Pumping system preliminary design

See also: Sizing of a pumping PV system: general considerations.

After defining the Location, click the System button to open a dialog where you can define:

On the right panel: the plane orientation.

NB: the Show optimization button opens a tool that shows the winter yield based on the plane orientation. For stand-alone or pumping systems, the plane orientation should be optimized according to the worst conditions—that is, for winter irradiance.

On the left panel:

• The Water needs (in yearly, seasonal or monthly values).
• The nominal head at which it should be pumped (level difference between water outlet and source surface).
• The diameter and length of pipes (optional, for eventual friction losses).
• A pump technology (centrifugal for rather low heads, positive displacement for high heads).
• An array-pump coupling strategy, which strongly affects system performance.

Now you can open the "Results" where you can specify:

• either the tank volume or the system autonomy in days. These parameters are linked based on daily water needs.
• the "Loss of Load" probability (P LOL), which is the fraction of time during which unmet demand (empty tank) is acceptable.

These parameters determine the array nominal power (that is, the installed STC power according to manufacturer specifications) and the pump nominal power required. These are rough estimations, as pumping system performance strongly depends on pump technology, head, flow rate, and the electrical matching between pump and PV array.

The first result graph shows the potentially available solar energy alongside the user's water and energy needs.

The second graph (accessible via the speed buttons on the left) shows the average tank filling state and the monthly distribution of missing water (P LOL).

The table holds all monthly values, including an eventual required back-up energy.

Finally, the rough economic evaluation provides estimates of investment and water cost.

You can now play with the parameters and immediately see the results.

You can print a report or store graphs and tables on the clipboard to export them to another software.

You can also save your project and load another one for immediate comparisons.

Computation

PVsyst performs a very simplified simulation, which runs over one year in daily values.

The evaluation of the available irradiance on the collector plane uses the Monthly Meteo tool algorithms, which calculate monthly average irradiation based on instantaneous data from one day per month.

This is insufficient for managing day-to-day water storage balance evolution and effective use of solar incident energy. Therefore, the program generates a random sequence of 365 days following the Collares-Pereira algorithms¹, renormalized to monthly sums, to calculate the daily balance and PLOL.

This simulation is repeated with different array and pump size arrangements, until matching the input requirements (namely the desired PLOL). The program is able to propose:

• the pump(s) size (power),
• the PV array nominal power,
• a rough estimate of the investment cost and the cost of water pumped.

If necessary, the predefined parameters (array, system matching, pump efficiency, etc.) can be modified by the user through "Preferences" > "Edit Hidden Parameter".

This early layout proposal should be verified by a detailed simulation using real commercially available components and accounting for all system features in hourly modeling.