Background – Solar Payback

Solar Collectors

Collector Types: Stationary

Fixed tilt or seasonally adjusted:

Flat plate collector or
vacuum tube collector

Vacuum tube collector with CPC

Collector Types: Tracking

Linear or two-axis tracking:

Parabolic trough collector

Linear Fresnel collector

Concentrating dish collector

WHAT TO CONSIDER WHEN CHOOSING A COLLECTOR TYPE

Typical operation temperature of the collector type meets the requirements for the industrial heat
Design accommodates chosen heat transfer fluid
Certified according to national or international standard, such as:
- Solar KEYMARK (Europe)
- Solar Rating & Certification Cooperation, SRCC (USA)
- Bureau of Indian Standards (BIS)
- NMX-ES-001-NORMEX (Mexico)*
- South African Bureau of Standards (SABS)*
- National Institute of Metrology, Quality and Technology, INMETRO (Brazil)*
- Chinese National Standard *
Energy output certified by accredited third party
Enough pressure resistance
Adequate stagnation handling and overheating prevention
Suitable weight for rooftop installation or appropriate size for ground-mounting

* These standards do not yet include concentrating collectors.

System Integration

Solar heat can be provided at different integration points. Preheating is the most common method of incorporating solar heat into the production cycle. However, it can also be used to generate steam or fed directly into the process loop.

Preheating

Cold water is preheated in the solar field and fed into a storage tank where it is heated up by a fossil fuel boiler to the required temperature of the production process.

Source: IRENA

Direct Steam Generation

Water is partly evaporated in the concentrating collectors. The solar-heated steam is then
separated from the remaining water in the steam drum before being supplied to the industrial process
or the steam network of the factory. The treated condensate – also called feed water – is fed back to
the collector field. Another option is indirect steam generation. In this case, the collector field heats
water or thermal oil in a closed circuit to generate steam via a heat exchanger.

Source: IEA TASK 49

Process Heating

The solar field provides heat at a certain temperature to maintain the temperature of a bath or a thermal separation process. Additional heat is provided to the production process by a fossil fuel boiler. Both circuits are closed so that the cooled off water returns to the collector field or the boiler respectively.

Source: IRENA