Sunpower publishes paper on LCOE

I just came across a whitepaper on SunPower’s website that extensively went over the Levelized Cost of Energy and how the drivers of solar power are working to decrease costs, and a glimpse of where we might end up in four years.

The report (PDF) is available and goes through the all of the steps on how to calculate the LCOE and what factors go into designing a large scale solar power system. There are a few places where I disagree with their numbers but overall the report is fairly accurate (their maintenance figures a little low – not too bad, but for us our maintenance cost per kWh is not close to one cent or half a cent as they might claim in some of their cases).

There are a few highlights to point out in this report. First was a reference to a report on panel degradation (source report PDF). They tested 23-year old solar panels and found that they had only degraded 4%. Further, there was nearly no noticed degradation from years 1 through 20, with nearly all the degradation coming in a few year window between years 20 and 22, with the last year of the survey having leveled off the degradation.

Next is that most plants are financed under forecast power production, and that is usually grossly underestimated. This I have also found to be true – our guaranteed output is far less than our actual output – by more than 10%.

The biggest item in the report is the following quote…

In SunPower’s case, the grams of polysilicon consumed to manufacture a watt at the solar cell level declined from 13 g/W in 2004 to 6.3 g/W in 2008 and is planned to decline to an estimated 5 g/W with SunPower’s Gen 3 technology now under development. By 2011 this approximately 60 percent reduction in the use of silicon, coupled with an approximately 50 percent decline in the price of polysilicon, will independently drive large cost reductions for PV panels.

So while panels might have cost $5-6/Wp back in 2004, the increase in cell efficency, reduction of the quantity of bulk silicon used as well as the reduction of the cost of silicon due to the crappy economy and oversupply due to added manufacturing capacity, the cost of a panel could drop down to $2/Wp, and reducing overall costs from $7-8/Wp to $5/Wp and closer to grid parity.

While this is sort of a PR/promotional piece, the numbers in the report are backed up by my real world experiences. As long as the world doesn’t fall apart anytime soon, solar power is on track.

[Edit 6/16: Updated link to Sunpower LCOE paper after their website redesign]


My boss at work turned me on to Coolerado air conditioners. The principle behind the cooler is novel, and seems to not be some vaporware or scheme (they have recieved awards and letters from the US Department of Energy and the Governor of Colorado). While I’ll be skeptical until I see a real unit and can measure things for myself, it does seem like its a real working product. Not only that, but their test system uses “all of the buffalo.”

Coolerado has posted a few YouTube videos (123) talking about their system and how it works. You can watch those or follow along with me.

Their system is broken into two parts – the fan and filter, which draw in outside air and filter it through standard filters you can buy at a hardware store. This will clean the air before it enters the home.

From there, it enters their heat and mass exchanger (HMX). This is where the cooling happens. The incoming air stream is split into channels, with half of the air being used as the “working” air stream which does the cooling work, while the other half is the product air stream (the resultant air that would go into your house).

The HMX is a multiple stage cooling system, where in each stage a fraction of the incoming air is used as the working air stream, and the rest is used as the product air stream that is cold. The working air absorbs water from the wet plate which cools the air by trapping the heat energy in the air in the water (water can hold about 100x as much heat than air can) this cools but also humidifies the air. The wet plate cools as water is evaporated from it, which cools the air on the other side of the plate.

Next, the working air that has already been humidified is used to cool the incoming air by a fraction. By reusing the “waste” air that is humid but still cooler than the warm incoming air, the Coolerado unit seeks to push beyond the “wet bulb temperature”, or the temperature of a wet thermometer bulb in an air mass. Theoretically, the wet bulb temperature is the lowest temperature you can get in an evaporative cooling system. By having a multiple stage process, the wet bulb temperature gets lower with every stage as the working air cools the air left in the system. Their theoretical minimum temperature is the dew point.

Their test system uses that humid waste air, which is still somewhat cool, to cool solar panels which power the fan and solenoid to control the water pump. As someone with extensive solar power experience I can tell you that a 10F degree drop in ambient air temperature can increase your output by 5% given the same atmospheric conditions (solar irradiation, wind, etc).

There are limitations to the system, most notaibly that it is still using evaporative cooling, and it wont be able to cool already humid air. It also requires water – their videos demonstrate a unit for 3,000 sq ft and 20 people uses 4 gallons per hour, or nearly 100 gallons per day, which is about the range a swamp cooler uses for half the size (1,500 sq ft).

There is tremendous upside – the unit uses a fraction of the power of a traditional air conditioner – as little as 10% of the standard energy. Cooling buildings in the dry summers in the southwestern US is a huge energy hog, and if the energy needs could be reduced dramatically it would be a huge relief to energy utilities who would need less transmission capacity and fewer new sources of energy.

I used about 30kWh/day (or about $3.30/day) last summer for cooling (I compared my summer and winter usage and just took the difference – 35kWh/day vs 65kWh/day), so reducing my A/C costs by 90% would result in a 3kWh/day difference between summer and winter, and reduce my monthly energy costs by $90 in the hottest summer months. And due to the lower energy variability on my bill, it would be easier to estimate and cheaper to fit my house with solar power to offset my energy usage.