Saturday, January 12, 2019

Elements and Basics of Solar Pumping (JR118)






















Elements and Basics of Solar Pumping (JR118)
Introduction
Solar water pumps are a cost-effective and dependable method for providing water in situations where water resources are spread over long distances; power lines are few or non-existent; or fuel and maintenance costs are considerable. The system operates on power generated using solar PV (photovoltaic) system. The photovoltaic array converts the solar energy into electricity, which is used for running the motor pump set. The pumping system draws water from the open well, bore well, stream, pond, canal etc. The system requires a shadow-free area for installation of the Solar panel.. Over last seven years, the technology and price of solar pumping have evolved dramatically - and hence the opportunities it presents. SWP system capacity and ability have expanded.
Range
Solar pumps had limited performance and were restricted to pumping installations with a shallow water source and a low water demand. Today, pumps can reach deeper wells (500 meters (m), compared to the previous 200 m) and push larger volumes of water (1,500 m3/day, compared to the previous 500 m3/day at low head). Efficiencies have also increased considerably. New pump and motor designs have increased water outputs over the entire pump range Solar pumps are specifically designed to accept DC power directly from the solar modules and are optimized for operating under less-than-ideal sun conditions. Where conventional AC-powered pumps require a stable voltage and frequency to operate, solar pumps can operate over a wide range of voltage and available current.
Prices
Prices of photovoltaic (PV) panels have dropped exponentially. High demand for PV modules for grid- tied applications has resulted in massive economies of scale in production as well as competition among vendors. The commodity price of silicon, the key material, has also dropped substantially. Solar modules once cost around $5/Wp (watt-peak); now, they are less than $0.75/Wp (ex-factory). These reductions have made larger SWP systems possible where previously the capital cost priced them out of range. A system with 1800 watt PV array capacity and  2 HP pump can give a water discharge of 1.4 lakh liters per day from a depth of 6 to 7 meters. This quantity of water is considered adequate for irrigating about 5-8 acres of land holding for several crops. (CAUTION: Solar prices are rapidly falling and process quoted here may well not be valid by the time you read this   

Approximate Cost

Capacity of SPV system
Total Head (Suction & delivery) in m
Solar PV (watt)
Cost (Rs)
2 HP (surface pump)
10
1800
2,90,000
4.6 HP (submersible pump)
30
4800
7,15,000

Market Conditions
The number of SWP manufacturers and suppliers has increased. Old monopolies have been broken, and although the technology leaders continue to innovate, competition is fierce on price, performance, and quality. SWP is cost-competitive with diesel and wind pumps in all size ranges.
News
SWP is being mainstreamed and awareness is growing. Good news travels fast, and markets are already demanding SWP in place of conventional pumping solutions. Further opportunities are arising as intensive awareness campaigns support and elaborate on the details of system performance and savings. Retrofits to diesel pump systems represent a market for further potential savings
Solar pumping current applications
The highest demand is within rural off-grid areas, currently underserved, or served by costly fossil fuel-driven pumps. The potential applications include: Potable water supply for institutions (traditional niche market for schools and health clinics); Community-scale water supply schemes (larger village schemes); Livestock water supply (individual or communal); and Small-scale irrigation (individual farmers or cooperatives)
Regions
Solar pumping is most competitive in regions with high solar isolation, which include most of Africa, South America, South Asia, and Southeast Asia. Although these regions all have high radiation   the availability and depth of water resources vary significantly. Solar availability maps and data for Pakistan have been developed ,one is presented as follows:

Advantages of solar pumping
·         No fuel cost - as it uses available free sun light
·         No electricity required
·         Long operating life
·         Highly reliable and durable
·         Easy to operate and maintain
·         Eco-friendly

SWP systems consume little to no fuel. By using freely available sunlight, they avoid the constraints of weak or expensive rural fuel supply networks.
Unlike diesel-based systems (i.e., where a diesel generator powers the pump), solar pumping produces clean energy with zero or much reduced exhaust gases and pollutants.
Solar pumping systems are durable and reliable. PV panels have a design life of over 20 years, and solar pumps have few moving parts and require little maintenance (unlike diesel pumps).
Solar pumping systems are modular so can be tailored to current power needs and easily expanded by adding PV panels and accessories.
Properly installed solar systems are safe and low risk due to low system voltage. Adequate protection minimizes fire risk.


Disadvantages and mitigation
Solar pumping systems have high initial capital costs, which can be discouraging. However, component prices are drop- ping substantially and investment payback is quick thanks to vast reductions in fuel usage  
Water tank storage is preferable to batteries, but still expensive. Hybrid solar/diesel pumping can reduce the need for storage and hence costs.
Solar pumps still require some servicing, and specialized technicians/providers may be difficult to access in some areas. This is gradually improving.
Panel theft can be circumvented by sensitizing communities and providing simple antitheft measures.
SWP can lead to excessive groundwater extraction because operators face near zero marginal-cost of pumping ground- water.
A solar-powered water pumping system is like any other pumping system, except its power source is solar energy. Solar pumping technology covers the entire energy conversion process, from sunlight, to electrical energy, to mechanical energy, to stored energy. The process is elegant and simple.

There are several technically viable options for new pumping systems, generally distinguished by their energy source—diesel pump, wind, solar, etc. Cost-benefit analysis (CBA) is often used to assess the economic merits of alternative investment options.
Pumping systems typically have a 20-year lifespan, and over that period they incur various costs, some at the outset, and others at different times throughout the system lifetime. Consideration of all costs incurred during the system lifetime is often referred to as a life-cycle cost analysis (LCCA). LCCA is particularly important for renewable energy projects because of the high initial investment costs. More conventional options based on fossil fuels may appear cheaper due to lower initial costs; however, operating costs can be considerable over the project life.

Although pumping systems have myriad costs during their lifetime, a proper LCCA would assess at least four key cost elements:
Initial costs with capital expenditures (CAPEX);  and installation/commissioning. These mostly consist of the acquisition of equipment for the solar pump system: PV panels, pump, control system, pipes and fittings, wiring, etc. Initial costs also include design engineering, system installation, commissioning testing and inspection; Operation and maintenance (O&M). Operation costs are labor and energy costs related to a pumping system’s operation. They can vary widely depending on the system’s complexity and duty. For example, a hazardous duty pump may require daily checks for emissions and operational performance, whereas an automated nonhazardous system may only require limited supervi- sion. Security and managerial costs are also included here. Maintenance costs comprise all costs entailed in keeping the system functional, including routine activities (e.g., cleaning solar panels)and small repairs to faulty components. System design can influence O&M costs through construction quality, components used, and ease of access to spare parts.
Energy : System energy consumption is often one of the largest cost elements in the LCC, especially if the pump runs more than 2,000 hours per year. Solar pumping systems have lower energy supply costs than systems based on fossil fuels, such as diesel.
Capital replacements. Some major parts of a pumping system have a shorter design lifetime than that of the overall system (often 20 years), requiring capital replacements along with the associated costs. The pump, for example, often needs to be replaced after 7–10 years.

A solar pumping system consists of PV modules, a pump set, a storage tank, electronic components, and interconnected cables. Electronics normally include an inverter, power conditioner or pump controller, controls/protections, and water sensors


The energy and power for driving an SWP system comes directly from an array of solar modules of the correct size and specification. The elementary component of a solar module is the solar photovoltaic (PV) cell. The cell directly converts solar radiation into electric current, through the photoelectric effect. The ratio of electric power produced to radiation received is the solar PV cell’s efficiency. For example, if a cell generates 0.15 kW of power for each kW received from the sun, its efficiency is 15%. The semiconductor materials most commonly used in commercial PV cells are crystalline silicon. These modules are either mono crystalline silicon modules, where each PV cell has a single silicon crystal; or polycrystalline modules, where each cell has multiple crystals. Mono-crystalline modules are more efficient than polycrystalline ones (16–17% compared to 14–16% in commercial applications).

PV modules are rated according to their power output, based on a solar irradiance of 1,000 W/m2 at a specified module temperature. Panel output data includes the peak power (maximum power generated by the panel, often referred to as watt-peak [Wp]), voltage (volts [V]), and current (amps [A]). In addition to irradiance, PV module temperature affects the amount of power produced, with higher temperatures decreasing power output. It is therefore a good design practice to ensure good ventilation of the modules to limit their temperature increase.

A challenge in many countries has been the lack of quality regulation, leading to an influx of cheap, substandard, and counterfeit products in the local market. Purchasers of solar panels should thus seek quality assurance, as there are now well-developed global standards and testing procedures for panels, notably from the International Electro technical Commission (IEC) or similar organizations.

The main global standard for crystalline silicon modules is IEC 61215, which, like similar standards, is awarded largely based on tests administered to samples of modules produced. Since modules cannot be tested throughout their 25-year life time, accelerated stress testing is performed. One of the main tests is the verification of the nominal peak power that a PV module can deliver under standard testing conditions (STC), which include 1 kW/m2 of insolation perpendicular to the panels and 25°C of PV cell temperature.

Quality of solar modules, and matching of solar module performance is especially important in SWP systems consisting of large arrays of modules connected in series, where array performance, hence SWP performance, depends on the performance of the weakest module. Even one module with inferior output can have a devastating effect. The commissioning of a SWP system should identify such weaknesses through I-V curve scanning of the array.



Pumps physically lift water from source to point of use/storage. Technological progress has radically improved pump performance over the years, with pumps now available for pumping ranges up to 500 meters deep or 150 m3/h  
Water pumps are driven by electrical motors, which convert electrical energy (produced, in the case of solar pumping, by PV panels) into mechanical energy. Most motors typically run on either direct current (DC), where the electrical flow does not switch direction periodically in the wires; or alternating current (AC), where it does.
DC motors are appealing for solar pumping because PV modules producing direct current can be directly coupled to the motor with limited power conditioning. This makes them an economical option for systems with low water demand and a short cable distance between the PV panel array and the motor. For long-distance cabling, however, low-voltage DC motors are not suitable because of power loss in the cable. DC motors are currently not available beyond the 5 kW thresholds.
AC motors can be used in larger SWP systems, although they require a DC/AC inverter.
Solar pumping systems use two main types of pumps: positive displacement and centrifugal. Positive displacement pumps are further divided into volumetric and helical rotor pumps. Broadly speaking, positive displacement pumps are suitable for lower flow rates and medium to high pumping heads (30–250 m), whereas centrifugal pumps are suitable for high flow rates and lower pumping heads (10–120 m). Within positive displacement pumps, helical rotor pumps are especially suitable for operation with low and variable solar radiation levels, since they can pump at low speed without loss of efficiency, unlike centrifugal pumps, which do not produce any water below a threshold speed and are thus much less efficient at low or fluttering irradiation.
It should be noted that these are generalizations for illustration. The most suitable pump and motor type for any situation should be determined based on manufacturers’ catalogues and motor pump manuals, and specifically on pump/motor pair performance curves   (characterized to the IEC 62253 standard) to ensure that the pump/motor pair can deliver the required flow against the total dynamic head (TDH)

Power conditioners convert DC power from the solar panels to match the pump motor’s requirements. Power conditioners can take several formats: a simple DC-DC converter,   fixed-frequency inverter for an AC pump, or a more complex variable speed drive(VSD)in single or three-phase AC power. In general, the power conditioner is matched to a specific pump and optimized to suit the pump performance for array voltage and power. Pump kits from larger pump manufacturers provide an optimized power conditioner and motor/pump as a matched set. Such power conditioners provide change-over between solar supply and diesel engine supply, enabling use in hybrid systems or systems with back-up.

System integrators are increasingly combining third-party power conditioners or programmable VSDs with other third-party motor/pump pairs, and branding them as their own or offering them as original equipment manufacturer (OEM) solutions. Although these solutions may be just as efficient, they have likely been less well tested and the performance depends entirely on the programming setup. In particular, the performance of the controller/motor/pump under intermittent sunshine solar conditions may be substantially lower if not properly set up. For that reason, the testing and characterization of the entire set under the IEC 62253 standard, which can include three test conditions (clear day, cloudy day, and intermittent sunshine), can yield valuable comparative results).


System Design
This design process is complemented by deeper awareness of the equipment to be used in the system   

The design capacity of the solar water system depends primarily on water demand, measured in m3/day or liters/day   Water is considered for human and/or livestock consumption or for irrigation.

Potable water for human consumption in a village/town is estimated from population size and daily per capita water consumption. For example, if the system is to serve a population of 2,000 and the supply standard is 30 liters per capita per day, then system design capacity should be at least 60,000 liters/day or 60 m3/day. Similarly, water demand for livestock will depend on livestock type and quantity.

Irrigation water demand assessment is considerably more complex, and depends on area, soil hydration and properties, evaporation rates, crop selection, spacing, crop seasons, irrigation type, etc., and is best determined by an agronomist, to avoid over- or under-estimating water needs, and to determine optimal cropping seasons. The standards used in determining the water demand can usually be obtained from the ministry or government agency for water in the country. Designs typically allow for population growth and seasonality of demand.

Fresh water is generally obtained through open sources or surface water, such as rivers, streams, and dams; or protected ground water sources such as boreholes and wells. Each is characterized with respect to security of supply, water quality, and replenishment. In general, groundwater is preferred for potable water.

In assessing surface water sources, the following aspects must be carefully considered:

Groundwater is a commonly used water source. Groundwater is contained in aquifers, natural underground water reservoirs accessed by wells or boreholes. A pumping test is conducted to evaluate the amount of water that can be pumped from a particular aquifer. The test determines the maximum yield (in m3/h) as well as the drawdown, or depth to which the water level in the borehole will fall for a given yield and duration (yield per meter of drawdown), while being dynamically replenished by the aquifer. Obviously, a low drawdown is desirable.
In conventional engineering design, a pump’s design flow rate is derived by dividing the daily water demand by the total number of pumping hours in a day. Solar pumping applications, however, use the number of peak sun hours to estimate the daily pumping hours.
For example, in a solar resource that averages 7.0 kWh/m2/day, peak sun time is 7 hours/day. For a daily water requirement of 70 m3/day, the design flow rate is 70,000 liters/day/7 hours/day = 10,000 liters/hour. The design flow rate should not exceed the maximum water source pumping rate or yield. The design flow rate is used for future water pressure drop calculations and pipe sizing.


Most solar pumping systems require water storage capacity to improve performance and reliability. Reliability is improved when a storage tank is used to store water extracted during sunshine hours to meet water needs at night, or in the event of cloudy weather or system downtime.

In general, SWP tanks should be sized to store at least a 2–3-days of water supply (daily demand (m3/day) x 3 days = storage volume (m3). Field survey data indicate that many SWP storage tanks are too small, and experience water overflows in the daytime and shortages in the evening. Optimal tank sizing must account for the hourly water demand pattern as well as possible insolation variations supplying the tank.

Diesel pump systems, or SWP switchable with diesel back-up, on other hand, allow for much smaller tanks for back-up storage since the diesel pump may be run at any time.


In pumping systems, “head” refers to the height to which water must be pumped relative to its normal level (e.g., underground). Total dynamic head (TDH) or total pumping head is the sum of three components Dynamic water level (DWL) is the depth of the surface of the aquifer. This gradually increases due to drawdown, hence the term “dynamic.” Discharge head corresponds to the height above the ground of the water surface inside the storage tank (usually 5–10 m).This water is discharged to users through gravity, thus the name “discharge.” Friction head accounts for the friction of the water against the inside of the pipes (both vertical and horizontal). It is typically 10% of the DWL plus discharge head. A pumping test can provide information on the DWL and the discharge head, whereas the friction head can be more accurately obtained from head loss charts for pipes at the required flow rate and pipe characteristics.


Although not critical to the initial system sizing, PV panels should be installed close to the pump and water source, equator-facing, at optimal tilt angle to the horizon, and unshaded in any part of the solar array for the solar day. Panels should generally be situated in a secure and safe location. These issues can be fine-tuned during final design and installation, but for purposes of preliminary design, it is conceivable that the solar array would not be closely located to the pump, and thus longer array cables are required, with possible energy losses. This scenario calls for a high allowance for power loss in array cables.


Solar insolation is a measure of the cumulative irradiance received on a specific area over a period of time. It is a measure of energy (rather than power), normally expressed in kilowatt-hours (kWh/m2/ day). The characteristics of the solar resource at the site are critical to system design. Sunshine reaches the earth through radiation. Solar irradiance is the power of solar radiation received per unit area. Irradiance is the instantaneous measurement of power, in watts or kilowatts per square meter (W/m2 or kW/m2). Irradiance is affected by the angle of sun, and at any time of day it is highest when a solar module is perpendicular to the incident sun rays. Since the sun’s position in the sky changes during the day, irradiance increases during the morning until noon (when it is highest), and then decreases until sunset, since the sun’s rays must penetrate more of the atmosphere

Solar insolation is effectively equal to the area under the solar irradiance curve. Peak sun hours per day is just another term for solar insolation and is always measured in kWh/m2/day.

Solar resources vary from area to area  solar radiation is generally higher in regions near the equator. Factors that affect the amount of solar radiation on a particular area include latitude, prevalence of cloudy periods, humidity, atmospheric clarity, and seasonal variations.

Long-term statistical weather data from meteorological stations is usually provided in the form of monthly averaged data for insolation on a horizontal surface, and includes daily variations of this insolation. Since sizing of SWP systems requires further adjustments and optimizations to this data to account for non horizontal or tilted solar arrays orientated toward the equator, the complex nature of these calculations and statistical basis of the data suits computer-based sizing approaches.


Seasonal changes in solar radiation. Essentially, SWP water output is more or less proportional to irradiation. First-pass sizing is usually based on average insolation for the year, or perhaps the worst month of the year. It is necessary to assess the output for days when radiation will be less than the annual average, and less than the monthly average. Tilt angle optimization is required.

Seasonal changes in pumping head. Similarly, drops in water levels will affect pump output. Water output is more or less indirectly proportionate to pumping head. Too conservative an estimation of water level will result in system oversizing.

Sunny versus cloudy days: Average insolation is insufficient. A key variable is the amount of cloud cover and intermittency of the sunshine. Especially, variable speed drives coupled with AC pumps tend to suffer degraded performance under stop-start solar conditions, since they require minimum power conditions start-up, and take considerable time to spool up once threshold levels are reached. So while 2 days might have the same amount of cumulative insolation, a clear morning with zero sun in the afternoon is likely to yield far higher water output than an intermittently cloudy day. Derating for this kind of local variability is important for certain motor pump types in particular.
Array location: Maximized solar energy production depends on panel location and orientation. Panels should be equator-facing, with panel tilt predetermined based on latitude and local weather conditions to maximize incident insolation and facilitate panel cleaning during the rainy season. Shading at any time of day should be avoided. Because many solar pumping systems are located in remote areas, the risk of vandalism and theft can be significant, and panels should not be easily accessible by the public. If the use of trees and vegetation for shielding is deemed acceptable, then adjustment to sizing may be required if this reduces the amount of available solar radiation due to shading, especially in early morning and late afternoon. This should be decided before installation.

Safety standards: PV systems present a unique combination of hazards and risks, which must be addressed by sound design and specifications followed by proper installation, operation, and maintenance of the system. In large pumping systems, high-voltage DC arrays require special cabling, switch gear, and clear labelling.
Equipment protection. Protecting equipment against faults on both the DC and AC sides requires careful attention to earthing design and protective components. Risk of lightning damage isis document, key considerations include: addressed by grounding (giving electrical lightning surges a direct path to the ground that bypasses valuable equipment) and by installing lightning arrestors and surge protectors.Another major risk is that of vandalism and theft. Measures to curb this risk include:Build community ownership; Locate the solar array in a populated area with regular foot traffic; Fence the array to make access more difficult; Arrange for security guards; Install motion-detecting sensors and alarms whenever possible; Spot-weld bolts or use tamper-proof bolts, screws, and fasteners; Use anti-theft array mounting frames. These metallic structures hold the panels and are designed to withstand strong winds. There are three types of frames: ground, roof, and post
Commissioning immediately follows installation and refers to the process of “handing-over” the system to the client, i.e., ensuring that all system components have been properly installed, are in good condition and that the system is operating as expected. Commissioning comprises three main elements: documentation, inspection, and testing, and should be carried out in ac- cordance with the IEC/BS EN 62446 (for high-voltage DC arrays and earthing). General installation, including the AC side, should be in accordance with IEC 60364-9-1 (low-voltage electrical installations; installation, design and safety requirements for photovoltaic systems), and/or with British Wiring Standards BS 7671. Documentation should include single line diagram, individual component documentation, an O&M manual, and equipment warranty information. Testing benchmarks the system’s performance against the design requirements and assumptions, notably by measuring the water output against solar radiation and pumping head

After the system has been installed and commissioned, focus shifts to O&M throughout its lifetime. System operation can be optimized by closely monitoring and recording key system parameters (data logging), enabling operators to assess system performance or demand changes.

One crucial aspect of maintenance is warranties, usually against defective components or poor workmanship. Under the defects period of 1 to 2 years, any items that fail, are not installed to standard, or are damaged by natural calamities must be corrected on site at cost to the contractor/supplier/ installer. During the warranty period, the supplier  is also expected to check system components and perform preventive maintenance at least quarterly (in any case, neither pumps nor panels require heavy maintenance, with panels only needing periodic cleaning) to attend to user


Component Usual warranty period
Solar panels 25 years
Pump/motor  2-5 years
Inverter         5-10 years
Remaining components   1-2 years



complaints within a reasonable period of time, and to resolve any system breakdowns within 3 days. In addition to component warranties, the supplier may also provide a performance warranty on the system as a whole, ensuring that it will meet or exceed the design performance for a number of years. (See Table 3 for some example warranty time lines.)

Sustainability of solar SWP has been a challenge in many countries and especially in rural areas, with systems failing often within a short time after commissioning due to lack of proper O&M. It is therefore increasingly common for communities to establish comprehensive maintenance contracts with suppliers during warranty periods, and it is a good practice to extend such contracts beyond the warranty period. Suppliers should further secure system sustainability by training system operators, namely on basic plumbing skills useful for repairing leakages in the pipe network and on handling the advanced inverters and sensors common in modern solar pumping systems.

Since solar panels have no moving parts that could be affected by rust or break down, solar power requires very limited maintenance, other than regular dusting. Cleaning the solar panels with water is recommended to remove any dirt or dust.
Solar Pumping and Pakistan

 
A solar powered water pump uses the suns energy to supply electricity for the pump. The solar panels absorb the suns energy and convert it into electrical energy for the pump to operate. These pumps work most effectively on sunny days and adjust their output to the varying irradiance. Therefore, they are most suitable for Pakistani farmers due to the high levels of solar irradiance in Pakistan. For people living in remote and rural areas the cost of running power lines, poles, and transformers or diesel pumping water is generally very expensive. Solar water pumps are an excellent alternative and are becoming more common for use in crop irrigation. Tube wells presently installed in the country are as follows (2011):



Type



Area
Number of Tube wells/Lift Pumps by Horse Power


Total
Less than 10 Hp


10hp to 15 hp
16hp to 20 hp
21hp to 25 hp
Greater than 25hp



Diesel
Punjab
3,224
110,890
542,419
25,404
89,701
771,638
Sindh
540
6,671
33,554
524
1,408
42,697
KPK
1,712
2,891
4,854
542
1,020
11,019
Balochistan
284
2,123
5,270
802
1,078
9,557
Total Diesel
5,760
122,575
586,097
27,272
93,207
834,911



Electric
Punjab
34,651
53,781
61,865
2531
70,990
223,818
Sindh
6,328
9,765
6,824
252
5,588
28,757
KPK
18,761
4,874
3,837
898
3,581
31,951
Balochistan
5,617
8,402
6,519
1343
8,129
30,010

Total Electric

65,357

76,822

79,045

5,024

88,288

314,536
Total
71,117
199,397
665,142
32,296
181,495
1,149,447
Solar Tube Wells for Baluchistan
The federal and Baluchistan governments have agreed to undertake feasibility for installation of 30,000 solar tube wells in the province by replacing the existing conventional tube wells. The reliance on solar-powered tube wells in Baluchistan will lead to annual savings of Rs23 billion as the federal government will not need to release billions of rupees in electricity subsidy. The Power Division minister, while expressing his views, said the federal government was paying Rs23 billion per year in subsidy on 30,000 tube wells in Baluchistan and their shift to solar power would ease the burden on the national exchequer. The switch to clean and renewable energy would also ensure power supply at affordable prices to agriculturists and would help increase crop productivity, he said. The move would help in mitigation of circular debt as all illegal connections associated with the tube wells would be exposed with the connection to solar panels and proper action would be taken against stealing. “Electricity theft from these tube wells will come to a halt.”
Solar Tube wells
Punjab and Sindh governments had a project to replace diesel pumps with solar. The projects had little success as in spite of the subsidy offered farmers were reluctant to put funds up front.

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