SUZHOU, China ( TheStreet) -- Canadian Solar is rallying on Tuesday, up more than 4% a day ahead of its fourth quarter earnings -- but will the share spike last once Canadian Solar reports? Canadian Solar shares are still trading significantly lower than a mid-February share price over $24 -- on Tuesday at midday Canadian Solar shares were up by 86 cents to $19.96. The reason for the slide in Canadian Solar shares is earnings-related. Canadian Solar guided investors to a lower gross margin number than expected in the fourth quarter, due to problems at Canadian Solar's new ingot and wafering plant, which drove up costs while lowering yields. In effect, Canadian Solar pre-announced earnings when it revealed the plant problems, stating that gross margins would be in the mid-teens, as opposed to high teens, and shipments would come in slightly higher than the expected 128 megawatts (MW) in the fourth quarter, at 138 MW. Canadian Solar shares dropped by as much as $5 in the time since the damage control-based pre-announcement of earnings. Canadian Solar's earnings might be the least interesting of this week's solar batch, given that the pre-announcement has taken away the potential for surprise. Suntech Power's ( STP) earnings, expected on Thursday, are considered to be a more important read of the solar outlook, particularly if Suntech provides specific guidance on growth opportunities in China. Gross margin has been a key factor this earning season for solar companies. Both First Solar ( FSLR) and Trina Solar ( TSL) earnings were met with a less-than-enthusiastic response from the market , at least partially driven by gross margin levels. In that sense, it might be good that Canadian Solar preempted its gross margin shortfall in the fourth quarter as opposed to waiting for earnings day. Since Canadian Solar has already confessed to its expected gross margin underperformance in the fourth quarter, the earnings are a fait accompli. Still, investors will be looking to Canadian Solar's guidance for 2010, and any indication that the plant problems will continue to impact earnings in the first half of the year.