1. Local Government Engineering Department (LGED) 

Demonstration of Solar Water Heating System in  Bangladesh  ( UNDP supported) 

Introduction

The entire stock of fossil fuels on earth is not worth more than a few days of sunlight. Solar energy can be effectively utilized in two ways- either by converting it into heat (solar thermal) or electricity (solar photovoltaic). A flat plate solar collector or evacuated tube solar collector is used to heat water by using sun’s energy. In Bangladesh average solar irradiation is found about 4.2 kwhm^-2day^-1 which is very suitable for installing solar water heater.

Sustainable Environmental Management Programme (SEMP from UNDP financed) addressed this intervention by installing three vacuum tube solar water heaters and one flat plate solar collector at different location of the country. Gross installation cost of each system was about Tk 65 Thousands. Hot water is stored in an insulated water tank having capacity of 200 litre. Maximum temperature of water raised is about 60⁰ C. So at night one can have a sun bath! Moreover, the system is introduced with a backup electric heater so that uninterrupted service could be obtained even in cloudy days.

 System Component

A solar hot water system consists of the following major components:

1. Solar Collectors

2. Insulated hot water tank with sacrificial Anode

3. Backup electric heater

4. Mounting Structure

Solar Water Heating System

Solar radiation falling on the collectors passes through the glazing and is absorbed by the absorber consisting of fins, raisers and headers. Water contained in the header & raisers gets and becomes less dense than the water in the storage tank. On the principle of “Thermosyphon”, it starts rising through collector and enters the top of the water tank. Simultaneously cold water from the tank descends to the bottom of the collector, gets heated up in the absorber and rises back to the hot water tank and the cycle repeats.

Thermosyphon system (Flat plate solar collector)

The movement of the heated water from the collector to the storage tank, placed above the collector, is due to the difference of density only. No other moving parts are required in the system and hence system reliability is very high.

The water retains its heat for a long time as the hot water storage tank is insulated to prevent heat loss. The sacrificial Anode provided in the hot water storage tank protects the system against Galvanic Corrosion.  

Operation & Maintenance:

Solar water heater system has very low maintenance. Under normal circumstances no maintenance of the system is required. Due to the shape of the tubes regular rainfall and wind keep the tubes clean. Broken tube can be easily replaced. 

Objectives of the project: 

• To provide hot water supply facility.
• To substitute electric/gas water heater by solar water heater.
• To replicate this model for hotels, hospitals and domestic purpose.

 Location of solar water heater installed: 

Benefits of Solar Water Heaters : 

There are many benefits of solar water heater out of which 

• No energy bill.

• Low maintenance.

• Help reducing GHG emission.

• Backup electric heater for cloudy days.

• Reduce dependency on fossil fuel.

 Environmental Impact : 

Solar water heaters do not pollute environment. When a solar water heater replaces an electric water heater, it avoids carbon dioxide emissions. Carbon dioxide traps heat in the upper atmosphere, thus contributing to the "greenhouse effect." 

Conclusions:  

A solar water heater is a long-term investment. It has the higher upfront cost but will save money and energy for many years. Like other renewable energy systems, solar water heaters minimize the environmental degradation for enjoying a comfortable, modern lifestyle. In addition, it provides insurance against energy price increases; helps reduce our dependence on fossil fuel, and are investments in everyone's future.