Are all Boat Lift solar chargers under powered?

jglwkl · April 7

We bought a lake property last year and we are loving it. However, I've found that our solar-charged battery-powered boat lift isn’t as effective as I would like it to be. I can lower / raise our 19 ft deck boat (~2,200 lb) about twice per day before running out of battery power. Installed a new battery and tried a third battery with the same results.

We have a 12VDC Duracell MARINE & RV SL127MDP Dual Purpose battery. Don't know the Brand/Model or output wattage of the charger. I do not have a charger controller. We have a ShoreStation aluminum frame boat lift and a LiftTech DC remote Wireless Gen1 winch (12 or 24 volt).

Bottom line – I’m looking for the most efficient (e.g., highest number of Down / Up cycles per day) solar charging system for our lift. We have a lot of waves at our dock, so we prefer to use the lift instead of having the boat get pounded on the dock. Our best case would be to lower the boat fully in the morning, raise and lower it as needed during the day (raised just enough to hold it in place), and raise the boat fully in the evening.

First - I understand that solar is not an exact science and many variables such as sun angle, cloud cover, exposure time all have an effect on the efficiency of any given solar charging system. I also understand that more powerful chargers require larger panels, and so some practical / safety limit must be considered when mounting one on a boat lift.

BUT - I've looked at many articles and products online, and have become quite confused about what is ‘needed’ for an efficient system .vs. what is currently available.

The battery manufacturer recommends a 8A – 16A (between 115W – 230W) charger and a programmable controller, based on the battery's maximum charge rate (e.g., a standard 100Ah battery charges at ~10A). However, most online products are only in the 10W - 40W range, and even the 'best' ones talk about the number of cycles per week rather than per day. Some even say that they've never had problems using a 12V 20W system! So, it appears that I may have some unrealistic expectations, but I want to know why. Aren't there any solar chargers made in a size suitable to mounting on a boat lift that are powerful enough to charge my battery at the manufacturer's recommended rate? I'm a retired computer engineer, not an electrical engineer, so I don't understand all of the intricacies of the electronics, but it seems that what the industry is offering is far less than what might be desired.

A secondary question is "how large (dimension) of a solar panel can I put on a lake dock before wind becomes a concern?"

BB. · April 8

What you need to do is to characterize your loads... Measure the time*Amps (*lift voltage) per lift... How many lifts per day. And how many lifts per maybe three days (worst case when weather/sun turns bad for a couple days).

Will you be able to mount your solar array in "full sun" (at least 9am=3pm)? Any shading (branches, buildings, local hills/etc.) that blocks the array will "kill" the harvest during "shade time". Even a single rope or a couple of power lines shading the array/panel can kill harvest by 50%.

Lastly, then figure out your need for poor weather performance (will the system be used during "winter", etc.--I.e., 9 months a year, etc.).

And how "critical" is the operation of your lift (and any work lights, trickle charger for boat batteries, etc.). It is not unusual to use a 66% or 50% derating to support a streak of poor/cloudy weather and/or perio ds of heavy use)--This is assuming that you want the system to operate fully solar vs shore wiring, genset, etc.

If you can tell us your daily usage (such as AH per Day @ xx volts, or Watt*Hours per day), rough location (nearest major city) to figure out "hours of sun per day", and any special case issues (shading, summer usage, 12 months a year, boat battery charging, etc.).

It is not unusual to size the solar array to supply close to 4x power usage (battery efficiency/losses, if using an AC inverter, Derating of solar panels for dust/aging, etc.).

Battery type can also make for sizing issues... Lead Acid batteries, usually around 80% charging efficiency. LiFePO4 (lithium Ion) batteries can be closer to 96% efficient. If you have an AC inverter or boat charger, you can run closer to 85% percent efficiency.

Sometimes you may wish to have (for example) two solar systems... One for charging the lift... The second for trickle charging the boat battery (just so that you keep "failures" isolated (I.e, don't want somebody leaving a cabin light on the boat draining and possibly damaging your lift batteries.

And plan for aging/cycling of your batteries.... A good quality lead acid battery may last 3 years. A true deep cycle lead acid battery (typically cycled to 75% to 50% state of charge) can last 5+ years. A well designed Li Ion system may last 5-10 years. Having something to prevent (for example) over discharging can also help battery life (lead acid, avoid discharging often below 50% SoC without quickly recharging--Li Ion avoid discharging below 20% state of charge).

Taking almost any rechargeable battery chemistry to 20% to 0% SoC can pretty much "kill" your batteries. Lead Acid really don't like to spend much time below 75% SoC without being charged back over 75% SoC within a day or two.

And there are differences between lead acid battery construction.

SLI--Starting/Lighting/Ignition (typical "car battery")--Don't cycle them below 75% SoC often--They will not last long
Deep Cycle--Used for Solar/Off grid applications... They can cycle to 50% SoC and occasionally to 20% (and quickly recharged) for decent life.
"Trolling Motor Batteries"--Really 1/2 way in-between... They really are not as rugged and Deep Cycle types.

-Bill

Are all Boat Lift solar chargers under powered?

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