Paraboloid Dishbased Solar System

Operations & Maintenance Manual

lR;eso t;rsMNRE

November, 2014

UNDP-GEF Project on Concentrated Solar HeatMinistry of New & Renewable Energy

Government of India

MSA RENEWTECHF O U N D AT I O N

Prepared By:

Index

Acknowledgement .......................................................................................................................................3About This Manual.......................................................................................................................................51. General Description.........................................................................................................................71.1. Interpreting Subsystem Specifications ............................................................................................. 81.2. Components ..................................................................................................................................... 92. Safety Information .........................................................................................................................102.1. General Precaution during Operation and Maintenance ................................................................ 102.2. Use of Personal Protective Equipment (PPE) ................................................................................ 102.3. General Precaution during Operation and Maintenance ................................................................ 113. How Tracking Works .....................................................................................................................123.1. How the Control System Works...................................................................................................... 124. Operating the System....................................................................................................................134.1. Start-up Sequence.......................................................................................................................... 134.2. Start-up Precautions ....................................................................................................................... 134.3. Normal Operation, Monitoring and Error Control............................................................................ 134.4. Shutdown Sequence....................................................................................................................... 134.5. Routine Maintenance...................................................................................................................... 145. Troubleshooting ............................................................................................................................14

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AcknowledgementThis document is the result of active mentorship, support and inputs from the following individuals:

Dr. S.K. Singh, MNRE

Dr. A.K. Singhal, MNRE-UNDP Project Management Unit

Dr. R.P. Goswami, MNRE

Shri Pankaj Kumar, MNRE-UNDP Project Management Unit

Mr. Siddharth Malik, Managing Director of Megawatt Solutions Pvt. Ltd.

Dr. Deepak Gadhia, Founder of Gadhia Solar Ltd. And Director of MSA RenewTech Foundation

Shri Kailash, Technician at Solar Energy Center, Gurgaon

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About This ManualThis document describes a typical paraboloid dish solar thermal system and the procedures needed tooperate and maintain it successfully. The document is intended primarily for instructors, supervisors andengineers to train the site level technicians. This manual is to be used in conjunction with the ‘Solar SchefflerDish Operation and Maintenance Manual’

The document maintains a focus on the practical day-to-day tasks of operating a paraboloid dish system.The design of the system and the engineering considerations behind its operation are not covered unlessthey have a direct bearing on operational decisions.

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1. General DescriptionThe paraboloid dish solar concentrating system uses a parabolic concentrating dish to focus sunlight on athermal cavity receiver. The receiver attains high temperature which in turn heats the water or thermal fluidinside the cavity. The heated fluid then transfer its heat to end industrial applications.

Figure 1: Solar Paraboloid Dish

Paraboloid dishes as shown in Figure 1 are capable of delivering very high temperature at output. Thethermal energy attained is in 100 – 400oC temperature range. The paraboloid can have a reflector area ofup to 90 m2. And a system like these can produce more than 50 kW of thermal output at 1000 W/m2 solarinsolation. The paraboloid dish can also have a tracking system. A tracking system enables the system toget optimum sunlight and attain maximum temperature. This dish tracks the sun’s movement accurately(with an error of 0.2 degree). This results in the concentration of sun’s light up to 1000 x at the focus.

A well thought out design can decrease the land footprint of a ~90m2 paraboloid dish to a mere 0.5 m2 onground. The average solar to thermal efficiencies of a paraboloid dish system about 60%.

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1.1. Interpreting Subsystem Specifications

Figure 2. Subsystems of a Paraboloid Solar System

As shown in Figure 2, the entire system can be thought of as made up of subsystems each performing acore function.

The receiving subsystem collects solar radiation in the solar field from paraboloid reflecting collectorsand transfers it to working fluid such as water or oil.

The tracking subsystem acts as a support to the receiving subsystem. It maximizes the solar energycaptured by moving solar collectors towards the sun throughout the day and throughout the seasons.

The circulation subsystem carries fluid and transfers the heat received by it to the end use application.Fluid circulates in the system at a certain desired rate to quickly and efficiently transfer the received heatfrom solar field to end use application. Circulation subsystem has a number of components such aspipes, pumps and valves to control fluid flow and temperature.

Finally, a control mechanism which acts as the brain behind tracking and circulation system. It sendssignals to these systems to control the tracking of the receiver based on pressure and temperature ofthe circulating fluid.

CirculationPump

SOLAR PARBOLOID

Receiving System

Control SystemTracking System

End useapplication ofprocess heat

Circulation System

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1.2. Components

Paraboloid Dish Collector Receiver at the focus of a Paraboloid Dish

Figure 2: Paraboloid Dish Collector & Receiver

Paraboloid dish comprise of following components:

Collector: is essentially used to concentrate sun’s light at a fixed point focus.

Receiver: is placed of the focus of the dish, to absorb and transmit concentrated heat to continuouslyflowing fluid through it

ReceiverCollects concentrated sunlight and transmits the energy to fluid through it.

Expansion Tank Maintains the pressure of circulating fluid in a closed system, allowing water to expand with rising

temperature

Minimizes pressure surge (to reduce water hammering effect) to save pipeline from damage

Hot Water Pump Pumps water to the solar field, and maintain water flow rate in the circulation system

Flow rate of water circulating in closed system is maintained/controlled through the SCADA system (ifrequired) / controller.

Thermal Storage TankUses buffering technique, i.e. it store excess heat generated by the solar field, which can be utilized duringnon-solar hours.

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2. Safety InformationAn understanding of safety involves three aspects:

A general awareness of safety risks on the site

Knowledge of protective equipment that should be available on-site and the specific scenarios whenthey should be used

Safety precautions that should be followed for every activity that is undertaken on-site

This section provides general coverage of all of the above aspects.

NOTE: This is a generalized discussion of safety aspects on solar paraboloid dish systems. By no means is this acomprehensive treatment of all safety risks and precautions. For a more complete understanding of safety, please referto the manufacturer manual or OSHA guidelines.

2.1. General Precaution during Operation and Maintenance The receiver can reach a temperature above 150°C, which is scalding temperature. So any contact with

fluid should be avoided.

Never put your body part between the solar paraboloid and receiver, and if at all you are working in thisregion, stay as close as possible to the dish and away from receiver.

Make sure that focus cannot accidently fall on any inflammable material.

Don’t touch receiver when the system is working.

The system is pressurized, with fluid/steam at a pressure much higher than atmospheric pressure. Thusthe fluid/steam can come out of any opening/breakage/crack as high pressure jet stream. This maycome in contact with human body causing burns.

Ensure that the pipes and other metal parts carrying fluid are insulated. Any exposed area can poseburn hazards.

2.2. Use of Personal Protective Equipment (PPE)Note: Please refer to the manufacturer’s manual for the specific make and grade of each equipment to be used.

Hand gloves of appropriate thickness and insulation to protect against hot surfaces

Industrial safety shoes

Protective sunglasses

Fire extinguisher

While working on height, use the following:

o Foot support (scaffolding / firm roof mounted platforms)

o Safety harness / Hand-grip rope

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2.3. General Precaution during Operation and Maintenance

Pipeline and Equipment Flexible hose pipes are generally susceptible to leakages due to high pressure in the system, hence

maintain safe distance.

Ensure isolating valves are closed to stop the flow of fluid before working on paraboloid reflector or othercomponent.

Drain hot fluid first through vents before opening any equipment. This will avoid any chance of skinburning.

Before loosening screws and connections, make sure that the system is not under pressure.

Wear gloves while removing insulation to avoid skin contact with hot surfaces.

Before draining out the fluid by opening the pipe flanges or coupling, ensure that majority of body partis above the pipeline.

Receiver & Header Pipe Paraboloid dishes should be completely defocused before any maintenance task near receiver area.

Release all the steam using safety relief valve before opening any equipment.

Avoid looking at receiver/dish/focus with naked eyes. Always use dark sunglasses in such scenarios.

Paraboloid Dish Close water level gauge before removing the receiver part to for maintenance work.

When working on the dish at a height, ensure that support for hands and feet is available to avoid falls.

Dish is usually made up of glass and is not strong enough to support extra weight – ensure that othersupports are available before undertaking any work that involves climbing.

Precautions during Operation Header pipe stores steam at high pressure, hence avoid going in the close proximity.

Don’t let unauthorized personnel / children wander near the focus of the dish.

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3. How Tracking WorksIn solar paraboloid dish, collector concentrate sunlight on receiver tube forming a point focus. With sun’smovement from east to west (diurnal) and north to south (seasonal), the collector continuously tracks abouttwo axis, tracking sun’s radiation and maintaining the focus of collector on receiver. The picture belowillustrates this concept.

Figure 4: Paraboloid Dish tracking Sun’s Movement from Morning to Evening

As shown in Figure , tracking sunlight from morning (east) to evening (west) helps to get the maximumutilization of the sun's rays by keeping the dish perpendicular to the sun for about 10 hours (useful radiation)per day.

The dish goes to ‘morning position’ at the start of the day when it is started from parking. It starts moving inwest direction with sun’s movement. By the end of the day, it moves to its ‘evening position’ while followingthe sun all the way. At the end of the day it goes back to parking position.

3.1. How the Control System WorksThe control system is like the brain of the system and instructs all the other systems. Figure 5 below showsthe flow of information to control the tracking system. Paraboloid solar dish controller based on a controllogic reads current coordinates of the dish (as input) and runs the tracking motors precisely to track the dishtowards the sun.

Figure 5: Paraboloid Dish Tracking System

Paraboloid Solar Dish Controller Controls and monitor movement of dish to track sunlight and ensure concentration at receiver

Controls and monitor dish’s parameters, position, and alarms

Gives alerts/alarms if operator’s attention is required

CONTROLLER

PARABOLOID SOLAR DISH CONTROLLER

Movement of Dishabout two axes

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4. Operating the SystemThis section details the typical steps for operating a paraboloid dish. Please note that some sites may havesteps that may differ slightly or considerably and the reader is advised to refer to the manufacturer’s manualfor the site. The description provided here is for a general understanding.

4.1. Start-up SequenceOn starting Paraboloid dish, actions are triggered automatically through pre-programmed logic.

Perform the following sets of actions & operations to start a paraboloid dish:

1. Before starting the system reflecting surface should be cleaned properly.

2. Before removing the parking, check that the mirror access ladder (cleaning ladder) is parked & lockedin its south position (w.r.t. dish).

3. Now remove the entire dish parking struts & engage them with parking locks provided so that they willnot hinder the movement of the dish along any axis. Please note that clutch should be turned ONbefore removing the parking.

4. After removing the parking put the "Parking Removed" switch on the panel to “YES”.

5. Select Auto Mode by Auto/Manual selector switch on the controller.

6. Select Initialize Mode to start the dish. The dish will go through Initialize and Align mode before it startstracking the sun in Sensor Mode.

7. By default, dish will start tracking the sun automatically (on Sensor Mode).

8. Note the dish receiver fluid temperature reading from the controller.

9. Dish will continue in tracking mode throughout the day until sunset time is reached.

4.2. Start-up PrecautionsFollowing field checks / precautions must be performed/taken every time when starting the system:

If thermic fluid is used in circulation system, it should be initially (first fill) heated up by 20°C per hourtill it reaches 100°C, so that all moisture is removed from the thermic fluid.

Check level of water in steam accumulator. It should be below high level and above low level.

Check the inlet/outlet valves to dish are also open.

Ensure that all drains & vent are closed.

4.3. Normal Operation, Monitoring and Error ControlThe system requires little intervention when in operation. However, periodic monitoring is essential.

Regularly monitor the control panel for alarms, and process parameters.

Regularly cross-check the tracking system of paraboloid dish for sun’s movement to optimize theperformance of the system.

It is extremely important to maintaining the pressure & temperature of fluid circulating in the system.

4.4. Shutdown SequenceFollow the following sets of actions to shutdown paraboloid dish solar system:

1. When the dish reaches near sunset position, it will automatically enter the parking mode and the dishwill be brought to parking position. Also one can select 'Parking Mode' for the same operation.

2. When it gets parking on both axes (sensed from the parking proximity switches), the dish will stop.This can be seen on controller when it's LED glows green.

3. Now engage all the parking struts.

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4. Now switch OFF circulation system and make up water pumps.

5. Switch OFF the main electrical panel.

6. Record the flow meter reading to know the quantity of steam delivered.

7. Close the outlet valve on steam delivery line.

8. In the end, open the by-pass valve of steam trap to avoid vacuum formation.

If System is Not Used for Long Time, then:

Keep the dish secured in Parking Position

If circulation system contains water / thermic oil and atmospheric temperature reaches below freezingtemperature, drain out water / thermic oil.

4.5. Routine MaintenanceThe system requires some simple and small-scale activities for general upkeep of the system. The followingtasks must be regularly performed when using the system:

Weekly

Clean paraboloid dish system

Use parking locks to lock the ladder

Use Sprayer to wipe of dust

Clean the dish every morning before starting the system

5. TroubleshootingA few process related troubleshooting points are given below. You can also refer to respective manual ofeach component for troubleshooting:

Observation Probable Cause Action

System temperature isabove safety limit

Power supply of the control panelis tripped causing watercirculation system to stop

Correct the system fault

Restart the pump at earliest

Release pressure in the system atearliest

Circulate water at higher flow rateuntil temperature drops to normallevel

Noise in circulation pump Alignment of pump motordisturbed

Refer to Pump/motor manual torealign the pump/motor

Pressure of suction pump loweror equal to saturation pressure ofwater at that temperature

Check pressure of compressed airin expansion tank

Rectify as required

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