TOKYO (Reuters) - Panasonic Corp said it would acquire smaller rival Sanyo Electric Co, creating Japan's top electronics maker and foreshadowing further consolidation in an industry hit by slowing consumer demand.

The acquisition, which one analyst estimated could cost about $8.8 billion, would fortify Panasonic's competitiveness in rechargeable batteries and solar power equipment as demand grows for greener energy sources.

Panasonic would at the same time become the world's second-largest conglomerate with a major electronics division, behind General Electric and surpassing Hitachi Ltd as the biggest electronics maker in Japan.

But the deal carries risks and Panasonic has not said what it might pay for Sanyo, or what it plans to do with the latter's loss-making businesses such as home appliances and microchips.

"Strategically (the deal) makes sense, though it doesn't necessarily make sense for Panasonic to take on every single bit of Sanyo Electric," said Hannah Cunliffe, fund manager at Germany's Union Investment, which holds Panasonic shares. "There has to be some relatively aggressive restructuring."

The announcement was well flagged and sources told Reuters last weekend that Sanyo and Panasonic, which sits on $10 billion in cash, had agreed in principle to a deal.

Panasonic, the world's top plasma TV maker formerly known as Matsushita Electric, wants Sanyo because of its leading position in rechargeable batteries, which are widely used in mobile phones, PCs, music players and increasingly to power cars.

Sanyo supplies nickel metal hydride batteries to Ford Motor Co and Honda Motor Co Ltd and develops lithium-ion batteries for cars with Volkswagen AG, while Panasonic runs a car battery venture with Toyota Motor Corp.

The deal would also enable Panasonic to enter the solar market. Sanyo is the world's seventh-largest solar cell maker, trailing Germany's Q-Cells, Japan's Sharp Corp and Suntech Power Holdings Co Ltd of China.

"Adverse business conditions are making it difficult for us to achieve the kind of growth we have been striving for," Panasonic President Fumio Ohtsubo told a news conference. "We need a new growth engine within our group."

CHALLENGES AHEAD

Panasonic was founded 90 years ago by Konosuke Matsushita. Sanyo was formed soon after World War 2 when Toshio Iue, his brother-in-law and right-hand man in the early days of Matsushita, broke off on his own.

But their shared history does not guarantee they will make a good fit or that Panasonic won't overpay at a time when an economic slowdown is hitting demand for cars and the falling oil price clouds the prospects for solar power.

Toyota shocked investors on Thursday by warning that its profits would fall to a 13-year low.

"Given the poor performance of car makers and tumbling crude oil prices, it could be a while before the development of ecologically friendly cars and growing use of solar panels will drive its earnings," said Mizuho Asset Management fund manager Yoshihisa Okamoto.

To win Sanyo, Panasonic will have to buy out its top three shareholders, Daiwa Securities SMBC, Sumitomo Mitsui Banking Co and Goldman Sachs, which bailed out the company in 2006.

The three banks hold nearly 430 million preferred shares, each of which can be exchanged for 10 common shares when a restriction is lifted in March. If converted they would hold a combined 70 percent stake.

Credit Suisse analyst Koya Tabata earlier this week said Panasonic could offer up to 140 yen per Sanyo share, valuing the company at 862 billion yen ($8.8 billion) assuming the preferred stock is converted, a 40 percent premium to its enterprise value. The price negotiations could hinge in large part on how much restructuring is factored in.

The deal, which sparked a rally in Panasonic and Sanyo shares earlier in the week, could trigger another round of consolidation in the overcrowded sector, analysts said.

"It's been said that Japan has too many electronics makers and if moves like this were to gain momentum, that would be positive for stock prices," said Soichiro Monji, chief strategist at Daiwa SB Investments.

Prior to the announcement, shares in Panasonic closed down 3.8 percent at 1,528 yen, while Sanyo fell 0.5 percent to 203 yen. The Nikkei average was down 3.6 percent.

(Additional reporting by Sachi Izumi, Elaine Lies and Aiko Hayashi; Editing by Chris Gallagher and David Holmes)