How many grand pianos does it take to equal the weight of the sun?

A lot and then a lot more 

Let's be specific here.

Grand Piano weighs: Aprrox 252KG

Sun's weighs: 1.989E30 kg

Divide the Pianos weight by the sun's to see how many fit in.

$${\frac{{\mathtt{1\,989\,000\,000\,000\,000\,000\,000\,000\,000\,000}}}{{\mathtt{252}}}} = {\mathtt{7\,892\,857\,142\,857\,142\,857\,142\,857\,142.857\: \!142\: \!857\: \!142\: \!857\: \!1}}$$

Ha...This is it (Approx).