Green Advice: Think Before You Spend
Before you rush out and buy alternative-energy sources, understand your needs and determine the best technologies to meet them. "Systems" from our April 2012 issue.
In this concluding installment of CW’s series on direct-current power systems (check out Part I and Part II), we take a look at how power generation via sunlight, wind, and water has incrementally evolved over, say, the last 10 years. These refinements, coupled with the improved efficiencies of the electrical devices we carry on board, mean that from a systems perspective, reducing our dependence on diesel engines and generators is increasingly possible—up to a point.
The question facing us isn’t “Can we go green?” It’s “How green can we go and still have our toys?” Unrealistic expectations are sure to disappoint, but with the right knowledge, a proper and effective system to supplement or even replace a petro-dependant diesel generator—with its required maintenance, noise, and exhaust fumes—is quite within the realm of possibility.
On Design, Back to Basics
As seemingly high-tech as green power sources appear to be, it’s important to remember that electrical-system design always centers around one fundamental: your “appetite for amps,” as I’ve referred to it many times before. How much power do you need? It all boils down to your desired comfort level and to how many electrical devices you intend to regularly use. This is true whether you’re running a battery-supplied DC system or a high-voltage AC system that relies on shore power or on a generator.
Thirty years ago, when my wife and I were cruising extensively, we were quite happy with a boat that didn’t have even a shore-power system! We loved our quaint gimbaled brass oil lamps when reading at night. Today, our needs are quite different, and having a renewable power supply on board is a must. The question boils down to this: Exactly how much power is enough?
So, much as with the engine-driven alternators and battery chargers that I discussed earlier in this series (see “New Tools for Managing Your Battery Bank,” March 2012), you need to begin by making an honest evaluation of your daily power consumption. Most folks I’ve worked through this drill with tend to go into a bit of denial about how much power they really use, possibly due to the simple reality that power generation costs money. The more electricity you use, the more you’re going to have to invest in equipment. 
With a typical 100-amp-hour A.G.M. battery priced at $300 or more, every time you add one to your system, it’s going to cost you some real dollars. So an accurate analysis of your electrical needs is always going to be the first step in determining what your system will look like: How big an alternator will you need? How much battery capacity is required? How many watts of solar-panel power can you install? Where on the boat will the panels fit? What about using a wind generator or a water generator when you’re passagemaking?
Answer these questions and you can begin to determine how you can generate enough power in a day to replenish what you will typically use.
Where We Stand
I’m often asked if there have been any significant improvements in efficiency with electrical systems in general, and solar panels in particular, over the last decade. The answers are mixed.
Let’s start on the consumption side of the equation. There have been significant reductions in power consumption over the last 10 years. Think L.E.D. lighting. L.E.D. lights typically use a tenth of the power that a similarly sized incandescent light uses. That’s significant. Combine that with improved battery absorption rates, which enable properly sized and rated charging devices to replenish discharged batteries more rapidly, and you’ll see a genuine uptick in overall efficiency.
In a general sense, in fact, most marine electronic equipment in use today is more electrically efficient than equipment available to us a decade ago. Voltage drop through typical battery and charging systems has been reduced as such system components as battery combiners and isolators have evolved using vastly more efficient electronic control circuits. But while display screens and other devices now consume less power, we tend to use more of them. So when it comes to green power and energy self-sufficiency, the real answer depends on the individual. Again, it’s a question of how much power will you use. Once you have the answer, you can then design a DC system integrating alternative power sources that will require fewer batteries to store the power you’ll consume on a daily basis.
On the supply side, it’s important to remember that the marine alternative-power market is minuscule in the grand scheme of things. Therefore, any improvements in technology are derived from other market sectors, such as land-based recreational vehicles and commercial and home applications in which there’s enough critical mass to entice companies to invest in product improvement and development.
As a result, many of the items you’ll be looking at and considering for your boat are really going to be land-based products. I mention this because it may impact critical choices in material selection. You’ll need to research, for example, whether an aluminum frame for a panel is anodized or not or whether screws are made of stainless steel or merely cadmium-plated mild steel. You’ll need to look for subtle nuances such as these when shopping for and comparing products.
With solar panels, we can narrow things down to three distinct categories and make some general statements regarding relative efficiency and how this impacts pricing.
Monocrystalline solar cells are the most efficient and also offer small improvements in low-light performance. The downside? They’re the most expensive types, but they can offer “efficiencies”—the rate of sunlight conversion—as great as 17 percent.
Polycrystalline panels are available in several variations and, depending on the manufacturing process, offer efficiencies in the 11-percent to 14-percent range.
Amorphous panels, sometimes referred to as “thin film,” are the most common type used with the flexible panels that are quite popular among cruisers. The trade-off for this flexibility is performance; their typical efficiencies are only about 5 percent to 6 percent.
A relatively new category of solar panels has emerged; it’s known simply as Group 3-4. These panels use a variety of materials, such as gallium arsenide, that offer much greater conversion efficiency than the silicon-based cells we commonly see today. These panels offer efficiencies in the range of 25 percent but are presently cost-prohibitive for most sailors.
So to answer the basic question, although we haven’t seen major improvements in actual efficiencies with silicon-based solar panels over the last five years, we have seen a steady decline in prices. This all contributes to a lower cost-per-watt hour. From that perspective, efficiencies have improved. With panels now readily available up to about 85 watts, and with the ability to parallel-connect groups depending upon the limitations of your onboard real estate, we can now generate quite a few amps of power in a given day, as long as the sun shines.
