Halocho #1691 - Matzah cannot be made in direct sunlight

One may not knead the dough of the Matza in direct sunlight, since sunlight causes dough to become Chametz very quickly.

On cloudy days, any place that is bright from the sunlight is considered to be in the sun.

That is the reason Matza factories tend to cover their windows, as it may become cloudy without anybody noticing and the Matza may inadvertently become Chametz.

One has to be careful that when moving the Matza to the oven that one doesn't pass under the sky, since on cloudy days that could cause the Matza to become Chametz.

However, one should be careful that the oven is nowhere near the kneading tables, as the heat from the oven would also cause the Matza to become Chametz.

The water and flour - before they are mixed - also have to be kept away from sunlight.

Source: Shulchan Aruch 459:1

 אֵין לָשִׁין בִּמְקוֹם  הַשֶּׁמֶשׁ. וּבְיוֹם הַמְּעֻנָּן  אָסוּר תַּחַת כָּל אֲוִיר הָרָקִיעַ, מִשּׁוּם דְּיוֹמָא דְּעִיבָא כֻּלֵּיהּ שִׁמְשָׁא. {הגה: וְעַל כֵּן נָהֲגוּ לִזָּהֵר מִלָּלוּשׁ נֶגֶד הַחַלּוֹן  הַפָּתוּחַ אֲפִלּוּ אֵין שָׁם שֶׁמֶשׁ, שֶׁמָּא יִהְיֶה  מְעֻנָּן וְלָאו אַדַּעְתֵּיהּ (ת''ה סִימָן קכ''ב). וְכֵן יֵשׁ לִזָּהֵר  מִלְּהוֹלִיךְ הַמַּצּוֹת לַתַּנּוּר תַּחַת הָרָקִיעַ  מְגֻלֶּה; וְכֵן הַמַּיִם אוֹ הַקֶּמַח (הַגָּהוֹת מַיְמוֹנִי פ''ה בְּשֵׁם סְמַ''ק וּמַהֲרִי''ו)}. וְלֹא יִתְקָרֵב לָלוּשׁ אֵצֶל הַתַּנּוּר, מִפְּנֵי חֹם הַתַּנּוּר.