Solar Power Basics for WiFi Networks & ICT Bruce Baikie BSME – Michigan Technological University

INVENEO – Broadband Specialist Green WiFi - Founder

Agenda • • • • • • • •

Solar Power Basic PV System Components The Solar Panel The Battery The Charge Controller The WiFi & ICT loads PV System Sizing for WiFi Costs

Why Solar?

Earth at Night: http://antwrp.gsfc.nasa.gov/apod/ap001127.html

Solar System - Functional Components Collect & Distribute Energy

Start

Collect Energy

Regulate Energy

Store Energy

Control Energy

Distribute Energy

Use Energy

PV Cell Basics

• Incoming light (photons) cause energized electrons to move to the n-silicon and out the connector • Nominal voltage of 0.55 V requires series connections to get useful voltage, 16 V • Short circuit current is proportional to light intensity

Maximum output when normal to cell is pointed at light (cosine of sun offset angle)

Ref.: FSEC

Charge controller

• Controls charge current to protect battery • Disconnects battery if voltage falls too low (10.6 V is typical) • Removes charge current if voltage rises too high (14V is typical) • Disconnects Solar Panels at night

Energy Storage • Energy may be stored chemically • Physically in water behind high dams • Electrically • Flywheels

World's largest storage dam, Uganda's Owen Falls Dam. The hydroelectric station at the dam supplies most of the electricity requirements of Uganda, and parts of Kenya.

Storage Battery • Lead-acid (car) batteries are economical but do not work for solar – Need be deep-cycle type batteries • Requires maintenance to ensure long life

Inverter

• Inverter converts low voltage direct current to 120 VAC • 12v or 24v DC input • High losses in solar setup +30% • DO not use if not need!!!

Typical PV WiFi setup

http://www.nunames.nu/about/SolarFi.PDF

Solar Panels • Photovoltaic (PV) module is the smallest replaceable unit in a PV array • Solar electric panels come in all shapes and sizes • 36 PV cells connected = 12v • Four factors for solar electric panel's output • efficiency of the cells • the load resistance • solar irradiance • cell temperature

Solar Panels - continued • Cell efficiency - 3% to 17% • Load resistance determines where module will operate • Maximum power point • Current and voltage (I-V) curve • Cell Temperature

Solar Panels - Shading • 50% drop in cell output • Cells connect in series – so weakest cell will bring the others down • Bird droppings also issue • Leaves & Dirt

Solar Panels - Position • Solar Insolation • Orientation • Tilt angle near the latitude angle

Batteries • Alessandro Volta in Italy credited with inventor of the modern battery • Lead Acid • NiCad • NiMH • Li-ion

Ancient cells discovered in Sumerian ruins origin around 250 BC

Batteries – Major PV Lead Acid Types • Flooded (wet) • Gelled • AGM (Absorbed Glass Mat)

Batteries • Temperature Effects Batteries • Cycles vs. Life • Battery Voltages • Amp-Hour Capacity • Battery Aging

Batteries - Mini Factoids • All batteries will not reach full capacity until cycled 10-30 times • Inactivity can be extremely harmful to a battery. It is a VERY poor idea to buy new batteries and "save" them for later. • Lead-Acid batteries do NOT have a memory, and the rumor that they should be fully discharged to avoid this "memory" is totally false and will lead to early battery failure.

Solar Charge Controller • • • • • • • •

Rated and Sized by Amps & Volts Blocking Reverse Current Preventing Overcharge Control Set Points vs. Temperature Control Set Points vs. Battery Type Low Voltage Disconnect (LVD) Overload Protection Max Power Point Tracking (MPPT)

WiFi Solar Charge Controller - DIY • Jaldi Charger - Pauli Närhi

– Affordable price – Locally made using commonly available tools and materials – POE injector

• Tier – Power Project – – – –

MPPT Status reporting - Ethernet POE Trickle charge http://drupal.airjaldi.com/system/files/Jaldi_Charger_design_1.6.3.pdf http://tier.cs.berkeley.edu/wiki/Power

ICT Loads Equipment

Power Load (Watts)

Laptop Computer

30-90

High end server

180-280

Wrap Router

4-10

VSAT Modem

15-45

OX Laptop

3

PC with LCD Monitor

150-180

Network Switch

6-8

WiFi Loads WiFi Gear

Power Load (Watts)

Linksys WRT54G

8

Soekris

w/o radio

Orinoco WP II ROR PC Engines WRAP Mikrotik 532

w/o radio

w/o radio

1.8 15 2 2.3

Senao 250mw radio

3

Ubiquiti 400mw radio

6

PV System Sizing for WiFi or ICT Units of measurement – Ampere: Amps - An unit in which electrical current flow is measured – Wattage: Watts – An unit in which electrical power is measured and is obtained by multiplying Voltage and Ampere – Voltage: Volt – An unit in which electrical force is measured. – Watt Hours: Whrs - An unit in which electrical power consumption is measured and is obtained by multiplying the wattage by the number of hours of use.

PV System Sizing for WiFi & ICT The Load Example - A Linksys WRT54GL Router draws 12v draws at 0.67 Amps. What is the Power consumption if it runs for 24 hours?

= volts x amps x hours = 12 x .67 x 24 = 192 watt hours

PV System Sizing for WiFi & ICT The Battery Example - The capacity of a battery is given in amp hours, but this is very cumbersome and since the battery voltage is always fixed, we divide the watt hours by the voltage. = volts x Amps x hours Volts

To get Amp hours

So if a battery is rated at 24 Amp Hour Capacity we can draw - 2 Amps from it for 12 hours or - 12 Amps for two hours or - 24 Amps for 1 hour etc.

PV System Sizing for WiFi & ICT The PV Example - A Solar Panel output is rated in terms of watts, but we need to know its daily output, watts per day, or sunshine period. This is given as the Solar Radiation period, From Mozambique to the South African border has a very good one, namely 5.5 hours per day. So a 40 watt panel will produce 40 watts x 5.5 hours/day which is 220 watt hours per day. But this power is stored in battery and battery capacity is given in Amp Hours so it is easier to express the Solar Panel Output in Amp Hours.

PV System Sizing for WiFi & ICT • Power Required per day - 200 watt hours • Using a 12 volt battery 200 watt hours = about 17 Amps Hours 12 volts Battery Capacity Required • Daily Load – 17 Amp Hours • To allow for inefficiency + added overhead - 50% of load – 25 Amp Hr Total: • Daily Load 17 Amp Hr • Daily Radiation Period is 5.5 hours 17 Amp Hrs = 3.1 Amps * 12v = 40 Watt Solar 5.5 Hrs Panel Needed

Costs • Powering a single WRT54GL

Description

Cost

40 Watt PV Panel

$ 289

25 Ah AGM Battery

$ 85

8 A Charge Controller

$ 60

Waterproof housing & wiring

$ 50

Total

$484

Costs • What is available Locally • Spend more on good Batteries • Maintenance

240 Watt Solution

Summary of Solar Power

Learning about solar electricity entails learning about • • • • • • • • • • •

the sun the earth electricity solar panels positioning the panel motion of earth around the sun inclination of earth’s axis sin, cos, … how the angle to the sun affects power generation how to store up electric power What is your WiFi gear power usage in watts

Questions & Answers