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Solar Panels and MPPT
#5
So we now have the technical background to understand how to create a solar panel that will achieve maximum performance under the challenging conditions in a world with shade.

In the ideal design, we have a MPPT controller that is connected to a single cell, and extracts its maximum output under all shading conditions, and boosts its voltage from .5 volts to a constant higher voltage, such as 6v.
Now we combine all cells optimal output together in parallel and get the maximum current at 6v.

While this ideal is possible, it would increase the costs significantly. The first problem is getting electronics to run at .5v, which is difficult. The lowest cost electronic components often need 2v or 3v to operate.
ST Micro does have a microMPPT controller that will operate at .3v, however it is limited to just 1.8 amps,
so it can't be used with a full 3 watt cell, it would require 1/3 size cell, and thus increases the cost by 3 times as well. The issue of the cost becomes significant when operating at a per-cell level. The alternative is to increase the 'grain size' of the microMPPT design to use more cells in series. This both increases the voltage to a more manageable level,
and also reduces the effective cost of adding the active electronics.

ST Micro has another chip that is closer to the ideal design, called the SPV1020. This chip will operate down to 6.5v, and can handle 9 amps of current. So we can use a solar panel with 14 cells in series as input for the SPV1020.
It can also operate up to 30v of input.

If we want to use 'off-the-shelf' solar panels, these panels are designed for 12v battery charging, and thus output approximately 16v volts. So a simple solution that can implemented quickly and easily is to use a circuit board with the SPV1020 chip that is designed to handle these off-the-shelf panels.

The SPV1020 can handle a maximum of 100 watt 12v panel, so if one wants 400 watts of solar power, the can purchase four 12v 100 watt panels and 4 of the SPV1020 boards.
The smaller the panel size, the better performance you can achieve. So one could use 8 50 watts panels,
or even 16 25 watt panels that are all connected in parallel. It comes down to a matter of cost, as panels less than 100 watts are usually more expensive. The smaller wattage cells are more expensive because they don't use full-size cells, the cells are cut into smaller pieces in order to create more in series to get the 16v output.

So we have designed a circuit board that uses the SPV1020. We are doing a kickstarter project to get the quantity of boards produced to at least 100. At quantity 100, the costs are significantly less, 500 would be even better, but at minimum is 100. At his quantity, we will be able to sell them at only $25 each.

At $25 each, it adds minimal cost to a 100 watt panel. It becomes more significant for a 50 watt panel, but is still not unreasonable given the significant increase in performance of the solar output in the shaded world of a sailboat.
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Messages In This Thread
Solar Panels and MPPT - jackb - 04-02-2015, 08:13 PM
RE: Solar Panels and MPPT - jackb - 04-04-2015, 08:38 AM
RE: Solar Panels and MPPT - jackb - 04-04-2015, 03:37 PM
RE: Solar Panels and MPPT - jackb - 04-05-2015, 07:03 PM
RE: Solar Panels and MPPT - jackb - 04-06-2015, 09:55 AM
RE: Solar Panels and MPPT - jackb - 04-17-2015, 10:53 AM
RE: Solar Panels and MPPT - jackb - 04-21-2015, 07:44 AM
RE: Solar Panels and MPPT - oldmonk - 05-23-2015, 12:46 AM
RE: Solar Panels and MPPT - jackb - 05-29-2015, 10:11 AM

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