PV – INSTALLATIONS
Foregoing explanation is focused on the unavoidable background information in studying the solar technology especially for PV – installations.
There are various designs of PV – installations depending on local circumstances and wanted facilities and capacity. The design of a PV – installation is most of the time tailor made and is prescribed by a number of parameters such as:
- place on earth,
- environment,
- circumstances,
- range of application,
- individual preferences,
- possibilities,
- cost price.
On forehand of a PV design a lot of research must be done with respect to energy-conscious behaviour.
Sometimes it is necessary to replace highly energy consuming devices foe more efficient hardware. The primarily question is how to save energy as much as possible. Eliminate unnecessary energy consuming machinery or make disconnection possible.
It’s always an individual decision to what extend one will go. Moreover the cost price of all energy saving measures is important.
It makes sense to define the energy consumption of all relevant devices in use. Such activities ask for a lot of discipline. A structured approach is highly recommended. For this reason so called “System Sizing Worksheets” are often used in practice.
Quite a number of different sheets exist for this purpose.
As there are:
1. Load estimation worksheet; for the estimation of future energy consumption.
2. Battery sizing worksheet; for the designing of the required energy storage in batteries.
3. Array sizing worksheet; for the design of the PV array and connections.
4. Controller sizing worksheet; for defining the required specifications of controller logic.
5. Inverter sizing worksheet; defines the required specifications in case of an inverter.
6. System wire sizing worksheets; for determination of the required cross sections and other measures of the wiring in the PV system in respect to safety and efficiency. Losses must be minimized as much as possible.
As you can se in former summarizing, a structured approach is highly recommended.
Next, the focus is set on the realisation of PV systems. In doing so, we prefer visualizing instead of a lot of text in order to explain PV system items.
The variety in PV design is prescribed by the degree of autonomous behaviour, hybrid systems and the possible energy storage. Another aspect is the possibility of grid connection or the use of a generator set.
6.1 FROM PV CELL UPTO PV ARRAY
Source: TIO Leende
The central part of a PV system is the PV cell with an effective voltage of 0.5 V if sufficient irradiated. A number of PV Cells are grouped together in series and / or in parallel in such a way that the wanted voltage and current targets are achieved.
This assembly is called a PV module. As an example:
A module with 36 cells in series gives without load in an open circuit, a voltage of 18 volts under standard test conditions (STC), That means in practice 12 V DC. The current output is mainly defined by the irradiated part of the surface and the efficiency of the installation.
In order to reach the current target, a number of PV modules are joined together in a solar panel.
A PV panel is an assembly of one or more PV modules.
A PV array is a group of modules or panels, firmly mounted in a frame in such a way that the desired voltage source exists which is able to deliver the wanted current.
A PV module must meet the STC standard. For this purpose standard measurement arrangements are designed resulting in characteristics of solar equipment.
An example is given in next figure.
Source: Photovoltaics Design and Installation Manual, New Society publishers, ISBN 978-086571-520-2
6.2 THE DESIGN OF A PV PANEL
Source: TIO Leende
In the above picture, the way of connecting solar cells is identical to the connection of single batteries. The pictures speak for themselves.
Cells in series increase the voltage. Through each cell flows the same current.
Cells in parallelthe voltage is unchanged and identical for all cells. Current capacity is increased.
In next figure a PV array.
Source: TIO Leende
6.3 A PV SYSTEM WITH A STORAGE FACILITY
Source: TIO Leende
The systems above have a storage battery with a charge controller.
6.4 VARIOUS PV SYSTEMS
Next we’ll show you the essential of various PV systems. First figure shows a simple and most basic design. A device is directly controlled by a PV array and is only operational at daylight. That’s why the name “day use system”.
Source: TIO Leende
The above showed system acts autonomous or “stand alone”.
Next system is somewhat more advanced and has a storage battery. So the system can also function at moments with no daylight at all, but for a limited time. We presume that during daylight hours sufficient energy could be spend for battery charge via a charge controller.
Source: TIO Leende
Another more complex system can manage both DC and AC devices. That’s because the system is extended with a DC / AC inverter. The DC current, directly delivered by the solar array or by the battery, is converted in an AC source. From then it’s also possible to energise normal AC consumer devices. The DC and AC parts of the installation are strictly separated.
There are separate connection panels for DC and AC. See the picture below.
Source: TIO Leende
In next example the operational safety and reliability of the system is improved by adding an extra energy source in the form of a generator set. This electric generator is driven by a mechanical combustion engine. Such a system is called a hybrid system.
Source: TIO Leende
In the picture below a PV system is combined with the normal electric main grid.
The PV system is no longer seen as a stand alone system but act as an supporting extra energy source in order to save grid energy. It is not always cost saving but certainly milieu friendly.
Source: TIO Leende
Next the same system is showed, but now with an extra energy storage battery. The functionality will be clear. Notice the bidirectional acting electric supply meter. Now back delivery of the excess solar energy to the grid is now possible on reward base.
An additional advantage of this system is the energy backup as the grid delivery fails.
Source: TIO Leende
