Tracker vs. MPPT controller

1 Posts
Feb 19, 2009 10:52 am
Tracker vs. MPPT controller

I've seen allot of % of performance increase figures for MPPT controllers (particularly in cold weather) but have yet to find any offered for trackers. Does anybody have an opinion on where the extra $ would be better spent?   

Sorry if this has already been discussed but I see no way to search this forum. But it has a spell checker!
578 Posts
Feb 19, 2009 11:05 am
Re: Tracker vs. MPPT controller

the best way to compare this is to look at tmy data for the area the array is to be implemented.

it should have the sun hours listed at different latitude tilts as well as have data for single and dual axis trackers.

you can find that data online, or in the back of this book.

by memory i think the 1 axis tracker change from fixed is a 30% increase.  what the owner has to weigh is

a.  is it cheaper to buy the same percentage increase in performance by purchasing more pv or a tracker

b.  am i willing to take something solid state and introduce movement and the potential for maintenance

c.  is it just so cool that a and b dont matter


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33 Posts
Feb 22, 2009 05:17 am
Re: Tracker vs. MPPT controller

Trackers generally give you more sun hours. The reflective quality of the solar panels substrate make them not want to absorb photons that hit it at high angles. So on a fixed panel installation you generally set it angles in the middle of the pathway between the winter sun and the summer sun. That covers one angle of the panel The other angle is that fixed panels just don't start working until the sun reaches a fairly high in the sky attitude. So you generally calculate 5 sun hours for a fixed panel as they produce power from 10 am to 3pm. You can get 7 to 8 sun hours with a tracker and that increases your yeild significantly if it weren't for one gotcha. Cloudiness is more prone to occur in morning and evening as the sun is better able to "break" up clouds with solar power during the time periods a fixed panel produces power. So cloudiness of your area has a large affect on whether a tracker is a good investment.

MPPT's take advantage of a peculiarity of solar panels current flows. Solar panels have to be built with alot of excess voltage to be able to function in less than ideal circumstances. That excess voltage is is simply wasted or thrown away power once it's connected to a battery system. If you take a 100 watt panel and it gives 100 watts at 18 volts and you attach it to a battery system at 12.5 volts you get 12.5/18x100 watts or 69.4 watts.The losses aren't always this extreme but there are situations where they can be even more extreme like if your battery system gets run down to 11.2 volts and it takes FOREVER for your array to finally bring it up to a voltage that allows it to efficiently fill up the rest.

Use of a MPPT solar controller is always firstmost and foremost the best way to gain more power from a panel as well as the easiest. If you are space constrained or want to minimize the panels to keep trees etc then adding a tracker can give you a decent boost to your panels but that boost will be magnofied many more times by having a MPPT controller in the first place.
« Last Edit: Feb 22, 2009 05:19 am by Jonathan Winters »

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