Design Your Own Off Grid System

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Photovoltaic Panels

Photovoltaic Panels generate electricity from the Sun. That much, I am sure you already know!

There are three basic types:
1. Mono-crystalline: Square and Round cells make up the design of the panel. These panels are the most efficient for space to power output ratio.
2. Poly-crystalline: Very similar to the single crystal panels above, these Panels have a speckled blue pattern and are almost as efficient for space to power output.
3. Thin Film: These panels used very little silicon to manufacture, if any at all. The photon-electron conversion system is part of a very thin layer of silicon and is attached to a non-silicon substrate, like steel, aluminum or plastic.

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Electric Generator

The Generator provide power when the sun, wind or water are not enough the power all that is required. The generator can be considered a balancer in an Off-Grid system. During the day, the Sunshine is providing as much power as it can, the homeowner is using as much as they need. If the Batteries get discharged too much, the generator can supplement power to the house.

Example: (Generac Quiet Source, More Information)

The key difference between Grid-Interactive Systems and Off-Grid Systems are:
1. Grid-Interactive Systems can also have generators, there may be some generator specification requirements for it to work correctly.
2. Off-Grid System can also have Electrical Meters. Off-Grid simply means the Inverter is unable or is programmed not to sell power by pushing energy out through the AC Input.

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AC Disconnects

1. Protects the AC Wiring from the Inverter from the Main in the House.
2. Protects the AC Wiring to the Sub-Panel in the House
3. Protects and controls the AC outlets and lights configured directly in the AC Disconnect.

1. MidNite Solar E-Panel series AC/DC Disconnect, More Information
2. Outback Power FLEXware FW500, More Information

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DC to AC Inverter

This Inverter has multiple converters for several tasks... Maverick says "They have two great engines:"
1. Backup engine
If you do not have grid power, then the inverter (backup engine) will generate power from the batteries in cooperation with the MX60 getting power from the sun or some other charge controller getting power from Wind or Water.

2. Charger engine
Converts the AC Power from the Generator (or from the Grid) to DC Power to charge the battery bank.

Example: (Outback VFX3524 Inverter, More information
1. VFX3524 is used with a 24 Vdc Battery Bank, like 4 each 6 Vdc batteries.
2. The VFX3524 can convert 3500 Watts of power from a properly sized battery bank -or- push 3500 Watts of power from PV, Wind or Water onto the Grid.

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DC Disconnect

1. Protects the DC Wiring from the PV Panels, Charge Controller and other small current connections [<70 Amps].
2. Protects the DC Wiring from the Inverter to and from the Battery [up to 360 Amps]
3. Provides the connection point all DC accessories like Battery Meters and DC Lights.

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Charge Controller

The Charge Controller (Solar, Wind or Water) converts electrical power from the PV Panels or Turbines. It matches the voltage of the battery bank providing just the right amount of charge.

Charge Controllers come in three basic sizes:
1. Small: Portable Power & Point-of-Use applications typically only require < 200 Watts of conversion.
2. Medium: Off-Grid, Backup, Water Pumping applications controlling >200 Watts to < 3000 Watts of power.
3. Large: Off-Grid, Grid-Interactive, Whole House systems with > 3000 Watts of power.

Example [Medium]: (Outback Power MX60 Solar Charge Controller, More Information)
1. The specification for MX60 is 60 Amps DC.
2. Using a 48Vdc Battery bank, the MX60 can handle 2880 Watts of PV.
3. Using a 24Vdc Battery Bank, the MX60 can handle 1440 Watts of PV.

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Charge Controller

The Batteries are an integral part of any Grid-Interactive System. When the Sun is shining or the meter ready, power is stored in the batteries. When the Sun is not shining and/or the Grid fails, power is converted by the inverter back into AC for use in the home.

The type and size of the battery bank depends on two main factors:
1. Amount of energy to power those backup items all at once (Some or All items ON at once).
2. The amount of time you expect Any item to have backup power.

1. You have 11 each 13 Watt Compact Fluorescent bulbs + on 75 Watt TV.
2. You need to run all of these items for up to 3 days in a row, 8 hours each day, with no Sun or Grid.
3. 11 x 13 Watts + 75 Watts = 218 Watts.
4. 3 days x 8 hours = 24 hours.
5. 218 Watts x 24 hours = 5232 Watt-Hours
6. As a Rule, batteries should not be drained more than 50%.
7. 5232 Watt-hours / 50% = 10464 Watt-hours. You need at least a 10464 Watt-hour Battery

Double Take: Most Batteries are measured in Amp-Hours of Capacity! How do you convert? Divide the battery bank voltage by the Watt-Hours you need.
1. 10464 / 24 Vdc = 436 Amp-Hour Bank
2. Each Battery is 6 Vdc.
3. 24 Vdc / 6 Vdc = 4 Batteries (each one having 436 Amp-Hour capacity, if not...
4. For instance, each battery is 218 Amp-Hours.
5. 436 Amp-Hours / 218 Amp-Hours = 2 Parallel Strings
6. Two Parallel String x Four Batteries in Each String = 8 Batteries Total. (That means lots of battery connector cables, so try to buy the right size battery and limit the number of strings to 1, 2 or 3.

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Bill of Materials for a Typical Example System [Intended for ONE 3500 Watt Inverter]:

Item # Quantity Description Notes
1 8 Suntech 170W Mono-crystalline Solar Panel with MC Connector The quantity of Panels is really based on the energy consumption calculation...
Series String the Minimum number of panels to exceed the Battery Voltage, but not Maximum number to exceed Open Circuit Voltage.
2 1 UniRac Four Rail Kit Available in different lengths and configurations based on Layout
3 1 UniRac 20pc Box "C" End Clamps 20pc box is usually cheaper than buying 16??
4 2 UniRac 20pc Box A-B-C Mid Clamps Like #3, it depends on the PV Layout and mounting
5 1 MC3 x 15' Male/Female USE-2 10ga cable Cut in half to connect PV string to combiner box.
6 1 MidNite Solar MNPV-6 6 circuit PV Combiner with 6 breakers  
7 6 MidNite Solar MNPV-15 15 Amp PV Breaker  
8 1 MidNite Solar E-Panel 175A AC/DC Disconnect System  
9 1 MidNite Solar GFP Ground Fault Protect Breaker Only Required for Roof Mounted Solar Panels
10 2 MidNite Solar 63 Amp DC Breaker  
11 1 MidNite Solar 15 Amp DC Breaker For Backup DC Light at Inverter
12 1 Outback Power MX60 60A Charge Controller  
13 1 Outback Power MATE Communication Controller  
14 1 Outback Power HUB Communication Manager  
15 1 Outback Power RTS Remote Temperature Sensor  
16 1 Outback VFX3524 Inverter/Charger  
17 1 4/0 x 10' Battery Cable Set, one Red, one Black Likely need conduit to Battery Box
18 3 4/0 x 12" Battery Interconnect Cable For 4 each 6 Vdc batteries in a 24Vdc Bank
19 4 Surrette S530, 6 Vdc, 400 Amp-Hour Battery Likely need Battery Box

Note: Estimate of items required. Job Site inspection/review is necessary to verify electrical, structural and permit requirements... Be sure to Contact Us if you have questions about your specific situation...

See Grid-Interactive page for Two inverter systems, just substitute the inverter type...

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Updated: July 02, 2010