PS Advisor July 15, 1998 Issue

PS Advisor 07/15/98

Solar Panel Trickle Charge
What do you recommend for purchase of a small solar panel to keep my boat batteries charged? I use two small deep-cycle 40-amp-hour batteries on my Morgan 22.

I spend a couple of days on my boat about every other weekend from April to November. The batteries alternately get a trip home for recharge a couple times before the season ends. I would like to avoid the hassle of doing this. From use and non-use they decline about .10 volts every two weeks. When they reach about 12.0 volts, they come home for recharge.

Would a small panel about 12" x 15" with a maximum output of 5 watts be adequate to charge back the loss? Each battery would only get hooked on the solar charge for a two-week period every other trip (4 weeks). What’s your opinion?

Harvey Wilson
Prairie Village, Kansas

In the March 1 and March 15, 1993 issues we reported on solar panels, including tests of about 10 brands of various sizes. This experience prompted us to again install a panel on our test boat. Previously we had two very small panels (about 5 watts or the size you’re proposing) on an older boat. They produced very little, and couldn’t keep up with any appreciable load. Their output began to diminish after about two years (they were Arco thin-film panels). So, after the PS tests we put a 50-watt Photocomm panel on our C&C 33, and later moved it to our Tartan. It has been one of the best upgrades we’ve made.

Let’s do the math. Say your 80 amp-hour battery bank is 25% discharged; this means you need to replace about 20 amp-hours over a two-week period (actually a bit more). Say the sun shines 70% of the time for a 12-hour day. A 5-watt panel at peak output will only give you .4 amps (in truth, you’ll only average maybe .225 amps over those 12 hours because the sun isn’t directly angled to the panel, you’re in Kansas and not on the equator, etc.). So, .225 amps x 12 x 75% or 9 hours = 2 amp-hours per day. 2 AH x 14 days = 28 AH. But don’t forget the tendency of batteries to self-discharge. Still, it’s not a bad proposition.

However, if you can afford it, we’d buy a somewhat larger panel, such as the Uni-Solar 11 or 22 ($129 and $229 at West Marine) or the Siemens 10 or 20 ($162 and $289 at West). These are all self-regulating panels (like the small 5-watt panels) so you don’t have to buy and wire in a regulator. They’re more expensive than the 5-6-watt panel at about $100, but we think you’d certainly see more for your money. With solar, bigger is better. Results of small-panel tests will appear in the September issue.

Copper or Hose for LPG?
Your review of the Wauquiez Pretorien 35 in the April 1 issue mentions replacing copper tubing in the propane distribution circuit with CG-approved rubber hose. Why?

While my copy of ABYC standards is old (1978) and revisions may have been made, section A-1.9 covering LPG systems including propane suggests the use of copper tubing, grades K or L in this application. Copper is prohibited, unless internally tinned, in section A-22.9, which deals with CNG systems only.

Martin Sandler
Huntington Bay, New York

The 1993 ABYC standard simply states, in terms of approved material, “one type is annealed copper tubing...” Next it says “The flexible LPG fuel line shall comply with UL 21 LP Gas Hose.” Either is acceptable. Our statement that copper “should” be replaced with flexible hose was probably too strong. However, many gas appliance manufacturers have advised us that many more problems are caused by cracked or corroded copper tubing than hose. Also, hose is much easier to route through a boat’s interior. Where it passes through a bulkhead, use a grommet to prevent chafe.

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