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Solar Powered WiMAX & WiFi



Intel has a Solar-Powered WiMAX Base Station white paper (pdf). In remote sites where there is no grid electricity, the cost of a diesel generator can be as high as 40 cents per kWh, including the cost of fuel delivery to the site. In some cases, an electric generator is transported to a repair site, which also adds to the cost.

With a lifetime of 25 years for the solar panels and 15 years for the battery array, Intel says these solar systems can generate electricity at a cost of 33 cents per kWh.

A daily consumption of 69.48 amp-hours, is multiplied by 1.2 as a safeguard factor to account for a slow loss of capacity over the lifetime of the battery. To compute daily power consumption, the base station is assumed to consume power equivalent to a 75% duty cycle at peak power consumption.

To provide a sufficient charging current of 18.53 amps, a total of eight, 200 watt SHARP ND-200U1 panels (pdf) or ten, BP Solar SX 170B panels (170 watts each) are connected in parallel to charge four, Rolls 5000 batteries.

To recharge the battery array, with an average daily recharge time of 4.5 hours, the solar panel modules should provide a current of 18.53 amps. The peak current drawn is 3.86 amps.

    Here are Intel’s references:

    Batteries

  • Rolls Batteries
    (www.rollsbattery.com)


Solar panel modules and complete power systems

Stand-alone solar-powered systems

Custom design of solar-powered systems

The Sunforce 50044 60 Watt Solar Charging Kit (above) includes a PVC mounting frame, 7 Amp charge controller, 175-watt inverter, and wiring/connection cables ($399). The $350 Xantrex Powerpack integrates a 60 Amp/hour AGM battery with a 1500-watt inverter on a hand truck. Xantrex’s $150 Powerpack, about the size of a lunch pail, has an integrated 5 watt solar panel, 400-watt inverter and 10 amp-hour AGM battery.

Via, a distant third in the CPU market behind Intel and AMD, has long championed the development of cheap, low-power processors. Their latest 500MHz Eden ULV chip consumes only 0.1W of power in idle mode. Today’s computers use around 14 watts of energy when idling. The XO laptop uses just 1 watt when idling and an average of just 2 watts.

Meraki’s WiFi Outdoor Repeaters cost just $99 and consume about 3.5 Watts. Meraki’s repeater and solar panel kit costs $150.

Paired with an existing access point (or a nearby Municipal Node), the Meraki Outdoor repeater might provide access for dozens of households sharing one high speed connection.

The Meraki Mini is based on an Atheros AR5315 SoC (system-on-chip) chip that weds an Atheros 802.11b/g radio to a MIPS 4KEc-based applications processor, resulting in a “wireless system-on-chip,” or WiSoC. It has some 32MB of RAM, with 8MB of flash memory for program storage. The OpenWRT page has additional information.

Perhaps a Mobile WiMAX client, WiFi hotspot, and powerpack could fit inside a cooler. The umbrella handle is the WiFi antenna and the removable solar panel goes on the lid. For patios, too. An 8 “D” cell Battery Charger like the Maha MH-C808M ($90) handles 8, 12ah “D” cells ($90) with charging time between 1-5 hours. Lithium-ion (Li-ion) and Nickel Metal Hydride (NiMH) batteries are used in cameras and laptops. NiMH batteries can handle high current drain while Li-ion has a low self-discharge rate, about 5% per month, compared with 30% per month with NiMH, but Li-ion should never be “deep-cycled”.

A 50 Watt panel ($300-$600) might charge a powerpack ($120) with a small 12 amp-hour Absorbent Glass Mat (AGM) battery in 3-4 hours. That should power a 3.5 watt Meraki for over 24 hours. BP’s 50 watt panel (pdf) costs about $375. A battery 3-4 times larger, say 48 amp-hours ($150), might run a hotspot 3-4 days on batteries alone.

How do you figure power requirements? Ohm’s law; P = I x E. The largest wattage input to a battery from a solar panel is (C/5 X 12 = maximum solar panel watts), where “C” = battery capacity, in Amp-hours. So a 60Ah battery would limit the solar panel’s power to; 60/5 times X 12 = 144 Watts. These calculations apply when using a charge controller.

A Mark 2 Metrix Box ($600) consumes about 12 Watts, so a 20 ah battery pack ($100) might power it for about 12 hours, two for 24 hours. Two car-size 45ah batteries ($300) should last a couple of days while an 80 watt panel ($500) should keep it charged.

A single $99 Meraki Wi-Fi repeater uses just 3.5 watts, so the cost is less and batteries last longer. One laptop is also developing a solar-powered WiFi repeater (right).

Please don’t take this as gospel, but here are my calculations for a solar powered Metrix Box:

Two stand alone solar units — with single 40-60 watt solar panels and 55 ah batteries — could be bolted together for double the juice.

You can get Optima deep cycle batteries at marine stores. A large 12 volt, 55 amp-hour battery ($200) can take a maximum of 10 amps for charging while a 120 Watt Solar Panel ($1050) delivers 6.8 amps of charge power. Using a strictly back-of-the envelope calculation, with two radios, (WiFi/WiFi or WiFi/WiMAX), you might get 2-3 days on two 55 ah batteries alone (by my calculation).

For truly remote locations, VSAT providers like Hughes Spaceway and WildBlue can provide backhaul (at a cost in power requirements).

WAAV makes “mobile access points” that allow Internet connectivity in mobile environments. Their $499 wireless router, with a single backbone connection, uses Sprint’s EVDO starting at $59.99/month.

Their new AirBox X2 ($1099), is the first mobile cellular router that establishes two cellular Internet connections, binding them together for additional speed. It can also utilize WiMAX or 4.9 GHz public service frequencies for the backhaul, mixing and matching various types of backbone providers (i.e. WiFi, WiMAX and/or cellular).

The $700 Junxion Box provides a similar cellular backhaul solution. It’s used on Seattle buses to provide mobile WiFi.

Sprint’s Linksys EV-DO/Wi-Fi Router costs less than $250 (plus monthly service charge). Kyocera Wireless announced a free firmware update for its Kyocera KR1 Mobile Router. The $219 access point now supports a variety of EV-DO Rev. A devices, including the Kyocera KPC680 ExpressCard as well as other Rev A devices including Novatel’s S720 PCMCIA card and U720 USB device, Pantech’s PX-500 PCMCIA card, and UTStarCom’s PC5750 PCMCIA card.

HeroLogic, a startup hopes to challenge Soekris and PC Engines for low cost, low power networking platforms running Linux. Their HL-463 system ($300) comes with 256MB of SDRAM soldered onboard, a miniPCI slot, a CompactFlash slot, 4 x USB ports and 3 x 10/100 Ethernet ports.

For backhaul, a Zyxel Mobile WiMAX client draws 10-15 watts (pdf) while their MAX-100 802.16e PCMCIA Card (left), draws just 2 watts (pdf).

Wavesat’s 5.8 GHz unlicensed mini PCI WiMAX Card might also supply backhaul with similar current draw.

Two (or more) $150 batteries along with a 120 watt panel ($1000) might feed a Soekris-like box with two radios. Feed it with licensed or unlicensed WiMAX. The $2,000 solar-powered Wi-Fi node.

Get Homeland Security to pay for it. Every county should have a dozen.

A $500-$2000 solar-power system might be cheaper than paying an electrician to get power to the roof and easier than stringing phone lines down an exterior wall to make the DSL connection.

Perhaps a $500 “information kiosk/repeater”, based on the XO laptop, could be installed on every bus stop. Advertising revenue might make it profitable.

The Solar Electric Power Association has more info. Sunwize has a Solar Design Guide with Worksheets. Eco-motion.com (below) is opening the NW’s largest electric vehicle dealership.

Related DailyWireless solar articles include; Wireless Camera Adapters, Minneapolis Bridge Collapse & Emergency Communications, Minnesota Solar WiFi, Park City: Solar WiFi, Solar Powered Solstice, Webcasting Concerts, TurtleNet, Meshing Tibet and Solar RoofNet Wiki.

Posted by Sam Churchill on Thursday, August 23rd, 2007 at 11:31 am.

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