Another critical part is the solar-charge controller, a device Marlow’s engineers have inconspicuously installed in a cabinet on the starboard side of the 70’s crew’s quarters at the rear of the vessel. It both registers the instantaneous outputs of the array’s individual panels and safely routes all solar-converted electricity to the system’s third and final important component—the solar battery bank.
Weighing about 1,300 pounds, the bank consists of nine dedicated high-capacity 8D Concorde AGM batteries that can be charged and discharged with exceptional frequency, ease, and safety. (Six more can be added if switched from thruster and other usages.) It serves as the electrical equivalent of a fuel tank, albeit one that fills itself for free on sunny days. Via inverters, converters, and other electrical devices, it energizes a long list of equipage onboard, including four Sub-Zero refrigerator/freezer drawers, three undercounter-style ice makers, a wine cooler, a whopping assortment of electric lights, four TV sets, a slew of galley appliances, and all the electronics for the upper and lower helm stations.
Sundown occurred about 7:30 p.m. on test day. Employees and friends of Marlow’s who’d dropped by earlier that afternoon in a triple-outboard Prowler departed shortly thereafter. We shut down the genset at approximately eight o’clock and after noting charge levels in excess of 24 volts on the service side of our electrical system, retired to the fully lit saloon to gauge the performance of the solar array based on the observations we’d made during the day.
It was a promising session. Although the array had apparently failed to produce the maximum 175-watt outputs our individual solar panels were rated for (most likely due to changing sun angles, cloudiness, and other meteorological factors), it had still averaged 125 watts per panel (25 volts x 5 amps) for a total outlay of 1,000 watts (125 volts x 8 amps). No wonder the lights were burning bright, the drinks were going down super-frosty, and Capt. Jack Sparrow was coming through gin-clear on the flat-panel TV.
The night passed uneventfully and the next morning brought a revelation. Once we’d pulled the anchor with the big Lofrans Titan windlass, our onboard electrics remained darn near as vigorous as ever (with charge levels on the service side still exceeding 24 volts), despite the fact that anchor and deck lights had been running all night, in addition to an assemblage of eight reefer units, four electric toilets, most of the electronics, and a whole bunch of courtesy lights. Solar power had kept the 70 operational through the darkness, and we had juice to spare.
“Of course, air-conditioning’s another matter,” said Marlow, cranking the mains. “Right now we don’t have the solar technology to keep an air-conditioning system running all night on a vessel this size while keeping refrigerators and everything else going, too. But I’m betting we’ll solve the problem in five years or less.”
This prediction sparked more. Marlow sees, for example, solar panels integrated into sheets of flexible film rolled onto the hardtops and coach roofs of boats or layered into their windows. He sees solar arrays fringed with prisms that rotate to maximize solar intensity with GPS latitude inputs. And finally, he envisions them cooled to maximize performance with heat exchangers embedded in the substrates beneath them.
“Nobody’s got all the answers to this thing, Bill,” Marlow concluded with a wry grin, “but I know that the evolution of green technology is critical to the survival of the marine industry today. And heck, I'm givin’ it a whirl!”
How Does a Solar Boat Perform?
While our Mark II 70E’s speeds were approximately the same as those we’ve measured for similar models with the same 1,001-bhp Caterpillar C18 ACERT twin diesel powerplants, she was generally more fuel-efficient and quieter (sound levels were recorded at the lower helm station) and posted significantly higher range numbers, most likely due to her relatively light-weight, high-tech construction and efficient hull form. Moreover, the 70 tracked like a train (thanks to a partial keel as well as Marlow’s prop-and-propshaft-protecting strut keels), even in the Manatee River (where we did our speed and other runs), despite the fact that soundings of 12 and 16 feet predominate.
This article originally appeared in the June 2009 issue of Power & Motoryacht magazine.