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FAQ

SYSTEM SIZING STEPS

DETERMINE

THE DEMAND

Watts & Watt-hours

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Step 1

DECIDE ON

PANEL TYPE AND SIZE

Mono, Poly & Watts

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Step 2

Step 3

DETERMINE TYPE OF INVERTER

Type & Size

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Step 4

DETERMINE BATTERIES

Type & Quantity

BASIC TERMINOLOGY

Different Solar Systems

Grid-Tied System

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  • Feeds directly into Utility Grid

  • Does not power the house/business

  • Reduces net consumption

  • Cannot function without the Grid

  • Will not provide power without Grid

Off-Grid System

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  • Normally a Stand-Alone or Residential Back-Up System

  • Do not feed Power to the Utility Grid

  • Design is important – Output must match the Electrical Consumption

Grid-Interactive System

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  • Loads Normally powered by Solar

  • Utility used as backup

  • Automatically switches to Utility if Sun/Battery supply not sufficient.

  • Can feed back into the grid – Depending on Inverter used

Electrical Fundamentals

  • Watts = Energy

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  • Watt = Power

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  • 1kW = 1000W

  • Be Aware!! Check Fuse and Cable Sizes!!

Examples

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SOLAR SYSTEM COMPONENTS

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UNDERSTANDING MPPT

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Battery is Charged from Panel:

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  • 30.7V In – 14.1V Out – Watts?

  • 8.15 A (Impp) X 14.1 V = 114.9 W

  • But we have a 250W Panel??

  • MPPT CC increases charge A: 30.7V ÷ 14.1V = 2.177 X 8.15A = 17.75A 

60A Maximum

Power Point Tracking (MPPT)

Charge Controller

12V Battery

Charge Voltage 14.1 V

PARALLEL CONNECTION TO FUSE ISOLATOR VIA BUSBARS

From Inverters to DC Fuse Isolator

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  • Cables must be same length

  • Cables must be same cross-section

  • Cables must be as short as possible

To DC Fuse Isolator

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  • Cables must be same length

  • Cables must be same cross-section

  • Cables must be as short as possible

  • Fuse size as per maximum possible load

From Batteries to DC Fuse Isolator

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  • Cables must be same length

  • Cables must be same cross-section

  • Cables must be as short as possible

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The cables running from the batteries to the busbar and from the Inverters to the busbar can be a smaller cross-sectional diameter than from the busbars to the DC Fuse Isolator.

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The cables between the busbar and DC Fuse Isolator must be able to withstand a Short-Circuit-Current of at least 417A.

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Example

For 5000W Inverters, the cables between both the batteries and busbar and between Inverters and busbar, must each be able to withstand a Short-Circuit-Current of at least 104A on a 48V Battery supply voltage.

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PROTECTION

  • Where possible, a cable is protected where it starts, sized according to the cable’s cross-sectional area.

  • We use Fuses or Circuit breakers to Protect.

  • We use Isolators – To Isolate a device for Safety.

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