When the Scottish Government set itself the target of generating 100% of the country's electricity from renewables by 2020 many people scoffed.

That goal is only six years away. Is it reachable?

The commitment is only for electricity. On the surface the target is ambitious but achievable. In 2010 Scotland generated almost 50,000 GWh of electricity, of which 19% came from renewables – mostly large-scale hydro and wind power. A necessary increase of 80% in 10 years sounds a lot. Although the future potential for large-scale hydropower is limited, Scotland could do it.

Studies show the trend is going in the right direction and the signals from Holyrood are generally positive. Scotland has some of the highest wind and wave potential in the world and significant untapped potential for small-scale hydropower. All that is needed is investment and political will. Some power stations will still be needed for export and back-up.

Meeting the electricity target is easy while the real target, demand, is falling, in part because of the economic slowdown. What would happen if that target were to increase?

Between 2008 and 2009 Scotland's total energy consumption fell by 7.4%. It is likely that demand is falling more slowly. Reducing demand through energy efficiency and changes in behaviour is vital to meeting the target. There are other challenges. Scotland's per capita energy consumption has historically been higher than that of the rest of the UK due to demand from industry, commerce, and Scotland's poorer-quality housing stock – and herein lies the real problem.

To meet the emissions reduction targets in the Climate Change (Scotland) Act and insure the country against rising gas prices and fuel poverty, the Scottish Government will need to oversee a nationwide shift to electric and renewable heating for homes and industry; no small task. Households are responsible for around one-third of Scotland's total energy demand, while services use around 16%, and industry takes around 21%. But the difficulties in converting transport from fossil fuels mean these sectors will need to contribute more than their share to cut emissions.

Building and water heating make up around 60-70% of total household energy demand while 76% of Scottish homes use gas central heating. To meet the emissions targets most heating demand will need to be met by renewable energy.

Although Scotland also has ambitious and innovative plans for renewable heat, some experts are concerned that the new proposals for beyond 2020 do not go as far as recommended. What cannot be met by renewable heat will have to be met by renewable electricity. While Scotland is home to a growing number of community energy projects, its geography, climate and building stock all pose barriers to microgeneration. There also are serious concerns about the sustainability of large-scale biomass power.

It is possible to achieve 100% renewable electricity generation by 2020, but for how long can it be sustained? Suddenly it starts looking like a very different problem, one that in the longer term will require a lot more than new wind, wave and hydro.

The biggest problem beyond 2020 will not be so much about how Scotland, and most places in high latitudes, generates its electricity but how it generates and distributes heat. There is hope that community-led solar thermal and small-scale biomass could make significant contributions to meeting demand, particularly in rural areas. But meeting demand in Scotland's dense urban areas will need significant and costly new infrastructure. As the people of the capital can attest – thanks to the Edinburgh trams debacle – infrastructure projects have a nasty habit of over-running on time and budget and being cut.

That is the real problem and that is why experts and climate groups have criticised the Scottish Parliament's second report on proposals and policies, in which the key item for Scotland's 14-year climate change plan was to spend £2m on low-energy bulbs for streetlamps.

A 100% renewable electricity-powered Scotland by 2020 is possible. But will it still be possible in 2021 and for years into the future?

Keith Baker is research associate in sustainable urban environments at Glasgow Caledonian University.

This article was first published at theconversation.com