Setting up a marine solar system on a boat involves mounting flexible or rigid panels on the cabin top, bimini frame or stern arch, connecting them to a waterproof MPPT charge controller, and wiring that to the boat's leisure battery bank. Marine installations require waterproof connectors, tinned copper cable rated for marine use, and components that can withstand salt air and vibration.
Solar power is particularly well suited to boats. The sun is often strongest when you are out on the water, away from shade, and you need a reliable power source for navigation electronics, lighting, refrigeration and communication equipment. This guide covers how to design and install a marine solar system safely and effectively.
Why Solar Works Well on Boats
Boats spend time in open, unshaded environments. Unlike land-based installations where nearby trees or buildings create shading issues, a boat at anchor or underway is often in full, unobstructed sunlight. A modest 200W to 400W panel array can keep a leisure battery bank topped up through normal daily use without running the engine or a generator.
Key Differences from Land-Based Solar
Saltwater environment
Salt air corrodes standard electrical components rapidly. Marine solar installations require tinned copper cable (not standard electrical cable), stainless steel fixings, waterproof cable glands and connectors rated for marine use. Never use standard household cable or connectors on a boat.
Movement and vibration
A boat pitches, rolls and vibrates. Panels and mounting hardware must be secured so they cannot work loose. Wiring must be properly clamped and supported at regular intervals to prevent chafing on sharp edges. Use flexible conduit where cables need to move slightly.
Limited mounting space
Boats have constrained surfaces for panel mounting. Flexible panels are popular because they can be bonded to curved surfaces on cabin tops and coachroof areas. Rigid panels work well on bimini frames, stern arches and pushpits where they can be mounted at a fixed angle.
Panel Types for Marine Use
Flexible panels
Flexible monocrystalline panels can be bonded directly to the cabin top using a suitable marine adhesive. They add minimal windage and are out of the way. The trade-off is that they run hotter (which reduces efficiency) and have a shorter lifespan than rigid panels. They are a good choice where weight and profile are priorities.
Rigid panels on a frame
Rigid panels mounted on a bimini frame or stern arch are more efficient and durable. The frame keeps them off the deck and often allows adjustment of tilt angle. They do add some windage, which is worth considering on a sailing vessel.
Sizing a Marine Solar System
Calculate daily consumption
List your onboard loads and their daily usage. Common boat loads include: chart plotter (15 to 30W for 8 hours = 120 to 240Wh), VHF radio on standby (5W constantly = 120Wh), LED navigation lights (15W for 8 hours at anchor = 120Wh), 12V fridge (30 to 50W average = 720 to 1200Wh over 24 hours), bilge pump intermittent (negligible), phone and tablet charging (50Wh per day). A total of 1100 to 1700Wh per day is typical for a live-aboard or extended passage scenario.
Panel wattage
In coastal UK waters in summer, you can expect 3 to 4 peak sun hours per day. For 1500Wh daily consumption: (1500 x 1.25) / 3.5 = approximately 535W of panels. A 400W to 600W array covers most cruising yachts adequately in summer. For year-round use or higher-consumption vessels, size up accordingly.
Battery bank
Marine battery banks are traditionally lead-acid (AGM or gel), but lithium iron phosphate is increasingly preferred due to weight savings and superior cycle life. For a cruising yacht, 200Ah to 400Ah at 12V (2400Wh to 4800Wh) is typical, giving 1 to 2 days autonomy between solar charges or engine running.
Charge Controller Selection
Use a waterproof or water-resistant MPPT charge controller rated for your panel array. Victron Energy controllers are popular in the marine sector due to their reliability, Bluetooth monitoring capability and extensive compatibility with other onboard systems. Mount the controller in a dry, ventilated location such as the engine bay or a navigation locker, avoiding direct contact with bilge water.
Wiring the System
Use only tinned copper cable with appropriate current rating. Fuse every circuit close to the battery positive terminal. Run positive and negative cables together (not separately) to minimise inductive loops. Use waterproof double-entry cable glands wherever cables penetrate the deck or cabin top. Secure all cables with stainless steel cable clips at intervals of no more than 300mm to prevent movement and chafing.
Monitoring
A battery monitor is particularly valuable on a boat because you cannot simply run a cable to the mains when the battery runs low. Victron's BMV series or a Victron Cerbo GX with a touchscreen provides real-time state of charge, input and output data, and historical records. This lets you manage your energy budget actively and avoid ever running flat.
Safety and Compliance
Marine electrical installations on UK-flagged vessels should comply with the Recreational Craft Directive (RCD) or its UK equivalent post-Brexit (UKCA). For commercial vessels, Maritime and Coastguard Agency (MCA) guidance applies. Use a qualified marine electrician for installations on vessels you are not confident working on yourself. Poor marine wiring is a significant fire risk.
