PV Gap

Ricky Said:

Solar pool heating in the state of Pa. How effective?

We Answered:

Here in the northeast, I've seen people use the bubble wrap style covers with moderate success. What looked even more promising is a long coil of black hose which hooks into the pump. As water is drawn from the pool, it is circulated through the very hot hose, filtered, and then returned back to the pool. It seemed to work well and is a very simple and effective way to heat the pool in a green way.

Laurie Said:

Any nice DWF in Phoenixville to Norristown, PA areas?

We Answered:

dont know mate

Dora Said:

Hello, anyone good with Physics?

We Answered:

OK so we answered your questions - who will answer them when you sit the exam?

Will you give the same people a share of your wages when you start work a few years later?

I call this laziness...

(By the way - the answer is 42.)

Kay Said:

Does alternative energy storage or off peak unused capacity have the greater loss.?

We Answered:

Pumped-storage hydro is a commonly used method. There are hundreds of working installations around the world.
http://en.wikipedia.org/wiki/Pumped-stor…
In Europe, about 5% of their total capacity is pumped storage. In the USA about 2.5%.

There is a basic, often-overlooked problem with compressed air storage (as well as hydrogen and CNG on vehicles). When you compress air (or a gas), it gets hot. Decompress air, it gets cold.

That leaves you with two options, both unpleasant:

1. Intercool the compressed air, and throw away all that heat energy, which you paid for. This slaughters your efficiency. And gives you a second problem: when that air expands, it will turn cold. If it is highly compressed, it will turn very cold. In the machine shop using air at 8 bar, it works in your favor because air tools need cooling. But it could be a serious problem in a large, powerplant-sized facility.

2. Or, store the air "hot", keep the energy, but raise daunting problems in the storage of this very hot air. Aside from finding a pressure vessel that wouldn't be melted by the heat, you'd also need to insulate the vessel to keep the heat contained, and then you'd need a much larger tank to store the same mass of compressed air, since hot air has proportionately more volume than cool.

I would guess #2 is so difficult as to be impracticable. In many cases it is definitely not an option, such as a vehicle which runs on compressed air. Hydrogen cars also have considerable losses in this area because they also discard the potential energy of compression; they only want the chemical energy available as a fuel.

Battery electric drive is about 90% efficient at converting joules in battery to rubber meets the road. This still ignores the "regenerative braking" capability of electric-transmission cars, which could push it over 100%.
http://en.wikipedia.org/wiki/Electric_ca…

Tesla claims a "Well to wheels" energy efficiency nearly 10 times that of an average automobile. Their page here compares it to the most efficient alternative fuel vehicles.
http://www.teslamotors.com/efficiency/we…

Gasoline engine drive is less than 20% effective at turning "joules in the gas tank" into joules of zoom. Fuel cells are about 50% but only if you ignore the considerable energy losses of compressing the hydrogen.

If you want to maximize the efficiency of "substation to tire", battery electric is vastly superior to other modes.

You claim that battery electric cars will use primarily coal. I dispute that assertion. If electric cars were commonplace today, that would be true. But they are not, and by the time they are, the shape of electric generation is likely to change. Remember, the same social/economic/environmental forces which push us toward alternative cars, also push us toward alternative power generation as well.

In California, our power is only 1/3 coal and about 1/3 carbon-free. (most of that being large hydro, we hate nukes.) http://www.energy.ca.gov/sb1305/power_co…

You are exactly correct that measuring the number of joules of "potential" energy loaded onboard a vehicle is not a particularly useful metric, and wrongly casts battery-electric in a terrible light. Once on a mailing list, someone claimed that batteries couldn't possibly have enough useful range. He said "There will never be a battery that has the same energy content (joules) as a 12 gallon tank of gas." I ran the math: if he had such a battery, using well-known "miles per KWH" figures from real electrics, he could drive from NYC to Colorado on one charge. The question is, could he stay awake that long? :)

Fred makes an interesting point that nighttime charging of electric cars is a very useful form of energy storage. More than that, if your car has a 120V inverter on it (as the weak 2005 Silverado hybrid did http://www.edmunds.com/insideline/do/Dri… ), you can power your house from your car during an outage.

Warren Said:

What are some careers in Alternative Energy?

We Answered:

Okay this will sound lame .... but google it- there are so many I can't remember. In addition to the Alternative energy jobs ( like solar/air power) there are Environmental Gov. jobs , Permaculture ( you can take classes in this and they are about two weeks long - you earn certificates then its up to you to go out and set up classes- good money if you can manage yourself well) Spend some time doing research and grab a couple of mags like- green living - there are a lot of tips in there. I wish I could tell you more I just got excited to talk about it then drew a blank