Help required in guidance of dc-dc converter

[curiousmech]

GREETINGS,
I AM EE STUDENT AND WHILE STUDYING ABOUT DC-DC CONVERTER I CAME ACROSS THIS FORUM, I HAVE SOME CONFUSIONS REGARDING DC/DC CONVERTER
IF THERE ARE 4 SOLAR PANEL EACH OF 250WATTS WITH RATINGS MENTIONED IN THE PICTURE, AND A BATTERY BANK OF 24V 200AH SO ARE MY FOLLOWING CALCULATIONS ARE CORRECT::
SOLAR PANEL TOTAL POWER= 250W*4=1000W
BATTERY BANK POWER = 24*200= 4800W



SO NOW I WOULD REQUIRE AN MPPT OF LETS SAY
1000(PV CELL POWER)/24(V OF BATTERY)= 41 AMPERES

THE QUERY IS I HAVE TO MAKE A DC-DC CONVERTER TO CONTROL THE ABOVE STATED CURRENT AND GET THE MPPT WORKING FOR MAX EFFICIENCY?

REGARDS

[Naptown]

Your calculations are correct.
Two things however
We really don't design equipment like controllers here this is more of an end user forum designed for homeowners.
Second if you use flooded lead acid batteries you don't have enough battery to absorb the current your controller will put out.
You would need to either increase battery size, reduce panel wattage or switch to an AGM type battery.

[inetdog]

GREETINGS,
I AM EE STUDENT AND WHILE STUDYING ABOUT DC-DC CONVERTER I CAME ACROSS THIS FORUM, I HAVE SOME CONFUSIONS REGARDING DC/DC CONVERTER
IF THERE ARE 4 SOLAR PANEL EACH OF 250WATTS WITH RATINGS MENTIONED IN THE PICTURE, AND A BATTERY BANK OF 24V 200AH SO ARE MY FOLLOWING CALCULATIONS ARE CORRECT::
SOLAR PANEL TOTAL POWER= 250W*4=1000W
BATTERY BANK POWER = 24*200= 4800W



SO NOW I WOULD REQUIRE AN MPPT OF LETS SAY
1000(PV CELL POWER)/24(V OF BATTERY)= 41 AMPERES

THE QUERY IS I HAVE TO MAKE A DC-DC CONVERTER TO CONTROL THE ABOVE STATED CURRENT AND GET THE MPPT WORKING FOR MAX EFFICIENCY?

REGARDS

There is one thing that you are missing, and it is a common error but what which as a student you need to avoid.

Solar panels are rated by power, the rate at which they deliver energy when in full sunlight. So in full sun (1000W/meter² incident light energy) your panels generate 1000 watts, or one kilowatt. Over the course of one hour, they will produce 1000 watt-hours (1kWh).
Batteries on the other hand are rated mainly by the amount of energy which they store. So the batteries store 24V x 200AH = 4800 watt hours or 4.8kWh.

Looking at it this way, the solar panels generate enough power to fully charge that battery in as little as 5 hours. This is too fast a charging rate for flooded lead-acid batteries, but may be OK for other battery types.

The design of the DC to DC convertor must support a nearly constant output voltage, but has to be able to adjust the input current to get the maximum power from the panels. This, in effect, means that the ratio of input voltage to input current (effective input resistance) must be variable and controlled by the MPPT algorithm.

[Mike90250]

Designing a DC-DC converter for "stable" voltage is very simple, and there are hundreds of off-the-shelf commercial converters to do that.

BUT, PV panels are a Current Source, and subject to variable power (clouds, bird shadows) and their voltage will collapse if they are loaded too much. MPPT controllers sample the source regularly, and trim their loading to continuously get the most power out of them. Then that output feeds a pre-programed battery charger which provides optimal battery charging for the system. That's an awful lot of work to do on your own, when there are several good, well engineered products in the marketplace.
Mfgs : Rogue Power, Midnight Solar, Morningstar, Xantrex/Conext/Schneider-Electric, Outback are some.

[Sunking]

One little problem you have. Solar panels are current sources, and your design is for voltage sources.

Go back to the drawing board. You failed the class objective.

[curiousmech]

Designing a DC-DC converter for "stable" voltage is very simple, and there are hundreds of off-the-shelf commercial converters to do that.

BUT, PV panels are a Current Source, and subject to variable power (clouds, bird shadows) and their voltage will collapse if they are loaded too much. MPPT controllers sample the source regularly, and trim their loading to continuously get the most power out of them. Then that output feeds a pre-programed battery charger which provides optimal battery charging for the system. That's an awful lot of work to do on your own, when there are several good, well engineered products in the marketplace.
Mfgs : Rogue Power, Midnight Solar, Morningstar, Xantrex/Conext/Schneider-Electric, Outback are some.

One little problem you have. Solar panels are current sources, and your design is for voltage sources.

Go back to the drawing board. You failed the class objective.

well i believe u might be correct in saying PV panel working as a CURRENT SOURCE but i couldnt find any relevant information saying PV panel to be current source, can you post some reference links for that.

[curiousmech]

There is one thing that you are missing, and it is a common error but what which as a student you need to avoid.

Solar panels are rated by power, the rate at which they deliver energy when in full sunlight. So in full sun (1000W/meter² incident light energy) your panels generate 1000 watts, or one kilowatt. Over the course of one hour, they will produce 1000 watt-hours (1kWh).
Batteries on the other hand are rated mainly by the amount of energy which they store. So the batteries store 24V x 200AH = 4800 watt hours or 4.8kWh.

Looking at it this way, the solar panels generate enough power to fully charge that battery in as little as 5 hours. This is too fast a charging rate for flooded lead-acid batteries, but may be OK for other battery types.

The design of the DC to DC convertor must support a nearly constant output voltage, but has to be able to adjust the input current to get the maximum power from the panels. This, in effect, means that the ratio of input voltage to input current (effective input resistance) must be variable and controlled by the MPPT algorithm.

what do you mean by not good for lead acid battery? i cannot change the irradiance point 0f 1000watt/m^2 it will kill the mppt technique

[Sunking]

well i believe u might be correct in saying PV panel working as a CURRENT SOURCE but i couldnt find any relevant information saying PV panel to be current source, can you post some reference links for that.

Look at any panel IR curves will tell you that. A panel is a current source from MPP down to ISC. A panel is a voltage source from above MPP to Voc. It is a knee curve. Horizontal is voltage source, and vertical is current source. The knee is MPP

[inetdog]

well i believe u might be correct in saying PV panel working as a CURRENT SOURCE but i couldnt find any relevant information saying PV panel to be current source, can you post some reference links for that.

Just look at the I versus V curves of typical solar PV cells. That will show you clearly, if you know how to interpret it, that for a fixed light levelthe panel output looks like a voltage source with a high series resistance, limiting the current or a current source with a moderate parallel resistance.
But the two key points are that:
1. The available current for a given light level is strictly limited and the current for maximum power is on the order of 80% of the short circuit current. and
2. The available current is directly proportional to the light level over a a range of several orders of magnitude. Yet the open circuit voltage remains pretty constant independent of light level over the same range.

Take a look at slides 8 and 9 at http://www.egr.unlv.edu/~eebag/Photo...ystems%20I.pdf or check the real published I versus V curves from manufacturers of particular panels.

Note particularly on slide 9 that the voltage of the MPPs on the family of curves is almost constant while the current at MPP varies widely. That is what your MPPT control algorithm must work with.

[russ]

well i believe u might be correct in saying PV panel working as a CURRENT SOURCE but i couldnt find any relevant information saying PV panel to be current source, can you post some reference links for that.

You want it in short words as well? Do your own research rather than demand others do it for you.

[Mike90250]

1 minute with google

http://www.pveducation.org/pvcdrom/solar-cell-operation/iv-curve

[inetdog]

1 minute with google
http://www.pveducation.org/pvcdrom/s...ation/iv-curve

Very nice, and the following pages are very educational too.
But playing Devil's Advocate on behalf of the OP, nowhere does that call a PV cell a "current source". That is a shorthand we use to approximate what is actually a more complicated behavior.
A very useful approximation, but still one which [Squirrel!] does not appear often in scientific or educations literature about panels.

[curiousmech]

Note particularly on slide 9 that the voltage of the MPPs on the family of curves is almost constant while the current at MPP varies widely. That is what your MPPT control algorithm must work with.

thanks for the brief info it really helped me.
also please tell by what means you are saying lead acid batteries are not good.

[Mike90250]

......also please tell by what means you are saying lead acid batteries are not good.

The high recharge amps from the PV array, can exceed the allowed amps for batteries, you will have to read the battery spec sheets to be sure you stay compliant with the allowed recharge rate.

[curiousmech]

@inetdog: can u tell me what is the best converter to use for high power pv panel like the specs of the pv panel in 1st post.
i have searched over buck-boost,cuk converter and charge pump controller. but they are all 1 stage, is it reliable to use these kinds of converter or multi stage is more beneficial