$re = '/Vortag<\/td>.*?\n?.*?<td>(-?\d+\.?\d+)</';
$str = '
<div id="divInfo" class="cInfo">
<table border="0" cellspacing="0" cellpadding="0" width="100%" height="100%">
<tr>
<td align="center">
<table class="tablebody" border="0" width="100%">
<tr>
<td class="cNavInfo">Online-Werte » Wechselrichter-Übersicht</td>
</tr>
</table>
</td>
</tr>
<tr><td> </td></tr>
<tr>
<td class="tablebody">
<table width="100%" border="0">
<tr class="tablehead">
<td colspan="7"><strong>Summe aller Wechselrichter</strong></td>
</tr>
<tr>
<td class="tablehead">Bezeichnung</td>
<td class="tablehead">Wert</td>
<td class="tablehead">Einheit</td>
<td> </td>
<td class="tablehead">Bezeichnung</td>
<td class="tablehead">Wert</td>
<td class="tablehead">Einheit</td>
</tr>
<tr>
<td>Aktuelle Leistung</td>
<td><b>8.404</b></td>
<td>kW</td>
<td> </td>
<td>Aktuelle Monatsenergie</td>
<td>1750.106</td>
<td>kWh</td>
</tr>
<tr>
<td>Aktuelle Tagesenergie</td>
<td><b>15.328</b></td>
<td>kWh</td>
<td> </td>
<td>Aktuelle Jahresenergie</td>
<td>2352.722</td>
<td>kWh</td>
</tr>
<tr>
<td>Tagesenergie Vortag</td>
<td>148.736</td>
<td>kWh</td>
<td> </td>
<td>Gesamtenergie</td>
<td>235217.714</td>
<td>kWh</td>
</tr>
</table>
</td>
</tr>
<tr><td> </td></tr>
<tr>
<td>
<table width="100%" border="0" class="tablebody">
<tr class="tablehead">
<td colspan="5"><strong>Übersicht einzelner Wechselrichter</strong></td>
</tr>
<tr class="tablehead">
<td width="10%">Adresse</td>
<td width="10%">Leistung</td>
<td width="15%">Einheit</td>
<td width="10%">Tagesenergie</td>
<td width="55%">Einheit</td>
</tr>
<tr><td CLASS="cLink"><A HREF="/httpGpmGotoWrID.cgi?0">1</A></td><td>2505</td><td>W</td><td>4.536</td><td>kWh</td></tr><tr><td CLASS="cLink"><A HREF="/httpGpmGotoWrID.cgi?1">2</A></td><td>2552</td><td>W</td><td>4.880</td><td>kWh</td></tr><tr><td CLASS="cLink"><A HREF="/httpGpmGotoWrID.cgi?2">3</A></td><td>693</td><td>W</td><td>1.304</td><td>kWh</td></tr><tr><td CLASS="cLink"><A HREF="/httpGpmGotoWrID.cgi?3">4</A></td><td>2524</td><td>W</td><td>4.608</td><td>kWh</td></tr>
</table>
</td>
</tr>
<tr><td> </td></tr>
<tr><td align="center"> </td></tr>
<tr><td> </td></tr>
<tr><td align="center"> </td></tr>
<tr><td height="100%"> </td></tr>
<tr>
<td align="center">
<table width="100%" border="0" class="tablebody">
<tr>
<td>Anmerkung: Die hervorgehobenen Werte werden alle 20s aktualisiert.</td>
</tr>
</table>
</td>
</tr>
<tr><td> </td></tr>
<tr><td> </td></tr>
</table>
<div class="x-align-right">
<div class="cStatuszeile"> Systemzeit 10:35:57 / 24.02.2018 </div>
</div>
</div>
</body>
</html>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php