Signature is a boat, however there are multiple elements she has in common with a tiny house when it comes to small spaces and off-grid operations. The onboard systems will provide an example of the types of decision making needed. Signature can manage with a small array of panels as we don’t have to face winter conditions.

Many of the household systems you will need in your tiny house can benefit from the marine orientation towards grid independence, compactness, low power consumption, DC systems, and water conservation. Take advantage of marine suppliers listed in the Resources section to find products and ideas for your design.

Energy Systems

Managing energy will be key in any living space, especially when operating off-grid or aiming to meet net-zero goals.

Propulsion

Signature operates mostly under sail with auxiliary propulsion from an electric drive that replaced the older Volvo diesel for the 2018 season. The 10 kW drive from Thunderstruck Motors connects to a 20 inch, 2 blade MaxProp through a 3:1 belt drive reduction system. Although only used part time, the electrical loads are similar to what you would need for a small heat pump. The propulsion system is the biggest load and operates at nominally 48 VDC, so that was chosen as the primary system voltage.

Other Loads

Most of Signature’s systems were installed before the propulsion was converted to electric, so they operate at the default 12 VDC level used in automotive systems. Other than household AC, the most common power supply level will be 12 VDC.

The largest current load besides the propulsion motor is the windlass, requiring high current at 12 VDC, but only for a short time when raising the anchor. The 12 VDC refrigeration requires much less current, but is switched on 24 hours a day, running the compressor about a third of the time, making it the largest consumer of total energy. Replacing original equipment incandescent lights with LED lighting has dramatically reduced the power consumption.

Energy Budget

For the 12 VDC system, these could be the loads on a typical day:

100 amp hours is a measure of energy, and to put it in customary energy units you also need the voltage. P=VI for DC current, so 100 amps at 12 volts is 1200 Watts. Thus, 100 amp hours at 12 volts is 1200 W hrs or 1.2 kWh, the unit usually used to measure household energy.

Primary Solar Power System

The primary system is nominally 48 VDC to match the propulsion load and includes multiple circuit breakers and a lightning suppressor to complete the system in addition to the primary components.

Two LG380N2T-A5 panels are mounted horizontally over the cockpit. These 72 cell, nominally 380 Watt panels from LG Electronics provide a high enough voltage to charge a 48 volt battery bank when 2 are connected in series.

The panels feed a MidNite Solar KID charge controller that provides maximum power point tracking (MPPT) to maximize the useful output from the panels in charging the batteries.

The battery bank is four Rolls S12-230AGM batteries wired in series to provide a 48 VDC supply with 230 amp hour total capacity. Rolls is a high quality supplier and AGMs provide a reasonable compromise on cost and maintenance in this application. This capacity translates to 11 kWh, far in excess of the household energy budget it supplies indirectly. The propulsion energy is actively managed to avoid running the batteries down and this capacity needs to be discounted because lead acid battery performance drops at high currents and because deep discharge significantly shortens battery life.

Backup Systems

An EU2000i Honda gasoline generator provides AC power to a Thunderstruck 25 Amp Charger for the 48V battery bank. With a little bit of sunshine this is enough to motor continuously at 4 knots without depleting the batteries.

Household DC Supply

A Battle Born LiFePO4 provides power to all of the 12 volt systems, separate from the propulsion power system. The battery can supply the occasional high current needs of the windlass.

Without the windlass load a DC-DC converter might be a better choice for the small household loads.

A Morningstar SunSaver MPPT charge controller is used to step down the supply from the 48 VDC bank to charge the household system. Although this is not the intended application, Morningstar confirmed it as a suitable application.

Cooking

All cooking is done with a non-pressurized methanol fuelled Origo 2 burner stove and a Magma propane BBQ.

Methanol is an alcohol that can be produced sustainably, although most of it is currently produced from natural gas and thus fossil carbon. Ethanol provides better performance, but is more difficult/expensive to obtain locally. Both are environmentally benign and dissolve in water making fires easy to extinguish.

Propane is fossil sourced, liquified petroleum gas (LPG) stored under pressure, gaseous and heavier than air at atmospheric pressure. This leads to pooling and explosion hazards, especially in the bilges of boats. Propane must be stored outdoors and proper safety systems installed when it is delivered to devices in enclosed spaces. It is significantly more dangerous than natural gas (methane) which is lighter than air and dissipates more rapidly if it leaks.

Water

Lake water is used untreated for washing and utility requirements, quantities unknown. City water is stored in a 60 litre aluminum tank for drinking and cooking. Both are supplied through flexible hose and on-demand 12 volt Jabsco pumps. The 60 litre tank is more than adequate for 2 people for two weeks, although there is also significant intake of packaged beverages.

Sewage

The toilet is a Jabsco Twist N’ Lock connected to a 90 litre polyethylene holding tank that requires a weekly pump-out with 2 people on board.