Solar Boat Lifts: Can I run my boat lift on solar?
“Can I run my boat lift on solar power?” a friend of mine recently asked. “Of course you can” I replied. But my friend had a problem. He bought a used boat lift which happened to run on standard AC power. Ah yes, AC. Alternating current. But no matter, boat lifts are still a great application for solar power. But why?
Why go solar for your boat lift?
Safety. My friend went on to explain that while the seller of his boat lift was fine with running an extension cord from the lift, along the dock, across the yard and to his house outlet, my friend was not. Electrical cords and water don't work well together. And he related the tragic story of a young woman that died from electrocution when an extension cord fell into the lake near her. No doubt, AC wiring can be safely routed to a boat lift, but a plain old extension cord isn't the way to go.
On the other hand, a solar powered boat lift system avoids even the temptation to run extension cords along the dock. Instead, a small solar panel would be mounted to the lift support structure or the immediately adjacent dock. The 12 volt PV wire would connect into an enclosed battery box (or a sheltered area under the lift awning) that ideally would house the battery, the charge controller, and the inverter (if an AC lift). The lift motor would then connect into that inverter (if an AC motor) or the battery (if a DC motor). All nice, close and short connections--out of the way and above the water.
Save $. Unless you have a safely installed AC outlet on your dock next to your boat lift (meaning no jerry-rigged extension cord jobs mentioned above), running an AC circuit to your dock can be an expensive proposition. It may mean trenching, conduit, electrician labor, etc. Those add up fast. A solar-powered DC system also has costs, but should be far less than trenching an AC circuit to your dock, etc. To save the most, start out right by buying a DC powered boat lift. If you buy a traditional AC powered one, then you'll also need to buy an inverter that's beefy enough to handle that AC motor. And since AC motors run at 110V (vs 12V for a DC motor) you'll need more battery storage and a bigger panel to fill them.
So what do I need to know for boat lift solar?
Sun. First, does your boat lift location have good south facing sun? If you're lift sits in the shade all day, solar won't be a good option for you. Even a little shade can reduce energy production, but you can compensate by upsizing your solar panel. Bottom line: understanding your site is key.
Need Batteries. Your boat lift system will be battery-based. You fill your battery with solar DC energy. To ensure your batteries are charged correctly and not damaged by over charging, your solar panel first connects to a solar charge controller. The battery stores the energy until you're ready to lower your boat to the water. The motor draws the energy from the batteries and then the sun refills the batteries. Voila! The key is to get the right kind of battery, keep it fully charged when not in use, and don't discharge it more than the recommended level.
Deep Cycle Batteries. Only use a deep-cycle battery. If the battery is labeled with “cold cranking amps” that's not a good sign. That's what you see on “starting” batteries (like the kind under your car's hood). Why does it matter? Because a deep-cycle battery is designed to power loads that steadily and fully discharge the battery to minimum point (it's depth of discharge (DOD) versus the sudden burst of current required to turn an engine over. Deep cycle batteries are also meant to be steadily recharged to 100% over and over again. Batteries are expensive, so it's important to use the right one for the job.
Volts and Amps. Boat lift motors designed for DC electricity will often require 12 volts, sometimes 24. Most often, a simple, single 12 volt deep cycle battery will be all you'll need. If you do have a 24V system, then you'll need 2 x 12 volt batteries wired in series (meaning the positive terminal of one battery is wired to the negative battery terminal of the other battery. By wiring in series, the battery voltage is doubled. A 12 volt deep cycle battery will list it's capacity in amp hours. As explained below, you'll probably want something close to 100 amp hours as measured by the C/20 rate. Huh? Let's just say for now that the more quickly a battery is discharged, the quicker the capacity is reduced. C/20 means a rate where the battery is fully discharged over 20 hours. That is the typical rate used to measure battery capacity for solar applications.
Flooded or Sealed/AGM/Gel? For a boat lift, the choice of battery type comes down to convenience and cost. A flooded lead-acid battery is cheaper than a sealed battery. But remember that a flooded battery's electrolyte levels must be checked and topped off periodically. Pop the caps and add distilled water. Not hard. But it must be done to ensure the batteries last like they should. A sealed battery may be either a VRLA or AGM or Gel battery. Most common are AGM these days. Without getting too technical, an AGM (or Gel or AGM) battery doesn't require any electrolyte maintenance. Just hook it up and forget it.
Inverter. As mentioned above, if you have an AC powered boat lift (like my friend did) you'll need an inverter to invert the DC power from the batteries to AC electricity that your motor needs. The inverter must be sized to provide the AC watts that your motor needs. Both continuous operating watts and surge watts. Motors often have higher wattage requirements when they start up (surge). A modified sine wave inverter may be sufficient, but you won't go wrong with a pure sine wave inverter. Pure sine wave inverters mimic the same quality AC wave form that your utility provides. Equipment runs best on pure sine inverters.
Sizing. Sizing the solar system components for your boat lift will depend on the specifics of your site, your boat lift specs and how often you use your lift. Once you know the watts of your DC motor, you can calculate the watt hours of stored energy you need each day. Just estimate how many times you'll raise and lower your boat in a typical day x the minutes per lift. Add them up and multiply by your system's watts. Give us a call at SolarPanelStore.com and we can help you size and get the right battery, charge controller and solar panel based on those watt hours. We can also help get you the right mount to attach your panel to your boat lift structure.
Solar boat lifts are a great way to go for safety, cost and simplicity. We're happy to help you with yours. And happy boating!
- Dan Baldwin