|
Home > Archive > Electrical Engineering > May 2006 > Efficient DC-DC converter for solar conversion?
You are viewing an archived Text-only version of the thread.
To view this thread in it's original format and/or if you want to reply to
this thread please [click here]
| Author |
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
here.
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.
Thanks,
Ed
| |
|
|
| Bill Kaszeta / Photovoltaic Resources 2006-05-11, 11:21 pm |
| On Thu, 11 May 2006 22:49:12 GMT, Ed <ed@NOSPAMmicra.org.uk> wrote:
>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
>here.
>
>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.
>
>Thanks,
>
>Ed
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
bill@pvri-removethis.biz
| |
| daestrom 2006-05-12, 3:21 pm |
|
"Ed" <ed@NOSPAMmicra.org.uk> wrote in message
news:IbP8g.18743$mX1.16729@newsfe2-gui.ntli.net...
> 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 here.
>
> 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.
>
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
daestrom
|
|
|
|
|