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Author Topic:   Solar Power Battery Charger?

cindalyn posted 02-05-2008 12:30 AM ET (US)
Is a Solar Power Battery Charger a worthwhile investment for a boat stored in an outdoor storage facility with no provisions for charging batteries or are they just another gizmo?
If they are worthwhile, what size would be adequate for a boat that would be used for several hours each week? Location is Myrtle Beach, SC.
AZdave posted 02-05-2008 01:23 AM ET (US)
If you use the boat several hours each week there should be no need for a trickle charger, the outboard will keep your battery charged. My take on solar chargers is that they will maintain full charge on batteries that are idle for long periods of time.. Dave
Whalin15 posted 02-05-2008 10:50 AM ET (US)
My buddy has a 70 year old wooden sailboat that he lives aboard without any battery charger. His solar panels maintain his batteries year round. When he does start his diesel motor once or twice a year, it starts right up even after using his glow plugs to pre-warm his motor. This boat does collect water in the bilges and the pump does cycle a few times a day. If your boat lays up for long periods of time 4-6 weeks between uses, a solar panel will keep your battery fresh.
jimh posted 02-05-2008 01:32 PM ET (US)
Re-charging a battery from a solar panel is not a workable solution for most marine applications on small boats. Solar panels which are affordable only produce a "trickle" of current, and they are useful for maintaining a battery's state of charge by preventing self-discharge currents or other parasitic currents from draining the charge. Solar panels of the size suitable for use on a small boat generally do not produce much current output. If you need to recharge a battery which is in a state of deep discharge, it will take a long time with a solar panel.
For example, a 50-Ampere-Hour battery (typical of a small boat's starting battery) is to be charged from a solar panel which produces 100-milliamperes output. The time required is
50-Ampere Hours / 0.1-Ampere = 500 hours
Considering that at best there is daylight only 12-hours per day, and that the solar panel probably only produces its rated output during about half that time, it will take
500-hours/6-hours-per-day = 83 days
of strong sunlight to charge the battery. On days with cloudy skies there will be less charging.
To effectively charge or maintain a battery you need to use a solar panel which can produce 13.5-volts. Because the output of the panel will vary, you need to use a higher voltage output from the panel and to add a regulator.
A battery's charge can be maintained by a solar panel, but given the size and cost limitations assumed to be associated with a small boat, a solar panel is not an effective way to restore charge in a battery which been deeply discharged and has the typical capacity for an engine starting battery in a small boat.
jimh posted 02-05-2008 01:36 PM ET (US)
[Fixed math typo]
Tohsgib posted 02-05-2008 02:53 PM ET (US)
The problem with solar panels is they are not waterproof. So unless you have a way of keeping it in the sun but out of the elements it is not going to last long.

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Author	Topic: Solar Power Battery Charger?
cindalyn	posted 02-05-2008 12:30 AM ET (US) Is a Solar Power Battery Charger a worthwhile investment for a boat stored in an outdoor storage facility with no provisions for charging batteries or are they just another gizmo? If they are worthwhile, what size would be adequate for a boat that would be used for several hours each week? Location is Myrtle Beach, SC.
AZdave	posted 02-05-2008 01:23 AM ET (US) If you use the boat several hours each week there should be no need for a trickle charger, the outboard will keep your battery charged. My take on solar chargers is that they will maintain full charge on batteries that are idle for long periods of time.. Dave
Whalin15	posted 02-05-2008 10:50 AM ET (US) My buddy has a 70 year old wooden sailboat that he lives aboard without any battery charger. His solar panels maintain his batteries year round. When he does start his diesel motor once or twice a year, it starts right up even after using his glow plugs to pre-warm his motor. This boat does collect water in the bilges and the pump does cycle a few times a day. If your boat lays up for long periods of time 4-6 weeks between uses, a solar panel will keep your battery fresh.
jimh	posted 02-05-2008 01:32 PM ET (US) Re-charging a battery from a solar panel is not a workable solution for most marine applications on small boats. Solar panels which are affordable only produce a "trickle" of current, and they are useful for maintaining a battery's state of charge by preventing self-discharge currents or other parasitic currents from draining the charge. Solar panels of the size suitable for use on a small boat generally do not produce much current output. If you need to recharge a battery which is in a state of deep discharge, it will take a long time with a solar panel. For example, a 50-Ampere-Hour battery (typical of a small boat's starting battery) is to be charged from a solar panel which produces 100-milliamperes output. The time required is 50-Ampere Hours / 0.1-Ampere = 500 hours Considering that at best there is daylight only 12-hours per day, and that the solar panel probably only produces its rated output during about half that time, it will take 500-hours/6-hours-per-day = 83 days of strong sunlight to charge the battery. On days with cloudy skies there will be less charging. To effectively charge or maintain a battery you need to use a solar panel which can produce 13.5-volts. Because the output of the panel will vary, you need to use a higher voltage output from the panel and to add a regulator. A battery's charge can be maintained by a solar panel, but given the size and cost limitations assumed to be associated with a small boat, a solar panel is not an effective way to restore charge in a battery which been deeply discharged and has the typical capacity for an engine starting battery in a small boat.
jimh	posted 02-05-2008 01:36 PM ET (US) [Fixed math typo]
Tohsgib	posted 02-05-2008 02:53 PM ET (US) The problem with solar panels is they are not waterproof. So unless you have a way of keeping it in the sun but out of the elements it is not going to last long.