diff --git a/city_model_structure/attributes/heat_pump.py b/city_model_structure/attributes/heat_pump.py
new file mode 100644
index 00000000..c6b059bc
--- /dev/null
+++ b/city_model_structure/attributes/heat_pump.py
@@ -0,0 +1,46 @@
+"""
+heat_pump module defines a heat pump
+SPDX - License - Identifier: LGPL - 3.0 - or -later
+Copyright © 2020 Project Author Pilar Monsalvete Alvarez de Uribarri pilar.monsalvete@concordia.ca
+"""
+
+
+class HeatPump:
+  """
+  HeatPump class
+  """
+  def __init__(self):
+    self._seasonal_mean_cop = None
+    self._seasonal_mean_coverage_factor = None
+
+  @property
+  def seasonal_mean_cop(self):
+    """
+    Get seasonal mean COP (-)
+    :return: real
+    """
+    return self._seasonal_mean_cop
+
+  @seasonal_mean_cop.setter
+  def seasonal_mean_cop(self, value):
+    """
+    Get seasonal mean COP (-)
+    :param value: real
+    """
+    self._seasonal_mean_cop = value
+
+  @property
+  def seasonal_mean_coverage_factor(self):
+    """
+    Get percentage of demand covered by the hp (-)
+    :return: real
+    """
+    return self._seasonal_mean_coverage_factor
+
+  @seasonal_mean_coverage_factor.setter
+  def seasonal_mean_coverage_factor(self, value):
+    """
+    Set percentage of demand covered by the hp (-)
+    :return: real
+    """
+    self._seasonal_mean_coverage_factor = value
diff --git a/city_model_structure/attributes/pv_system.py b/city_model_structure/attributes/pv_system.py
new file mode 100644
index 00000000..35748c1c
--- /dev/null
+++ b/city_model_structure/attributes/pv_system.py
@@ -0,0 +1,114 @@
+"""
+pv_system defines a pv system including all components: PV panels, transformer...
+SPDX - License - Identifier: LGPL - 3.0 - or -later
+Copyright © 2020 Project Author Pilar Monsalvete Alvarez de Uribarri pilar.monsalvete@concordia.ca
+"""
+
+
+class PvSystem:
+  """
+  PvSystem class
+  """
+  def __init__(self):
+    self._modules_mean_seasonal_efficiency = None
+    self._total_area = None
+    self._module_area = None
+    self._number_of_modules = None
+    self._overall_system_performance_ratio = None
+    self._electricity_generation = None
+
+  @property
+  def modules_mean_seasonal_efficiency(self):
+    """
+    Get mean modules efficiency (-)
+    :return: real
+    """
+    return self._modules_mean_seasonal_efficiency
+
+  @modules_mean_seasonal_efficiency.setter
+  def modules_mean_seasonal_efficiency(self, value):
+    """
+    Set mean modules efficiency (-)
+    :param value: real
+    """
+    self._modules_mean_seasonal_efficiency = value
+
+  @property
+  def total_area(self):
+    """
+    Get total modules area (m2)
+    :return: real
+    """
+    return self._total_area
+
+  @total_area.setter
+  def total_area(self, value):
+    """
+    Set total modules area (m2)
+    :param value: real
+    """
+    self._total_area = value
+
+  @property
+  def module_area(self):
+    """
+    Get module area (m2)
+    :return: real
+    """
+    return self._module_area
+
+  @module_area.setter
+  def module_area(self, value):
+    """
+    Set module area (m2)
+    :param value: real
+    """
+    self._module_area = value
+
+  @property
+  def number_of_modules(self):
+    """
+    Get number of modules
+    :return: int
+    """
+    return self._number_of_modules
+
+  @number_of_modules.setter
+  def number_of_modules(self, value):
+    """
+    Set number of modules
+    :param value: int
+    """
+    self._number_of_modules = value
+
+  @property
+  def overall_system_performance_ratio(self):
+    """
+    Get overall system performance ratio (-)
+    :return: real
+    """
+    return self._overall_system_performance_ratio
+
+  @overall_system_performance_ratio.setter
+  def overall_system_performance_ratio(self, value):
+    """
+    Set overall system performance ratio (-)
+    :param value: real
+    """
+    self._overall_system_performance_ratio = value
+
+  @property
+  def electricity_generation(self):
+    """
+    Get electricity generation (J)
+    :return: real
+    """
+    return self._electricity_generation
+
+  @electricity_generation.setter
+  def electricity_generation(self, value):
+    """
+    Set electricity generation (J)
+    :param value: real
+    """
+    self._electricity_generation = value
diff --git a/city_model_structure/attributes/surface.py b/city_model_structure/attributes/surface.py
index b364553a..eacb8e76 100644
--- a/city_model_structure/attributes/surface.py
+++ b/city_model_structure/attributes/surface.py
@@ -9,6 +9,7 @@ from __future__ import annotations
 import numpy as np
 import uuid
 from city_model_structure.attributes.polygon import Polygon
+from city_model_structure.attributes.pv_system import PvSystem
 
 
 class Surface:
@@ -31,7 +32,8 @@ class Surface:
     self._global_irradiance = dict()
     self._perimeter_polygon = perimeter_polygon
     self._holes_polygons = holes_polygons
-    self._solid_polygons = solid_polygon
+    self._solid_polygon = solid_polygon
+    self._pv_system_installed = None
 
   @property
   def name(self):
@@ -201,7 +203,7 @@ class Surface:
     solid surface
     :return: Polygon
     """
-    return self._solid_polygons
+    return self._solid_polygon
 
   @property
   def holes_polygons(self) -> [Polygon]:
@@ -213,3 +215,19 @@ class Surface:
       [Polygon] -> one or more holes in the surface
     """
     return self._holes_polygons
+
+  @property
+  def pv_system_installed(self) -> PvSystem:
+    """
+    PV system installed on the surface
+    :return: PvSystem
+    """
+    return self._pv_system_installed
+
+  @pv_system_installed.setter
+  def pv_system_installed(self, value):
+    """
+    PV system installed on the surface
+    :param value: PvSystem
+    """
+    self._pv_system_installed = value