I am wondering how much energy we use from nbArianrhod’s batteries (3 x 110Ah) per day; I know this number will change over the course of a year; and that most of our peek energy requirements come from gas rather than electricity; however on average we still run the engine about two hours every day to feed the batteries. The things we do power electronically are:

• Water Pump
• Lighting
• Radio
• Angry Technology³
• Laptops⁴

So using the following calculation from [Note Narrowboatworld forum: Solar Panels]:

Ergo work on £1.75 an hour to run the engine; So with the saving on not running the engine for 2 hours a day, and even adjusting for a bit for ‘over estimating’ the numbers come out at about £3 a day, or £21 a week. James and Amy have 136W of installed capacity on nbLuckyDuck[notenbLucky Duck - Any Questions v.6] mounted directly to the roof.

Given these bits of information I have been looking for about 100-200W installed capacity; Looking around for information on Solar Panels; I have found the following information out about panels; There are three main types of Traditional panels; Monocrystalline, Amorphous and Polycrystalline

• Polycrystalline Solar Panels – Low CostThese make up the lowest cost solar panels, This is in part because they are the most established of the three main silicone technologies, offering a compromise between technical performance, physical size and price. Smaller than amorphous panels, but larger than mono-crystalline; less efficient than mono, but more efficient than amorphous; polycrystalline panels are a balance between the two.
• Monocrystalline Solar Panels – ExpensiveMore expensive than poly-crystalline, but also more efficient that poly as well; they work out at an efficiency of about 21.5%, making them about 30-50% smaller than equivalent capacity panels in other technologies. They are also are far less affected by changes in ambient temperature and sunlight intensity.
• Amorphous Solar PanelsAmorphous solar cells are a special type of solar cell, and their unique microscopic manufacturing process makes them highly versatile. The silicon used in amorphous solar panels is not very crystalline or rigid in nature.These solar cells represent the future of solar panel technology and despite their utility they aren’t all that difficult or expensive to manufacture, however due to still being a specialist product with limited production runs the cost is still quite high.These solar cells are typically composed of a layer of conductive silicon and a solid plate of glass. The amorphous solar panel is divided into many sections, defined by separations in N and P layers of the silicon substrate used in the solar panel. These sections are the individual solar cells.

Looking On-line for cheap panels; I came across these 100 Watt at 12V Solar Panel PV Monocrystalline, available from ebay for £119 (£119 + £8pp):

• Nominal power: 100 W
• MPP⁵ volatage: 18.5V
• MPP current: 4.81 A
• open clamp voltage: 22,18 V
• Short circuit current: 5.95 A
• 36 mono-crystalline cells in the module
• Dimensions: 1205mm x 545mm x 35mm
• Weight: ~8 kg

So with one of these; assuming that it cuts our engine usage dramatically it should pay for itself in about two months; and with two of them we should be looking at a better return.