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Message started by William of Orange on May 11th, 2008 at 10:48pm

Title: Spending dosh to save it ! MPPT Charge Controllers
Post by William of Orange on May 11th, 2008 at 10:48pm
Every now and again new technology emerges that can save you money. Now MPPT (Maximum Power Point Tracking) Solar Charge Controllers have been around for 3 or 4 years now, the most popular being the Outback MX-60. These charge controllers are not cheap in Spain around the 800-900 euro mark, but they can be considered a shrewd purchase in specific circumstances. Anybody who has or is considering fitting a PV Solar array in excess of 600 watts will find that the addition of such a MPPT solar charge controller will be a smart move over adding another panel or two.

There are two main features of the Outback MX-60 and the new Xantrex XW60-150 and also the Apollo T80 that make them a smart buy.Note not all MPPT units have both these features so be carefull, but the three listed do . Do not confuse the tracking part of MPPT with solar arrays that physically follow the sun. These MPPT units work with fixed arrays


Is the power harvest. these MPPT units can achieve over normal standard Pulse Width Modulation Controllers (PWM). The MPPT units have the ability to utilise the higher PV voltages created on colder and cloudy days, (see my previous post) capture this extra voltage and convert it in to high amperage or charge and put the extra back into your batteries. On a cool crisp winters day a MPPT charge controller can harvest up to 30% more power that a standard PWM unit. Cloudy days when the solar panels cool when the sun is covered also can see 30% extra harvest of power (volts x amps = watts) Even on sunny warm days a MPPT will harvest between 5/10 % more power. But when you need solar recharge power the most in the colder shorter sun hours of winter or spasmodic cloudy days the MPPT comes up trumps I have 3 charge controllers 2 x PWM and an Xantrex XW60-150 I have two identical arrays wired into each controller one the MPPT the other plain PWM and the figures are impressive, in my case I see a continuous 10 % net gain at all times and over 30% power yield on colder and or cloudy days. I have seen a peak output of 1360 watts from my 1200 watt array (STC) when the most Ive seen on my normall PWM controller is 1020 watts. Very impressive.

Now lets say for ease you have 5 x 200 w panels and you want more power. A new 200 watt panel will set you back 800+ euros,makes sense to hang fire on the panel and upgrade you charge controller first.

If your starting from scratch a new 60 amp MPPT unit will cost at most 900 euros. A similar Quality 60 amp PWM Solar Charge Controller with display will cost say 350 euros .
550 euros extra but a minimum power yield of five percent a maximum of 30%, especially in Winter, thus after about 600 watts of solar panels it pays to buy a MPPT controller b4 another panel.


If the power yield isnt enough there is a second asset of these MPPT charge controllers that Ive named which can save you money or give you more flexability or both ! On a new install or upgrade. The above named MPPT units all have the facility of voltage boost buck, in which the solar array can be wired to a higher nominal voltage than your battery bank. You could for instance wire you solar panels to 48volts and let the MPPT charge controller charge your 24 volt battery bank by converting the extra voltage to the correct battery bank voltage just like it does on cold and cloudy days. Why would you do this I hear you ask ? Well by wiring your solar array to a higher voltage less current is shifted so thinner cheaper wiring can be utilised from the array to the controller, without loosing system efficiency the MPPT controller then bucks the voltage and boosts the currentl to charge your batteries as fast and efficient as possible. This boost buck facility could save you hundreds of euros if your panels are any distance frm your batteries.

Put the two together and above 600 watts of PV more that 20-30 ft between panels and controller in becomes a no brainer......WoO HTH someone

PS Ive kept the function of MPPT as simple as possible, it is a lot more involved than Ive explained here, but trust me it works Im keeping it as light as possible because Im aware that Nobrot and others may take to the bottle in a darkened room when the physics and electrons start bumping into each other ! or is that after taking to the bottle ? ;D

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