The price of inverters has most certainly come down over the past 10 years. I did a few Google searches, and was unable to find a price history on inverters. However, I can tell you that from personal experience of purchasing inverters, that the price has certainly come down significantly in the past 10 years. You don't even see square-wave inverters any more (Thank goodness), modified sine wave inverters are dirt cheap (I've purchased 1.5KW sustained 3WK peak inverter for $100 USD) and pure sine wave inverters (which is what you would have to use in a grid tied environment) would have been absurdly expensive 10 years ago.

Most of that was due to the use of MOSFETs in inverter technology, which are substantially cheaper than prior tech used. I'm not an EE, however. (I just have nerds for friends and such tendancies myself.)

Even so, you're correct in stating that the inverters are a real barrier for solar penetration in the market. Inverters usually range around 1/3 of the cost of a solar installation. Hopefully further improvements will be made in this area.

Coal, along with nuclear, is a base-load power supplier. Very little of it is cycled on a daily basis to meet demand. Solar is a peaking power supplier, for it operates best noonish (or later or earlier depending upon the orientation).

To reduce coal usage, base load must come down considerably. Solar first and best replaces natural gas and to some extent the limited remaining oil-fired generators. To eat into coal, we will need more/better electrical storage capability, and even if that is available, the progression will be to replace oil, nat gas first before eating into coal.

We'll get there...it is just a question of how much pain is involved before we do.

With respect to cost, I am a bit skeptical since it is not sufficient to bring down the costs of the solar panels. One must also bring down the costs of the inverters and other accessory equipment. From what I have seen at Solarbuzz, little or no progress has been made on these items.

I was looking into that a while back & it's definitely all that 'other stuff' that gets to be a problem as the cost of the panels come down. In an off grid system (i.e., with batteries), PV modules make up 50-60% of the total installed cost (solarbuzz numbers); installation is around 20% and the inverter is roughly 7%. The batteries & charge controller are 25%. If you deduct out the battery & charge controller cost for a grid tie system then PV modules make up 67-80% of the total cost. So cutting the cost of the PV modules dramatically (say from $5/peak watt to $1/pw) would make a nice impact on the overall cost. At that point, the installation cost gets to be the next biggest chunk.