diff --git a/pyproject.toml b/pyproject.toml
index 3123e7f5e..7bae7dccb 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -56,6 +56,7 @@ dependencies = [
     "CoolProp",
     "attrs",
     "utm",
+    "HOPP",
     "orbit-nrel>=1.1",
     "electrolyzer @ git+https://github.com/jaredthomas68/electrolyzer.git@smoothing",
     "ProFAST @ git+https://github.com/NREL/ProFAST.git",