With the world going for Green energy, installation of solar PV by power utility companies and residences is continuously rising. Your rooftop solar generates the power during daytime when the sun is shining at its best, during this time the power usage by homes is not high, they peak at night when the sun is not shining. You need expensive batteries to store the energy generated during day time by your solar PV. So most of the home users end up buying uninterrupted power supply system (UPS) which can be charged during daytime. Here your electric vehicle can replace as your UPS. Whatever way you charge electric vehicle using grid or solar PV or any Green energy source, most of the times at night electric vehicle/car stay at home unused. The same can become your energy source/energy storage unit. To ensure your electrical power consumption is fully green, you must charge your car during daytime either at office or home using solar or any other green energy sources such as wind mill.
However if you empty the power stored in car during night time you end up with no charge to travel. In that case a combination of home battery storage unit and electric vehicle can combine to give you enough power. Typically an average home consumes 5 to 10 kwh during night time, if electric car has a battery capacity of 3 to 4 times of this consumption which comes around 30KWh+ can still ensure 70% of its charge left for travelling during any sudden requirement before the sun started shining in the early morning. Today's most of the electric vehicles have that much battery capacity.
But you hardly find electric vehicles with the feature to reverse supply electric power back to the grid. There are few companies started working on this feature. Power semiconductor manufacturer Infineon, and power electronics systems manufacturer Delta Electronics have developed three in one system integrating solar, energy storage and charging of electric vehicles using bidirectional inverters.
Electric vehicle maker associations and industry bodies can keep this in mind in creating safety standards and protocols in deciding power storage specifications of electric vehicle.