What I am looking to do is use either my Arduino Diecimila or Mega to control a system where a Solar panel would supply the power to a low wattage DC water proof pump to allow water to circulate in a pond when the sun is out. When it is night time I'd like the battery pack that would have also charged during the day to supply the pump with a lower amount of power so it at least allows the water to circulate at night.
I know I would use a photosensor to allow me to know if it was light out or dark (or over cast) so we can switch over to the battery.
What I am not sure is the following:
Solar Panel
Low Wattage DC water proof Pump
What rechargeable batteries I should use, be it quite a few 1.2V standard batteries, or 3.6V 2000mAh batteries which would offer me longer lasting juice.
Looking forward to whatever suggestions and follow up questions people may have.
Its not possible to answer any of your questions without knowing how much water you want to circulate.
How big does the pump have to be , in terms of water flow . litres per minute.
Does the pump have to lift water vertically?
Well it would pump the water up to an eventual waterfall, so it wouldn't necessarily having to be a straight 90 degrees up, it could be a 30 or 45 degree angle until it gets to the top of the waterfall then let gravity do the rest.
I honestly have no idea how much water flow I am looking for, it is a relatively small backyard pond. Probably up to 6 litres/minute though I could probably get away with half or a quarter of that as long as enough water can fall down the waterfall without any break in the flow.
The energy needed to pump water is determined by the flow rate , ie how many litres per minute , and the head, ie
how far vertically the water has to be pumped.
Unless these values are known , its impossible to determine how much power you will have to generate with the Solar Panel.
I strongly support what @cjdelphi recommended, with one caveat - the voltage and current may be displayed on the packaging and a local suitable garden centre might have operating pumps so you could decide what water volume you need as well as getting the voltage and current data for free.
If you live in a country with plenty of sunshine and if you want the pump to run through the hours of darkness you will need a solar panel that can produce perhaps 3 to 4 times the consumption of the pump and a battery with a capacity at least 3 times the amp-hrs draw of the pump during the longest night.
If you live somewhere like the UK where the sun is a fleeting visitor it would probably be best to plan on the pump only working intermittently unless you either have a very large solar panel and very large batteries or are prepared to use mains power to keep the battery topped up.
