Solar may be popular but environmentalists must be hard-headed about how to reduce CO2 in the cheapest way

Summer solstice. At dawn. What better time could there be for resolving a duel, albeit one not fought with flintlocks? The time is of my choosing, as the other party, though he accepted the challenge, would not agree terms. It is appropriate in another sense too, as this is the day with the longest hours of sunlight and therefore – for I honour the sporting tradition – it offers my opponent the best shot.

Three years ago, in the course of our debate about the best means of generating electricity, I bet £100 against a claim made by Jeremy Leggett, chairman of the company SolarCentury. He had asserted that domestic solar power in Britain would achieve grid parity by 2013. This means that it would cost householders no more than conventional electricity.

I'm interested in this question because I want to see carbon emissions cut as quickly and effectively as possible. If public money is used to back the wrong technologies, that represents a wasted opportunity. It is easy to become enthusiastic about domestic solar power, because it is produced on a small scale, gives people a satisfying sense of self-reliance, and is unobtrusive, unlike most other forms of generation.

In fact it's arguably the only form of electricity production which has widespread public support. The fact that it has been exceedingly lucrative for homeowners who installed their panels when state subsidies (the feed-in tariff) were high has contributed to that enthusiasm.

But those of us who want carbon emissions to be greatly reduced should ask questions that are wider than only self-interest and aesthetics. We also have to ask whether a technology works. Solar power works well at low latitudes, especially in places where peak electricity demand coincides with peak sunlight, which is often the case where air conditioning is widely used. In terms of replacing conventional electricity, it works less well in places like the UK, which are far from the equator and have different patterns of use. Here, peak demand occurs between 5pm and 7pm on winter evenings.

I was sceptical of Jeremy's claim. So I bet that his prediction would not come to pass: grid parity would not be achieved by 2013. He accepted. I undertook to write an article in 2013 revealing the results, whether I won or lost. Here it is.

To discover who had won, I first contacted the energy regulator, Ofgem, but it turned down my request. So I tried the Department for Energy and Climate Change. I asked two questions:

• How should the outcome best be measured?

• Who will have to pay out £100?

Solar power is unlikely to make a large contribution to electricity supply in the UK. Photograph: Michaela Rehle/Reuters

This is what it told me:

"Grid parity can be defined as the point at which government support for a technology is no longer required."

That seems like a reasonable definition to me, and one I'm prepared to accept. I hope Jeremy feels the same way: in 2010 I wrote to him several times to try to reach an agreement about how the outcome would be determined, but did not receive a reply.

Here is Decc's answer to my second question:

"Grid parity for domestic scale solar power has not been reached. The feed-in tariff scheme currently provides generation tariff of 15.44p per kWh, plus an export tariff of 4.64p per kWh for domestic scale installations."

Here is the source (pdf) it gave me.

In other words, though the subsidy has come down sharply from 2010, which partly reflects a real decline in the price of solar power and partly reflects the extraordinary generosity of the initial tariff, we're a long way from grid parity.

This, I think, highlights the danger of believing what we want to believe. Climate change is too serious to mess about with. We should be hard-headed in addressing it, and should subject the technologies which attract us to as much scrutiny and rigour as the technologies which repel us.

It was this process which, after my initial enthusiasm, turned me away from solar power in the UK and led to my reluctant endorsement of large-scale wind and (later) nuclear power as the UK's most viable sources of low-carbon electricity.

I wish it were otherwise. But what counts for me is achieving the steepest and fastest possible cut in greenhouse gases. None of our options are great, but these are the best of a bad bunch. (We should of course simultaneously pursue sharp reductions in energy demand).

Though the costs will keep falling, solar power is unlikely to make a large contribution to electricity supply in the UK, unless a radically different technology becomes viable. This is because of the inherent constraints I mentioned earlier. It has some potential for mitigating carbon emissions in the summer, especially with the use of smart grids, but it seems to me that for a long time to come there are likely to be cheaper and simpler means of achieving the same aim. I would like to be proved wrong on this, but I don't think it will happen.

For all that, looking back across the past three years it seems to me that there is something of the circular firing squad about our duel.

Two months after we struck our bet, the government changed. I don't think either of us would have guessed just how bad it would be. In fact it wasn't until the Any Questions programme two weeks ago that we were able to see how far the madness has gone. Owen Paterson, the environment secretary, revealed that he rejects the science of climate change, and trotted out a series of discredited factoids and myths. This is what he said:

"The climate's always been changing, er, Peter [Hain] mentioned the Arctic and I think in the Holocene the Arctic melted completely and you can see there were beaches there - when Greenland was occupied, you know, people growing crops. We then had a little ice age, we had a middle age warming. The climate's been going up and down, but the real question which I think everyone's trying to address is, is this influenced by man-made activity in recent years and James [Delingpole] is actually correct. The climate has not changed - the temperature has not changed in the last 17 years …"

You can read a powerful deconstruction of these claims on the Skeptical Science website.

Alongside an environment secretary in denial about climate change, we have a chancellor who seems to be attempting to sabotage every green initiative. We see constant efforts by both the press and MPs to prevent the deployment of wind farms. There is a widespread belief in government that the best substitute for natural gas is, er, natural gas, ideally extracted by the most damaging means. We've witnessed the abandonment of the energy-saving schemes launched by the last government and their replacement with a useless green deal.

The European emissions trading scheme has collapsed, international negotiations have ground to a halt, CO2 concentrations in the atmosphere have already passed 400 parts per million and there are no serious global efforts to prevent their rise, let alone bring them down. Far from leaving most fossil fuels in the ground – without which no progress on climate change can be made – energy companies and nation states are making unprecedented efforts to extract them from ever more remote and hazardous places.

In other words, Jeremy and I have both lost. And so has everyone, except the fossil fuel companies.

So I fire my shot into the air. We differ profoundly on which technologies are best deployed to address climate change. But we confront a government which appears to want none of them, and in this respect we are united.

Monbiot.com