Efficiency is where it’s at

This PC power supply is not provided pre-installed in an enclosure. Great care is advised during installation and use, because it can easily short out and get damaged. That’s why we built our own enclosure for this power supply, which also gave us a good way to mount the fan for this 12-volt device. We used Plexiglas for its construction, cut into carefully measured pieces and glued together.

The cable strands for this power supply are pretty short, which makes it tricky to find a good place to put it inside a PC case. Remember that many parts suppliers offer extension cables, and don’t be afraid to call them into service to help out.

Best Choice: AMD Athlon 64 X2 BE-2350

In choosing a CPU for our solar-powered PC we put strong emphasis on two criteria: low power consumption and a dual-core architecture.

To prepare for our selection we studied the energy consumption of various processors. We learned, for example that the AMD Sempron 64 uses very little power, but we didn’t consider it for our system because it includes only a single CPU core.

In our solar-powered PC we have to worry about every Watt drawn, because all of the necessary energy comes from our solar panels, not from a wall socket.

If you look at our measurements of power consumption at idle and when fully loaded, the AMD Athlon 64 X2 BE-2350 represents a good combination. It consumes only 8.49 W when idle, and 38.66 W when fully loaded. Intel’s Core 2 processor with L2-stepping may use a little less power, but our measurements also showed us that the motherboards in which they must be housed use too much energy. On the one hand you find the memory controller in the chipset, and on the other you find the energy consumption from Intel and Nvidia chipsets generally higher. The lower power consumption of the Core 2 processor is negated by these higher numbers.

That’s why we selected an AMD processor for our solar-powered PC—namely, the Athlon 64 X2 BE-2350.

1-Watt Active Cooling Takes Very Little Power

When it comes to cooling our solar-powered PC, we can take one of two general approaches: either we can cool the processor actively with a cooler, or we can construct some kind of passive cooling system. To help decide which way to go, we measured the processor’s energy consumption at various temperatures.

The stock cooler included with the processor consumed about 1 Watt at maximum fan rotation. If we used a passive cooler instead, the energy consumption of the Athlon 64 X2 BE-2350 increased by about 1.1 W in “Cool and Quiet” mode, and by a hefty 12 W at full load.

Although the CPU cooler fan consumes a steady stream of energy, the use of processor power decreases when it’s active. Because our Gigabyte motherboard includes a fan controller, the fan is also very quiet. Thus, we decided to employ active cooling because of the better energy budget it gave us to work with.

Energy-saving motherboard: Gigabyte with HDMI and DVI

The limits of solar energy mean that we can’t even consider a separate graphics card in our build because they require much too much power to run—whether we consider a passively cooled graphics card or a high-end model. According to our measurements, even a small, passively cooled ATI Radeon X1300 draws 88.5 W at idle. This level of energy consumption exceeds that of our entire system, including the monitor.

To take advantage of the most up to date technologies and to permit our solar-powered PC to function as a video playback device, we chose the Gigabyte GA-MA69GM-S2H motherboard. This motherboard is equipped with the AMD 690G chipset, and supports both HDMI and DVI with HDCP output, as well as VGA. In tandem with the CPU, this chipset delivers enough computing powers to play back high-definition video (HD-DVD or Blu-ray).

This Gigabyte board comes in micro-ATX format. A great many motherboards with integrated graphics are available in this form factor because they’re widely used by OEMs for machines where add-on cards are seldom needed. Nevertheless, this motherboard does include a PCI-e x16 slot, as well as two PCI slots, and a PCI-e x1 slot as well.

This Gigabyte motherboard also features a Realtek ALC 889 High-Definition 7.1 surround sound audio chip, and the motherboard includes an optical output as well. The network adapter is also built around a Realtek chip, the RTL8110SC, but this interface is connected via the PCI bus. Our chosen motherboard also includes a Firewire chip from Texas Instruments, the TSB43AB3.

The Southbridge offers connectors for up to four SATA and two IDE drives.

Comparing Energy Draw: MSI vs. Gigabyte

The foundation for our solar-powered PC is the AMD 690 chipset. The Northbridge portion of this chipset uses 80 nm technology, and consumes less power because the memory interface is integrated into the CPU. That explains why this Northbridge includes fewer transistors and requires a smaller surface area.

The capabilities and functionality that the Southbridge SB600 delivers is pretty meager, as compared to competitive chips. But because we don’t need RAID support, it’s perfectly adequate for our solar-powered PC. The SB600 also uses 80 nm technology, and additionally consumes far less power than competitive chips.

Even the three-phase voltage regulator that handles power for the CPU contributes to lower energy consumption.