Balance of system

What is BOS ?

Everything in the “gap” between PV modules &

the Grid.

The balance of system or BOS encompasses all

components of a photovoltaic system other than

the photovoltaic panels.

This includes wiring, switches, a mounting

system, one or many solar inverters, a battery

bank and battery charger. For ground-mount

systems, land is sometimes included as part of the

BOS as well.

Power Electronics

• Inverters

• batteries

Mounting Structures

• Racking - Fixed tilt

• Tracking systems

I. Single axis

II. Dual axis

Cables and connectors

Weather measurement

Control the electricity generated by a solar module

Charge regulators are the link between the PV modules

and battery.

Control the amount of charge flowing in and out of a battery

Protect the battery from overcharge or excessive discharge.

High temperatures tend to reduce battery life because they

accelerate corrosion and self-discharge.

The resistance of lead-acid batteries to freezing is reduced

when they are discharged, so batteries should be kept charged

when they are left in low temperature conditions during the

winter.

Single module need charge controller of between 4A – 6A &

larger arrays may need charge controller of 40A or even more

Store electric energy

The simplest means of electricity storage is to use theelectric rechargeable batteries, especially when PVmodules produce the DC current required for chargingthe batteries.

Batteries store the electrical energy generated by themodules during sunny periods, and deliver it wheneverthe modules cannot supply power or cloudy days.

Most of batteries used in PV systems are lead-acidbatteries. In some applications, for example when usedin locations with extreme climate conditions or wherehigh reliability is essential, nickel-cadmium batteries areused.

The following factors should be considered when choosing a

battery for a PV application:

Operating temperature range (e.g.: -15°C to 50°C)

Self discharge rate (% per month)

Cycle life to 80% depth of discharge (DOD)

Capacity (Ah) at 10 hr & 100 hr rates (C10 & C100)

Robustness for transport to site

Resistance to overcharging

Cost

battery efficiency for most PV application is 85%

Inverters

DC to AC Converter

• The inverter's main functions are: transformation of

DC electricity into AC, wave shaping of the output

AC electricity.

• The most important features of an inverter for PV

applications are its reliability and its efficiency

characteristics. They are designed to operate a PV

system continuously near its maximum power

point.

• Inverters have efficiencies ranging from 85% to

95% for most PV application.

Mounting Structures

Main support of module

The structuring that supports the modules

Typically aluminum, galvanised iron

Should be corrosion resistant

Choose depending on soil, wind and weather

conditions!

Overwhelming majority : Fixed tilt

Rare: Single or double-axis trackers

Fixed Tilt

Single Axis

Double Axis

Fixed tilt

Source: Schletter

Type of Tracking systems

A. Manually operated

B. Motor operated

• Single Axis

• Dual axis

Available in both single axis and dual axis modes

Source: Linak

AS

Single axis

Dual axis

Cable and Connectors

The electricity carriers

Energy output directly related to ambient

conditions like

Amount of sunlight(Irradiation)

PV Module temperature

Ambient temperature

Irradiation sensors

Module and ambient temperature meaurement