Reversing Entropyvideo
Off Grid: Efficient Water Heating for Your Sailboat.
20 June 2025 · 8 min · 9K views
What this video covers
Paulo aboard Starry Night, a sailboat restored after 12 years of abandonment, outlines four off-grid methods for heating water without running the engine or connecting to shore power.▶ 0:50 The baseline system most sailboats carry — a boiler with a mains-powered resistance element and an engine-cooling coil — works fine at a marina or under motor, but fails at anchor on solar alone.▶ 1:39 The first solar workaround uses an inverter to feed the existing AC boiler once batteries reach roughly 95% charge, redirecting surplus production that would otherwise go to waste.▶ 3:15 The second replaces the boiler's coil with a custom DC resistance element — 24V or 48V, sized to match available solar output, such as a 700W resistor on an 800W array.▶ 3:33 The third method runs a water pipe in a coil beneath existing solar panels: a small DC pump circulates water through the coil, cooling the panels (improving their efficiency) and transferring that heat to the boiler.▶ 4:15 Paulo used this on a previous boat; the pump failed because it lacked a 100% duty cycle rating.▶ 5:03 A fourth option is the Prisma PVTRBX hybrid panel, which integrates a stainless steel water conduit on the back of the panel.▶ 5:50 For cold-weather use, Paulo installed a Webasto diesel parking heater — sourced secondhand for around $50 — which circulates heated coolant through the boiler instead of heating air.▶ 6:27
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