Pay Back Period (EPBT) of PV Module installations

PV Modules (or PV Panels) pay back period has to be considered in two perspectives. Namely;

• Economic,

and

• Environmental

Economic aspect

Out of this economic pay back will depend on the type and price of PV Modules , method of Installation, the electricity consumed in your home, the tariffs in your area, whether there is a power export arrangement with the utility company, the life span of the PV modules, the depreciation of conversion rate per year etc. It therefore is a simple mathematical exercise to work out the Payback period. One odd man out in this working is the human angle. If you waste electricity by your negligence or use in your household out dated inefficient appliances you your self will be extending the payback period.

Environmental impact

The average man on the street may be more interested in the economic aspects while it need not be so as the environmental pay back itself has a bearing on your very survival on this planet.

But the environmental pay back is the least discussed by the end user when bent on a sustainable energy solution for his home. Whether it is PV modules or CHPs the manufacturing process and installation consumes energy. This does not just start at the factory production line. Actually the excavation of the raw material itself consumes energy and from that point onwards every single stage of Solar Module production and installation (including the transport of raw material, cables, fixings etc.) utilizes energy. This energy is called embodied energy of the PV panel system.

How long it will take for the PV modules to recover that energy and how much additional energy will be saved during its life span (typically guaranteed 25 years but lasting over 35 years)? Modern ribbon /shingle Solar Panels have considerably less embodied energy than mono crystalline and polycrystalline solar modules.

Importance of environmental pay back

This is important because the generation of electrical energy utilized for the PV module system with fossil fuels is a contributory factor to dreaded global warming. The process of production of components itself can be causing green house gas emission. (e.g. metal and glass components). Waste disposal fortunately does not mean much of an issue as the glass and metal is easily recycled which may happen 35 years later anyway!

Calculation of Energy Payback (EPBT)

The relationship goes:

EPBT (Years ) = Specific Energy (kwh)/ Annual energy generation ( kwh/year)

Where,

Specific energy = energy needed to produce a PV system

Annual energy generation =system's energy generation rate

The EPBT is about 2 years for mono crystalline PV module system .This for the Polycrystalline, and thin film ribbon type modules reduce to 1.7 years and 1.5 years respectively. This is based o 4.7 sun-hours per day as applicable for southern Europe .

Performance and maintenance

Good maintenance of PV modules is important when expecting the rated EPBT. The installation should ensure good wind play around the modules, best exposure to sunlight, low loss inverters and switch gear, and cabling for the least voltage drop and power loss.

A thin film of dust is good enough to drastically reduce the energy conversion efficiency. Therefore good maintenance is too important for a low EPBT.