The September 1998 issue contained test results of 10 solar panels-the Siemens SP-70, SM-50, SM-46, SM-20, SM-10 and SM-6, Solarex MSX-18 and MSX-10L, and the Uni-Solar rigid US-32 and flexible MBC-525. Several additional panels arrived too late to be included-the rigid Kyocera KC-60, Uni-Solar US-11 and US-5, and the flexible Uni-Solar USF-32.
To normalize the data collected for this report, we re-tested the same Siemens SM-46 panel included in the September report at the same time we tested the four new panels. A multiplier was established for both the current and power data. The data is correlated in Table 1 and the panels are illustrated in the photograph. Figure 1 illustrates the panels output charging current versus any battery voltage between 10.5 volts and 14.2 volts. Figure 2 illustrates the power output of the panels versus the same range of battery voltage.
The Kyocera panel uses polycrystalline-silicon cells that are warranted for 12 years. The cells are covered by tempered glass and the frame is anodized aluminum. The shape of this panel is closer to square than the more common rectangle. It may be a better fit in some installations. The user should be aware that the plastic junction box mounted underneath for connection, juts out 3/4″ beyond the plane of the aluminum frame. It is rugged and well sealed but we wonder why they do this, despite the fact that panels should never be mounted flush. Allowing air to circulate around the back of panels is important in keeping them cool. As panels heat, output decreases.
We also wonder why Kyocera paralleled two diodes (see photo at left) for both the isolation diode and bypass diode functions. (The diodes are necessary in series systems to minimize loss by shadows and to protect against open circuits in high-voltage strings.)
Parallel diodes do not share current equally unless they are specifically matched-a very expensive procedure. In fact, the only legitimate engineering reason to parallel diodes is for redundancy. If one diode fails in the open mode, the other one works. And, both diodes must be capable of handling the system current independently.
The diodes installed in the Kyocera unit had no markings so we couldn't determine the current-carrying capability. Yet, physically, they too small to handle the panel current alone. We therefore assume Kyocera installed them to share the load. When we called Golden Genesis, distributor of the Japanese-made Kyocera panels, we were told that diodes are required by regulation on large arrays, but they could not tell us the current carrying capacity of the diodes, nor why they are in parallel. One spokesperson theorized it is to save cost.
Although these amorphous panels have little more than half the efficiency of standard designs, we are fascinated by the shadow protection where the output power is reduced almost proportionately to the percentage of shadow. Clearly, rigging and antenna shadows will have minimum effect on these units, which makes them practical for use on boats.
At one point, we experimented with a dirty window shadow in an effort to measure their worth for mounting inside of a hatch or windshield, for example. We sprayed different stuff on a piece of glass to create diffusion, but before we could collect much data, a gust of wind jerked the glass away and turned a few heads as it shattered in a million pieces. We still think the idea might have merit.
The USF-32 model is flexible while the US-11 and US-5 are standard rigid units framed in aluminum. We still have concerns about the longevity of flexible panels, though they may last forever if they are well cared for. We flopped them around within their given limits and noticed no change in performance.
If there is a major drawback to flexible panels, it is this: Solar panels, by their very nature, are subject to complete shut down during extremely high temperatures like those experienced in the tropics. We have witnessed this on our own boat. Even the slightest breeze can cool a panel enough to let it work. The flexible units are difficult to cool compared to a rigid unit which, because of its frame, has space behind it. The flexible unit must lie flat on and in contact with a surface. No wind can pass underneath and therefore cooling is more difficult.
Solar power is getting cheaper and more reliable; panels are valuable for a boat that sits on a mooring away from shore power. Cruisers can ascribe a portion of their electrical budget to solar panels.
As reported last September, the crystalline panels are more efficient than the amorphous panels, but the amorphous panels don't suffer as much loss when partially shaded. In our tests, crystalline panels can lose up to almost 90% with just one cell shaded. Amorphous panel losses are roughly proportional to the amount of panel shaded.
The last time we reported on a Kyocera panel (March 15, 1993), we rated it a Best Buy. It still is on a dollars-per-rated watt basis. But we have concerns about the diode configuration. Still, if they were changed or watched carefully, we suspect the unit will last for many years. And it is warranted for 12 years.
Any of the Uni-Solar units are reasonable choices, especially where shadows are a problem-common on a sailboat. However, the very small units like the US-11 and the US-5 are really only of use for tending well-charged batteries. Their current outputs are simply too small for any useful re-charge capability. And the USF-32 is big for what it puts out-slightly larger than the Kyocera KC-60, which has nearly twice the output.
Your choice may well depend on mounting options. If you plan on installing panels on the stern pulpit or on top of a dodger, frame size will dictate what is feasible. Flexible panels, capable of handling more abuse, are ideal for stowing below and flopping out on deck, unfastened, when convenient. They also conform to curved deck surfaces better, but as noted earlier, this does not provide for ventilation on the back side.
Contacts- Kyocera, Golden Genesis, PO Box 14230, Scottsdale, AZ 85267-4230; 800/544-6466. United Solar Systems, 9235 Brown Deer Rd., San Diego, CA 92121; 800/397-2083.