0.5%/C (or about 1%/F). The panels, since they are absorbing solar energy, will be warmer than the surrounding air. Therefore, air temperature will not be a good indicator of panel temperature. Also, some panel ratings are given at 20C (68F). Hence, on a warm summer day of 90F, and ignoring the increase in the panel’s temperature due to solar absorption, the output power will be about 20% less than the rated power.
Cell material. Solar panels fall into three distinct groupings: monocrystalline, polycrystalline, and amorphous. The table above compares the different properties of these panel types.
Our Survey
We last looked at solar panels in 1998 and 1999. At that time we evaluated panels by Kyocera, Siemens, Solarex, and Uni-Solar. This time, we decided to ask you, our readers, to help us in our evaluations. Last fall and early winter, we ran a website and mail-in survey for subscribers’ comments about the solar panels installed on their boats. By the time we needed to put this article together we’d received 82 responses, out of which we were able to distill good data from 69. Many thanks from us and your fellow sailors for taking the time to complete the survey.
We’ve tabulated the survey data in the various tables and figures shown here, and excerpted quotes from owners on pages 10-11. According to the survey data, the average boat length is 32′, with a range from 19′ to 45′.
Conclusions
Overall, we were impressed with the high level of satisfaction from the sailors who responded to our survey. They have had their solar panels for an average of 3.02 years, with the longest time being 10 years.
For measuring satisfaction, we asked for actual solar panel performance and longevity versus manufacturer claims. These scores were measured on the basis of 0 to 100%, where 100% meant that the panel lived up to all its claims. In this category, the perceived power output versus manufacturer claims was 94%, with longevity at 98%. The reason that we specify power output as perceived is that almost all sailors responded with 100% and subjective comments, such as “batteries always charged,” “boat is energy-independent,” and “extremely happy.”
Likewise, the retailer and manufacturer support, on average, was also very satisfactory. On a scale of 1 to 4, where 1 is “poor” and 4 is “excellent,” sailors gave retailers a 3.42 rating and manufacturers a support level of 3.39. But even more telling, almost two-thirds gave both retailers and manufacturers a 4 for their support (Figure 4, page 9). We didn’t receive enough information to say that one retailer (29 responses) or manufacturer (19 responses) was much better than another.
Siemens dominates among the installed solar panels (Figure 2, above left) with Uni-Solar in second place and Kyocera in third. If you’re planning to do some research on your own now, note that Siemens is now Shell Solar. Solarex and Arco are now BP Solar. And Kyocera acquired Photocomm. Egad!
It’s good to know that the satisfaction level is so high across the board that the brand may not matter as much. However, because of the ownership changes, be aware that the manufacturer support results may not reflect current realities.
One fascinating piece of data was that fully 90% of the respondents installed their solar panels themselves. That figure, together with the great numbers for support, suggests to us that either the instruction manuals are extremely thorough, that the retailer/manufacturer support is great, or that the installation isn’t that difficult. We think it’s a combination of the three, with the weight on the third element:
A basic installation is a truly a piece of cake-see the photo and caption at the beginning of this article. However, many of the installations described by our readers were not basic-they were often complex in terms of both mounting schemes and wiring, so we can only tip our hats and say “well done.”
There were a few comments from folks who had their solar panels cook their batteries. Comments like “With my solar regulator, this panel has been great,” and “Very satisfied while in NE, but overcharged battery without controller while in Bahamas,” lead us to believe that charge controllers (a.k.a. voltage regulators in this instance) should be installed in all solar panel applications, no matter how small the panel.
Now comes the tough part of this survey review-what do we recommend? The short answer is that all the different solar panel technologies work extremely well according to our survey results. However, we would recommend that a purchasing decision be based not just on price and wattage. Instead, we would ask ourselves the following questions and base our selection on the answers:
1. Will I be able to keep the solar panel out of all shadows most of the time? If so, then a monocrystalline or polycrystalline panel will give you more wattage in less space. If shadows are a problem, go with the amorphous panel.
2. What will happen if I step or walk on the panel due to its location on my boat? If you can only mount the panels in places where there’s a good chance that they’ll be walked on, the flexible amorphous panel is the only way to go.
3. I have a sloop/yawl/ketch. What type of solar panel should I use and where should it go? This is a tough question, since aesthetics comes into play. The goal here is to maximize the sun area and minimize shadows. We’ve all seen boats with panels hanging onto pushpits and stanchions, and on top of dodgers, biminis, and radar arches. However, if we were to make some general comments, boats with lots of potential shadows, like yawls and ketches, probably will do better with the amorphous panels, unless you can rig or buy a proper stanchion mounting system like the one shown at left. If you have the clear space, a monocrystalline or polycrystalline panel will deliver twice the power of the amorphous panel for the same size area at approximately the same cost per watt.
4. Do I need a solar panel regulator? What kind should I get? The answer to the first question is yes. While panels often come with blocking diodes to keep the current flowing only toward the batteries, and to prevent a voltage drop in other panels in an array if one is shaded, only some of the smaller panels used for slow trickle-charging and battery maintenance come with regulators built in-so for any kind of serious charging you’ll have to buy a regulator separately. We haven’t evaluated regulators as a group, and can’t make specific suggestions along those lines-but it’s good grist for a future article.
Regulators can be very simple and inexpensive, like the 7-amp ICP Charge Controller shown on page 6-it simply lies between the panel and the battery, starts the charging when the battery voltage drops to 13 volts, and stops it at an upper end of 14.2 volts. Or they can can be more sophisticated and energy-efficient themselves. Several survey respondents spoke highly of their Flexcharge controllers (see contact information).
Solar energy systems for marine use are now a fully matured, reliable, and not-too-expensive technology. This is a most welcome evolution-especially at a time when banging, smoking, fossil-fuel-burning engines are regarded with even more distaste than usual. As we said at the top of the article, it’s difficult to think of any battery-carrying sailboat that wouldn’t benefit from collecting some energy from the sun’s rays for use on a rainy day.
There are now dozens of excellent online information sources for sailors interested in adding solar panels to their power arsenal. Start with the maufacturers’ websites to get an idea of product range and specs. For person-to-person advice on how to specify a system that will meet your boat size and type, your sailing area, and your amp-hour demands, get in touch with the folks at Jack Rabbit Marine in Stamford, CT, or with Hotwire Enterprises in Madeira Beach, FL, mentioned earlier (see contact information at left) or with any reputable local alternative energy purveyor who can walk you through the details and help you get set up and energized.
Also With This Article
Click here to view “Solar Panel Types.”
Click here to view “Solar Panel Installation.”
Click here to view “Solar Panel Survey Quotes.”
Click here to view charts with this article.
Contacts
BP Solar, 410/981-0240, www.bpsolar.com
Hotwire Enterprises, 727/217-9809, www.svhotwire.com
ICP Global Technologies, 514/270-5770, www.icpglobal.com
Jack Rabbit Marine, 203/961-8133, www.jackrabbitmarine.com
Kyocera Solar Inc., 800/223-9580, www.kyocerasolar.com
SES Flexcharge USA, 231/547-9430, www.flexcharge.com
Shell Solar Industries (Siemens), 805/482-6800, www.shell.com/solar
United Solar Systems (Uni-Solar), 800/843-3892, www.uni-solar.com
