Photovoltaic Training - Session 6 - Off-grid installations


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* Criteria of higher winter production versus annual production maximization
* Hybrid systems.
* Storage Systems.
* Types of Batteries.
* The importance of energy efficiency in consumption in the isolated systems.
* Maintenance.

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Photovoltaic Training - Session 6 - Off-grid installations

  1. 1. Photovoltaic Systems Training Session 6 – Off‐grid installations Javier Relancio & Luis Recuero Generalia Group October 6th 2010 construction-operation-and-maintenance
  2. 2. PHOTOVOLTAIC SYSTEM Design, Execution, Operation & Maintenance STAND ALONE FACILITIES Javier Relancio. Generalia Group.  06/10/2010 2
  3. 3. INDEX Introduction Elements. Storage System & Backup System Trends: Hybrid Systems. Efficiency. Smart Grids Applications. Examples Design Maintenance 3
  4. 4. INDEX Introduction Elements. Storage System & Backup System Trends: Hybrid Systems. Efficiency. Smart Grids Applications. Examples Design Maintenance 4
  5. 5. Basic topology PV modules PV regulator DC Consumption Inverter AC Consumption 5
  6. 6. Introduction Differences with a grid connected system Designed for self-consumption An electricity storage is required Regulator / charger Batteries Inverters with capacity " to create a grid" For facilities with consumptions in DC and output power below 2 kW, we may require modules with particular characteristics: If the consumptions are in DC 12 V, modules of 18 V If they are in DC 24 V, modules of 30-32 V NOTE: The modules of 12 V are more expensive, but it is possible to avoid their use by using regulators with power maximizers. Only for powers over 2 kW 6
  7. 7. Introduction Criterion of “winter production maximization” VS “annual production maximization” In the grid connected facilities, the objective is to obtain the maximum annual profitability of the installation In stand-alone facilities, the objective is to feed the demand for any day of the year. For it: We have to design the installation for the " worse day of the year " We will choose the modules tilt that maximizes the production in the above mentioned month Sofia, Bulgaria Madrid, Spain 6 Ed (32º) Ed  (61º) Ed (34º) Ed  (60º) Jan  1,65 1,79 2,66 2,96 5 Feb  2,25 2,34 3,05 3,19 Mar  2,75 2,63 4,32 4,23 4 Apr  3,42 3,01 4,1 3,63 3 May  3,61 2,95 4,63 3,75 Jun  3,79 2,97 4,78 3,69 2 Jul  4,06 3,23 4,91 3,85 Aug  3,95 3,37 4,79 4,08 1 Sep  3,48 3,28 4,38 4,14 Oct  2,68 2,74 3,54 3,63 0 Nov  1,71 1,84 2,66 2,9 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Dec  1,3 1,41 2,15 2,39 Sofia, Bulgaria (32º) Sofia, Bulgaria (61º) Total year 1050 960 1400 1290 Madrid, España (34º) Madrid, España (60º) 7 Note: we can use backup system for the worst production months
  8. 8. INDEX Introduction Elements. Storage System & Backup System Trends: Hybrid Systems. Efficiency. Smart Grids Applications. Examples Design Maintenance 8
  9. 9. Elements Inverter Lower range of powers than for grid connected facilities Possibility of connection in parallel or series Prepared for auxiliary inputs in parallel, in case of hybrid systems: diesel, grid, modules … Manufacturers: Manufacturer Power (per unit) System Power Observations • It integrates a battery charger • It allows to inject surplus to the grid Xantrex 6 kW 36 kW • It allows different configuration modes for the management of the generation and the consumption • It integrates a battery charger 100 kVA Victron 10 kVA • It allows different configuration modes for the (90 kW) management of the generation and the consumption • It integrates a battery charger Ingeteam 15 kVA 120 kVA • It allows different configuration modes for the management of the generation and the consumption 9
  10. 10. Elements Regulator / Charger It is used to: ... protect the batteries against overcharging To avoid excessive discharges within a cycle It is recommended to work with a oversizing of 125 % Differences between regulator and charger Charger: it is only used to charge the batteries Regulator: it is used both for charging the batteries and managing the loads in DC NOTE: The chargers are not simple devices: The battery charge stage depends on many factors and is difficult to determine Multiple algorithms exist to optimize the battery charging and to increase its lifetime 10
  11. 11. Batteries Introduction Batteries are used for storing the energy that is produced by the modules during the day, for being consumed in the periods that there is no solar irradiation This storage takes place due to chemical reversible reactions A battery is composed by the connection of several "cells” in series Between the electrodes there is a certain potential difference (Generally: 2V) In photovoltaic applications we can generally find batteries of 12, 24 or 48 volts Normally, the system is designed to store energy for several days of consumption In case of several days of low irradiation: clouds, rain, etc Three days can be a good recommendation, depending on each case 11
  12. 12. Batteries Capacity Electricity that can be obtained during a full discharge of a completely charged battery The capacity, in Amperes - hours (A - h), is the current that the battery can supply, multiplied by the number of hours in which the above mentioned current is delivered Real capacity Theoretically, a battery of 200 A - h might supply: 200A during an hour, 100A for two hours, 1A for 200 hours and so on. However, in the reality, the capacity of the battery will change according to the regime of charge and discharge. (Generally, lower speed of discharge implies a bigger capacity) For example: a battery which specifies a capacity of 100 A - h during 8 hours (C-8): It might supply 12,5 A during 8 hours. C = 12.5 x 8 = 100 A - h But it might provide 5.8 A during 20 hours. C ' = 5.8 x 20 = 116 A - h 12
  13. 13. Batteries Depth of discharge Percentage of the total capacity of the battery that can be used without need of recharge and without damaging the battery. As a general rule, the less depth of discharge is reached in every cycle, the longer the battery lifetime will be Classification: Light cycle Deep cycle ‐ Designed for high current in the initial  ‐ Designed for long periods of utilization without  discharges being recharged ‐ Constant charges and discharges ‐ They are more robust and have higher energetic  ‐ Depths of discharge lower than 20 % density ‐ Depth of discharge around of 80 %' Note: This classification is generally used for Lead-Acid batteries Several manufacturers Isofoton, Hoppecke, BAE, TABB, Tudor, etc
  14. 14. Batteries Type of batteries For photovoltaic applications the most suitable batteries are the stationary ones, designed to have a fixed emplacement and for the cases in which the consumption is more or less irregular. The stationary batteries do not need to supply high currents during brief periods of time, but they need to reach deep discharges Lead – Acid Lead – Acid Gel-Cell NiCad (deep cycle) (light cycle) Observations • High commercial • High commercial • The acid is in gel • Better performance availability availability state with high temperature • Sudden death could • Sudden death could • They need less • They cost the double happen happen maintenance than Lead – Acid • They are • They are manufactured • They can operate in batteries manufactured with with lead - calcium any position lead – antimony • They are more expensive than lead batteries Discharge depth 40-80% 15-25% 15-25% 100% Self – discharge per month 5% 1-4% 2-3% 3-6% Typical capacity (Ah/m3) 35,314 24,720 8,828 17,660 Capacity range (Ah/m3) 7,062 to 50,323 5,791 to 49,000 3,672 to 16,400 3,630 to 34,961 Typical capacity (Ah/Kg) 12.11 10.13 4.85 11.10 Capacity range (Ah/Kg) 4.18 to 26.65 2.42 to 20.26 2.20 to 13.87 2.64 to 20.90 Minimal temperature (oC) -6.6 -6.6 -18 -45
  15. 15. Diesel generator The diesel generator as a backup (I) The use of a diesel generator can allow us to avoid the oversizing of solar modules and batteries. The diesel generator would cover the periods of low irradiation or the situations of extraordinary consumption Nowadays, the energy generated by a diesel group can be more expensive than the energy obtained from a photovoltaic solar system It will depend on the price of the fuel in each country NOTE: In the following slide we can find an example 15
  16. 16. Diesel generator Price per kWh: Diesel generator VS Solar Facility  1,40  1,20  1,00  0,80  0,60  0,40  0,20  ‐ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Precio kWh hibrido Precio kWh    G Diesel Precio kWh    G Diesel CO2 Notes: 1. For this study we have considered that the price of the electricity from a Diesel Generator is, today, 0.35 € per kWh (Including the costs that the logistics of the fuel supposes). 2. The study has considered a radiation of 1500 HSP 3. In the graph we can find, in green, an estimation of the repercussion that would suppose the extra charges for the emission of pollutant gases (Price of ton of CO2). 4. The prices are in Euros 5. The word "hybrid" refers to a photovoltaic installation with a diesel generator as a backup. 16
  17. 17. INDEX Introduction Elements. Storage System & Backup System Trends: Hybrid Systems. Efficiency. Smart Grids Applications. Examples Design Maintenance 17
  18. 18. Hybrid System: Diesel - Solar Inverter PV regulator DC Consumption AC PV modules Consumption The generator is connected to the AC BUS The chosen diesel generator must have The diesel generator is automatically switched on if automatic starter: the batteries are under a certain level Using its own electronic starter to The generator can produce energy exclusively to automatically switch on when an auxiliary supply the consumption or, also, to charge the batteries signal is received The inverter has to be specially designed with Using an external electronic starter this function (AC/DC Converter) specially designed for this function 18
  19. 19. Hybrid System: Wind - Solar Description This type of system is currently being studied on the R&D departments of many institutions and companies. Good correlation between the wind and the solar resource Generally, the wind & solar systems are connected to the DC BUS (of the batteries) There is not too much information about the wind resource The guarantees for the wind system are lower than for the PV system Average, three years The wind potential is determined by: Speed of the wind: the kinetic energy of the wind  increases according to the cube of its speed Wind resources become exploitable where  average annual wind speeds exceed 4‐5 m/s Also it is influenced, to a lesser extent, by the  characteristics and density of the wind 19
  20. 20. Hybrid System: Wind - Solar Topology PV modules PV DC Consumption regulator DC BUS Wind regulator Inverter AC Consumption Wind generator 20
  21. 21. Efficiency in the consumption (I) The importance of reducing the consumption … Nowadays, we can find great evolutions in the consumption reduction of many massive devices: electrical appliances, lighting, air conditioning, PCs, etc Considering the high initial investment per kWp for an isolated solar system… and considering the dependency between this peak power and the consumption… …every stand alone solar facility should begin by the optimization of its consumption efficiency Example: Electricity price: 0,40 € per kWh Fridge consumption “A+ Class”: 150 kWh/year Saving: 260 € per year Source: IDAE Fridge consumption “G Class”: 800 kWh/year * If we reduce our energy consumption, installing a more efficient 21 device, we will be able to reduce the price of our solar PV Facility
  22. 22. Consumption efficiency (II) Examples Low Ordinary Element Energy Energy consumption consumption More efficient class consumption Evaluation Class A Class G Fridge 150 kWh/year 800 kWh/year LOW Washing Class A Class G Machine 1.42 kWh 6.9 kWh MED Incandescent LED Lighting 1 100 W 10 W HIGH Incandescent Low Consumption Lighting 2 Less efficient 100 W 18 W PC 250 W 70 W (Desktop) 22
  23. 23. Smart Grids (I) Global objective International governments commitment (such as the EU) Minimize the environmental impact. Reduce the CO2 emissions Reduce the dependency from fossil fuels Increase the use of Renewable Energies Reduce costs & Increase the energy efficiency To success: Increase the integration of renewable energies in the Global electric grid The need of dealing with an intermittent & distributed generation 23
  24. 24. Smart Grids (II) Mechanisms towards the smart grids Improve the control & supervision of the generation Demand profile for an average day in Spain Intermittent generation profile of the Renewable Energies Low forecast on the production Improve the demand management High peak–valley ratio Low correlation with renewable production Improve the international grid connection Source: REE Improve the electricity storage New facilities to pump water and then produce energy R&D for new in situ storage systems: hydrogen/ batteries The electrical vehicle
  25. 25. INDEX Introduction Elements. Storage System & Backup System Trends: Hybrid Systems. Efficiency. Smart Grids Applications. Examples Design Maintenance 25
  26. 26. Application Areas Zones distant from the grid Zones currently supplied by diesel generators Exceptionally, areas with instabilities from the grid Great potential in African countries Especially, areas with high fuel prices Source: World energy outlook 2009 26
  27. 27. Application examples Single family houses Public buildings: hospitals, schools, etc Public lighting and traffic lights Communication Stations Water pumping For human consumption For agriculture Desalination & Water sewerage Industrial uses 27
  28. 28. Particular case: Water pumping facilities Great advantages to be fed with solar energy: There is no need for batteries The construction of a high water tank can be used as a energy storage Therefore we do not need regulator either Neither inverters Nowadays, we can find great quality DC bombs Installation with few elements: We reduce the price of the installation We reduce the possibilities of breakdown 28
  29. 29. Other considerations Limits on the system Lead-Acid batteries, each cell allows a maximum of Maximum power output 3.000Ah en C-10(2V). If we are using 48 V rows, It is limited by the inverters: nowadays <120 kWp which is generally the maximum voltage that we can use, each row would store Maximum capacity of storage up to: 3.000 Ah x 48 V = 144 kWh It is limited by the batteries Lead - acid: it is recommended not to install more than three or four blocks of batteries in parallel If we use Ni-Cad this quantity can be higher (according to the manufacturers) * * It is recommended to verify this information with the manufacturer Towards the system scalability With the goal to supply energy to growing populations By the mix of different technologies 29
  30. 30. INDEX Introduction Elements. Storage System & Backup System Trends: Hybrid Systems. Efficiency. Smart Grids Applications. Examples Design Maintenance 30
  31. 31. System design (I) Study of consumptions We begin by creating a table with all the consumptions we will find in the system Device Number of  Peak  Average  Hours of usage  Consumed energy Units Power (W) Power (W) (h per day) (Wh per day) Lamp 10 11 88* 8 880 PC 1 300 150 6 900 Fridge 1 1000 400 24 9600 TV 1 90 90 8 720 TOTAL 1500 W 728 W 12.100 Wh per day * Simultaneity ratio 80% The peak power will affect the inverter calculation The daily energy consumption will affect: The storage system The solar modules 31
  32. 32. System design (II) Solar generator calculation According to the consumption study, we have to produce 12.100 Wh per day (average) As we have explained previously, this production must be guaranteed even the worst day of the year, in this case, in December Madrid, España We have to consider the losses in all the elements of the system: Ed* (34º) Ed*  (60º) Jan  2,66 2,96 modules, inverters, chargers, batteries and cables. Feb  3,05 3,19 Mar  4,32 4,23 Apr  4,1 3,63 The battery losses can be estimated around 15 % May  4,63 3,75 Jun  4,78 3,69 The whole system losses, can be estimated around 34 % Jul  4,91 3,85 Aug  4,79 4,08 Sep  4,38 4,14 Energydemanded 12100 Oct  3,54 3,63 Psolar = = =7.670,85W Nov  Dec  2,66 2,15 2,9 2,39 HSP× Losses 2,39 × 0,66 Total year 1400 1290 *Ed: Average daily electricity production for 1kWp We could install, for example: 34 modules of 230 W = 7.820 Wp 32
  33. 33. System design (III) Battery calculation According to the consumption study, the batteries should supply 12.100 Wh/day (average) In this example, the system will consider that the batteries have to be able to store energy for two days without solar radiation The batteries, then, should be able to store 24.200 Wh For this example, we will choose Lead-Acid batteries, with a Cycle-Depth of 80% In order to increase the battery life-time, we will consider a maximum discharge depth around 60 % We will consider the battery losses around 15%. Energy demand × nº days 12100 × 2 Capacity A−h = = = 1977.12 A − h Discharge depth× Losses × Voltage 0,6 × 0,85 × 24 Conclusion: 12 batteries of 2000 A-h (C-20) 33
  34. 34. System design(IV) Inverter calculation (I) Now, we have to consider the peak power of the system In this case, the maximum power would be 1500 Wp However, usually we use a “Simultaneity Ratio”, because normally all the devices will not be connected at the same time Furthermore, the inverters are prepared to supply the double of their nominal output power, during a certain period of time In this case, we will consider that the peaks from the washing machine and the fridge will not be longer than these periods 34
  35. 35. System design (V) Inverter calculation (II) We will reach a maximum output power of 1500 Wp, so the Nominal Output Power should be higher than 750 Wp Considering the average consumptions, and applying a “Simultaneity Ratio” of 80% for the lights, the nominal Output Power of the inverter should be higher than 728 Wp So, we will choose any inverter with a Nominal Output Power higher than 750 Wp 35
  36. 36. System design (VI) Conclusions Demanded energy: 12.100 Wh Solar modules peak power: 7.820 Wp Batteries capacity: 2.000 A-h (C-20) x 24 V = 48.000 W-h Inverter nominal output power: 750 – 1000 Wp Observations We have considered that the consumption is homogeneous during the year If this was not the case (For example, if we had an air conditioning system) we would have studied also the maximum demanding day We could reduce the amount of batteries, by reducing their autonomy or increasing their discharge depth and introducing a diesel generator as a backup for the periods that the batteries cannot assume 36
  37. 37. INDEX Introduction Elements. Storage System & Backup System Trends: Hybrid Systems. Efficiency. Smart Grids Applications. Examples Design Maintenance 37
  38. 38. Solar modules maintenance Periodical cleaning of the modules Depending on the pollution of each area Generally, once per year Checking the cables and connections Retightening the screws Checking the structure If it is not protected against open air (aluminum, galvanized steel, etc) it will require a periodical antioxidant paint Checking any shadowing effect 38
  39. 39. Batteries maintenance (I) The battery is a dangerous element, due to its chemical and electrical properties Main risks The electrolyte is, generally, dilute acid: it may produce burns if contacting the skin or the eyes Electrocution risk Recommendations: From 24 V, in wet environments Use appropriate gloves and shoes Use plastic handle tools From 48 V, in dry environments Avoid wearing any metallic object Risk of fire or explosion Avoid sparks and flames close to the batteries The batteries produce hydrogen gas An appropriate ventilation system is needed 39
  40. 40. Batteries maintenance (II) Main tasks Checking that the room is well ventilated and protected against the sun light Checking that the electrolyte level is between the manufacturer limits Add only distilled water Except for Gel type batteries Protecting the connection terminals with antioxidant grease to avoid sulfurizing Checking the tightness of the battery connections Cleaning the battery covers and terminals 40
  41. 41. End of Session 6 Thank you for attending construction-operation-and-maintenance 41