Solar panels were cheaper than wind turbines for the first time last year in certain markets, per unit of capacity, and are rapidly closing a remaining gap in the full cost of power generation.
Until now, wind power has been the leading low-carbon alternative to oil, coal and gas, outside large niche markets such as Germany, which has seen a huge ramp-up in installed solar.
But that could change, with deep implications for the health of both industries if one substitutes the other.
As soon as this year, solar could for the first time surpass wind in annual global installed capacity, given an expected contraction in the wind market.
The full costs of wind power generation remain less than solar because of higher productivity and lower installation costs, but those advantages are eroding rapidly given current trends in equipment prices, with a glut of Chinese-made solar panels sending prices tumbling.
Both sectors have struggled to shake off over-capacity, but in different ways, and with different outcomes for prices.
In solar power, over-capacity is largely a result of global commoditisation of the finished modules and the influx of cheap Chinese producers, which now dominate the market.
The result has been bankruptcies and continuing, sharp falls in solar panel, or module, prices.
In wind, over-capacity is a result of subsidy cuts and lower energy demand in western markets following the financial crisis, coupled with competition from low gas prices in the United States and a stagnating Chinese market.
But wind turbines are heavy, complicated pieces of moving machinery in which sales depend on local servicing.
They have not become commoditised, and three western producers lead the world market: Vestas, GE and Siemens.
The result of over-capacity has instead been a variety of cost-cutting strategies, including idled production, while prices have remained fairly stable.
Recent manufacturing data show that average selling prices for solar panels, or modules, are now lower than wind turbines per watt in some markets.
For example, one of the world's leading turbine makers, Denmark's Vestas, reports average selling prices for the first quarter of this year at €1.04 ($A1.35) per watt.
That compares with solar module prices among leading manufacturers at $0.7-$0.8 per watt last year.
The pace of module price falls means that these will also rival wind turbines in lower-priced Chinese markets this year.
The short-term price trajectory for each suggests that solar modules will continue to fall, although much more slowly than previously, while wind turbines remain flat.
Because of their far bigger size, wind turbines are still cheaper to install per watt.
The installed cost of wind is around €1.25 ($1.62) per watt, according to a recent report by the trade body the Global Wind Energy Council.
Data for the installed cost for utility scale solar is hard to glean; Britain's Department of Energy and Climate Change reported a total installed cost for solar PV projects over 250 kilowatts as low as 1.2 pounds ($1.85) per watt as of March last year.
Full energy costs, per generated kilowatt hour, depend on performance and capacity factor as much as equipment and installation costs.
Again wind is cheaper but solar PV is catching up, with wide ranges depending on location.
Wind turbine manufacturers are targeting both incremental technology development in existing platforms as well as more fundamental advances, in particular towards bigger turbines for the offshore market.
Linear growth is expected in the market share for turbines larger than 3 MW, reaching half the global market by 2020, according to Madrid-based turbine maker Gamesa.
In the case of solar module makers, the technology focus has been steady improvements in the efficiency of conversion of sunlight into electricity.
It is plausible that the annual solar market (meaning new installed capacity) this year will leapfrog wind for the first time.
Wind turbine makers report a global market of around 48 gigawatts installed last year, but expect that to drop following a slump in orders in 2012.
Vestas new orders halved last year compared with 2011.
Vestas quoted a forecast by independent research company Emerging Energy Research for a steep decline in the global turbine market to 39 GW in 2013. Gamesa has forecast a shallower decline, to 42 GW.
Meanwhile, the European solar trade body, the European Photovoltaic Industry Association, estimated last year's solar market at 31.1 GW.
It forecasts the market this year at 28-47 GW, a wide range which especially reflects some uncertainty over the level of European solar subsidies.
Either way, the solar market will probably pass wind this decade.
That has implications for the speed of growth for each and the fortunes of equipment manufacturers, as well as for the cost of low carbon power.