# Solar Storage System Design¶

Solar energy systems that are not connected to an electrical grid system usually require back-up or storage equipment to provide energy during unusually cloudy days. Unusually cloudy conditions occurring over consecutive days continually draw reserve power from batteries or other storage devices for solar systems not connected to an electrical grid. Storage devices must be designed to withstand continuous below-average conditions in various regions of the globe.

Different industry organizations use different methods to size either battery or other types of backup systems. One example of this is an international aid organization requires that all stand-alone medical equipment must be able to operate for 6 Black or No-Sun days in parts of the tropics. Other requirements or methods of storage need different solar insolation parameters. The following sections expand the updated parameters along with their symbols and equations provided in V10 POWER data set.

Parameters for Solar Storage System Design

• Minimum and Maximum Insolation Over a Consecutive Day Period
• Solar Insolation Deficit Over a Consecutive Day Period
• Surplus Insolation Over a Consecutive Day Period
• Equivalent No-Sun Days Over a Consecutive Day Period
• Minimum Insolation Percentage Over a Consecutive Day Period

## Minimum and Maximum Available Insolation Over a Consecutive Day Period¶

Available on a climatological basis, minimum or maximum available insolation over a consecutive day period (1, 3, 7, 14, 21 or a month) is the extreme value during multi-year (Jan 2001-December 2020) period for each month. The running summation is computed over the indicated days within each month.

Mathematical Procedure

The running summation for each day of a given month and year for a period, p, is:

\begin{align} \normalsize{Where:} \\ \normalsize{\text{SRAD}_d: } & \normalsize{\text{ Daily averaged surface insolation for day } i \text{, in month } j \text{, and year } k \text{.} } \\ \normalsize{d: } & \normalsize{\text{ Day for summation in month } j \text{, year } k \text{.}} \\ \normalsize{p: } & \normalsize{\text{ Averaging period of 1, 3, 7, 14, or 21 days. }} \\ \end{align}

The minimum and maximum value of the summation is computed for each month:

Finally, for the user defined multi-year time span, the summation minimum (maximum) can be computed by:

\begin{align} \normalsize{Where:} \\ \normalsize{n: } & \normalsize{\text{ Number of years in user defined multi-year time span. }} \\ \end{align}

## Solar Insolation Deficit Over a Consecutive Day Period¶

Solar radiation deficits below expected values incident on a horizontal surface over a consecutive p-day period is calculated as follows, using previous parameter declarations:

Equation
\begin{align} \normalsize{Where:} \\ \normalsize{\text{MeanRAD}^p_{j}: } & \normalsize{\text{ Daily averaged surface insolation for a consecutive p-day period. } } \\ \end{align}

## Surplus Insolation Over a Consecutive Day Period¶

Surplus Insolation in each month is the difference between the maximum available insolation sum and the climatological averaged monthly value over the p-day period in the given month. It is calculated as follows, using previous parameter declarations:

Equation

## Equivalent No-Sun Days Over a Consecutive Day Period¶

Equivalent number of Black or No-Sun or days is based upon the deficit solar radiation below expected multi-year monthly averaged value and calculated as follows:

Equation

## Minimum Insolation Percentage Over a Consecutive Day Period¶

Minimum insolation percentage is the ratio of minimum solar insolation over consecutive p-day period and the climatological averaged monthly value over the same p-day period.

Equation

### Solar Storage Systems Parameters (p=1,3,7,14,21 and month)¶

Abbreviation Parameter Units Statistics Available
MIN_AVAIL_INSOL_CONSEC_p Minimum Available Insolation
Over a Consecutive Day Period
Agroclimatology: MJ/m^2
Sustainable Buildings: W/m^2
Renewable Energy: kW-hr/m^2
Climatology
MAX_AVAIL_INSOL_CONSEC_p Maximum Available Insolation
Over a Consecutive Day Period
Agroclimatology: MJ/m^2
Sustainable Buildings: W/m^2
Renewable Energy: kW-hr/m^2
Climatology
SURPLUS_INSOL_CONSEC_p Surplus Insolation Over a
Consecutive Day Period
Agroclimatology: MJ/m^2
Sustainable Buildings: W/m^2
Renewable Energy: kW-hr/m^2
Climatology
SOLAR_DEFICITS_CONSEC_p Solar Insolation Deficit Over a
Consecutive Day Period
Agroclimatology: MJ/m^2
Sustainable Buildings: W/m^2
Renewable Energy: kW-hr/m^2
Climatology
INSOL_CONSEC_p_MIN Minimum Insolation Percentage
Over a Consecutive Day Period
Agroclimatology: %
Sustainable Buildings: %
Renewable Energy: %
Climatology
EQUIV_NO_SUN_CONSEC_p Equivalent No-Sun Days Over
a Consecutive Day Period
Agroclimatology: Days
Sustainable Buildings: Days
Renewable Energy: Days
Climatology
MAX_EQUIV_NO_SUN_DAYS Maximum Equivalent No Sun
Days
Agroclimatology: Days
Sustainable Buildings: Days
Renewable Energy: Days
Climatology
MAX_SOLAR_DEFICIT Maximum Solar Deficit Agroclimatology: MJ/m^2
Sustainable Buildings: W/m^2
Renewable Energy: kW-hr/m^2
Climatology