# Solar panels

1. May 3, 2005

### Pengwuino

So whats the deal with solar panels? How much do you end up paying per average watt-hour your house consumes through solar panels to equal your use? As in... if a panel costs $2000 for that generates 200Wh, im paying$20/Wh for the panel to equalize it. What are some real world figures though? And how many panels do you need relative to your average kwh use in say, California?

Also, is it worth it and what are the tax incentives like?

2. May 3, 2005

Real costs of solar homepower

If I recall correctly, amortized over 20 years, it is roughly 25 to 75 cents per kwh.

Power is not energy. Watts are units of power and watt-hours are units of energy. Your panel would generate 200 watts (this is assuming dead-on sunlight at an intensity of exactly 1000 watts per square meter; 1000 watts per square meter is only seen on Earth when the sun is directly overhead and skies are perfectly clear; this level of insolation is impossible anywhere within the geographical United States because no part of the geographical United States is in the tropics), not watt-hours (which would be nonsensical). You would be paying $20 per peak watt. Solar panels these days actually retail for about$4 per peak watt.

A solar panel, or a collection of them, is not a solar homepower system and is not even the heart of the system. The heart of a solar homepower system is its power storage and power conditioning equipment. Complete solar homepower installations cost about 10 to 20 dollars per peak kilowatt to install. For comparison, a brand new nuclear power plant with AP1000 reactors built today would cost about $1.50 per peak watt to install -- and, unlike your solar homepower system, the nuke plant would produce peak power 95% of the time, 24/7/365. Typical solar homepower installation include about 3 peak kilowatts of solar panels. This would cost ~$12,000 and is less than you would need for average California household electricity usage. Homepower folks usually resolve this power discrepancy by also making their households ultra energy efficient.

Unless one lives extremely far from the grid, homepower today is always a financial loser no matter how it is done and will continue to be a financial loser into the forseeable future. Generally, wind homepower is cheaper than solar homepower and microhydro homepower is cheapest of all.

3. May 3, 2005

### Pengwuino

Bah, got that stupid watt/watthour thing confused agian.

What is microhydro homepower?

4. May 3, 2005

No problems. I know MIT students who mix those up sometimes.

It is hydropower. It is smaller than commercial hydropower, so it is called micro. Homepower folks also call it low-head hydro. If you have a stream on your property and you set up a turbine (and associated components such as a pipe called a penstock which serves to feed the water with minimal friction and turbulance downhill to the turbine) in it (or next to it, which is more often the case) to produce power for your house, you are doing microhydro. Ivan Seeking is into low-head (micro) hydro, so he can probably tell you all about about it. Also, I have found this site useful for learning about it:
http://www.microhydropower.net/intro.html

5. May 3, 2005

### Pengwuino

Well i live on a lil normal 1/2 acre house in a neighborhood and all so theres no streams around here :D. Oddly enough though, we have a LOT of canals in our city and i doubt they use the water for power.... any reason why they wouldnt?

6. May 3, 2005

### FredGarvin

Most likely the cost/benefit of setting up the distribution and monitoring of the sites. I would doubt that it would be financially viable once you take into account the number of people to maintain and keep track of those stations. Not to mention the up front costs that are probably pretty steep as well. Are there fluctuations in those canals' flows? That could be another issue as well.

7. May 3, 2005

### Staff: Mentor

Not enough flow, most likely. Usually for hydro, one needs a height of water (which implies dam) to generate the potential energy ($\rho$gh, aka head of water), which is then converted to the rotational kinetic energy of a turbine. Flow could be used directly with a magneto-hydrodynamic system, but that requires a conductive fluid (any salts or soluble minerals in the canal water?) and magnetic field, so too expensive in general. Nevertheless, one needs an appreciable flow.

8. May 12, 2005

### Ivan Seeking

Staff Emeritus
This came up somewhere else. There are a couple of engineers who think they have come up with a practical windmill style design for very low head systems, like canals. I don't know if the math adds up or not but they seem to think so. I believe that this story ran on Discoveries This Week, on the science channel - SCI.

For anyone interested, as for low-head home projects, I can't tell you all about it, but I have looked into this quite a bit, [also took a minor in hydraulic engineering] and the Banki Crossflow Turbine is the best solution for most applications. It is relatively cheap and easy to design, make, and install, and it performs well over wide ranges of both flow and head. By chance, one classic paper on this is available at Oregon State University's Mechanical Engineering Dept.

9. May 12, 2005