Hi Jonny,
The very first step is to conserve. Replace the most used incandescent lighting with inexpensive led's. (ebay?)
Solar costs only once. Currently the "toll" to get "on board" is running around $3 per watt on a DIY installation. Rule of thumb on size is between 150 and 60 watts of panels per 100 amp-hours of storage. It is a bell curve, so a small battery bank requires more wattage than a medium size bank.
Here is a simple flow chart.
Budget-->Energy Audit-->Battery bank size-->number of watts-->PWM or MPPT.
Here is a link to the rather special spreadsheet which includes an energy audit that N8GS has created to help size solar battery charging systems!
Solar Spread Sheet N8GSFor a nice explanation of solar, try this link:
Golden rules of solar
