PV Gap

Carla Said:

what is cost of coal,solar,wind power plant per MW?

We Answered:

A subtlety...

Per MW (megawatt) is a 'capacity' cost, the construction cost to built a plant of a certain size, the maximum output under ideal conditions - a 600 MW coal plant or a 100 MW wind farm.

What people are typically really asking for is the cost per MWh (megawatt-hour), the long term cost of the energy produced by the facility.

This is affected by many things, but mostly by the 'capacity factor' of the facility, the percentage of time it will actually produce it's full rated output. Conventional thermal facilities such as coal will have a CF of 85% or greater. A 'good' wind site will have a CF of around 30%, while solar is about 18%.

So, assuming an equal plant capacity of 100 MW for all three resources, coal (or natural gas) would produce about 744,600 MWh per year, wind 262,800 and solar 157,680.

There are many variables in determining the output cost, but coal (assuming a plant could actually be built over environmental objections) would provide electricity for a cost of between $35 and $50/MWh. Wind farms are in the $80-$115 range and solar is $120-$250 (I know, the 'next big thing' will reduce solar costs - that prediction has been made continually since the 70's. Someday it *will* actually turn out to be true. I'm not going to hold my breath waiting for it).

Martin Said:

What are the drawbacks of solar power?

We Answered:

kgib808 is correct. Solar power is currently way too expensive to be widely used. While sunlight is obviously free, solar panels (also called photovoltaics) are expensive to manufacture. There are two main approaches to bringing down the cost of solar power: you can increase the efficiency of solar cells, or you can produce them more cheaply. Most research on solar energy focuses on one of these pathways. For the former, technologies of importance include multijunction cells, which while expensive, have reached efficiencies of over 40%. To bring down solar panel costs, researchers have looked at thin film technologies such as CdTe, CIGS, and organic photovoltaics, which can be processed more cheaply (for example, by printing) than crystalline silicon and use smaller amounts of raw materials.

As you note, another problem with solar is the capacity factor. Capacity factor is a measure of what percentage of maximum capacity a power source typically operates at. For example, if you had a power plant with a 500MW capacity that produced an average of 400MW over some time period, the capacity factor would be 400/500=80%. For power plants that can crank out electricity as long as they are kept fueled (coal, gas, nuclear, hydro, etc.), shutdowns for maintenance and repairs limit the capacity factor to between 70 and 90% for most plants.

For wind, solar, tidal, and other power plants with an intermittent energy supply, the capacity factor is lower - about 40% for wind, and 20% for solar in a sunny area. This low capacity factor causes two problems with widespread use of renewables. Firstly, you need to build a lot more capacity - 1GW of solar panels won't produce as much energy as a 1GW coal plant. Secondly, as you note, power output is intermittent, meaning that you need to have a way of storing and releasing energy (one promising method is to pump water into a raised reservoir, then release it through turbines when power is needed), or supplement the power supply with peak load generators, such as small gas turbines.

Available area is not really a huge problem; if you were to power the US with 10% efficient solar cells*, the area covered would be less than the area currently covered by roads (I've heard this before, but can't find a source at the moment; regardless, the rate that solar energy hits the Earth greatly exceeds human energy consumption). In addition, solar panels can be installed on buildings and other already-developed land, allowing them to be used in urban areas to some degree. While lack of land can be a locally-limiting factor, it shouldn't be a problem over large scales.

*This is a fairly low efficiency for silicon and some thin film technologies, already readily obtainable, but is higher than some experimental technologies, such as organic photovoltaics (currently being researched, best cells are at about 5% efficiency).

Francis Said:

How much does a coal power plant cost to build?!?

We Answered:

Hope this helps:

Because of rising construction prices, a coal power plant has been estimated to cost over a billion dollars.

Erik Said:

estimated cost of building a solar power plant in haiti?

We Answered:

The cost per watt-peak of solar power fell from $10.80 in 1998 to $7.50 in 2008:
http://www.greentechmedia.com/articles/r…

However, most of the solar power until now has been provided by silicon panels. Silicon was initially chosen because we already had factories for silicon semiconductor. We are now making materials optimised for solar cell performance, like cadmium telluride (CdTe) and CIGS (Copper Indium Gallium (di)Selenide).

First Solar has built a CdTe power station at about $3-3.50 per Watt-peak. It costs them about $0.85 to manufacture a Wp of panel:
http://pg.jrj.com.cn/acc/HK_DISC/stock_N…
So to get your


So to work out your cost, multiply your power output in watts-peak by about $3.50 (US). Hawaii probably gets something like 2000kWh/Wp-year, so it depends on how many solar panels you think you need.