Research&Development of Solar Selective Coatings Pays Off
07 Nov 08 | General, Solar ElectricFrom just up the road a short distance, researchers at RPI (Rensselaer Polytechnic Institute) have discovered a process that greatly increases the absorption of sunlight by photovoltaic panels and allows those panels to use the entire solar spectrum from nearly any incident angle.
“To get maximum efficiency when converting solar power into electricity, you want a solar panel that can absorb nearly every single photon of light, regardless of the sun’s position in the sky,” said Shawn-Yu Lin, professor of physics at Rensselaer and a member of the university’s Future Chips Constellation, who led the research project. “Our new antireflective coating makes this possible.”
It is possible by using nano technology to create seven layers nano rods. Each layer is designed to transmit a specific wave length (color) of light. The result is an absorption efficiency of greater than 96%. This is indeed great news for PV cell producers, as the current light absorption efficiency is about 67 percent for the typical PV panel.
The seven layers, each with a height of 50 nanometers to 100 nanometers, are made up of silicon dioxide and titanium dioxide nanorods positioned at an oblique angle - each layer looks and functions similar to a dense forest where sunlight is ‘captured’ between the trees.
The major implication for solar manufactures is smaller more powerful PV cells can be produced with less raw material. Is this the breakthrough the solar industry has been waiting for? Maybe. In any case, it certainly seems like a step in the right direction.
The one problem I see with all of this is the efficiency of the photovoltaic cell itself. A PV cell is essentially a large exposed transistor. When a photon strikes a P-N junction, one of four things happens; it bounces off, it passes through to the other side, it gets converted to heat, or it knocks an electron free. Of course the first situation is mostly cured by the selective coating. The last situation is the desired outcome. Conversion to heat remains a problem.
Currently manufactured PV cell technology has roughly a 15% efficiency from insolation rate to electricity production. As we learned above, some of this efficiency loss is due to reflection of light from the surface of the PV cell. A comparison of the total light reaching the PN junction (67% of the available sunlight) compared to the output of the PV cell, shows that the actual conversion efficiency of the PN junction is about 22%. The remainder either passes through the PV cell substrate or generates heat. The selective coating applied to a PV cell will increase the heat in the PN juction by 25-30%.
Heat is a major problem to semiconductors. Heat reduces efficiency and lifespan of a traditional silicone based PV cell. The computer industry has gone to great lengths to improve the heat tolerances of the semiconductors used in computer chips, therefore, this is not an insurmountable problem. It does, however, need to be addressed in cells that will use the selective coating developed at RPI.
It will likely take several years for this technology to make it onto the general market. In the mean time, every watt of installed PV is one less watt generated by fossil fuels.
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Tags: photovoltaics, solar power R and D
Five Good Reasons to Install a Solar Energy System
02 Nov 08 | Conservation, Environment, Solar Electric, Solar Hot Water, solar thermalA friend of mine has a blog called “Today’s Green Construction.“ Todd is a principle engineer for a large construction company and when it comes to construction, he knows what he is talking about. Recently, he wrote an article called “OPEC is the Best Reason to go Green,” which I thoroughly agree with. That got me thinking about other reasons to go green and more specifically, to install solar systems.
So here they are, Five (really) good reasons to install a solar energy system:
- Energy independence. No two ways about it, solar systems save energy. If you heat your hot water with oil, propane, natural gas or electricity, you are almost certainly using fossil fuels. Some percentage of that is likely to come from imports originating in countries that don’t like us, except for our money. These countries include Saudi Arabia, Iran, Venezuela, and Russia. The less energy we use from those source, the less petro dollars that will have to use against us. My last customer stated “Every dollar that I don’t send to the middle east makes me happy.” Amen, brother.
- Cost savings. Saving energy means saving money. With fuel prices rising, all energy costs are going up, even domestically produced natural gas. Solar systems will pay for themselves many times over during their operating lifetime. By installing solar equipment, expenses are fixed at their current levels, so as inflation and other economic pressures cause prices to go up, a homeowner that has solar installed will be paying the same price as before. Remember when gas was $1.00 per gallon?
- Environment. Saving energy also means reducing emissions. This varies from fuel to fuel, but almost all fossil produce sulfur dioxide and nitric oxides, additionally, carbon monoxide, carbon dioxide, volatile organic compounds VOC’s and toxic metals can also be released into the atmosphere. Reducing energy also means reduction in energy used to extract energy being used. The fuel oil delivery truck uses diesel to bring the fuel to a building, that is energy used to supply energy.
- Green Jobs. The more demand for solar (and other green) equipment, the more jobs will be created right here in the United States. As a solar contractor, I only purchase equipment that is manufactured here. Last summer, when my normal supply of solar thermal panels dried up, I could have purchased panels made in Israel. I opted to wait for the US panels, even though it meant loosing business. Not that I don’t like Israel, I just thought that there was a lot of transportation overhead involved with shipping a panel from half way around the world, and I would rather support the company making products that I know here in the US.
- The future. The earth has a finite amount of oil and other fossil fuels. Some of those fuel, like natural gas (which is mostly methane) does regenerate, but in much smaller amounts through landfills and large manure digesters. Others, like oil and coal, do not replenish themselves. Most geologists agree that we are approaching or have passed the peak oil point, which is the point where oil extraction begins to drop off as resources are depleted. In order to maintain the society that we and our forefathers have built, a replacement energy system needs to be implemented, else we will find ourselves in a new dark age. Some predictions are dire, but that does not have to come to pass.
These reason also apply to wind power, geothermal, tidal, and all other renewable energy sources. Renewable energy is no longer alternative energy, it must grow into our primary energy source.
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Tags: photovoltaics, solar economy, solar thermal
Sizing a grid tied PV system
01 Sep 08 | Solar Electric
I get several calls per week from potential customers wondering how much or how little of a PV system they will need to off set their electrical use. Grid tied PV sizing is pretty straight forward. A Basic due south facing system should be tilted at latitude (~42 degrees in the Hudson Valley). This is the bench mark for system sizing. Unfortunately, most systems are not tilted at latitude and/or facing due south. The benchmark system looks something like this:
- Annual kWh ÷ 365 days = kWh per day
- Percentage of electricity to offset (decimal)
- kWh per day ÷ sun hours (about 5 hours in the Hudson Valley)
- Figure in losses (temperature loss 88%, system derate 84%, inverter 94%)
For example, my house uses about 8,000 kWh (obtained from utility bills) per year. Therefore:
8000 kWh ÷ 365 days = 21.9 kWh per day.
I want to offset 100 percent, so 21.9 kWh × 1.0 = 21.9 kWh
I have an average of 5 sun hours per day, so 21.9 kWh ÷ 5 hours = 4.38 kW
Calculate system temperature loss, 4.38 kW ÷ 0.88 = 4.98 kW
Calculate system derate, 4.98 kW ÷ 0.84 = 5.93 kW
Calculate inverter loss, 5.93 kW ÷ 0.94 = 6.3 kW
Therefore, I would need a 6.3 kW system facing due south, tilted at 42 degrees to off set 100% of my electrical use. That is the simple answer. It gets more complicated (and larger) as the azimuth and elevation of a typical installation are not usually ideal. A site visit and investigation with a solar path finder will usually nail down the specifics.
Installed, with all federal and state credits and rebates, that system would cost about $4.50 per watt, or about $28,350.00.
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Tags: photovoltaics
Central Hudson is requesting a rate hike
29 Jul 08 | Solar ElectricIn one of the stranger press releases I have read in a while, Central Hudson Energy Group (NYSE:CHG) states:
Higher energy costs induced our customers to use less energy… the weakening economy has further induced our customers to use less energy… As a result, we believe it is necessary and prudent to take two actions. First, we are reducing our earnings guidance for 2008, and second, we are filing a utility rate case to bring our revenues into line with the costs to serve our customers. (emphasis mine)
Which is interesting in a way. The stock holders of a publicly traded company expect a certain payout over time, the utility company does everything in it’s power to provide that payout, including reducing line men and support staff, ect. However, when the economy really hits the floor and people begin conserving electricity so they can still pay for it, it is time to ask for a rate increase. Nice. By the way, I am already paying ¢16.8/kWh. How much higher can it go?
This is the problem with a publicly traded utility company. The most important thing is not the customer or the quality of service, its the bottom line on a P&L. It is more important to the CEO and the board of directors to keep the stock value high so they can get their yearly bonus and retire to Martha’s Vineyard than to provide good, reasonably priced electrical service to the community.
So, what is a homeowner to do? If you have read this blog, you already know the answer to that. Take control of the situation and be your own power company. Photovoltaics are looking more and more competitive these days especially with the state incentives available. As energy prices continue to rise and PV prices either stay relatively the same or drop, the utility companies will find themselves competing head to head with renewable energy products. They may find that they are pricing themselves out of a customer.
Update: It looks like they are filing for 3.5% increase on electricity and 10% on natural gas.
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Tags: energy costs, photovoltaics, utility companies
How long do Solar Systems last?
26 Jul 08 | Solar Electric, Solar Hot WaterThat is a very common question. The answer is, it depends. Solar systems, like all other mechanical systems require some maintenance. Last week, I came across a solar hot water drain back system that was 28 years old. The great thing is, it was still working just like the day it was installed. The only problem the home owner had encountered was a bad circulator pump, which the plumber replaced.
Properly installed drain back solar hot water systems using distilled water could, in theory, last almost indefinitely. Solar Hot water systems that use antifreeze will likely last only 30 years or so. Still, that is a great payback. For either system, over the course of its operational life, it should easily pay for it self 4 to 5 times over.
Photovoltaics are said to last 25 years however, their output slowly declines over time. After 25 years, most current photovoltaic panels will be producing about 80% of their rated power. Still, that is not bad, and a well designed photovoltaic system should pay for itself at least two to three times over its operational life (with current incentives).
The advantages of renewable energy systems, for those that are in it for the long haul, are:
- Stabilizes energy prices at or below their current levels, gives the property owner more control over expenses.
- Increases the property value of the residence or building they are installed on.
- Reduces emissions and environmental pollutants from nearby electrical plants.
- Reduces overall electrical load on grid, thus reducing the need for more power plants and high tension distribution lines.
- Spreads out electrical generation capacity, thus making it more difficult for any one catastrophic event to cause a regional blackout (distributed generation).
- Reduces the use of fossil fuels and thus dependence on other countries to provide energy for us.
As you can see, there are many advantages to a solar thermal, photovoltaic, wind, or microhydro system