A Hybrid Approach to Solar Power

When photovoltaic cells make electricity from sunlight, they collect a lot of heat along the way. And they don’t work as well warm as they do cold.

Four years ago I wrote about a hybrid system that was intended both to make electricity and gather usable heat on residential rooftops. That company, now called Echo Solar, is offering its product around the country.

But the market for such hybrids goes beyond homes, especially if the second product is hot water, which can make steam and then electricity. Now another company, Cogenra, is supplying a hybrid solar electricity and hot-water system for big apartment buildings, dormitories, retirement homes, wineries, food processing plants and, most recently, a dairy, all of which use large amounts of hot water. It has 40 installations worldwide.

The basic problem, according to Gilad Almogy, the chief executive of Cogenra, is that a photovoltaic cell captures only about 15 percent of the sun’s energy. Another 5 percent or so reflects back off the solar cell. “Where’s the rest? It’s heat,’’ he said. On a 100-degree day in a sunny location, the cell, which is black, can reach 160 degrees Fahrenheit, he explained.

So his company mounts the cells on water pipes in the center of trough-shaped mirrors. The mirrors concentrate the sun’s energy by a factor of 10. The result is electricity and water that is warmed to as much as 158 degrees. The temperature can be varied, according to the application; water for sterilizing a food processing tank is hotter than water for a shower.

The trough design is not new; it is similar to the one used at solar thermal power plants, which boil water into steam to spin a turbine, turn a generator and make electricity. But in Cogenra’s installations, the water does not reach the boiling point. If it did, the solar cells would not work very well.

As measured by heat content, the bulk of the production is hot water, but the electricity sells at a higher price. The economics vary by location; in most parts of the United States, the value of the hot water is set by the value of the natural gas that did not have to be burned because the solar system did the work instead.

Since natural gas is currently very cheap, the small electricity production may be more valuable. But in Hawaii or India, where fuel to heat the water has to be shipped in, the value of the hot water would be higher, Mr. Almogy said.

If a quantity of electricity is worth four times as much as the equivalent amount of natural gas, then the hot water and the electricity produced by his system have about equal value, he said. At the moment, though, the electricity is worth far more than four times as much, because the price of natural gas is depressed by a surplus brought on by fracking.

The economics of his system works well in California because that state offers a rebate for the installation of renewable systems for heating hot water, he said. The rebate is equal to $12.82 per therm of gas saved in the first year, which is well above what a therm actually costs most consumers at the moment.

While Cogenra’s system starts with the same concept as Echo Solar’s, they are not quite competitors. They are both backed by the same alternative energy investor, Vinod Khosla.

Courtesy: green.blogs.nytimes.com

How does Our Energy Use Compare to our Friends Across the Pond?

Figures from the US Energy Information Administration show that energy use in homes across the US remains high, with just under a quarter of energy (22.15 per cent) designated as domestically used in 2010.

Here in the United States we are often criticized for our energy use and seemingly high carbon footprint, so it’s always interesting to see how we compare with other places. A new index from UK insurer Castle Cover has made the comparison process a little easier, by producing a clear visualisation of UK use of electricity, gas, water and coal between 1970 and 2011.

According to the index, the country’s spend on energy has risen exponentially in this time, alongside increased reliance on technology and prices of crude oil moving upward. Figures from the Department of Energy and Climate Change also suggest that the use of energy within the home is something that Brits need to address, with the percentage of energy used within the domestic sphere rising from 25 per cent in 1970 to 32.3 per cent in 2010. So, what does this all mean? Is there anything we can do to quell the rising tide of home energy use here or in Blighty? With such a significant amount of the energy consumption in both countries being domestic, it’s very possible that we can all make a difference by putting in place a few small changes in the home. Some of these are things that some households on both sides of the Atlantic do without question, but you may have previously dismissed as having little impact. Here are three favourites:

1)    Updating your appliances can make a whole heap of difference to your energy use as government figures suggest that 56 per cent of energy used in the home is channelled into heating or cooling. With this in mind, making sure you have a good quality boiler and air conditioning system should be top of your list for being green in the home.

2)    Keeping a check on the amount of energy your appliances use with the help of a monitoring device will make you think twice about how often you use them. If you regularly forget to turn items off, why not invest in a timer to do it for you?

3)    Make sure you aren’t allowing energy to flow out of your home. This can be as simple as buying draft excluders and changing your soft furnishings, but could also mean trying to harness energy to feed into your home with solar panels.

Veggie Power

We haven’t developed a Flux Capacitor like in “Back To The Future,” but a pilot plant in Stuttgart is taking a step in that direction by turning over-ripe fruit and vegetables into fuel for automobiles.

Make Your Next House Move a Green One

Guest Post by Kathryn Thompson

          Photo Courtesy: Flickr

There’s an enormous and much welcomed spotlight on green issues and solutions at the moment: from creative recycling ideas to renewable energy and electric cars. ‘Green’ initiatives are cropping up pretty much everywhere and becoming more and more accessible. With an increasing number of eco-savvy customers demanding earth friendly options for all their needs, innovative solutions are appearing in the most unusual of places.

The latest industry to harness a more environmentally friendly approach is the courier and house removal industry. It’s now possible to ship belongings or move house without it costing the earth – quite literally.

Removal lorries are generally gas-guzzling vehicles that cough out harmful toxins into the environment. However, several removal companies are pledging to reduce their CO2 emissions by converting to LPG (Liquid Petroleum Gas), which, as well as being super fuel efficient, releases 20% less CO2 than standard petrol or diesel.

Of course, when moving, you can do your bit too. Approach local supermarkets and retails outlets for sturdy cardboard boxes to pack your belongings in. They will be more than happy for you to take them off their hands, and you can feel happy in the knowledge you have protected your pocket as well as the earth. If you do buy new, make sure the boxes are made from recycled material.

Save old newspapers, or use sheets and towels to wrap your breakables in, a good alternative to traditional bubble wrap.

Several removal companies are also now offering a free collection service that allows them to collect and recycle used packing material – very green and extremely useful in those stressful days following a house move. Some will even go as far as to collect usable but unwanted items you discover whilst unpacking and take them to a charity shop– how many times have you started unpacking a box, only to find it full of items you haven’t seen for five years anyway!

Of course, it’s a good idea to have a good clear out before the move, selling or recycling unwanted items – one mans trash is another mans treasure! This will make packing and unpacking much easier and avoid filling the lorry with unnecessary items, the lighter the lorry the better the fuel consumption will be.

Generating Solar Power…Underwater


Photovoltaic cells produce electricity directl...

(Photo credit: Wikipedia)

It sounds like a child’s question: can you generate solar power underwater? The answer, according to Phillip Jenkins and his team at the US Naval Research Laboratory, is yes. The researchersrecently demonstrated a method for harvesting solar power underwater at depths of 30 feet.

Currently, the only option for underwater energy is batteries, which shortens the amount of time an underwater system can be powered. Having a source of renewable energy underwater opens up the possibility for long-term installations of autonomous systems, including systems for communication, environmental monitoring and networks of sensors.

Jenkins says the technology is meant to be “a new tool in the toolbox,” opening up further possibilities in renewable energy, and new options for powering underwater systems.

To date, the solar cells are capable of generating 7 watts of energy per square meter at depths of 9.1 meters, which is enough to demonstrate the technology’s potential for use in shallow water, such as in the areas near shorelines. (Aboveground solar cells typically generate about 110-220 watts per square meter.)

To achieve this breakthrough in efficiency, the researchers needed a solar cell optimized to absorb the narrow wavelength spectrum of visible light available underwater. Instead of crystalline silicon solar cells or amorphous silicon cells, the researchers opted for high-quality gallium indium phosphide (GaInP) cells. GaInP cells are better at absorbing wavelengths in the blue/green spectrum, making them ideal for capturing light that has been filtered through water.

Power density of GaInP and crystalline silicon cells, underwater, as a function of depth. Credit: U.S. Naval Research Laboratory

The researchers’ next step is to test how the technology will fare during long-term deployment. This includes understanding how water quality variations affect performance. “You see it in rivers,” says Jenkins. “One day they’re murky, and one day they’re clear. Water quality varies all over the world, and we have to take this into consideration.”

In addition to understanding how water quality affects energy harvesting, the researchers need to test how the system will age and degrade. Speaking to the permanence of these solar installations, Jenkins says there is no reason why they couldn’t last a long time, providing they can withstand potential biofouling and sedimentation.

The development of efficient underwater solar cells is about creating options, because other renewable energy systems are not one-size-fits-all solutions. For example, other water-related renewables, such as wave power, operate at the water’s surface, limiting the scope of the power’s reach. Jenkins and his team aim to generate power at the bottom, which requires an underwater system.

This breakthrough has the potential to help everything from monitoring pollution levels to learning more about underwater creatures than ever before. Although underwater solar cells still have far to go before they are developed at the commercial scale, this development put the option of long-term underwater installations on the table, which is an exciting prospect for the future.


Courtesy: www.science20.com