Efficient DC-DC converter for solar conversion?

Hi all,
I have an 85W solar panel. Its maximum Pout is at 18volts 18V@4.7A. At
the moment I have this connected straight to a battery.
The max charge currents I am getting is about 4.7-5A @ approx
12.5-13.5v, so 65W if I'm lucky. Basically I'm wasting a potential 20w
I had a thought that if I could make a switcher or some kind of DC-DC
converter that was able to operate on 18v in, drop this to 14v out I
would make much better use of the power generated by this panel.
It seems such a waste to connect this directly to the battery where I am
getting only around 75% of energy available. I may also be getting
another panel, in which case perhaps a 36v to 14v DC-DC converter would
possibly work better? or if not ill just run both in parallel/
Any help or ideas would be VERY welcome.
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Further to my first post would something like this do the job do you think?
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The Max Power voltage of 18 volts is at 25C cell temperature. In full sun the Max Power voltage decreases by about 0.0077 volts per degree C. A 50-60 C increase in temperature in full sun in hot weather can thus decrease the Max Power voltage by 3.5-4.0 volts. Then there is a voltage drop in wiring, controls, diodes, etc. The Max Power voltage also decreases in less than full sun. That is why most solar modules have 36 series cells and a Max Power voltage of 17-18 volts.
A device called a maximum power tracker is a solar charge regulator that includes a dc/dc conversion so as to always operate the PV modules at close to their optimum voltage. You have to balance the extra cost and some efficiency loss with the extra output in cooler weather. If you have only one panel, the cost increase is not usually justified. Bill Kaszeta Photovoltaic Resources Int'l Tempe Arizona USA snipped-for-privacy@pvri-removethis.biz
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Bill Kaszeta / Photovoltaic Resources
You have the right idea. Look for MPPT chargers. This is basically the idea they use. By controlling the voltage/current on the panel side of the circuit to maintain maximum power output, then converting it to the voltage/current needed by batteries/inverters, it improves the total energy throughput of the system.
cross-posted to alt.solar.photovoltaic
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