diff --git a/revealjs/alternative_energy/index.html b/revealjs/alternative_energy/index.html
index db1c482..6c98908 100644
--- a/revealjs/alternative_energy/index.html
+++ b/revealjs/alternative_energy/index.html
@@ -1,5 +1,5 @@
 <!DOCTYPE html>
-<html>
+<html lang="de">
   <head>
     <meta charset="utf-8">
     <title>Andere Energie</title>
@@ -78,21 +78,21 @@
               <div id="type-1" class="fragment">
                 <h1>Typ 1 <span class="expand">(10<sup>16</sup>W)</span></h1>
                 <div class="expand">
-                  <img src="img/type-1.svg">
+                  <img src="img/type-1.svg" alt="Symbolbild Typ-1-Zivilisation">
                   <p>Geothermie, Biogas, Gezeitenkraft</p>
                 </div>
               </div>
               <div id="type-2" class="fragment">
                 <h1>Typ 2 <span class="expand">(4·10<sup>26</sup>W)</span></h1>
                 <div class="expand">
-                  <img src="img/dyson-sphere.svg">
+                  <img src="img/dyson-sphere.svg" alt="Dyson-Sphäre">
                   <p>Dyson-Sphäre*</p>
                 </div>
               </div>
               <div id="type-3" class="fragment">
                 <h1>Typ 3 <span class="expand">(4·10<sup>36</sup>W)</span></h1>
                 <div class="expand">
-                  <img src="img/smbh.svg">
+                  <img src="img/smbh.svg" alt="Spiegel um Supermassives Schwares Loch">
                   <p>Spiegel um Supermassives Schwarzes Loch</p>
                 </div>
               </div>
@@ -244,8 +244,8 @@
             <aside class="notes">
               <ul>
               </ul>
-            </aside>-->
-          </section>
+            </aside>
+          </section>-->
         </section>
         <section>
           <section>
@@ -391,7 +391,7 @@
                 <ul>
                   <li class="image">Unsplash/<a href="https://unsplash.com/photos/vCqclUnCg_8">Frank Denney</a></li>
                   <li class="image"><a href="https://de.wikipedia.org/wiki/Datei:Geothermie_verfahren.png">Geothermie verfahren.png</a>: Jkrieger Public Domain (angepasst)</li>
-                  <li>Wikipedia (de): <a href="https://de.wikipedia.org/wiki/Geothermie">Geothermie</li></li>
+                  <li>Wikipedia (de): <a href="https://de.wikipedia.org/wiki/Geothermie">Geothermie</a></li>
                 </ul>
               </td>
             </tr>
@@ -428,7 +428,7 @@
               <li class="imageplus">Inhalts- und Bildquelle</li>
               <li>Inhaltsquelle</li>
               <li class="image">Bildquelle</li>
-            <ul>
+            </ul>
           </div>
         </section>
       </div>
