The cleantech sector has been on a rollercoaster ride since experts started bigging it up after the dotcom boom. At that time, analysts in the US said startups across the industry would soon rival modern digital giants such as Google and Apple for size and stature.

Silicon Valley was becoming a centre for cleantech exploration in the same way Saudi Arabia led the oil export business. VCs from all over the world started ploughing in money, causing annual deals to multiply in value from a few hundred million dollars to $4.1 billion in 2008.

But the credit crunch put a stop to the buzz. Investments in cleantech topped out the same year and subsequently fell to around 30–40% of what had been going in before. Many of the cleantech-specific investment companies, set up hastily to take advantage of all the new innovations hitting the market, were quietly wound down.

US government support in the sectors, valued in the tens of billions of dollars, couldn’t prop it up because of competition from natural gas and troublingly unreliable silicon prices, as well as the sudden drying up of credit.

But despite the dramatic fall in oil prices last year global cleantech investment is back on its way up – and then some. Technological advances have placed downward pressure on the cost of producing green energy and greater political will to support green energy – evidenced in December’s Paris climate change talks – has provided additional momentum.

As well as better sources of clean energy, the world is also quickly envisioning new inventions that either harvest the energy more efficiently or use it more sparingly.

A stark example is the cost of silicon PV cells used in solar energy, which in 1977 cost $76.67 per watt of energy produced and in 2014 cost just 36 cents for the same amount, according to Bloomberg New Energy Finance.

In January this year the same organisation reported that cleantech had defied the oil price slump, delivering record global investment of $329 billion. Money is pouring into places like China, Africa and, once again, the US.

It said the record was set despite difficult prevailing economic factors. Apart from the low oil price, three other forces played a part: the strength of the US dollar, weakness of the European economy and further declines in the cost of solar photovoltaics – meaning more can be installed for less investment.

In more good news, 2015 also saw the biggest ever commissioning programme of renewables with 64GW of wind and 57GW of solar PV contracted, a 30% increase on the previous year.

Responding to the figures, Michael Liebreich, Chairman of the advisory board at Bloomberg New Energy Finance, said: ‘These figures are a stunning riposte to all those who expected clean energy investment to stall on falling oil and gas prices.

‘They highlight the improving cost-competitiveness of solar and wind power, driven in part by the move by many countries to reverse-auction new capacity rather than providing advantageous tariffs, a shift that has put producers under continuing price pressure.

‘Wind and solar power are now being adopted in many developing countries as a natural and substantial part of the generation mix: they can be produced more cheaply than often high wholesale power prices; they reduce a country’s exposure to expected future fossil fuel prices; and above all they can be built very quickly to meet unfulfilled demand for electricity.’

He added: ‘It is very hard to see these trends going backwards, in the light of December’s Paris Climate Agreement.’

In his TED talk in February, Al Gore updated his audience on progress since his film An Inconvenient Truth was released a decade ago. After charting the dramatic decline in cost of green energy and the corresponding uptake of green tech, he illustrated the investment opportunity now on the table.

He said: ‘This is the biggest new business opportunity in the history of the world, and two-thirds of it is in the private sector. We are seeing an explosion of new investment.

‘Starting in 2010, investments globally in renewable electricity generation surpassed fossils. The gap has been growing ever since. The projections for the future are even more dramatic, even though fossil energy is now still subsidised at a rate 40 times larger than renewables.’

Meanwhile, with big-name entrepreneurs like Elon Musk and Bill Gates associated with the drive to tackle climate change through innovation along with a host of smaller – yet no less relevant – players in the market, cleantech is once again a darling of the investment industry.

This is relevant even if you’re not a cleantech investor specifically. Companies with green credentials, those that are carbon neutral or put a focus on the environment as part of their core operations, will attract customers faster than those that don’t.

Green is back with a bang. It has endured its very own ‘dotcom boom and bust’ and now low-cost, viable technologies are making inroads into markets globally. Time to start your research?