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As we know, the voltage level of a solar cell is lower than what a rechargable battery needs, and thus a DC converter is placed in between.( With feedback control for optimum V-I curve)

This just confused me, so what the solar cell is delivering?? DC converter provides power from outlet not the cell. Wasn't the whole point of solar cell to provide power? We could just charge the battery from outlet without the solar cell.

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    \$\begingroup\$ A dc-dc converter provides power from whatever's connected to its input. In this case, what's connected to its input is the solar cell. \$\endgroup\$ – Hearth Nov 16 '18 at 15:18
  • \$\begingroup\$ A solar cell doesn't always need a dc-dc converter. I have a solar cell connected directly to a 12v lead acid battery. It works fine. \$\endgroup\$ – HandyHowie Nov 16 '18 at 15:21
  • \$\begingroup\$ My small solar panel (18” by 15” approx) gives between 12v and 15v : ample to overcharge most small batteries without any control... \$\endgroup\$ – Solar Mike Nov 16 '18 at 15:49
  • \$\begingroup\$ I think I understand. The whole point of the battery is to act as a power bank. So yes you could charge a tonne of batteries from mains such when there is power outage you don't need solar. But the whole idea of off grid solar is not to be reliant on the grid. \$\endgroup\$ – sidA30 Nov 16 '18 at 15:58
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In most cases, in order to charge a battery, we need to control the input voltage/current and achieve the maximum power point (via a MPPT method).

Next figure shows a simplified model.

enter image description here source: https://outbackjoe.com/macho-divertissement/macho-articles/design-guide-for-12v-systems-dual-batteries-solar-panels-and-inverters/

There are plenty of textbooks and sites that explains how DC/DC converters work and how to utilize them in a battery charging system.

For example, a Boost Converter (Step-up DC/DC Converter) increases the output voltage of a solar panel and tries to find the point where the power transfer from the panel to the battery becomes maximum (MPPT).

Charging a battery from a wall outlet is also possible - of course by using a proper AC/DC converter - but then you are using the energy that comes from the grid (eg. coal) and not a renewable source, like the sun.

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  • \$\begingroup\$ I understand, but DC converter itself is powered from grid, and us delivering grid power to battery not solar power. That's why I'm confused \$\endgroup\$ – doubleE Nov 16 '18 at 16:18
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    \$\begingroup\$ @Novice The converter is not powered from the grid, though. It's powered from the solar cell; that's the entire point of it. Some might have a grid connection that can let them use grid power if the solar power isn't enough, but they still use the power from the solar panel. \$\endgroup\$ – Hearth Nov 16 '18 at 16:29
  • \$\begingroup\$ @Novice I don't understand what do you mean exactly by "DC Converter". As Felthry said, the entire point is to use or store a renewable energy source, instead of the power grid. If we have more energy than we can use or store, we can sell it to the grid. So the energy flow is from the solar panel to the wall outlet - not the other way. \$\endgroup\$ – thece Nov 17 '18 at 17:23

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