diff --git a/CHANGELOG.md b/CHANGELOG.md
index 59e9c884f..48e782521 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -80,6 +80,7 @@
 - Added `HYGOV` governor model implementation for PhasorDynamics.
 - Added `REPCA` controller model implementation for PhasorDynamics.
 - Added `REECB` electrical-control model implementation for PhasorDynamics.
+- Implemented `tagDifferentiable()` for `PowerElectronics` models.
 
 ## v0.1
 
diff --git a/GridKit/Model/PowerElectronics/Capacitor/Capacitor.cpp b/GridKit/Model/PowerElectronics/Capacitor/Capacitor.cpp
index aab348679..31ec1b0e2 100644
--- a/GridKit/Model/PowerElectronics/Capacitor/Capacitor.cpp
+++ b/GridKit/Model/PowerElectronics/Capacitor/Capacitor.cpp
@@ -49,6 +49,8 @@ namespace GridKit
   template <class ScalarT, typename IdxT>
   int Capacitor<ScalarT, IdxT>::tagDifferentiable()
   {
+    // All variables are differentials
+    tag_.resize(size_, true);
     return 0;
   }
 
diff --git a/GridKit/Model/PowerElectronics/CircuitComponent.hpp b/GridKit/Model/PowerElectronics/CircuitComponent.hpp
index becbc4208..c40c8d3e5 100644
--- a/GridKit/Model/PowerElectronics/CircuitComponent.hpp
+++ b/GridKit/Model/PowerElectronics/CircuitComponent.hpp
@@ -128,14 +128,14 @@ namespace GridKit
      */
     int allocate() override
     {
-      jacobian_coo_rows_   = std::make_unique<IdxT[]>(static_cast<size_t>(nnz_));
-      jacobian_coo_cols_   = std::make_unique<IdxT[]>(static_cast<size_t>(nnz_));
-      jacobian_coo_values_ = std::make_unique<RealT[]>(static_cast<size_t>(nnz_));
+      jacobian_coo_rows_   = std::make_unique<IdxT[]>(nnz_);
+      jacobian_coo_cols_   = std::make_unique<IdxT[]>(nnz_);
+      jacobian_coo_values_ = std::make_unique<RealT[]>(nnz_);
 
-      y_ext_            = std::make_unique<const ScalarT*[]>(static_cast<size_t>(size_));
-      yp_ext_           = std::make_unique<const ScalarT*[]>(static_cast<size_t>(size_));
-      f_ext_            = std::make_unique<ScalarT*[]>(static_cast<size_t>(size_));
-      connection_nodes_ = std::make_unique<IdxT[]>(static_cast<size_t>(size_));
+      y_ext_            = std::make_unique<const ScalarT*[]>(size_);
+      yp_ext_           = std::make_unique<const ScalarT*[]>(size_);
+      f_ext_            = std::make_unique<ScalarT*[]>(size_);
+      connection_nodes_ = std::make_unique<IdxT[]>(size_);
 
       if (!allocated_)
       {
@@ -250,7 +250,7 @@ namespace GridKit
     {
       assert(rows.size() == cols.size());
       assert(rows.size() == vals.size());
-      assert(current_jac_size_ + rows.size() <= static_cast<size_t>(nnz_));
+      assert(current_jac_size_ + rows.size() <= nnz_);
 
       for (size_t i = 0; i < rows.size(); i++)
       {
@@ -265,22 +265,22 @@ namespace GridKit
   public:
     IdxT size() final
     {
-      return size_;
+      return static_cast<IdxT>(size_);
     }
 
     IdxT size() const
     {
-      return size_;
+      return static_cast<IdxT>(size_);
     }
 
     IdxT nnz() final
     {
-      return nnz_;
+      return static_cast<IdxT>(nnz_);
     }
 
     IdxT nnz() const
     {
-      return nnz_;
+      return static_cast<IdxT>(nnz_);
     }
 
     IdxT sizeQuadrature() final
@@ -491,11 +491,11 @@ namespace GridKit
 
   protected:
     /// The number of variables in this component. Should be equal to `n_extern_` plus `n_intern_`. \see size()
-    IdxT size_{0};
+    size_t size_{0};
     /// The number of nonzero elements in this component's Jacobian. \see nnz()
-    IdxT nnz_{0};
-    IdxT size_quad_{0};
-    IdxT size_opt_{0};
+    size_t nnz_{0};
+    IdxT   size_quad_{0};
+    IdxT   size_opt_{0};
 
     // COO Jacobian buffers
     std::unique_ptr<IdxT[]>  jacobian_coo_rows_;
diff --git a/GridKit/Model/PowerElectronics/DistributedGenerator/DistributedGenerator.cpp b/GridKit/Model/PowerElectronics/DistributedGenerator/DistributedGenerator.cpp
index dfa6f1a98..af707aea8 100644
--- a/GridKit/Model/PowerElectronics/DistributedGenerator/DistributedGenerator.cpp
+++ b/GridKit/Model/PowerElectronics/DistributedGenerator/DistributedGenerator.cpp
@@ -3,7 +3,6 @@
 #include "DistributedGenerator.hpp"
 
 #include <cmath>
-#include <iostream>
 #include <vector>
 
 namespace GridKit
@@ -74,6 +73,8 @@ namespace GridKit
   template <class ScalarT, typename IdxT>
   int DistributedGenerator<ScalarT, IdxT>::tagDifferentiable()
   {
+    // All variables are differentials
+    tag_.resize(size_, true);
     return 0;
   }
 
diff --git a/GridKit/Model/PowerElectronics/InductionMotor/InductionMotor.cpp b/GridKit/Model/PowerElectronics/InductionMotor/InductionMotor.cpp
index 0224e6ebe..69f0dcc39 100644
--- a/GridKit/Model/PowerElectronics/InductionMotor/InductionMotor.cpp
+++ b/GridKit/Model/PowerElectronics/InductionMotor/InductionMotor.cpp
@@ -60,6 +60,8 @@ namespace GridKit
   template <class ScalarT, typename IdxT>
   int InductionMotor<ScalarT, IdxT>::tagDifferentiable()
   {
+    // All variables are differentials
+    tag_.resize(size_, true);
     return 0;
   }
 
diff --git a/GridKit/Model/PowerElectronics/Inductor/Inductor.cpp b/GridKit/Model/PowerElectronics/Inductor/Inductor.cpp
index b192cebc5..ff521fd65 100644
--- a/GridKit/Model/PowerElectronics/Inductor/Inductor.cpp
+++ b/GridKit/Model/PowerElectronics/Inductor/Inductor.cpp
@@ -48,6 +48,8 @@ namespace GridKit
   template <class ScalarT, typename IdxT>
   int Inductor<ScalarT, IdxT>::tagDifferentiable()
   {
+    // All variables are differentials
+    tag_.resize(size_, true);
     return 0;
   }
 
diff --git a/GridKit/Model/PowerElectronics/LinearTransformer/LinearTransformer.cpp b/GridKit/Model/PowerElectronics/LinearTransformer/LinearTransformer.cpp
index fcfc4a02d..d8f453bf7 100644
--- a/GridKit/Model/PowerElectronics/LinearTransformer/LinearTransformer.cpp
+++ b/GridKit/Model/PowerElectronics/LinearTransformer/LinearTransformer.cpp
@@ -62,6 +62,8 @@ namespace GridKit
   template <class ScalarT, typename IdxT>
   int LinearTransformer<ScalarT, IdxT>::tagDifferentiable()
   {
+    // All variables are differentials
+    tag_.resize(size_, true);
     return 0;
   }
 
diff --git a/GridKit/Model/PowerElectronics/MicrogridBusDQ/MicrogridBusDQ.cpp b/GridKit/Model/PowerElectronics/MicrogridBusDQ/MicrogridBusDQ.cpp
index ffc02dfb3..0c3c6331c 100644
--- a/GridKit/Model/PowerElectronics/MicrogridBusDQ/MicrogridBusDQ.cpp
+++ b/GridKit/Model/PowerElectronics/MicrogridBusDQ/MicrogridBusDQ.cpp
@@ -77,6 +77,8 @@ namespace GridKit
   template <class ScalarT, typename IdxT>
   int MicrogridBusDQ<ScalarT, IdxT>::evaluateInternalResidual()
   {
+    // No internal variables - tag doesn't matter.
+    tag_.resize(size_, false);
     return 0;
   }
 
diff --git a/GridKit/Model/PowerElectronics/MicrogridLine/MicrogridLine.cpp b/GridKit/Model/PowerElectronics/MicrogridLine/MicrogridLine.cpp
index 65c3fb0a0..0b467b6d4 100644
--- a/GridKit/Model/PowerElectronics/MicrogridLine/MicrogridLine.cpp
+++ b/GridKit/Model/PowerElectronics/MicrogridLine/MicrogridLine.cpp
@@ -62,6 +62,8 @@ namespace GridKit
   template <class ScalarT, typename IdxT>
   int MicrogridLine<ScalarT, IdxT>::tagDifferentiable()
   {
+    // All variables are differentials
+    tag_.resize(size_, true);
     return 0;
   }
 
diff --git a/GridKit/Model/PowerElectronics/MicrogridLoad/MicrogridLoad.cpp b/GridKit/Model/PowerElectronics/MicrogridLoad/MicrogridLoad.cpp
index a14a038f1..a83ffcbb7 100644
--- a/GridKit/Model/PowerElectronics/MicrogridLoad/MicrogridLoad.cpp
+++ b/GridKit/Model/PowerElectronics/MicrogridLoad/MicrogridLoad.cpp
@@ -58,6 +58,8 @@ namespace GridKit
   template <class ScalarT, typename IdxT>
   int MicrogridLoad<ScalarT, IdxT>::tagDifferentiable()
   {
+    // All variables are differentials
+    tag_.resize(size_, true);
     return 0;
   }
 
diff --git a/GridKit/Model/PowerElectronics/NodeBase.hpp b/GridKit/Model/PowerElectronics/NodeBase.hpp
index 3c7f7c80b..077854b97 100644
--- a/GridKit/Model/PowerElectronics/NodeBase.hpp
+++ b/GridKit/Model/PowerElectronics/NodeBase.hpp
@@ -145,7 +145,7 @@ namespace GridKit
           allocateVectors(static_cast<IdxT>(size));
         }
 
-        tag_.resize(size);
+        tag_.resize(size, false);
         variable_indices_.resize(size);
         residual_indices_.resize(size);
 
diff --git a/GridKit/Model/PowerElectronics/SynchronousMachine/SynchronousMachine.cpp b/GridKit/Model/PowerElectronics/SynchronousMachine/SynchronousMachine.cpp
index c3a647762..5972a4530 100644
--- a/GridKit/Model/PowerElectronics/SynchronousMachine/SynchronousMachine.cpp
+++ b/GridKit/Model/PowerElectronics/SynchronousMachine/SynchronousMachine.cpp
@@ -77,6 +77,8 @@ namespace GridKit
   template <class ScalarT, typename IdxT>
   int SynchronousMachine<ScalarT, IdxT>::tagDifferentiable()
   {
+    // All variables are differentials
+    tag_.resize(size_, true);
     return 0;
   }
 
diff --git a/GridKit/Model/PowerElectronics/SystemModelPowerElectronics.hpp b/GridKit/Model/PowerElectronics/SystemModelPowerElectronics.hpp
index 174e28568..b5470b9c9 100644
--- a/GridKit/Model/PowerElectronics/SystemModelPowerElectronics.hpp
+++ b/GridKit/Model/PowerElectronics/SystemModelPowerElectronics.hpp
@@ -4,6 +4,7 @@
 
 #include <algorithm>
 #include <cassert>
+#include <format>
 #include <vector>
 
 #include <GridKit/Constants.hpp>
@@ -12,6 +13,8 @@
 #include <GridKit/Model/PowerElectronics/NodeBase.hpp>
 #include <GridKit/ScalarTraits.hpp>
 
+#include "GridKit/Utilities/Logger/Logger.hpp"
+
 namespace GridKit
 {
   template <class ScalarT, typename IdxT>
@@ -149,8 +152,6 @@ namespace GridKit
         abs_tol_.setToZero(memory::HOST);
       }
 
-      tag_.resize(size_);
-
       { // Start node internal indexing after all component internals for proper KLU ordering
         size_t node_internal_idx = component_internal_size;
         for (node_type* node : nodes_)
@@ -295,6 +296,38 @@ namespace GridKit
 
     int tagDifferentiable() final
     {
+      for (size_t i = 0; i < components_.size(); i++)
+      {
+        component_type* component = components_[i];
+
+        if (int err = component->tagDifferentiable())
+        {
+          return err;
+        }
+
+        if (component->tag().size() != component->size())
+        {
+          GridKit::Utilities::Logger::error() << std::format("Component {} has an ill-configured tag(). Expected tags for {} variables, got {} instead.\n", i, component->size(), component->tag().size());
+          return 1;
+        }
+      }
+
+      tag_.resize(size_, false);
+
+      size_t idx = 0;
+      for (component_type* comp : components_)
+      {
+        const auto& external_indices = comp->getExternIndices();
+        for (IdxT i = 0; i < comp->size(); i++)
+        {
+          if (!external_indices.contains(i))
+          {
+            tag_[idx] = comp->tag()[i];
+            idx++;
+          }
+        }
+      }
+
       return 0;
     }
 
diff --git a/GridKit/Model/PowerElectronics/TransmissionLine/TransmissionLine.cpp b/GridKit/Model/PowerElectronics/TransmissionLine/TransmissionLine.cpp
index 3adbbef58..38a4e6c1d 100644
--- a/GridKit/Model/PowerElectronics/TransmissionLine/TransmissionLine.cpp
+++ b/GridKit/Model/PowerElectronics/TransmissionLine/TransmissionLine.cpp
@@ -60,6 +60,8 @@ namespace GridKit
   template <class ScalarT, typename IdxT>
   int TransmissionLine<ScalarT, IdxT>::tagDifferentiable()
   {
+    // All variables are algebraics
+    tag_.resize(size_, false);
     return 0;
   }
 
diff --git a/GridKit/Model/PowerElectronics/VoltageSource/VoltageSource.cpp b/GridKit/Model/PowerElectronics/VoltageSource/VoltageSource.cpp
index 9a4accd0b..de1f8a8bd 100644
--- a/GridKit/Model/PowerElectronics/VoltageSource/VoltageSource.cpp
+++ b/GridKit/Model/PowerElectronics/VoltageSource/VoltageSource.cpp
@@ -49,6 +49,8 @@ namespace GridKit
   template <class ScalarT, typename IdxT>
   int VoltageSource<ScalarT, IdxT>::tagDifferentiable()
   {
+    // All variables are algebraics
+    tag_.resize(size_, false);
     return 0;
   }
 
diff --git a/examples/PowerElectronics/Microgrid/Microgrid.cpp b/examples/PowerElectronics/Microgrid/Microgrid.cpp
index 74497fc41..ca94e575b 100644
--- a/examples/PowerElectronics/Microgrid/Microgrid.cpp
+++ b/examples/PowerElectronics/Microgrid/Microgrid.cpp
@@ -223,6 +223,29 @@ int main(int /* argc */, char const** /* argv */)
     sysmodel->getCsrJacobian()->print();
   }
 
+  sysmodel->tagDifferentiable();
+
+  bool all_internal_diff = true;
+  bool all_external_alg  = true;
+
+  const size_t num_node_vars = 4 * 2 + 1;
+
+  for (size_t i = 0; i < sysmodel->size() - num_node_vars; i++)
+  {
+    all_internal_diff = all_internal_diff && sysmodel->tag()[i];
+    if (!sysmodel->tag()[i])
+    {
+      std::cout << "Broken on " << i << '\n';
+    }
+  }
+
+  for (size_t i = sysmodel->size() - num_node_vars; i < sysmodel->size(); i++)
+  {
+    all_external_alg = all_external_alg && !sysmodel->tag()[i];
+  }
+
+  std::cout << "Verify all internal variables are differential: " << all_internal_diff << ", and all external variabels are algebraic: " << all_external_alg << '\n';
+
   // Create numerical integrator and configure it for the generator model
   auto* idas = new AnalysisManager::Sundials::Ida<double, size_t>(sysmodel);