How much V of energy storage does photovoltaic require

The storage requirements generated by diurnal fluctuations in solar output are insignificant relative to the storage requirements generated by seasonal fluctuations. The storage batteries are 100% efficient, with no conversion losses and no charge/discharge restrictions.

A solar PV system on the Equator does not need large amounts of storage because solar generation doesn't change much through the year and because the solar cycle is only six months rather than a year long.

Said another way, with a fixed amount of solar PV (if you are land-constrained, for example), you can provide more firm capacity with the same amount of storage if you are willing to charge from the grid sometimes [see Figure 1]. Figure 1. Solar capacity, in MW, required to create a 100 MW renewable peaker.

To generate 5,000 kWh in a year we need 3.8 kW of installed PV capacity on the Equator (load factor 15%), 3.4 kW at latitude 20N (load factor 17%), 3.6 kW at latitude 40N (load factor 16%) and 5.7 kW at latitude 60N (load factor 10%). The load factors are from the Estimating global solar PV load factors post.

For more information about solar photovoltaic energy, visit the following resources: Solar Photovoltaic Technology Basics (U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy) Energy Kids: Solar Photovoltaic (U.S. Energy Information Administration) Energy Saver: Using Solar Electricity at Home (U.S. Department of Energy)

The key to optimally sizing the storage system probabilistically is understanding the tradeoff between marginal cost of additional solar or storage and the penalty for being unavailable to meet a peak in a rare situation.