Solar Pumps and Solar Circulators
Solar pumps are used in open loop systems to raise water to a specified height and solar circulators are used in closed loop systems to circulate a fluid for the purpose of exchanging heat. 12VDC circulators powered by photovoltaic panels to circulate solar heated water through closed loop systems are often called solar pumps, but almost any pump could be used to harvest the sun's heat. As long as a pump can handle high temperatures over an extended period of time it may be used for solar heating applications. The main things to consider when purchasing a pump or circulator involve an understanding of head pressure, flow rate and energy consumption. The flow rate for heat collection should be between(.02 GPM and .04 GPM) /ft2 of the solar collector surface. Pumps normally have high head pressure and circulators normally have high flow rates, but pumps may be used to circulate water and circulators may be used to pump water.
I am using a Taco 007 as a pump for an open loop solar heated drainback system although the 007 is commonly used to circulate water inside home heating system. This pump works for me because the water from the storage drum only needs to be raised a height of 6' and the return tube has a diameter of .75" so flow restriction is also minimized. Click on the above illustration to see an animation of a centrifugal pump in action.
The performance chart below demonstrates the relation between flow rate and total head pressure for Taco pumps (003 to 013)
Notice that the the Taco 007 only has a total flow rate of 5 GPM at a height of 9'. Also note that the actual flow at 6' is only about 3 GPM. This is because the total flow head is the sum of the flow head head restriction and the flow height. To clarify this concept click on above illustration...
Great! Now that you understand how pumps work Let's now take a look at some popular "solar pumps" such as the March, the Hartell and the El Sid.
These small pumps work well with small PV powered solar hot water systems. A 10 or 20 Watt PV 12VDC power supply may be all you need to power these durable long lasting pumps, but be forewarned these little guys cost between $200 and $400 each. If you're a do it yourselfer and you're still in the experimental stages of solar heating you may want to check out some of the less expensive alternatives below. These are just a few basic ideas and a few links to help you get started on a search for a pump that's right for your solar heating or solar hot water system.
SIZING A PUMP