Designing Stand Alone Systems. Overview, components and function, Elements in Design

Transcription

1 Designing Stand Alone Systems Overview, components and function, Elements in Design

2 What Stand Alone System Does

3 Loads that are Reasonable for a Stand Alone System to Power:

4 Yes or No Dishwasher? Refrigerator Computer Electrical space Heating Electric Water Heating Hot tub Water pumping?

5 Three Approaches 1. Sole (soul-ly) Solar Electric with Battery. 2. Hybrid: Solar Electric System with Battery backed up by generator 3. Hybrid: Solar Electric combined with wind, water

6 Today, Focus on Soul-ly Solar

7 Stand Alone Residential System Solar Array Charge Controller DC to AC Inverter Distribution Panel AC Battery Distribution Panel DC

8 Stand Alone: Postives Total Energy Independence Power where and when sun Disaster Ready

9 Design Considerations Loads: Seasonal AND Day vs Night Solar Resource: Seasonal matched to seasonal loads Expandability Aesthetic: Mounting System: Ground, Pole, Roof Cost

10 Loads Your Assignment perform a simple practice load analysis.

11 Load Analysis for Stand Alone System Consider loads for each month or season of the year Consider: Summer; Fall, Spring, Winter

12 Power Production: Grid Tie Grid tie we care about maximizing annual power production. So, we angle our array for this. Also, may want to maximize power production tied to TOU metering.

13 Power Production: Stand Alone Stand Alone: We want to match power production to loads AND we design with the toughest season in mind, usually winter.

14 Tasks for a PV Installer Conducting a Site Survey Selecting a System Installing the System System Checkout & Inspection

15 PV System Advance Organizer Put PV Here Permits, Utility Interconnection Agreement, Rebates System Placement & Shading Solar Resource Assessment and Energy Estimation

16 Solar Insolation Solar insolation data is used to calculate the energy output of an array. Example: PV array produces 3 kw AC at peak sun. How many kwh will it produce if it receives 5 sunhours? 3 kw AC x 5 Sun-hours = 15 kwh AC

17 What is Required for Energy Estimation While there are several methods to determine PV system performance, the following parameters are required Nominal Array Size Peak Sun-hours - Sunlight Energy incident on the PV array Array Tilt Array Azimuth Angle

18 Energy Conversion Equation Simple Method PV System Energy/Day = STC Array Power x Empirical DC to AC Conversion x Sun-hours at tilt/day x Azimuth Correction

19 Basic Energy Estimation Equation STC Array Power = Array Rating from Manufacturer at Standard Test Conditions Empirical DC to AC Conversion = 0.7 for Grid Connected only, 0.6 for grid connect with battery banks (based on data collected at FSEC) Sun-hours/day = Sun-hours from closest city to installation location using average data from closest tilt angle Azimuth Correction = Cos( ), where is the angle (in degrees) between true south and the direction the array faces (only valid for angles up to 45 degrees)

20 Energy Estimation for the Watts Nominal Array Size - Look at several different array sizes Peak Sun-hours - Available from National Renewable Energy Laboratory for different locations around the country Array Tilt - Same plane as roof, 18º (Site Survey) Azimuth Angle - 4º W of due South (Site Survey)

21 Array Tilt at the Watts Home Since the array will be mounted in the same plane as the roof deck, the array will be tilted at

22 Array Orientation Tilt Angle Optimal performance of PV arrays is achieved by facing the array south (north in the southern hemisphere), and at a tilt angle from horizontal using the guidelines below: Application Best Array Tilt Angle Maximum Annual Energy Latitude Production Winter Peak Load Latitude plus 15 degrees Summer Peak Load Latitude minus 15 degrees

23 Summary Understand the difference between solar irradiance and insolation Name the factors that influence the energy output of a PV system Given a particular site, estimate the output the PV system on a monthly basis and compare that to usual energy load

24 Tasks for a PV Installer Conducting a Site Survey Selecting a System Installing the System System Checkout & Inspection

25 When you size a system you have to size every component AND You need to know how your system will be used: E.g.: Weekend cabin 24 hour a day monitoring system 7 days a week home People home during day or mainly in evening Teenager?

26 Key Elements in Sizing System Size of Solar Array Size of Battery Size of Charge Controller Size of Overcurrent Devices Don t forget to derate

27 Note on Solar Array Power Production will be effected by Orientation Angle Shading (solar access) Climate Number of Peak Sun hours AND

28 Battery Key to Battery longevity is: How deeply is it discharged How often it is fully recharged Quality of Charge Controller Maintenance Type of Battery

29 Inverter: Will effect overall system Performance True sine wave? Size Efficiency Quality Sized for Expansion?

30 Sizing: Efficiency One dollar spent on efficiency equals $4 spent on solar electric system Will work through a couple of examples: Lighting Computers Refrigerators

31 Charge Controller Types: PWM or MPPT Variable Voltage LVD Shunt (on and off) Easy installation Select for Battery type? Sized for Expansion Quality Monitoring?

32 Single Line Diagram: Stand Alone Residential System Solar Array Charge Controller DC to AC Inverter Distribution Panel AC Battery Distribution Panel DC

33 Three Line Diagram: Solar Array Small Stand Alone System Charge Control Storage: Battery Fuel Gauge Inverter DC to AC

34 Designing Stand Alone Systems System Sizing

35 Example: more complex Load Watts Hrs/night Hrs/daytime Watt-Hrs Ambient light 20 watt fluorescent fixture #1 25 watts watt-hrs Ambient light 20 watt fluorescent fixture #2 25 watts watt-hrs LED Spotlight 10 watts 5 50 watt-hrs LED nightlights 4 watts 5 20 watt-hrs Suctioning watt-hrs Diathermy (cauterizing) watt-hrs Walkie-Talkies and head lamp batteries TOTAL 952 watt-hrs Total from Battery at night 650 watt-hrs

36 Example: Nigeria Simplified Load Watts Hrs Watt-Hrs Ambient light 25 watt fluorescent fixture #1 50 watts 5 hrs 250 watt-hrs LED Spotlight 10 watts 5 50 watt-hrs LED nightlights 4 watts 5 20 watt-hrs Suction machine 135 watts watt-hrs Diathermy (cauterizing) 360 watts watt-hrs Walkie-Talkies and head lamp batteries TOTAL 10 watts 5 hrs 50 watt-hrs 1000 watthrs

37 Size Array Least Sunny month in Zaria, Nigeria: Peak Sun Hours: 5 hrs/day Energy Needed: 1000 watt-hrs Array size = Energy/hrs of sun = 1000 watt-hrs/5 = 200 watts

38 Size Array (2) Add margin to allow for inefficiencies of array charging and battery charging of 40% and get 0.40 x 200 watts = 80 watts Array size = 200 watts + margin of 80 watts = 280 watts

39 Size Battery Energy Needed:1000 watt-hrs Voltage of Battery is 12 volts. Watts = Volts x Amps Watt-hrs = volts x amp-hrs Amp-hrs = watt-hrs/volts Amp-hrs = 1000 watt-hrs/12 volts = 84 amp-hrs

40 Select Depth of Discharge Add margin to increase battery longevity: For this case I will double battery size: 168 amp-hr, 12 volt battery.

41 Must be deep cycle Note on Batteries 1

42 Batteries (2): Three Major Types of Lead-Acid Flooded Gel Cell: sealed with VR AGM: Absorbed Glass Mat: sealed with VR

43 Batteries (3) Depth of Discharge No lead acid wants to be fully discharged More shallowly cycled, the more cycles Note: what is a cycle Need to be regularly charged full

44 Types of Batteries Shallow- cycle batteries that is only meant to be discharged 10 to 20 percent not suitable for RE systems. Deep cycle - Batteries that can be discharded up to 80 percent commonly used in RE systems. VRLA Valve Regulated Lead Acid FLA Flooded Lead Acid

45 Types of Batteries: Flooded

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47 Flooded Batteries Fully Charge Regularly Aim for room temperature: every 18 degrees above 77 degrees shortens battery life by 50% Simple Trojan T 105s average cycles.

48 Sealed Batteries: VRLA Valve Regulated Lead Acid: Gel Cells and AGM

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