by Gavin Sorrell

Solar Charging  

  By now you will have gained the impression that I am keen on having batteries maintained at 100% level. If you keep your boat at home or on a marina, you will have access to 240 volt power for battery charging. On a mooring, it’s a different story. 
  Your only option is to maintain the batteries by solar or wind power – unless you can arrange an extension lead many kilometres long. Solar tends to be the preferred option especially to keep the bilge pump operational. 
  Solar panels have two different basic structures. The most common are crystalline panels (the sparkly ones), either mono or polycrystalline. Less common are amorphous panels (the grey ones). 
  Amorphous panels have the following advantages: cheaper than crystalline, they wake up earlier in the day and go to sleep later, perform better in high temperatures, are shade tolerant and can usually withstand more abuse. 
  The big drawback is that they are less efficient and therefore require more real estate than crystalline for the same power output. There is also a perception that because most amorphous panels emanate from Asia and are priced accordingly, they are inferior to crystalline panels. 
  Amorphous panels do tend to lose power over their lifetime while crystalline tends to be more stable. 
  My experience is that I have had a 32-watt Unisolar flexible amorphous panel beavering away on my boat for ten years now, with no discernable degradation in performance. These are great panels for boats but unfortunately are temporarily unavailable. 
  About now, solar power articles usually delve into the mathematics of appliance ratings, battery capacity, amphour calculations, days of autonomy and system efficiencies. If maths isn’t your forte, then some basic assumptions will suffice. 
  Firstly, if your aim is to keep the batteries topped up with intermittent use of perhaps the bilge pump and lighting, then a solar panel rated at 10% minimum of the battery capacity will suffice. 
  A 10-watt panel will be enough to trickle charge a 100Ah battery and keep it at 100%. Make sure the panel has a direct path to sunlight and is not obscured by rails or booms. Place the panel flat if the boat moves around, or at an angle if the position of the boat is fixed, aiming it toward north and in Sydney, at an angle of 35 degrees to horizontal. 
  A regulator is not mandatory for this 10% ratio, however at only $30, is desirable. Without a regulator, connect a blocking diode in series with the positive lead to prevent current feedback to the panel at night. The grey band on the diode goes towards the battery. Also fuse the solar panel. For larger systems, or where significant loads such as refrigeration must be maintained by solar power, calculations must be made. A complete system analysis can be obtained at nominal cost. Otherwise, simply mount the biggest panel you can afford that will fit on the lid of your boat. 
  But don’t expect a 60-watt panel to keep the beer cold. Invest in upgraded wiring and regulator and possibly a battery monitor. Then you can observe the number of charge or discharge amphours, percentage of charge left in the battery and predicted charge or discharge times. 
  If there is insufficient solar input, add another panel or if you haven’t enough space, perhaps a portable charger to top up the batteries or run the alternator for a while. 
  Don’t use one of the cheap 240 volt petrol generators with a DC output. The charging output is technically known as ‘bugger-all’. 
  The thing to keep in mind is that the sun shines a fair bit in Australia. Its output is free (although can come at some cost). Why not use it? Most boaties know this, especially yachties who tend to favour free things. 
  Pity Australia seems incapable of formulating a long term strategy for the use of solar power for mass electricity generation. The industry is fragmented and indecisive. Incentives are all short term and politically motivated. The take-up has been pathetic and now the manufacturing industry have packed their bags. Maybe we can make a difference.  
  Next month: Solar regulation

*Gavin Sorrell works in collaboration with Aquavolt Electric Boat Parts. Tel: 02 9417 8455 www.aquavolt.com.au