Negotiations for the new deal will start next year, and it should be signed by 2015 at the latest, but the commitments will not take effect until after 2020.

Below are key questions for low-carbon energy investors.

Q. Will the deal boost low-carbon investment?

A. Not in the short term.

While a new legally binding deal is being worked out by politicians, investments in renewable energy sources such as wind and solar power will still be affected by the wider economic climate, which has made it difficult to raise capital.

"It is better than nothing but will not open floodgates and allow vast amounts to be invested in next few years," said Richard Nourse, managing partner at renewable energy investment fund Novusmodus.

Over the next few years, significant growth across renewable energy sectors will depend on national governments to give clear and consistent market signals to investors so that private sector capital can flow at the speed and scale needed.

"EU and national policies will remain the primary driver for investment in clean tech, at least until the detail and strength of international political commitment behind the deal becomes clearer," said Richard Salomone, energy adviser at the UK manufacturers' organization EEF.

HSBC estimates that $10 trillion in capital expenditure will be required from 2010 to 2020 for low-carbon energy alone.

But a dire economic environment is forcing many clean energy firms to postpone investments or diversify their portfolios to survive, and record low carbon prices are not high enough to spur utilities' investment in renewables.

Solar panel makers have seen their profit margins nearly erased this year as prices for renewable energy systems plummeted by about 40 percent, forcing some into bankruptcy and others to seek mergers to survive.

Wind power is struggling to compete with cheaper natural gas and depends on government support.

"The modest achievements at Durban point to some policy upside to our forecast of a low-carbon energy market valued at $2.2 trillion in 2020. The size of this upside is now all to play for," said Nick Robins, climate analyst at HSBC.

Q. What about investment in the longer term?

A. In the longer-term, the emergence of an international deal could reinforce national policies and help spur investment, analysts said.

However, much will depend on the exact form of the international deal by 2015 and how deep countries' legally binding emissions cuts go.

"While we now have a road map and an ambitious timetable, the precise destination remains unclear. Even the length of the second commitment period under the Kyoto Protocol was parked," said analysts at PriceWaterhouse Coopers.

"There is still a 40 percent gap between the 2 degrees climate goal and emissions targets through to 2020. Reaching 2 degrees will require a revolution in how we produce and use energy."

Pension funds have often been touted as huge sources of capital, but they need much stronger and more consistent policies before they will invest large sums of money in clean technology firms or specific projects.

"A significant amount of private sector capital would be unlocked if mechanisms shifted decisively the risk-return balance in favor of low carbon investments," said Stephanie Pfeifer, executive director of the Institutional Investors Group on Climate Change, representing 77 climate investors with assets totaling 7.5 trillion euros.

Q. What is the impact of a second phase of Kyoto?

A. The decision to extend the Kyoto Protocol to a second phase from 2013 was initially seen as a positive sign by investors in Kyoto's Clean Development Mechanism (CDM), which gives developed nations and firms carbon offsets in return for investing in carbon-cutting projects in poor nations.

But uncertainty remains about whether Kyoto will be extended until 2017 or 2020 and over which U.N. carbon offsets generated by the scheme would still be eligible for trade.

"It is too early to prescribe a value of this outcome to any of our investments in (that sector)," said Max Slee, alternative energy analyst at UK-based investment manager Ecofin, which has $1.9 billion of assets under management.

CDM investors say the European Union will have to clarify which offsets it will accept in its emissions trading scheme for market confidence to increase.

Chinese wind developers could benefit from the extension.

"(They) had ascribed only a low possibility to carbon income for wind farms registered (in the CDM) after 2012, but the continuation of Kyoto takes this possibility much higher," said Alexander Ivanovitch, managing partner and portfolio manager at the Environmental Investment Partnership hedge fund.

"This is not without risk. For example, new CDM registration may restrict or impose a cap volume from China, which could affect the value of carbon income from China."