two solar topics for your feedback...

Re: two solar topics for your feedback...

alyaz wrote: »

1. People commenting that their pv system is raping the sun and that they were getting 'x' amps. My thinking is that amps, without knowing how many volts, means nothing? Do mppt controllers for example search for optimum voltage in order to make the most power?

"raping" the sun??? Typo?

Yes, without knowing Amp*Voltage -- We do not know the power (Watts). However, we do "guess" sometimes based on equipment (i.e., 12 volt or 24 volt inverter listed in signature). Also, time needs to be taken into account for almost all things we calculate here. Watt*Hours (and Amp*Hours at what voltage) is also a big question. Whether it is Hours of Sun, or hours of operation of an appliances at Amps/Watts--All is needed.

MPPT controllers do "search" for the optimum solar panel output voltage (which tends to be related to the present cell operation temperature). The software "sweeps" the panel (by changing the current drawn from the solar panel) and gets a list of Volts*Amps... The Controller then looks for the Vmp*Imp=Pmp for that point in time and uses that Vmp number for the next few minutes (before the next sweep) by having the computer vary the current drawn from the panel/array to keep Vmp at "optimum" voltage.

MPPT controllers are not magic. They will not get more power from a panel than it is capable of supplying. Unless you are in a very cold region (sub freezing and below), getting ~10-15% more harvested power vs a PWM controller with a "matched set of panels" (i.e., ~17.5 volt Vmp panels charging a 12 volt battery bank) is about the best you can expect.

MPPT controller are nice though--They allow you to use Grid Tie designed solar panels (which are not Vmp~17.5 volts) and have the controller "match" the solar array high voltage/low current and efficiently down convert to low voltage/high current for the battery bank. This allows the use of large format (>100 watt panels--which are usually less expensive) for off grid solar power systems. Also--The high voltage Vmp-array allows the use of smaller AWG copper wire and/or send power longer distances for reasonable cost.

2. People/installers who hook up different spec panels and/or panels in different locations to the same controller. My thinking is that panels, location, shading, sun needs to be within 5% or else you are asking for problems such as burning cells out in your panels and/or robbing yourself of maximum performance. ???

The MPPT optimizes the Vmp for that panel's (or array's) average cell temperature. If you have arrays with different orientations/exposure to wind/etc., then the optimization of the charge controller can be compromised.

I was never sure that (for example) east/west panels could not share a single MPPT controller as the panels would be roughly similar temperatures, and when the sun was illuminating only one array, the other's output would not matter much anyway.

However, Solar Guppy (who did a lot of design and testing of solar charge controllers) said that he would always recommend separate MPPT charge controllers for different solar array orientations--So there you go.

-Bill