This is the first of several blogs to follow on my understanding of generating and using solar energy.
I am going to China 12/4-12/19, visiting Hong Kong, Shenzhen, Xian, and Beijing and giving talks at Tsinghua University, Beijing Institute of Technology, Hong Kong University of Science and Technology, and Xian JiaoTung University. You can find the talk abstract at the end of this blog.
I’ll blog more about my technical and market views on solar energy later on the road. Before that, I describe here in this blog my experience with solar energy. As you may know, I live in Fountain Hills in Arizona where I have plenty of space, sun, as well as wind. Perfect for the kind of electric vehicle I described in the talk abstract below. By the way, I drive a Prius and is scheduled to have a Nissan Leaf delivered by January.
You figure by now I am a green energy user and promoter. This past year, I have been turning green, so this blog tells you my initial experience.
On average, an American pumps more than 1 ton of carbon dioxide into the atmosphere per month, including household and automobile use and excluding industrial production. For example during the hot summer months of Arizona, my house electricity bill is more than $300, which is more than 2MWh of energy or the equivalent of 1 ton of coal burned to form slightly less than 4 tons of carbon dioxide. Add another two tons due to transportation for me and my wife, we are way above the national average.
I installed solar panels on my roof in June. I have a fairly big flat roof top, but the parapet around the roof substantially reduced the area not shadowed and left usable for photovoltaic generation. My installer told me that I can generate about 4.2 KW peak. That is 20 Kyocera panels each generating 210W of power. Here is a video showing the system on my roof:
At around the same time, I explored the use of solar thermal water heating. For years, I had used solar heating for my pool with vinyl panels. I found that pretty useless: the panels overheat my pool in summer and are not adequate heating even in autumn or spring. This spring, I asked installers for an assessment of the cost of installing solar water heater. It costs around $6000 for a good system, with out of pocket cost around $3000. I figured that I may save at most $20 per month as my 3 children have gone off to college, so I gave up on installing a solar water heater. But I do think solar water heating makes sense, but unfortunately the subsidy is not quite there. It would make a lot more sense if the solar PV panels also generate hot water.
After installation this summer, I found that peak generation is around 1pm for around 3.2 KW. The difference from peak capacity of 4.2KW installed is due primarily to the inefficiency of the DC solar output converted to 120V AC household use (<80% efficient); and secondarily to the slightly oblique angle of incidence of sunlight even during peak generation. My feeling is that during the summer months, I have the equivalent of 4 peak hours generation per day or 16KWh DC (12 KWh when inverted to AC). At say 20 cents per KWh, I generate about $2.4 dollars worth of electricity, saving me about $100 per month during the summer months when peak charge of electricity is 27 cents per KWh.
I have not gone through the whole year to see how much money I can save per year, but most likely less than $1000. For places like Arizona, a typical number for annual generation is 1,800 KWh per KW peak capacity, and that is before DC to AC inversion. If you take this number, multiply that by 4.2KW peak capacity I have, you get slightly more than 7000 KWh per year of DC or slightly more than 5000 KWh per year of AC. So the estimate of saving about a thousand dollar a year is founded.
Is it worth the effort and money to install solar panels on your roof. I got a very sweet deal. My installer (American Solar Electric in the same SkySong complex where Nuon is located) charged me $5.2 per W installed for a total charge of $22,000 ($5.2 per W times 4,200 W). Out of that $5.2/W, Kyocera panels (polycrystalline silicon) cost $2.5 per W. My installer charged me $525 per panel back in March, but you can get them for $475 or less as of today. The DC to AC inverter costs $3000, included in the $5.2/W cost. The bulk of the cost is design, installation, approval, documentation and an unknown profit margin for the installer.
Each Kyocera panel (KD210GX-LPU) has 9 rows of 6 solar cells (each about 6 inch squared) per row. These 54 cells are connected in series at around 0.6 V per cell for a total panel output voltage of about 30V and power of 210W. Ten panels are strung up in series for an output voltage of about 300V. I have two strings of 10 panels each feeding 300V and about 7A peak (current is roughly proportional to light intensity) into a fairly large size inverter, which in turn feeds into the power panel of my house. The meter can run backward if the solar output is larger than the instantaneous usage of my house. I figure that I do not generate enough to have the grid buy back electricity from me. There is no such reverse tariff anyway for my utility (SRP) to buy from me.
The reason why the deal is so sweet is that I paid only $3000 out of the pocket, so at a saving of about $1000 per year, my investment is paid back in 3 years. Pretty good return on investment I figure. The reason is there is a lot of rebates and subsidies. First SRP pays me $2.75 per W of rebates that SRP pays directly to my installer. Second the Fed offers a tax rebate of 30% of total installation. Third Arizona offers $1000, which is much less than say California. (There is more motivation to install solar in California because of the higher tariff and state subsidy, though arguably we have more sun in Arizona and it is hotter here in the summer to justify solar generation for air conditioning). Without these rebates, solar energy is unaffordable for the home. In the long term, government incentives such as mandating a fraction of utility generation to be renewable and a carbon tax are essential for the near term mass deployment of solar PV generation.
The take home lessons from my solar experience can be summarized as follows:
1. Government policy is absolutely necessary to subsidize the end users. Unfortunately, the US lags behind Germany (the largest installation of solar energy in the world) and Europe, as Germany abandons nuclear (or importing nuclear energy from France). China has no rebate program to date, even though China produces the majority of solar panels on earth. Even worse, the largest component of the rebate is from finicky power utilities which often run out of rebate money if the rebate is too attractive. I witness first hand how installers are really at the mercy of the rebate rate (for SRP, it dropped from $2.85 last year to $2.15 this year, with cap on total amount of rebate to a few million KW capacity) and rumors that the rebate program is running out of money.
For me the household user, I care more about the net out of pocket cost (though the Fed portion is a tax refund at year end), which I have seen wild fluctuation this year. I do not expect the sweet deal that I got is going to last. In August, I checked with another installer that "lease" solar systems without upfront payment. I did not find that attractive as your lease payment is about the same as your saving of your utility bill per month.
2. There is much to be desired in efficiency and cost of PV panels. At a retail price of $2.5/W, cost would have to come down substantially to about $1.5/W in two years if US demand for panel were to pick up with reduced subsidy from the utility companies. The industrial leaders in low cost solar panels are First Solar (less then $1/W production cost using Cadmium Tulleride thin film technology) and Chinese manufacturers which produce their silicon cells before panel assembly.
Efficiency can be improved in terms of W generation per square meter of direct sunlight. To start with, strong sun has a power intensity of 1KW per square meter. At a 15+% efficiency typical for polycrystalline or mono-crystalline silicon wafers, you obtain 150W DC power output per square meter. There are many technologies offered with efficiency and production cost per W estimates as follows:
Mono or poly silicon (e.g. Suntech, Yingle, and many Chinese manufacturers) costs around $2/W retail with around 15+% efficiency (SunPower has panels with up to 20% efficiency). This technology shall dominate in the next few years for rooftop household PV generation.
Amorphous triple junction silicon thin film technologies (UniSolar) costs around $2/W with around 9% efficiency. This technology has low weight per Watt (in g/W) and also a relatively high KWh per year generation per KW peak capacity (~20% improvement over crystalline silicon).
Cadmium Tulleride thin film (First Solar) cost around $1/W with 11% efficiency. Problem here is that Cadmium is highly toxic so deployment has been mostly for utility scale generation. Flexible panels using Cadmium Tulleride is out of the question due to toxicity and mandated end-of-life recycling of toxic Cadmium.
CIGS thin film technology (Solyndra and a majority of the solar startups) has highly variable cost (Solyndra cost more than $3/W due to its unique cylindrical solar cells) and a higher efficiency of 12+% compared with other thin film (CdTe or aSi).
Triple junction Gallium Arsenide based technology (SpectroLab) is expensive per cell (cost $10 for a 1 cm square unmounted cell to generate 18W of power at a 500x solar concentration) at an efficiency of 34% (next generation 38%). Originally developed by Hugh (acquired by Boeing), these cells were deployed on satellites for high efficiency. Its high efficiency makes it very attractive for concentrated solar PV generation, using cheap mirrors to focus sunlight up to 1000x on a small area of high efficiency solar cells.
Which technology to adopt is the subject of later blog, but that depends more on bigger system issues than just $/W. The right technology depends also on weight and available surface area and other parameters concerning weight (Kg/KW), area (KW/square meter) and energy generation (kWh/KW generated per year) are equally important.
3. Solar tracking can generate 50% more generation of KWh/KW. Most solar panels on rooftops are fixed as solar panels are heavy (<100 lbs not including supporting structures). The fixture are there primarily to prevent uplift from strong gust of wind. Not all rooftops are strong enough to prevent the roof from being ripped apart by uplifted solar panels. At ASU, you find solar panels on top of parking structures may track the sun on one axis (E-W sun tracking). Two axis sun tracking (an azimuth tracking and an elevation tracking) are available at higher cost.
Here the weight and size/shape of the solar panel matters. A higher solar efficiency is necessary to reduce weight and size. Also thin film technologies on flexible panels are advantageous for a low Kg/KW, and a good reference is 100Kg/KW including all supporting structure. A game changer for solar PV generation is solar concentration via parabolic mirrors with high efficiency solar cells at the focal point of the mirror.
4. Total system cost, dominated by installation cost, needs to be reduced. Even if panel cost were to go down 60% from $2.5/W I paid to $1/W, the percentage reduction of installed cost is only $1.5/$5.2 or less than 30%. I went to an Energy Summit organized by DARPA and ASU, and there they cited $1 per W installed as the goal for large scale adoption here in the US for unsubsidized solar PV generation. It is simply not possible to achieve this $1 goal if I have to hire installers and they charge a profit margin.
New system concepts have to be introduced to reduce or remove installation cost. For example, the use of flexible panels with adhesive on rooftop could enable DIY (do it yourselves) installation of solar panels. Here I have plenty of ideas, as described in the following talk abstract.
The $1/W may be achievable with Concentrated Solar Power (CSP) on a utility scale. Here there are three principal technologies. Solar Thermal Power (STP) with two variations: first a single EW axis of half cylindrical sun tracking mirrors with a pipe carrying oil in the focal point superheated for steam turbine generation, or second a two axis solar tracking parabolic dish with a Stirling engine that convert heat at 600 degree Celsius directly into kinetic energy driving an AC generator. The third technology uses sun tracking mirrors focused on high efficiency solar cells. Rehnu.com uses cheap parabolic mirror made from flow glass, with 1000x solar concentration on triple junction GaAs solar cells from SpectroLab. On their website, they broke down total cost per W and suggest a $1/W installed cost is possible for GW scale generation.
5. Integrating other functions into solar PV generation. Unfortunately, it is rather difficult to achieve $1/W for non-utility scale generation, due to the lack of scale. To make domestic PV generation economically feasible, we may need to integrate other functions into the PV generation platform. As my talk in the following suggests three extra functions: mobility, wind generation, and hot water generation. My design involves integration all three functions.
Here is the abstract for my talks in China:
Integrating Solar and Wind Power Generation for Electric Vehicles
We present the Monarch Power/Electric Vehicle (MPEV) that integrates solar and wind power generation for electric vehicles. The design of the MPEV is done to meet the needs of people with no access to power, fuel, hot water, or paved road, but have an abundance of solar and wind. We anticipate use of the MPEV by soldiers in the Middle East, the Navajo Indians in Arizona, the nomads in Africa and Arabia, or the vast hinterland of NW China.
New system concepts are introduced. First we use Concentrated Solar Power (CSP) and Concentrated Wind Power (CWP) that is integrated into the structure of the MPEV. Second, we introduce new energy management techniques with intelligent batteries that are exchangeable. Third, we create a telematics system based on the RFID, WiFi, Bluetooth, and 4G wireless for MPEV mechanical control and energy management. Fourth, we also design the MPEV to transport water that is used to cool high efficiency (38%) triple-junction GaAs solar cells that are 1000X solar focused, and in the process generates hot water for domestic consumption.
We show a 1/10th model of the MPEV which we plan to mass produce by the end of 2011. We explain the efficiency and cost effectiveness of our MPEV and why this form of distributed non-grid-tied solar and wind generation can change the landscape of renewable energy generation.