July 4th BBQ + A Sunny Solar Day

I received this by email over the weekend from Mike Rader over at SEIA. Just passing it along.

There’s a reason solar advocates love Independence Day. The bright July sunshine means that solar energy systems from Maine to California are pumping out free, clean energy for their owners. These solar pioneers are harnessing our abundant solar resources and are helping make America energy independent this Fourth of July.

Most people don’t know that America is the birthplace of the modern solar energy industry. In 1891, an inventor from Baltimore named Charles Kemp filed the patent for the first commercial solar water heater. The Carnegie Steel Company modernized the design a few decades later.

In the 1950’s, Bell Labs created the first modern solar electric cell using silicon, which is still the semiconductor of choice for many solar panel manufacturers. Bell’s technology leap helped the U.S. win the space race by providing the “killer app” for satellite power generation.

In 1974, five major industry members decided to form the Solar Energy Industries Association; the first trade association for solar energy businesses in the U.S. In 1979, the White House installed what would be the first of many solar installations at that site. (This article from the Washington Post discusses the first installation during the Carter administration and the recent announcement by President Obama, but doesn’t mention the panels that the Bush administration installed in 2003.)

In 1986, the first large-scale concentrating solar thermal-electricity facility opened in Kramer Junction, California. Beyond the solar thermal collectors, it works just like a traditional steam-turbine power plant.

I won’t take up more valuable fireworks-and-barbeque time with a lengthy dissertation on solar energy in America, but if you’re a geek like me, we’ve got some great resources for you. For example, Solar Works for America tells the stories of regular people across America who have found jobs in the solar industry. As one of the fastest growing industries in the country, we hope that solar can help you be economically independent through “going solar” yourself, training for a solar job or maybe even starting your own solar company.

Solar energy is a classic American success story of technology, innovation and competition. In the coming months, SEIA will be announcing a lot of new ways to help you fight for a solar-powered America. Enjoy the fireworks, but stay tuned: the real solar revolution is just beginning.


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Solar Photovoltaic Panel Watt Ratings: How much power do you really get?

Solar PV (Photovoltaic) panels, in the industry referred to as modules, come with a label stating the wattage. This can be very confusing to the public, and is poorly understood even by some people within the industry.

A watt rating on a solar module is a measure of “watts peak”, that is, the maximum amount of instant energy that can be produced under STC (Standard Test Conditions) and it is this wattage that goes on the “nameplate” rating of the module.  STC is the expected performance when a module is receiving precisely 1,000 watts of insolation (sunlight) per square meter of module aperture (area exposed to the sun) at a specific module operating temperature ( 77F) and when the module is installed at a certain angle to the sun (incidence angle).

Rated power can vary widely from actual power as conditions change. Changing the insolation, incidence angle, or temperature raises or lowers the instant power that will be produced. Temperature is a good example of variance. Each panel manufacturer specifies the thermal values for their panel to state the expected degradation caused by increased operating temperature. This degradation is usually somewhere close to .5% of efficiency loss for each degree C of temperature rise above 25C (77F). As you might imagine, solar modules frequently operate at temperatures much higher than 77F.

PTC ratings are a more realistic projection of a modules real world performance than STC. PTC is short for PVUSA Test Conditions. It is not “Performance Test Conditions” as some say, and actually PVUSA stands for Photovoltaics for Utility Systems Applications. What a mouthful.

It is possible when comparing two modules, that the module with a higher STC rating could also be the one to have a lower PTC rating. The CEC (California Energy Commission) uses PTC. You can look at their approved list of modules and see the difference between PTC and STC ratings. http://www.gosolarcalifornia.org/equipment/pv_modules.php For example, a Suntech Power STP230-20 is rated at 225 watts (STC), however the PTC rating is only 208 watts which may be closer to what you could actually get most of the time.

It should be noted that in cold weather, it is also possible for a module to produce more power than its nameplate rating. This variance in power production is what makes inverter selection and string sizing so important, because the modules best and worst case performance limits must fall within the inverters maximum and minimum operating range.

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Calculating BTU Transfer Using The Water Formula

I thought it might be cool to write about how BTU transfer is calculated and share a little shortcut. There is a quick back of the envelope formula used for calculating the BTU/h values for heating water. The “water formula” says:

Q (Energy) = 500 x  f  x DeltaT (in F)

Q = rate of heat transfer (Btu/hr.)

f= flow rate (gallons per minute or gpm)

DeltaT = temperature change (degrees F)

500 = the “fluid factor” this is based on water as the heat transfer fluid. The fluid factor is obtained by using the weight of a gallon of water (8.33 lbs.) multiplied by the specific heat of the water (1.0) multiplied by 60 (minutes). This comes out to 499.8 when using water.

Simply put, if you know a beginning temperature, an ending temperature, and a flow rate, you can calculate the heat transfer in BTUs.

As mentioned, water has a specific heat of 1.0. But a 30% or 50% aqueous glycol solution has a different value. Of course if you are using glycol you must know the specific heat for the brand of glycol you are using, at the temperature range used, and the % of the mixture. For example, a 30% glycol-water mix would have the specific heat of around .90. All propylene glycol (PG) brands will have similar values; here you can see the chart of specific heat of a cool corn-based glycol. Anyway, in the temperature range used in most domestic water heating applications (100-200F) for 30%  glycol use 450 instead of 500 in the water formula.

Here’s an example, using 100% water for simplicity. Lets say we know the flow rate is 5 GPM and the entering temperature of a system (solar, boiler, heat recovery, whatever) is 120 and the leaving temperature is 125. So, 5 degrees are added at 5 GPM. The BTU of this transfer is 5 x 5 x 500 or 12,500 BTU per hour.

If a 30% glycol solution was used, de-rate it by multiplying using 450 and you would get 11.250 BTU/h.

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Household Air Conditioning Unit Doubles As Water Heater – The Washington Post

Household Air Conditioning Unit Doubles As Water Heater – The Washington Post.

I mentioned this heat recovery company HotSpot in a previous post, looks like mainstream media is catching up. The Post article seems to miss a couple of key technical points but overall it is accurate and it is encouraging to see the public becoming aware of this technology. Hope to see more of this.




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Solar PV Prices Keep Falling

Today’s lower PV prices are a big windfall to some of the suppliers of slow moving, awarded-but-not funded grant projects because some awards were based on bids placed last fall at a time when PV panels cost 40%  more than they cost today.

But many panel manufacturers are looking at slowing sales and reduced profits in the near term. The global solar market slowdown and reduced selling prices are directly related to declining government incentives across Europe.

Highly susceptible to supply and demand, photovoltaic prices are still heading downhill after steadily declining over the past 90 days. Export prices of Chinese grade A panels are now approximately equal to the cost of the materials. Chinese PV makers are nervously watching Europe and are anxious about orders. Prices of US made PV panels, which serve a narrower, mostly US government market, were dragged down as well but not as severely.

This makes solar cheaper for Americans to buy, and easier for solar contractors to sell!

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Wake-up, Virginia – The Sun is Shining!

I just returned from a business trip that included travel in China and Germany where it’s not very sunny compared to the USA, but where it seems like you can’t travel 100 feet without seeing a solar PV panel or solar water heating collector. It never fails to strike me as odd, upon returning home, the lack of solar power usage in the USA, especially where I am today here in sunny Virginia Beach. Of course, Virginia is home to many high tech companies that invest in, design, develop and/or manufacture solar products, but where do solar energy products end up being installed?

Below, 2010 state rankings from the Solar Energy Industry Association.

1. California: 47 percent with 971 MW
2. New Jersey: 14 percent with 293 MW
3. Colorado: 5 percent with 108 MW
4. Arizona: 5 percent with 101 MW
5. Nevada: 5 percent with 97 MW
6. Florida: 4 percent with 73 MW
7. New York: 3 percent with 54 MW
8. Pennsylvania: 3 percent with 54 MW
9. New Mexico: 2 percent with 45 MW
10. North Carolina: 2 percent with 42 MW

So there may be some surprises here – who would have guessed that New Jersey would have more solar installed than Arizona and Florida combined? Or that New York and Pennsylvania would each beat New Mexico and many other much more sunny places like Texas, Louisiana, Alabama, Mississippi?

It’s not all about sunshine, as you could guess, it’s also about state government support and local energy costs.

Virginia has no real state support and cheap electric rates. Virginia is a coal state with powerful coal and electric utility lobbies.  The coal companies want to sell coal. The power company helped push through voluntary renewable energy portfolio standards, and then elected not to participate. Wake up, Virgina.

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Heat Recovery

I was just reading an article about a grocery store that was able to recover enough heat from it’s many refrigeration and freezer compressors, to provide heat for the grocery store and in some months reduce the heating bill to zero.


See, heat recovery has been around for a long time. It is extensively used in large and medium sized industrial and manufacturing facilities to save millions of dollars in annual energy costs. Unknown to most, smaller sized heat recovery systems that can generate big savings are also available for smaller users, like grocery stores, restaurants and even home owners. One company that makes the smaller size stuff www.hotspotenergy.com

A typical heat recovery system includes a heat exchanger, a pump, several temperature sensors, and a control system. When used with a refrigeration compressor, it connects to the hottest area of the host system(s) which is the compressor discharge line, and using a heat exchanger it captures the waste heat ( the heat that was going to be thrown away) and pumps it into the hot water system.

In the case of a grocery store, the heat could be used in the winter for space heating. However, it could also be used year round to provide hot water for the food preparation, food service areas, the butcher and bakery operations, store cleaning etc., which all consume a lot of hot water in a grocery store.

And, there is a side-benefit of heat recovery – the host system runs cooler and uses less energy. It’s normal to save 10-20% on electrical consumption on a compressor, when heat recovery is engaged.

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