太阳能照明系统的铅酸蓄电池设计手册(英文版)

Battery Guide for Small Stand Alone PV Systems. IEA PVPS Task III 9 91223_______________________________________________________________________________________________________________1 33Lead-Acid Battery Guide forStand-Alone Photovoltaic SystemsIEA Task IIIReport IEA-PVPS 3-061999December 1999Battery Guide for Small Stand Alone PV Systems. IEA PVPS Task III 9 91223_______________________________________________________________________________________________________________2 33CONTENTSFOREWORD . 5SUMMARY 61. INTRODUCTION. 61.1 Solar energy 71.2 Sun power into electricity. 71.3 Lead-acid batteries all over the world. 72. THE BATTERY - A ” CONTAINER” FOR ELECTRICITY 93. A CLOSER LOOK INSIDE A LEAD-ACID BATTERY . 103.1 Positive electrode design. 103.2 Negative electrode designs 103.3 Electrolyte. 113.4 Cell cases made of moulded plastics. 123.5 Battery boxes for small systems 123.5 Standardised terminals and connectors. 124. WHAT TYPE OF BATTERY SHOULD BE CHOSEN 135. BATTERY VOLTAGE CHARACTERISTICS 155.1 The higher the discharge rate - the lower the battery voltage 155.2 Higher voltage with series connection 156. BATTERY CAPACITY - THE AMOUNT OF ELECTRICITY STORED. 166.1 Capacity can differ from battery to battery 166.2 Design your system based on 80 of nominal battery capacity 166.3 How to size the battery for a certain system and load. 176.3 Higher capacity with parallel connection 186.4 Capacity will increase slightly in the beginning of operation 186.5 Temperature effect on capacity 187. CHARGING FILLS YOUR ENERGY STORAGE. 207.1 Different steps in the battery charging procedure. 207.2 Always use a good PV charge controller 218. YOUR BATTERY IS A SMALL POWER STATION. 22Battery Guide for Small Stand Alone PV Systems. IEA PVPS Task III 9 91223_______________________________________________________________________________________________________________3 338.1 A shorted battery - a dangerous hazard. 229. HOW TO STORE A BATTERY BEFORE INSTALLATION. 239.1 Dry and cool 239.3 Periodic recharging 239.4 Dry-charged batteries is one option. 2310. HOW TO INSTALL NEW BATTERIES 2410.1 How to arrange the “battery room“. 2410.2 Batteries are heavy and need space 2410.3 Good ventilation - a safety factor. 2411. GOOD MAINTENANCE - HIGH RELIABILITY 2511.1 Voltage chain 2511.2 Terminal lubricants against oxidation. 2511.3 Low electrolyte level - an alarm signal. 2511.4 Centralised watering systems. 2511.5 Expansion of the battery terminals can crack the cover. 2611.6 Read the cell/battery voltage periodically 2611.7 Acid density measurements 2611.8 Rinsing and drying. 2711.9 Replacements of cells in a larger system 2712 SAFETY PRECAUTIONS. 2812.1 Always use insulated tools. 2812.2 Protect eyes and skin 2812.3 Protection against explosion. 2812.4 How to carry a battery. 2912.5 Disposal of the battery at end of life. 2913 BATTERY STANDARDS 2913.1 IEC standards. 2913.2 Other standards 30REFERENCES 31NOMENCLATURE. 31Battery Guide for Small Stand Alone PV Systems. IEA PVPS Task III 9 91223_______________________________________________________________________________________________________________4 33TO REMEMBER 33Battery Guide for Small Stand Alone PV Systems. IEA PVPS Task III 9 91223_______________________________________________________________________________________________________________5 33ForewordThe international Energy Agency IEA founded in November 1974, is an autonomous bodywithin the framework of the Organisation for Economic Co-operation and DevelopmentOECD which carries out a comprehensive programme of energy co-operation among its 23member countries. The European Commission also participates in the work of the Agency.The IEA PhotoVoltaic Power Systems Programme PVPS is one of the collaborative R thus its use in stationary applications is only possiblewith reservations.If still a SLI battery is going to be used in a PV system, choose a truck battery . They havethicker plates than a car battery almost of the same thickness as special solar batteries. Thiswill extend the battery life in a PV system significantly compared to a car battery.Tubular plates are often used for traction batteries, i.e. for electric industrial or road vehicles.The main feature is a fairly high specific energy per volume and good capability for deepdischarge. The charging time is medium, 5 - 10 hours.In tubular plates, where a lead spine issurrounded by a highly porous, plastic tube,the active mass is located between the leadspine and the tube. The high current capabilityof this type of electrode is nevertheless limited,since one cannot reduce the dimension of thetubes. The normal tube diameter is 8 mmdischarge time 3 - 10 h, which can bereduced to 6 mm for specific higher powerapplications discharge time 1 - 3 h.Rod plates are used in batteries for lighter traction as well as for some stationary applications.Rod plates consist of vertically arranged rods. The active mass surrounds the rods, and iscompletely enveloped in a pocket. The lead rods correspond largely to the spines of the tubularplate. Because of the construction, the utilisation of the active material is high, so is also thehigh current capability.3.2 Negative electrode designsThe negative electrodes in all types of lead-acid batteries are of a pasted grid plate design.Battery Guide for Small Stand Alone PV Systems. IEA PVPS Task III 9 91223_______________________________________________________________________________________________________________11 333.3 ElectrolyteThe lead-acid battery electrolyte is a solution ofsulphuric acid in water. The specific gravity of the acidin a fully charged battery is 1.20 - 1.30 g/cm 3depending on the type. Stationary batteries have lowerconcentration than traction batteries. A typical valuefor a fully charged SLI car battery is 1.28 g/cm 3. Theacid is participating in the reactions as its sulphate ionsare consumed. As a result, the specific gravity isdecreasing when the battery is discharged. The gravityis traditionally used for measuring the battery state ofcharge. But readings can be very misleading too lowvalues especially during the slow charge withoutmixing of the electrolyte in a PV system.During charge strong acid is created at the electrode surfaces. During overcharge, the acid inthe cell is stirred by the gas evolution, which helps the concentration equalisation. If the chargerate is low and the overcharge limited, it happens that the strong and heavy acid does not mixwith the bulk electrolyte, but accumulates at the bottom of the cell. This is often the case fortall cells 200 mm plate height. The time for equalisation will be several days. Such strongacid increases the corrosion of the electrodes, which decreases life. As the acid sample is takenat the top level of the electrolyte very wrong results too low state of charge values can bederived if mixing has not occurred. This is most often the case in a PV system. Therefore aciddensity measurements in a PV system during charge is often misleading gives too lowvalues on state of charge.The electrolyte is a strong acid. When working with abattery, safety glasses should always be worn.Rubber gloves should be used when working directlywith the acid. Droplets or mist of acid will destroy manymaterials used for clothing. This is often not observeduntil the clothes are washed.The concentration of the acid has to be adjusted on aregular basis by addition of deionized water. This isautomatically done when topping up the electrolyte levelwith water. The acid is never leaving the battery exceptfor very long overcharge periods when electrolyte mistcan carry acid away. If the electrolyte level is too low,the acid concentration is accordingly higher, whichincreases the corrosion.Especially during the end of the charging process water will be separated into hydrogen andoxygen gas at the electrodes. These gasses will leave the battery in an open or vented battery.This gives a water loss that has to be replaced by distilled water at regular intervals. A waterloss of at least 0.5-1 litre per year can occur even in a small stand-alone system. A goodcontroller can minimise this loss but a check of electrolyte level every half year is aminimum recommendation. If the water level is not adjusted in time parts of the batteryBattery Guide for Small Stand Alone PV Systems. IEA PVPS Task III 9 91223_______________________________________________________________________________________________________________12 33plates will be above the electrolyte surface and exposed to air, in time those parts will becomepermanently damaged. The water loss also has the result that the acid strength will beincreased and the corrosion of the electrodes will accelerate.In cold climates the electrolyte may freeze if the battery has a too low state of charge . Thiscan seriously damage the battery. In case of a stratified electrolyte the risk of freezing is evenhigher. A good controller with automatic low state of charge warning and disconnect willreduce the risk of freezing significantly. If the controller has a built in equalisation stage in thecharge control this will further reduce the risk of freezing.3.4 Cell cases made of moulded plasticsThe first thing you see when you have a lead-acid battery in front of you is the case.Historically, rubber was found to be a suitable material for cell cases and covers. They wereeasily formed to the right dimensions and the cells were easily sealed. However, the materialwas quite brittle, especially at low temperatures, which made these cells sensitive to mechanicalabuse.Most cell cases manufactured today are made from injection moulded plastics. Such cases areform stable and quite resistant against mechanical abuse. The cost for tooling is very highwhich requires quite large production volumes for each size of battery to lower componentcosts.Some cell case materials may have a dimensional instability. If the cell walls are bulging, theelectrolyte level will deviate from that predetermined. To avoid this situation, such cells shouldbe put into a frame, which facilitates the dimension integrity.On top of each cell there is a plug that in the case of a vented battery has small holes that willrelease gasses but will prevent acid to come out. In a sealed or valve regulated battery the plugcontains a catalyser and a safety valve that will release overpressure in case of catalyser failureor too high charging rate.3.5 Battery boxes for small systemsFor small systems an extra battery box covering also the wiring and connectors on top of thebattery can be recommended. This box will also take care of water and electrolyte droplets thatotherwise may destroy the floor. When a battery box is used the battery can be placed indoorsmore freely closer to the load. Still the requirement for good ventilation in the room should notbe forgotten.3.5 Standardised terminals and connectorsThe positive and negative terminals are part of the cell cover. There are standardconfigurations with a conical layout for standardised connection cables and different layoutsfor special connectors.In a monoblock e.g. a 12 V battery the series connection between the individual 2V cells aremade inside the case, penetrating the walls between the cells.If a metal object is dropped onto the battery so that the terminals are connected, the battery isshorted which can end up in an explosion. Use only insulated tools when working withbatteries. Do not wear watches with metal bracelets.Battery Guide for Small Stand Alone PV Systems. IEA PVPS Task III 9 91223_______________________________________________________________________________________________________________13 33When connections are made, protect the terminals by an insulated material like rubber, plasticsor wood to prevent short cuts between the terminals.It is very important to keep the terminals clean from oxides to avoid voltage drop due to higherresistance between terminal and connector. Clean terminals will also help to reduce creepcurrents between the terminals. Otherwise this will increase the rate of self-discharge.4. What type of battery should be chosenThe chart on the next page presents an overview of advantages and limitations with differenttypes of lead acid batteries concerning their use in PV systems.For a typical small PV system 10Wp to 1kWp both the initial investment cost and the lifecycle cost has to be kept low and the following battery types can be recommended accordingto the order in brackets. 1Solar Batteries, 2Leisure/Lighting, 3SLI truck batteries ref. 2.SLI car batteries should be avoided due to the short lifetime in a PV system. In practice ofcourse also the local availability of batteries will decide. Therefore SLI truck batteries can bethe best option in some developing countries with no other batteries than SLI ′ s available.It has also been shown that local factories for SLI batteries can be changed to also producemodified SLI batteries with thicker plates that has a significantly better performance in smallPV systems.For professional use the more advanced and expensive batteries are often more cost effectivein the long run. Their lifetime is longer, the maintenance requirement is sometimes lower andthe performance higher, concerning frequent deep cycling. Therefore a smaller battery bank innominal Ah can be used for the same load and the number of exchanges during the systemlifetime is lower. The main disadvantage is the higher initial investment costIn professional applications comprising daily discharging and recharging, the traction batterydesign is preferred. A semi-traction design with pasted plates can be acceptable if the lead gridis stable enough. The stationary battery design is recommended for applications with randomdischarge/charge cycles but where a reliable power source is needed for emergency alarmsystems, etc.Stationary batteries of the Plante′ type are not recommended for PV systems as the lifetimewill be very short due to the special charging conditions in a PV system Ref. 2. They arealso very expensive.Battery Guide for Small Stand Alone PV Systems. IEA PVPS Task III 9 91223_______________________________________________________________________________________________________________14 33Battery selection table for PV systemsBatterytypeStandardapplicationareaSLICarsSLITrucksLighting/LeisurecaravansboatscottagesSolarmodifiedfor PVuseSemiTractiongolf carts,lawnmowersetc.Tractionfork lifttrucks i.e.Stationarytelecomi.e.PositiveplatedesignPasted Pasted Pasted Pasted Pasted/RodTubular Tubular/RodAdvantages HighpowerHighpowerFairly highpowerAcceptsdeepdischargeRuggedRapidrechargepossibleRapidrechargepossibleAcceptablecycle lifeAcceptsoverchargeReliableLongerPV- lifethan carbatteryLongerPV- lifethan carbatteryLongerPV- lifethan carbatteryGood forcyclingapplicationDisadvant-agesSensitiveto deepdischargeSensitive