add CHP topping diagram to docs/SAM-EM_End-Uses-and-Surface-Applications.md

Author: softwareengineerprogrammer

docs/SAM-EM_End-Uses-and-Surface-Applications.md

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+.. raw:: html
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+    <style type="text/css">
+        a.image-reference {
+            max-width: 66%;
+        }
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+        a.image-reference > img, a.image-reference > img:active {
+            max-width: 100%;
+        }
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+        a.image-reference {
+          display: block;
+          margin: auto;
+          align-content: center;
+        }
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+    </style>
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 # SAM Economic Models: End Uses and Surface Applications
 
 [SAM Economic Models](SAM-Economic-Models.html) support a variety of geothermal end-use options and surface applications.
@@ -44,6 +63,10 @@ costs were omitted.
 Combined Heat and Power (CHP) end-uses simulate both electricity and direct-use heat generation.
 The model outputs allocated metrics for both product streams, including `Electricity CAPEX ($/kWe)`, `Heat CAPEX ($/kWth)`, LCOE, and LCOH.
 
+*Schematic of a GEOPHIRES Combined Heat and Power (CHP) Topping Cycle. High-temperature geofluid first drives electricity generation in the upstream power plant before residual heat is extracted for direct-use applications prior to reinjection:*
+
+![](_images/chp-topping-diagram.png)
+
 ### CHP Cost Allocation Ratio
 
 To separate the levelized costs of electricity and heat, GEOPHIRES utilizes the `CHP Electrical Plant Cost Allocation Ratio`.