diff --git a/packages/web/components/ScenarioWizard.tsx b/packages/web/components/ScenarioWizard.tsx
index 3d705a5..337ac1e 100644
--- a/packages/web/components/ScenarioWizard.tsx
+++ b/packages/web/components/ScenarioWizard.tsx
@@ -219,7 +219,12 @@ function StepSolar({
               value={state.solar_ac_mw}
               step={5}
               min={1}
-              onChange={(v) => set("solar_ac_mw", Number(v))}
+              onChange={(v) => {
+                const ac = Number(v);
+                const ratio = state.solar_dc_ac_ratio;
+                set("solar_ac_mw", ac);
+                set("solar_dc_mwp", parseFloat((ac * ratio).toFixed(3)));
+              }}
             />
           </Field>
           <Field label="DC:AC Ratio">