An all-electric narrowboat needs considerably more than a list of appliances and a large battery bank.<\/p>\n
Priscilla\u2019s electrical system must support two very different demands:<\/p>\n
Both ultimately draw from the same finite supply, but propulsion can consume far more energy than the domestic systems. The design must therefore consider energy consumption, peak power, charging capacity, seasonal generation and operational resilience together.<\/p>\n
Two measurements are central to a power audit:<\/p>\n
A 2,000W induction hob operating for 15 minutes uses 500Wh:<\/p>\n
2,000W \u00d7 0.25h = 500Wh<\/strong><\/p>\n This distinction matters because the inverter, cabling and protective devices must cope with peak power, while the battery bank must provide sufficient stored energy. A system could have enough battery capacity for the day but still be unable to start an appliance because the inverter or cabling cannot safely deliver its peak demand.<\/p>\n Every planned electrical consumer should be recorded, including equipment that runs continuously, intermittently or only in emergencies.<\/p>\n Small continuous loads should not be overlooked. A device drawing only 10W consumes 240Wh if it operates throughout the day.<\/p>\n For each item, the audit should record:<\/p>\n Where only current is given, power can be estimated using W = V \u00d7 A<\/strong>. For example, a 24V pump drawing 4A uses approximately 96W.<\/p>\n For AC equipment, the manufacturer\u2019s measured energy-consumption information is preferable to a simple calculation from the fuse rating. A 13A plug does not mean an appliance continuously consumes 13A.<\/p>\n A 50W fridge running for 24 hours would consume 1,200Wh each day only if its compressor operated continuously. Refrigerators cycle according to their insulation, thermostat setting, ambient temperature, ventilation and frequency of use. A better estimate would come from the manufacturer\u2019s annual energy figure or direct measurement.<\/p>\n The same principle applies to many devices:<\/p>\n The audit should use realistic daily energy rather than multiplying every appliance\u2019s maximum rating by the time it remains switched on.<\/p>\n The figures below are illustrative rather than a proposed specification.<\/p>\n This example produces a domestic requirement of approximately 6.7kWh per day before conversion losses<\/strong>. Actual consumption could be considerably lower or higher. Electric water heating, space heating and intensive video editing would have a particularly significant effect.<\/p>\n A 230V appliance supplied from the batteries requires an inverter. If AC appliances require 4kWh and the inverter is 90% efficient at the relevant loads, the battery must supply approximately 4kWh \u00f7 0.90 = 4.44kWh<\/strong>.<\/p>\n Only the AC portion of the audit should normally receive this adjustment. Applying an inverter-loss allowance to equipment supplied directly from DC would overstate its consumption. Inverter efficiency also varies with load, and the inverter itself may consume energy whenever it remains active.<\/p>\n Priscilla may therefore benefit from:<\/p>\n Daily energy alone does not determine the required inverter capacity. An induction hob, kettle, combination oven, washing-machine heater and immersion heater could together demand 8.5kW before other equipment.<\/p>\n Designing for every appliance to run simultaneously could result in an unnecessarily large and expensive system. Designing without considering simultaneous use could cause overloads. Priscilla should therefore have a deliberate load-management strategy, potentially pausing the immersion heater or preventing selected appliances from operating together.<\/p>\n The audit should identify maximum theoretical demand, credible simultaneous demand, short-duration starting loads, continuous and surge inverter ratings, battery discharge-current limits, cable and protective-device capacity, and loads that can be shed automatically.<\/p>\n Propulsion must not be treated as another domestic appliance. Its energy consumption depends upon boat length and displacement, propeller and drivetrain efficiency, cruising speed, water depth and channel width, wind, river flow, manoeuvring, hull condition and bow-thruster use.<\/p>\n The relationship between speed and required power is not linear. A modest increase in cruising speed can require a disproportionately large increase in propulsion power.<\/p>\n A motor drawing an average of 4kW for six hours would consume 24kWh; at 8kW, the same cruising period would require 48kWh. Either substantially exceeds the illustrative domestic requirement.<\/p>\n The propulsion audit should use modelling and measured evidence from comparable boats. It should include low-speed and typical canal cruising, extended river passages, strong currents or adverse wind, manoeuvring and locking, emergency reserve, stationary days, charging while cruising and equipment-failure scenarios.<\/p>\n Battery capacity is often quoted in amp-hours, but that figure is meaningful only with voltage. For example, 200Ah at 12V is 2.4kWh, while 200Ah at 48V is 9.6kWh.<\/p>\n The correct conversion is Ah = Wh \u00f7 V<\/strong>. However, kilowatt-hours provide a clearer common measure for domestic loads, propulsion, batteries and charging.<\/p>\n A battery bank\u2019s advertised capacity is not necessarily the amount available for routine use. Allowances may be required for permitted depth of discharge, battery-management-system limits, ageing, low-temperature performance, conversion losses, cell balancing and emergency reserve.<\/p>\n If Priscilla requires 30kWh between charging opportunities and only 80% of nominal capacity is allocated to normal operation, the bank would need at least 30kWh \u00f7 0.80 = 37.5kWh<\/strong>, before any further design allowance.<\/p>\n Providing several days without charging sounds reassuring, but it can create an exceptionally large, heavy and expensive battery bank. If domestic consumption is 7kWh per day and propulsion averages 25kWh per cruising day, two days of autonomy would require 64kWh before reserve and system losses; three days would require 96kWh.<\/p>\n The better question is: What operating pattern must Priscilla sustain, and what reliable charging opportunities will be available?<\/strong><\/p>\n Different scenarios include stationary days with domestic loads only, canal cruising followed by overnight charging, consecutive cruising days with solar assistance, demanding river passages with a protected reserve, winter occupation with little solar generation and extended periods away from shore power.<\/p>\n Lithium batteries can provide high usable capacity, good charging efficiency and substantial power from comparatively limited space and weight. They also require a properly engineered installation.<\/p>\n The Boat Safety Scheme\u2019s lithium-battery guidance<\/a> advises the use of marine-suitable components and competent installation to appropriate industry standards.<\/p>\n The design should cover battery chemistry, battery management, contactors and emergency isolation, overcurrent protection, short-circuit capability, temperature monitoring, low-temperature charging, compartment design, fire detection, ventilation where required, mechanical restraint, water protection, system communication and safe loss-of-power behaviour.<\/p>\n Solar can make an important contribution to domestic energy and may extend cruising range, but roof-mounted panels are unlikely to provide guaranteed propulsion energy in every season.<\/p>\n A simplified estimate is: daily generation = array rating \u00d7 equivalent sun hours \u00d7 system efficiency<\/strong>. A 2kW array receiving four equivalent full-sun hours at 80% overall efficiency might produce 6.4kWh, but this is not a reliable year-round daily output.<\/p>\n Production is affected by season, latitude, cloud, panel temperature, shading, orientation, dirt, system losses, available battery capacity, tunnels and covered moorings. Solar generation varies with weather and time, so storage is needed when generation and demand occur at different times, as explained by the US Department of Energy<\/a>.<\/p>\n Priscilla\u2019s design should be tested against poor winter generation, not merely an attractive summer average.<\/p>\n Shore power could provide the most dependable means of fully recharging a large battery bank, where a suitable supply is available.<\/p>\nBegin with an equipment schedule<\/h2>\n
Domestic services<\/h3>\n
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Boat systems<\/h3>\n
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Occasional or exceptional loads<\/h3>\n
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Record the right information<\/h2>\n
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Use realistic operating times<\/h2>\n
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A worked domestic example<\/h2>\n
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\n \nEquipment<\/th>\n Typical power<\/th>\n Daily use<\/th>\n Estimated energy<\/th>\n<\/tr>\n<\/thead>\n \n Fridge\/freezer<\/td>\n Variable<\/td>\n \u2014<\/td>\n 700Wh<\/td>\n<\/tr>\n \n LED lighting<\/td>\n 40W<\/td>\n 5 hours<\/td>\n 200Wh<\/td>\n<\/tr>\n \n Water pumps<\/td>\n 100W<\/td>\n 0.5 hours<\/td>\n 50Wh<\/td>\n<\/tr>\n \n Induction cooking<\/td>\n 1,500W average<\/td>\n 1 hour<\/td>\n 1,500Wh<\/td>\n<\/tr>\n \n Combination oven<\/td>\n 1,200W<\/td>\n 0.4 hours<\/td>\n 480Wh<\/td>\n<\/tr>\n \n Kettle<\/td>\n 2,000W<\/td>\n 0.15 hours<\/td>\n 300Wh<\/td>\n<\/tr>\n \n Washing machine<\/td>\n Programme total<\/td>\n \u2014<\/td>\n 700Wh<\/td>\n<\/tr>\n \n Television<\/td>\n 60W<\/td>\n 3 hours<\/td>\n 180Wh<\/td>\n<\/tr>\n \n Laptops and editing<\/td>\n 200W<\/td>\n 5 hours<\/td>\n 1,000Wh<\/td>\n<\/tr>\n \n Phones, cameras and accessories<\/td>\n \u2014<\/td>\n \u2014<\/td>\n 300Wh<\/td>\n<\/tr>\n \n Router and monitoring<\/td>\n 25W<\/td>\n 24 hours<\/td>\n 600Wh<\/td>\n<\/tr>\n \n Heating pumps and controls<\/td>\n \u2014<\/td>\n \u2014<\/td>\n 350Wh<\/td>\n<\/tr>\n \n Miscellaneous and standby loads<\/td>\n \u2014<\/td>\n \u2014<\/td>\n 300Wh<\/td>\n<\/tr>\n \n Estimated daily total<\/strong><\/td>\n <\/td>\n <\/td>\n 6,660Wh<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Account for inverter losses correctly<\/h2>\n
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Peak demand matters<\/h2>\n
Keep propulsion separate<\/h2>\n
Battery capacity should be expressed in kWh<\/h2>\n
Nominal capacity is not usable capacity<\/h2>\n
Two or three days of autonomy may be unrealistic<\/h2>\n
Battery chemistry and safety<\/h2>\n
Solar generation<\/h2>\n
Shore power<\/h2>\n