Power Solar Options General

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Solar, Bio-Mass & Power Options

F.D Romeijn (Consulting Engineer)

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Current Energy Uses

• Grid Connected Electricity (PLN)– Process, Cooling and Utilities.

• Own Steam Generation (PGN)– Hot water (Sanitation/Production)– Product Heating (Boiling)

General Way Of Working:

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Proposed Energy Uses

• Bio-mass gasification/combustion.• Self Generation by Gas-Engine/turbine

– Electricity– Hot water + HRSG

• High Temperature Solar Devices– Cooling (8 or 24 hrs. with storage)– Steam (with accumulator)– Hot water (8 or 24 hrs. with storage)

Bio-Mass Options

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Three major energy conversion processes can be considered, I.e.,

•Combustion > Steam > Power Generation and Heat.•Gasification > Producer Gas > Power Generation and Heat.•Anaerobic Digestion > Methane > Power Generation and Heat.

Bio-mass, or agricultural waste is in many forms available in Indonesia. More often than not, much of the bio-mass is discarded or plainly burned on the fields. The most common types are listed below;

•Rice husk – LHV ~ 14 MJ•Coconut Shells (Meso/exocarps) – LHV ~ 16 MJ•Woody Types – Cassava waste – Bamboo waste etc. LHV ~ 18 MJ•Captive Waste – Saw Dust – Organic waste/effluent etc. LHV varies.

Combustion

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Combustion takes place in a steam generator where the fuel (bio-mass) is converted into steam of a certain pressure. This conversion can reach a efficiency of approximately 88%. (Q-in vs. Q-out)The steam can be utilized in a condensing steam turbine for electrical power generation, or in a extracting steam turbine for power en heat generation.The total efficiency is approximately 25% depending on whether a extracting or condensing approach is followed.Fly-ash can be an additional income stream while, in case of rice-husk, silica can be a by-product as well.As indicated, system efficiency is low, while Capex is considerable, especially when higher steam pressures (thus higher efficiencies) are employed.

A point of concern is the reliability of feed-stock supply. Although previously stated, bio-mass is readily available and is often discarded on the field. However, when a buyer appears, it (the bio-mass) becomes instantly an commodity. It is therefore important to strike long-term agreements with communities, private suppliers en local leaders in order to guarantee supply and price.

Gasification

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Gasification is a process whereby under low oxygen conditions, a combustible fuel (bio-mass / BM) is converted into a gas that can be used by internal combustion engines. The process comprises of 4 distinct phases as follows:

•Drying – in order to reach a MC of 10% or lower.•Pyrolysis – to raise HV by further removing water.•Combustion – BM is partly combusted to maintain reactor temperature.•Reduction – BM is converted into gas. (CO + H2 + CH4)

All phases take place in the reactor on different levels. Feedstock is added from the top, ash is removed from the bottom. The ash can be compressed into briquette and be considered an additional income stream.

Efficiency of the entire cycle, gasification to generation is of the same order as a steam process, however, Capex is much lower. Moreover, it is possible to store gas for later use, which considerably increases flexibility.

Anaerobic Digestion

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Digestion is a biological process whereby methanogenic bacteria convert an organic waste into methane (CH4) in a anaerobic atmosphere. The process takes place in a ‘digester’ which can be ‘plug-flow’, a covered lagoon/tank or ‘batch-flow’ when feed-stock is produced intermittently.

The resulting gas is of a high energy value, comparable with natural gas, but has to be cleaned from unwanted elements before using it in a internal combustion engine.

The efficiency of a particular system depends largely on the conditions under which the process takes place. Thermophilic digestion will yield higher gas rates than mesosphilic digestion but need an additional heat source.In all, the process is complicated and needs knowledgeable personnel in order to maximize yield and avoid break-down.

The residue, non-volatile solids, are usually sold as fertilizer.

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Solar Energy• Solar energy, both heat and electricity is an option to accommodate

power/cooling/lighting demand.• Photovoltaic options are as yet not feasible for power applications, however,

lighting and small appliances can be served.• Indirect channeling of solar irradiation can be utilized for factory lighting.• Solar energy is intermittent, therefore back-up power must be available or the

‘solar-field’ must be of such size and yield that all possible circumstances are accounted for.

• Indonesia is located in a tropical region, but this does not mean that the sun is always “on”. Climate issues play a significant role, but cannot always be predicted. I.e El Nino and La Nina phenomena and even volcanic activity.

• Some solar panels work well in diffuse light, others not at all.• Solar Panels come in a great variety, one should carefully analyze what

applications can be powered.• High temperatures > lower efficiency > need for advanced equipment.• Storage (TES) is a key-element in successful implementation of a solar

option. (Thermal Energy Storage)

How much energy is available?

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In order to establish how much energy can sensibly be captured we need to know what amount of solar irradiation/insolation actually reaches the earth surface. This can be established in two ways:

•Empirically – By installing pyrano-metering devices at the desired location and measuring insolation levels for a period of at least a year.•By making use of satellite data that is collected since the late 80’s and provides us with a rich data set (20+ years) of direct insolation and other climate related information.

It is preferred to make use of the satellite data, although the area’s measured are rather large; between geographic degrees these area’s measure 1° x 1° or 110 x 110 km. However, for the purpose of calculation the average insolation values, this method is sufficiently accurate.

For example; in the next slide, the data that is collected for a specific area, namely 7 degrees South and 112 degrees East. The area South-East of Surabaya.

Actual Data

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Insolation data valid for Latitude; 7S and Longitude; 112E (MultiBintang)

Major values in terms of thermal energy are in kWh per square meter per day.Obviously a day means the time that the Sun is apparent above the horizon.Direct – Diffuse etc. shall indicate:•Direct – Unobstructed insolation.•Diffuse – Obstructed insolation. I.e, Clouds, Dust etc. UV and IR spectra will be captured as well as reflective irradiation.•Global – The sum of above, safe for ‘assumed’ thresholds, beneath which capture is not sensible. (This depends largely on the type of absorber installed)•Clear – Days per month that no obstruction is apparent.•No Sun – Days per month that no sun is apparent. (Total cloudy days)•Dir+Dif – The sum of direct and diffuse, without thresholds.

    Lat Lon Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann/av a/kWhDirect Insolation kWh/m2/d -7 112 3.53 3.62 4.58 5.19 5.99 6.10 6.90 7.33 7.36 6.36 4.97 3.83 5.48 2,000

Diffuse Insulation kWh/m2/d -7 112 2.30 2.36 2.24 1.94 1.59 1.46 1.36 1.44 1.65 2.00 2.20 2.25 1.90 694

Global Insolation kWh/m2/d -7 112 4.71 4.89 5.47 5.46 5.42 5.21 5.68 6.31 6.80 6.48 5.62 4.85 5.58 2,037

22Yr Clear d/m -7 112 7.44 7.53 7.40 6.99 6.33 5.97 6.16 6.68 7.25 7.44 7.43 7.43 7.00  

22Yr No Sun d/m -7 112 6.11 5.08 5.14 4.60 3.89 3.89 3.67 2.60 3.27 3.73 6.19 8.57 4.73  

Dir+Dif kWh/m2/d -7 112 5.83 5.98 6.82 7.13 7.58 7.56 8.26 8.77 9.01 8.36 7.17 6.08 7.38 2,694

How to interpret the Data

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The data presented in the previous slide is ‘gross’ energy, in other words, that what reaches the earth surface and is collectable. It is prudent to use the ‘global’ data-set before is known which type of collector will be used. With this data we can calculate the ‘net’ energy which can be sensibly utilized. (In the form of hot water or steam.) During calculation of efficiency of a particular device, the lower threshold can be determined and insolation yields adjusted accordingly.

In order to arrive at useful figures, we need to find the efficiencies of various devices that are intended to convert solar energy into hot water and steam.

On the next slide we present some options. From least efficient to most efficient.Note that we do not consider domestic sun boilers, since these are usually less efficient for industrial purposes.

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Solar Capturing Devices• Advanced flat plate collectors (AFPC)

– Temperatures up to 130 °C.– Medium efficient. (Direct and Diffuse)– Can drive single effect chillers.

• Evacuated tube collectors. (EHTC) and (EDFC)– Temperature up to 90 - 170 °C.– Less efficient on higher temperatures. (Direct and Diffuse)– Can drive purpose build single and dual effect chillers.

• Concentrating devices. (CPC and HPC)– Temperatures; 120-170 °C and >250 °C.– High efficiency. (Only direct for CPC)– Can drive dual effect chillers (Hot Water and Steam).

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Advanced Flat Plate Collectors• High efficiency on lower

temperatures.• Also used for cooling

applications.• Can be used as roof-

coverage, very good insulation effect.

• Orientation is important.• Captures both direct as well

as diffuse irradiation.• Relative expensive,

expected 220-250 €/m2

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Evacuated Tube Collectors• Many different manufacturers available.

(Mostly China)• Proven design.• Both in ‘heat-pipe’ as in ‘direct-flow’

configuration. I.e, Evacuated Heat Pipe Collectors and Evacuated Direct Flow Collectors.

• Higher diameter tubes are more efficient. (100mm)

• Orientation is important.• Captures both direct as well as diffuse

irradiation.• Reasonable price, 150-200 $/m2

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Concentrating Devices• Both parabolic troughs as well as

evacuated heat pipes.• Sun-Tracking is required.• High efficiency for both.• Parabolic Trough Collectors need

‘direct’ irradiation contrary to the heat-pipe variant.

• Temperatures:– PTC 170 °C – 250 °C– HPC 120-170 °C

• Prices:– PTC 150 – 200 €/m2– HPC 120 – 150 €/m2

• HPC (concentrating) – also named CHPC• PTC - also named CPC ‘concentrating parabolic collector’

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Efficiencies of Solar Devices1. In order to calculate efficiencies of collector devices, we need important

information regarding internal heat losses under various circumstances. Further data regarding average ambient temperatures as they influence efficiency as well. This data is for most collectors available with certification institutes, while ambient data can be retrieved from meteorological institutes.

2. It has to be determined, what level of heat must be captured in relation to usage. F.I, Hot Water at a certain temperature, or steam at a certain pressure. Thermal oil can be used as well, normally this method serves higher temperature applications like spray dryers etc.

3. The amount of energy (per shift or per hour in kWh) needs to be determined. An example is shown on the next slide.

4. As operations extend after sun-hours, Thermal Energy Storage (TES) must be considered. F.i, Hot water storage, cold water storage and steam accumulators.

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Efficiencies of Solar DevicesThis example concerns superheated water at a pressure of 8 Bar(a). The efficiency at G=900 W/m2 is 61%. Naturally, the insolation varies with sun-position at a certain time of day, therefore when plotted in a graph, we can calculate an average efficiency of 47% over the entire day. With an daily insolation of 5,600 W/m2, total collected energy will be 2.656 kWh per square meter aperture per day.

If applied to office cooling, a field of 2000 m2 would generate 2,264 RT per day.This can be utilized during 8 office hours, or longer if appropriate storage is installed.

Next slide will explain that higher efficiencies and lower usage temperatures have an impact on total efficiency.

Steam Process (Superheated water)  Maker   XX              Type   U tube - 2-16 (100mm) Example 2-stage abs. cooling    Gross area 4.2 m2   M2 2000 5,307 kWhd  Aperture area 2.9 m2   Panels 482      Absorber area 2.8 m2   COP 1.5      Min Flow Rate   l/h   kWc/d 10,404      Max Flow Rate   l/h   RT/d 2,264      Nominal Flow Rate 457 l/h                               Calculation of Gross performance excludes heat losses in piping & vessels                     

1 Conversion factor η0 0.841   from testreport    2 Loss coefficient a1 1.047 W/(m2K) from testreport    3 Loss coefficient a2 0.010 W/(m2K) from testreport    4 Daily Insolation Gd 5580 W/m2/d from tabel      5 insolation level G 900 W/m2 calculation      6 Ambient T   TA 30 °C input      7 Average Manifold T TM 130 °C calculation (Ti+To)/2    8 Manifold in T Ti 90 °C input      9 Manifold out T To 170 °C input      

10 X value   X 0.111   calculation (TM-TA)/G    11 Aperture area m2 2.93   from testreport    

                   12 Calculation η(x) = η0 - (a1*X) - (a2*G*X2)        

                   13 efficiency η(x) % 61%          

                   14 yield vs G   W/m2 550.2          15 yield panel vs G W 1612.0          

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Efficiencies of Solar DevicesThis example concerns heated water at normal pressure. The efficiency at G=900 W/m2 is 76%. Naturally, the insolation varies with sun-position at a certain time of day, therefore when plotted in a graph, we can calculate an average efficiency of 70% over the entire day. With an daily insolation of 5,600 W/m2, total collected energy will be 3.944 kWh per square meter aperture per day.

If applied to office cooling, a field of 2000 m2 would generate 1,683 RT per day.

This is importantly lower than the first example. The reason is that the application (absorption chilling in single stage) is less efficient compared with the previous example. In this case it would be prudent to utilize the energy for other purposes.

Hot Water Process  Maker   XX              Type   U tube - 2-16 (100mm) Example 1 stage abs. cooling    Gross area 4.2 m2   M2 2000 7,889 kWhd  Aperture area 2.9 m2   Panels 482      Absorber area 2.8 m2   COP 0.75      Min Flow Rate   l/h   kWc/d 5,917      Max Flow Rate   l/h   RT/d 1,683      Nominal Flow Rate 457 l/h                               Calculation of Gross performance excludes heat losses in piping & vessels                     

1 Conversion factor η0 0.841   from testreport    2 Loss coefficient a1 1.047 W/(m2K) from testreport    3 Loss coefficient a2 0.010 W/(m2K) from testreport    4 Daily Insolation Gd 5580 W/m2/d from tabel      5 insolation level G 900 W/m2 calculation      6 Ambient T   TA 32 °C input      7 Average Manifold T TM 78 °C calculation (Ti+To)/2    8 Manifold in T Ti 60 °C input      9 Manifold out T To 95 °C input      

10 X value   X 0.051   calculation (TM-TA)/G    11 Aperture area m2 2.93   from testreport    

                   12 Calculation η(x) = η0 - (a1*X) - (a2*G*X2)        

                   13 efficiency η(x) % 76%          

                   14 yield vs G   W/m2 688.1          15 yield panel vs G W 2016.2          

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How to Proceed?The previous slides show that the choice of collectors and size of the field highly depends on the following considerations:

•Efficiency of the collectors. (Initial yield, internal heat losses)•The end temperature of the medium heated; usually (superheated) water but thermal oil is possible.•The temperature variance, meaning the heat dissipated to equipment or product in a certain unit of time. (heat-flow)•Reliability of operations, in terms of available back-up.•The duration in which the collected energy is used. (one shift operations or more, in which a TES must be provided)•Coverage:

– Auxiliary source of energy. “Take what you can get”– Main coverage, based on a certain size. Top-up with conventional sources.– Total coverage. Includes ‘oversized’ solar field and large or eutectic TES.

•Cost and ROI.•Possible emission reduction.

Investment & ROI

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Capex, Opex and ROI are important drivers in this energy sector, many projects end-up on the shelf because these figures are difficult to obtain or remain shady due to misinterpretation and or misunderstanding. However, if one would be able to factor-in all the available data, one could ‘paint a picture’ that is more appropriate for a decision making process.

This requires in-depth analysis of the entire concept that must include;

Current an future demand and cost to generate. In order to calculate Capex, returns and pay-back time.

Options for energy replacement. In order to establish the most suitable solutions in respect to expected developments.

Lowest recorded insolation levels Months with low recorded insolation. Number of ‘No-Sun’ days per year.

In order to establish the most appropriate seizing for the ‘solar field’. Also in relation to investment cost and returns.

Highest insolation incidents. Both momentarily and over time.

In order to establish seize and type of TES.(Accumulators, conventional TES and Eutectic TES.)

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End

Thank You