Monday, September 8, 2008

Is SolarCity's SolarLease Right for You?

A friend of mine emailed me a few days ago about SolarCity's SolarLease program. Instead of purchasing solar panels upfront, SolarCity offers a leasing option would only charge an initial fee of $1,000 and rest are paid off in potential electric bill savings.

In a local news broadcast, SolarCity claimed it would save customers about 20% of their current monthly electric bill. Assuming customers could pay the initial $1,000 downpayment and their monthly bill must be $150 or higher to see the savings.

According to SolarLease Calculator from SolarCity's website, the 20% saving claim is correct if the customers are using APS (Arizona Public Service Company) as their utility provider seen in Figure 1.

Figure 1 - APS customer's potential saving if switched to SolarCity

Figure 2 - SRP customer's potential saving if switched to SolarCity

However it is not true for SRP (Salt River Project) customers.

In figure 2, it shows SRP customers would need to spend a monthly average of $800 on their electric bill before SolarCity's program would save them any money.

Matter of fact even at that rate, SRP customers will never recoup their initial investment even after 15 years!

There are other limitations about SolarCity's program, such as customer's credit score must be higher than 720, and it only serves small territories along Oregon, California & Arizona.

SolarCity's SolarLease is a nice concept, however it is not for everyone, definitely not for SRP customers.

For now, let us all hope it would not turn into like the ZAP car hype.

Friday, September 5, 2008

Arctic Cooling Freezer 7 Pro is Great!

For over two years, I have been using Cooler Master's Hyper48 as CPU cooler for my Intel Prescott 3.6 GHz. Although it does a good job of cooling the CPU, one thing really bugged me was its loud noise. Since its fan is pulse-width modulation (PWM) controlled by mainboard's BIOS, whenever the CPU load increases, so does the noise.

A few days ago I saw Arctic Cooling Freezer 7 Pro on sale at for US$24.99 including shipping, so I gave it a try.

The improvement was amazing!

Figure 1. BIOS screen of PC operating with Cooler Master Hyper48

With the ambient temperature at 29C, PC operating with Cooler Master Hyper48 is showing CPU temperature at 44C and fan speed at approximately 2400RPM. The noise level is at 31.7 dBA.

Figure 2. BIOS screen of PC operating with Arctic Cooling Freezer 7 Pro

After replacing the CPU cooler with Arctic Cooling Freezer 7 Pro, the CPU temperature dropped to 41C and its fan speed to 1500RPM. Keep in mind both CPU coolers use 92mm diameter fans. The noise level has significantly reduced thanks to slower fan speed.

Figure 3. Arctic Cooling Freezer 7 Pro suspends its fan from heatsink body to reduce noise caused by vibration

Figure 4. Cooler Master's Hyper48 clips its fan onto heatsink body where smallest vibration could be amplified into a loud rattle

There are three areas of improvement I saw between Cooler Master's Hyper48 versus Arctic Cooling's Freezer 7 Pro.

First, Arctic Cooling used rubber tips to suspend the fan away from the heatsink body. Any noise-causing vibration coming from the fan would be minimized by these four little rubble tips. Less vibration equals less noise.

Cooler Master's Hyper48 clips its fan onto heatsink body via an aluminum clip. Even the smallest fan vibration is amplified into a loud rattle.

Secondly are the fans' bearings. Arctic Cooling uses ceramic bearings, which produces very small friction between shaft and housing. Cooler Master uses traditional steel rifle bearing (also known as plain bearing), where the shaft grinds on its bushings. Although rifle bearing is much cheaper to produce, Hyper48 is about average US$40 retail and Freezer 7 Pro is US$25.

Figure 5. Gigabyte GA-8S661FXM-775 mainboard with Cooler Master Hyper48

Figure 6. Same mainboard with Arctic Cooling Freezer 7 Pro

There are also differences in heatsinks. Six heat pipes were used in Freezer 7 Pro, where only four in Hyper48. Hyper48 is over 820 grams in weight, however since copper's density (8.96 g*cm^-3) is higher than aluminum (2.70 g*cm^-3), the excess weight did not increase cooling fins' surface area (heatsink: 105x94x70 mm; fin area: 2,200 cm^2). Freezer 7 Pro used aluminum fins to both cut weight down to 520 grams and increased cooling fins surface area (heatsink: 104x58x126.5 mm; fin area: 4,700 cm^2). For convection cooling, more heat dissipating area is better.

In conclusion, Arctic Cooling's Freezer 7 Pro is much quieter than Cooler Master's Hyper48. It also provided better cooling at much lower cost, which is a good news for consumers.