Referring a purchase of Tesla Model S or X results in free, unlimited Supercharging and $1,000 purchase credit – but he cash discount is now to be phased out on October 31st.
"Owners can give five friends free, unlimited Supercharging with the purchase of a new Model S or Model X. Referral orders placed before October 31, 2017 will also receive a $1,000 purchase credit. Referral orders placed after October 31st, 2017 will still receive free unlimited Supercharging, but not the purchase credit."
In the case of solar, referring will result in 5-year extended limited warranty:
"Owners can give five friends a 5-year extended limited warranty on a new solar energy system installation, and will be eligible to receive referral awards."