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January 2012 Archives

Energy systems will increasingly have to cope with variable supply inputs, as more renewables come on the grid. The grid system already has to deal with variable demand patterns, and it is usually argued that the strategies used to do that can be extended to also deal with variable supply. So, for example, in addition to short term frequency adjustments, variable wind can be backed up using power from the flexible fast start up gas turbines, or plants kept on spinning reserves, that normally deal with demand peaks or sudden plant shut downs. But there are limits (maybe above a 20% input) to how much variable supply can be accommodated in this and similar ways, and it is often suggested that more energy storage will be needed.

There are some new short to medium term storage options emerging, which can buffer variable outputs from wind etc, for example various types of flow battery, liquid air storage and even conversion to hydrogen gas via electrolysis, but the problems with storage is that it's inefficient and expensive. Much more so than just adding more cheap backup capacity. So some say the best type of storage is natural gas, stored ready for use when power is needed from back up plants. Using that of course incurs an emission penalty. The next best option, and one that is 100% carbon free, is pumped hydro storage, but there is not much of that available in the UK.

Several other counties in the EU, do however have very large hydro capacities (there is 30GW in Norway alone) and some of these reservoirs are now being converted to pumped storage; e.g. Germany's Thuringia State has identified 13 potential sites, including 3 existing dams, for constructing pumped- storage plants that would total 5,130 MW.

However, even without pumped storage, hydro reservoirs can be used to help balance variable renewables by simply delaying their output when there is plenty of power - a head of water in kept back until extra power is needed. But that does not help with what is probably going to be a bigger issue than occasional low power availability from wind - the regular excess power that wind, and also solar, wave and tidal power, will produce when demand is low.

A possible solution to that is transmission to locations where there are shortages: even if it means long distance transmission. You would need that anyway to link to hydro around the EU. As well as being used to balance variable renewables around the EU and for liking to offshore wind in the North Sea and hydro across the continent, High Voltage Direct Current (HVDC) links could also be used for importing solar derived power from the desert areas of North Africa and the Middle East. HVDC supergrid grids can do that with low losses (2-3% /1000km) compared with conventional HVAC grid (up to 10%/1000km).

HVDC has its disadvantages- you have to have expensive transformers/invertors to upload AC from generators and to download DC to AC end-users (assuming that generation and use can't actually be done with DC), and so it's best for long distance interconnections. AC is best locally and perhaps also regionally. Interestingly, while backing HVDC for longer distance links, the SRU, Germany's Advisory Council on the Environment, has suggested that, to avoid the problem with local uplinks, there could be a lower frequency 16.7 Hz overlay AC grid in Europe, at 500 kV. They say that would 'reduce the ratio between line length resistance and frequency, which would represent a threefold reduction relative today's 50 Hz frequency'.

All the foregoing is on the supply side. What about managing demand? There is much interest in 'smart demand' system , e.g. time-shifting electricity use by incentivising customers to run their energy consumption appliances off-peak, through time-of-use tariffs delivered through smart meters. More aggressively, some loads than are not sensitive to short interruptions can be turned off remotely for a while.

A study by Delta says that shaving system 'peaks' reduces the need for peaking plants which are often less efficient and/or use more polluting fuels, to run; it can also enable delay or prevention of the need for investment in new network capacity. And it can fill system 'valleys' - helping to increase and optimise the operation of lower carbon baseload plant. Based on studies by the Brattle Group they suggest that demand response across all sectors (through the use of time-of-use tariffs) with a 43% take up, can shift 5% of the system peak to off-peak times. Delta:

Smart grids can also offer other benefits, including diagnostic checks on the performance of heating & ventilation systems, heat pumps, refrigerators, etc. with savings of up to 20% being claimed in some cases. In addition, providing on line 'smart meter' information to consumers about their energy use, could help them cut out waste, change their lifestyles and/ or lead them to invest in more efficient systems.

So there are a range options on both the supply and demand side. They are not the only ones. For example, the emphasis above has been on electricity production and management, but there are also heat production and storage options. Heat is much easier to store than electricity and heat stores could be used as a way to balance variable renewables.

Whichever route is taken some of these options will take longer to deploy than others, and all will be relativelycostly. But then so will continuing to relay on fossil fuels- in economic and environmental terms. We have to shift away from them.

The key issue then is - will the new supply and demand management options be enough to allow variable renewables to expand to the 50% and even 100% that some say is possible at some point?

Optimists, including NGOs like Greenpeace and WWF, but also many energy analysts, say yes. For example see National Grids recent scenarios, which include a version with up to 67 GW of installed offshore wind generation capacity by 2030. and on a wider scale, the new roadmap to 2030 from the European Climate Foundation:

Pessimists, including some from traditional engineering and/or conservative political backgrounds, say no, renewables can't be used on a wide scale, but offer few alternatives except maybe nuclear and /or Shale Gas with Carbon Capture and Storage. For a recent example see the report published by the Adam Smith Institute:

It will be interesting to see which view prevails.

Both the optimist and pessimists seem to be listened to by government and both are also being backed by corporate money to some extent, whether its EDF and EON being willing to invest in nuclear, or Siemens, Vestas, GE and Mitsubishi investing in off shore wind turbine manufacturing plants in the UK . Some think you can and should do both, and also CCS, but given limited resources, it may be hard to do that well, and there are operational conflicts between basically inflexible nuclear and variable renewables. We may need to make choices.

In my next Blog I'll look in a bit more detail at some off the arguments on grid balancing in relation to wind.

Give up in the UK?

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'Only a system with its base-load provided by nuclear power, supplemented by gas for peak demand, and retaining the existing wind investment, can possibly supply the UK long-term with the huge amounts of secure and reliable, predominantly electrical energy, it needs. To actually achieve a changeover to a largely non-fossil fuel economy without wreaking catastrophe on our industries, the targets set by the Climate Change Act 2008 will have to be pushed back no matter whatever combination of electricity generating technologies is built'. So says Prof. Stephen Bush from Manchester University, writing, with David MacDonald, in The Chemical Engineer, ICE's magazine, last Oct.

This conclusion is reached in part by wheeling in the standard arguments about the low energy intensity and high variability of renewables and consequent large land areas needed. Is that so? It's certainly a view widely promoted these days in the media. See my earlier ( New Year) Blog.

As I pointed out there, it's been argued that PV can mostly be on roof-tops, so there is no extra land-use. With offshore wind, the land-use issue disappears, but variability is certainly an issue. The ICE article says 'to store a week's supply of electricity from the current 3,226 MW grid-connected wind capacity working at the annual average 25% load factor would require 4.5m m3 of hydrogen stored at 10 bar, or a lithium-ion battery stack 100 m2 by 34 m high. Extrapolated ten times to the 32 GW of wind capacity proposed in National Grid's Gone Green scheme, it can be seen that this buffer storage concept to use wind power on this scale is another blind alley'

Whoever said we needed to be able to store a full weeks wind output? Some storage would be helpful, especially pumped hydro, but when there are local UK wind shortfalls, in addition to all the usual backup available from the rest of the grid system, what about importing power via a super-grid, shifting demand peaks by interactive load management, and using biomass-fired backup? It's certainly going to be challenging to meet the targets, but that's what targets are for- to set the pace.

However some say it will cost a lot. In Fraunhofer Institutes Working Paper S7/2007 on Sustainability and Innovation, Frank Sensfuß, Mario Ragwitz and Massimo Genoese look at the so-called 'Merit-order' effect, offering a detailed analysis of the effect of renewable electricity generation on spot market prices in Germany. It's argued that when there is a lot of wind energy on the system, less generation is required from other sources. This cuts wholesale electricity prices, which reduces (non-wind) generator profits, but benefits consumers. It's claimed that the overall savings is greater than the subsidy paid for wind. So the net cost of supporting wind can be negative. See also Awerbuch, S. and M. Berger, 2003 'Applying Portfolio Theory to EU Electricity Planning and Policy Making', OECD/IEA, which comes to similar conclusions.

That is not to say the initial capital cost will not be significant. The new report 'Positive Energy' from WWF, claims that renewable sources of energy could meet up to 90% of the UK's electricity demand by 2030, but it notes that this may not be achievable in that time frame. Based on a series of scenarios produced by consultants GL Garrad Hassan, it concludes that the amount of renewable capacity the UK can build is determined by economic constraints - not available resources. Garrard Hassan assume that it's economic to supply around 60% of demand from renewables. WWF say that going beyond 60% depends on whether there's a market in other countries for the excess electricity the UK would generate at times of high renewable production/low demand. Therefore, given uncertainty over future markets, in the core scenarios, they do not assume a European market for UK renewable power, and they only have a 3GW supergrid interconnection.

By contrast, in the 'stretch' scenarios, it is assumed that interconnection creates a European market for the UK's excess power, and that it becomes economic to build much more renewable capacity in the UK- with up to a 35GW supergrid interconnection. In addition to providing an export option, that provides a balancing option for when weather conditions across the country mean little power from renewable generation (like wind power). Otherwise that has to be done mostly using gas plant. However they say that, even then, decarbonisation targets could still be reached, with an ambitious roll out of CCS on a significant proportion of the UK's gas capacity, but with CCS plant run at 80% of their load factor (capacity) and non CCS plant run at considerably lower load factors. Clearly though they would prefer a high levels of interconnection.

WWF says that the government must give investors enough certainty to be willing to make large-scale investments necessary in the UK renewables supply chain. It's therefore called on the government to commit to a target of getting at least 60% of UK electricity from renewables by 2030. .

'Positive Energy: how renewable electricity can transform the UK by 2030'

Broadening the view to cover the whole EU, Power Perspectives 2030, phase 2 of the groundbreaking Roadmap 2050 report from the European Climate Foundation, looks at the key steps to power sector decarbonisation across the EU for the next two decades. It says that while the existing energy policy framework to 2020 represents an adequate first step towards the EU 2050 emission reduction goals, the decarbonisation process will need to accelerate significantly in the decade 2020-2030.

In what it labels an "on track" scenario, based on the EU managing fully to implement its plans up to 2020, and assuming there are projects in 2030 in line with targeted emissions cuts, it anticipates a power mix in 2030 made up of 50% renewable energy. The rest would include 34% fossil fuels, plus a further 8% abated by CCS, 17% by nuclear. After that could come a push to get to near 100% from renewables by 2050, as outlined in their original report, with nuclear phased out.

The ECF led the project with McKinsey, E3G, KEMA, and Imperial College:

The European Commission has come up with something similar in its new 2050 Roadmap, which aims to get to virtually carbon free electricity, and an overall cut in emissions of 80-95%, by 2050. So the UK will not be alone if it perseveres in seeking radical change.

This weekend I joined a town hall forum in Cuero, TX, (DeWitt County, Texas) on the edge of the very hot Eagle Ford formation in South Texas.  The Eagle Ford is currently a hot bed of activity for hydraulic fracturing for both natural gas and liquids production, depending upon where drilling occurs. As with many regions, local people there are concerned that hydraulic fracturing, and the associated activities surrounding that process (e.g. injection of 'produced' water and waste fluids, trucks on the road, extraction of drinking well water), might cause some deleterious impacts such as depleting or contaminating groundwater supplies.  This town hall was one way of getting information out to landowners and the public.

There is much anecdotal 'evidence' and stories of one water well or another getting contaminated soon after hydraulic fracturing commences in area.  Actually, sometimes water quality has gotten better!  A local water well driller and service provider noted some of the things he thought might be going on, and they made a lot of sense.  Before the actual hydraulic fracturing process commences, the oil and gas companies fill up a man-made pond at the drill site that will hold the 4-8 million gallons of water typically needed for the fracturing.  In the case of much of South Texas, and the Eagle Ford formation, the water comes from the local underground sources of drinking water.  As explained at the Cuero town hall, the rate at which groundwater is being pumped into the holding ponds might be causing much or all of the impacts on local water wells.

Under normal conditions, water flows in a preferred direction in an aquifer, and relatively slowly at that.  This slow flow rate and constant preferred direction settles out sediments and orients them against rock pore surfaces accordingly (like getting sediment build-up at a dam). If a water well begins extracting water at a high enough rate, it can cause pressure changes in the aquifer such that reversal of local water flow can occur.  When this reversed flow occurs, it can dislodge sediments and minerals that will then move with the water flowing in a new direction.  With these sediments now mixed with the aquifer water, they can sometimes be seen in individual water wells when before there were no sediments.  Thus, it would be easy to conclude that hydraulic fracturing IS the cause of water well contamination, at least temporarily.

The reality is that the life cycle impacts of hydraulic fracturing can be larger than the specific process of fracturing itself.  In some cases, which seems likely in DeWitt County, Texas (but more study and cataloging of data would be needed to know for sure), obtaining the fracturing water from local groundwater sources could be the major/only impact of any consequence. More than that, the rate of the well water pumping could be a major factor such that slower pump rates could prevent changes in aquifer flow and stirring of sediments.

While the folks at this town hall meeting are now much more informed, the same cannot be said for most local residents.  The next step for the stakeholders could be (provided funding can be obtained) the collection of data on well water quality, timing for any changes in quality and water level, and timing of hydraulic fracturing activities to understand the likely relationships between fracturing, well water withdrawal rates, and local well water quality.
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Energy in Industry

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In some industries, such as steel and aluminium production, energy is the main cost, so it is not surprising that, since it is increasingly expensive, efforts have been made to use it more efficiently. But in most industries, cost savings are possible, and have been made by careful attention to waste, new technology and improved process control. As well as saving money, using conventional fuels more efficiently can, by reducing the amount of energy needed, also reduce greenhouse gas emissions. The UK Carbon Trust's Industrial Energy Efficiency Accelerator is looking at fourteen industry sectors, and has identified energy, carbon and cost savings typically averaging 25-30%.

Energy supply companies are also gradually switching over to using renewables sources, so that the carbon content of the energy used by industry is falling. However some industries have adopted a more radical approach - actually generating green power themselves.

For example, Ford has installed 3 large 1.8MW wind turbines at its diesel engine plant in Dagenham, NE of London, supplied by green energy company Ecotricity. Ford say that 'Green power from Ecotricity is saving Ford money and there are huge environmental benefits too. Thousands of tonnes of power station emissions are saved by switching our electricity source for the Dagenham Diesel Centre to wind power' .

Ecotricity has also installed a series of 3 wind turbines at Avonmouth Docks near Bristol
and at a Sainsbury warehouse depot in East Kilbride in Scotland. Sainsbury seem very pleased with this involvement with wind power : 'With this project, Ecotricity has helped us to meet our environmental goals and our energy needs. We have this fantastic state-of-the-art wind turbine on our site, which not only looks great but is providing almost half the depot's electricity, with no carbon emissions and at a cheaper price'.

These are examples of what Ecotricity calls Merchant Wind Power. Ecotricity pays for everything from the feasibility stage, through planning and construction to lifelong operation and maintenance. It claims that it can supply power at less than the cost of conventional electricity, with a guarantee of lower electricity prices for up to 30 years.

The Bristol Port Company commented 'Ecotricity has taken on the complex task of delivering this ambitious project, and we are delighted with the results. The three wind turbines are now delivering The Bristol Port Company with substantial environmental and financial savings.'

How can companies like Ecotricity do this? Firstly, on site power avoids having to pay for power to be delivered on the national grid from energy supply companies like E.ON and EDF. That avoids losses on long distance transmission and associated overhead costs. Secondly, renewable energy sources like wind power are rapidly becoming competitive in good sites, but still get a subsidy via the UK Renewables Obligation. Ecotricity gets Renewable Obligation Certificates for each MWh it supplies from its projects and these have a market value.

Will it spread?

It is actually quite common for large industrial estates estates to generate their own power, and also often heat, themselves, on site e.g. in medium scale combined heat and power plants, burning fossil fuel, e.g. gas. This can be cheaper than using power from the public supply. Using renewable sources like wind is just an extension of this idea, but adds an environmental bonus, and also protection from likely increases in fossil fuel costs. The fuel is free- and local. Analysis carried out by the UK Carbon Trust indicates that there is a strong case for businesses to produce their own renewable energy, with a potential for returns in excess of 20%.

And it's not just wind. Where there is a large daytime energy demand e.g for office equipment, air-conditioning, refrigeration, PV solar can be very relevant. It is fast approaching price parity with conventional sources of power in some applications and locations.

PV arrays have been installed on company warehouse roof-tops, like the German discount store LIDL, with 1.2 MW on its Logistics centre, and the 2.42MW PV FedEx Ground Woodbridge distribution hub in New Jersey in the USA. Google is also moving into PV with 1.6MW so far installed. Coca-Cola's Plant in Los Angeles, California has a 329 kW array.

PV is also being used increasingly in the automobile manufacturing and service sector e.g. General Motors has an 11.8 MW PV array at its plant at Zaragoza in Spain, Toyota's parts centre in Belgium has 1.8MW, Goodyear Dunlop has 2.4 MW at its logistics centre Philippsburg, Germany. There's also a 2.4MW Volkswagen roof at Wolfsburg, Germany.


Power production is not the only option. Heat from renewable sources is being supplied in some cases, for space and water heating e.g. solar preheating of the water needed for some industrial processes, or biomass heating for industrial processes.

The UNIDO assessment of the 2050 potential of renewables in industry says that by 2050 conventional solar heat collectors could be providing 5.6 EJ of process heat globally, while Concentrating Solar Power (CSP) using focused sunlight for high temperature heat, could add a further 2.4 EJ- making 8EJ in all, nearly 8% of total process heat needs.

However, biomass already provides over 8% industrial final energy, and UNIDO concluded that the use of biomass, primarily for process heat, has the potential to increase in the pulp and paper and the wood sectors to reach a global average share of 54% and 67% respectively of the total final energy use in each sector. It also suggests that, by 2050, biomass could constitute 22% of final energy use in the chemical and petrochemical sectors and that alternative fuels could constitute up to 30% of final energy use in the cement sector.

Globally, UNIDO suggests that up to 21% of all final energy use and feedstock in manufacturing industry in 2050 could be of renewable origin. This would constitute almost 50 exajoules a year (EJ/yr), out of a total industry sector final energy use of around 230 EJ/yr. This includes 37 EJ/yr from biomass feedstock and process energy and over 10 EJ/yr of process heat from solar thermal installations and heat pumps.

Obviously none of these renewable energy options would make sense unless attention had already be given to all the usual energy saving options- insulation, process efficiency upgrades and so on. And with solar /PV and wind you have to accept that they will not deliver power 24/7, so unless you have energy storage facilities, you still have to import power from the grid- although at times you may also be able to export excess power to pay for the imports. Biomass avoids this problem, but it has land-use and biodiversity limits.

What next?

While there are a range of renewable sources that can provide on site power directly for industrial activities, in many cases it will be more convenient and possibly more efficient to take power from large renewables projects linked up via the grid - e.g. large offshore wind farms, wave farms, tidal farms, or desert solar projects. And as the proportion of energy on the grid from these sources rises, the attraction of self-generation may decrease.

However industrial patterns may change, with new types of industry emerging, using renewables to make liquid and gaseous fuels, as well as heat and power- we are likely to see new industrial complexes using renewables to process a range of feedstocks.

This approach can be extended to a complete industrial ecosystem, e.g. recycling 'waste' outputs from industrial and agricultural processes as feedstock or energy inputs for other industries and users - cascading and integrating to increase overall materials and energy efficiency, and, where possible topping up with renewables to drive the system. As well as cutting cost ad emissions, innovation in industry can open up many new commercial opportunities in existing and new sectors.

Energy Efficiency in industry


The case for renewables in UK businesss:

UNIDO report on Renewables in Industry globally:

The new UK Carbon Plan had some sensible things to say about energy and industry- it backed biomass CHP:

Developing Asia is at a crossroads, transport-wise. And integrating co-benefits in transport decision-makes the difference. That in a nut-shell is the message of the book Low Carbon Transport in Asia - Strategies for optimizing co-benefits by Zusman, Srinivasan and Dhakal, just getting published at Earthscan.

The book builds on established approaches to quantify co-benefits of sustainable transport benefits. According to perspective, climate change mitigation is a co-benefit of air pollution combat or transport management or, the other way around: a better air quality is the co-benefit of ambitious climate protection. With close to half of the world population living in mostly densely populated Asia, the exposure of transport impact is particularly relevant on this continent - a co-benefit approach will deliver most in Asia. The book, an organized collection of articles around this topic summarizes conceptualization efforts and developes case studies on realizing transport co-benefits. Crucially, the book manages to transcend pure quantification efforts and analyzes barriers to co-benefit strategies and corresponding solution strategies. Zusman et al. identify two main avenues: A) clean and affordable technologies for motorized vehicles that can have huge impact on improving the health of billions of Asians while also substantially reducing non-CO2 greenhouse gas emissions; and B) transport demand management strategies that are even more comprehensive, also addressing congestion, safety, and accessibility issues, but are also more ambitious.

While there is some overlap across chapters, all a well edited and are a very good read. The true value of this book, however, is its success in bringing the transport co-benefit literature together, providing an excellent overview for scientists and policymakers. 

Disclosure: I contributed to this book project.

The battle over the UK PV solar Feed-In Tariffs (FiTs) continues, following on from the cuts of around 50% proposed by the government. That had led to major protest by PV companies and environmental groups, with a 'Cut don't Kill' campaign emerging, founded by a coalition of 20 major companies from across the solar industry. It kicked off with a Westminister demonstration calling for revision of the plans. While some reductions in the FiT were seen as fair, the scale and timing of the cuts (to be backdated to last December) were not, and would, it was claimed, cripple the industry. Alan Simpson a one time Labour MP, who has helped create the FiT system, noted that PV was 'the only sector that has delivered 25,000 new and sustainable jobs in the last 18 months'.

There were also disputes over some of the numbers used. Thus Energy Minister Greg Barker had said that the new 21p/kWh FiT for 4kW or under 'will attract the highest level of any subsidy of mainstream technologies'. But critics pointed out that micro wind turbines under 1.5 kW got 36.2p/kWh while those with under 15 kW received 28p/kWh. The trouble with this argument is that all the FiTs, these included, were under review- and they may get cut to below PV!

MP's debated the proposals just before Christmas, but, despite heavy lobbying, a motion opposing the PV FiT cuts was defeated by 292 to 220. Undeterred, Friends of the Earth, Solar Century and Home Sun then sought and obtained backing for a legal challenge from High Court Judge Mr Justice Mitting, who said ministers were 'proposing to make an unlawful decision' and as a result the court would be 'amenable to a judicial review'.

In January DECC submitted an appeal in which they noted that 'the High Court's decision was based on the view that the proposed approach to implementing new tariffs for solar PV is inconsistent with the FIT scheme's statutory purpose of encouraging small-scale low-carbon electricity generation' But DECC said 'The overriding aim of the proposed reduction in tariffs for solar PV (as set out in the recent consultation) is to ensure that over the long term as many people as possible are encouraged to install small scale low-carbon generation (including other technologies as well as solar PV) and benefit from the funding available for the FIT scheme. Without an urgent reduction in the current tariffs, which give a very generous return, the budget for the scheme would be severely depleted and there would be very little available for future solar PV generators, or for other technologies. Our view is that the urgent steps we have proposed to protect the scheme for the future are fully consistent with the scheme's statutory purpose'. It also said that 'the judicial review was premature as no decision has yet been taken, and a decision will only be taken after a full analysis of the responses to the consultation'.

Meanwhile, Energy secretary Chris Huhne acknowledged the difficulties experienced by solar firms as a result of the government's decision to cut incentives with just six week's notice, promising that the government 'will try harder next time' to minimise disruption caused by changes to the feed-in tariff scheme. But he said the ConDems had inhererited the system from the previous administration. He was reported to have complained that the fact the feed-in tariffs did not include an automatic degression mechanism for reducing the level of incentives meant the government had no choice but to impose the cuts at short notice, after "massively attractive" tariffs combined with a "dramatic crash" in panel prices had led to a surge in installations that threatened to push the scheme over budget. Critics pointed out that in fact the government could have adjusted it earlier without causing so much dislocation, and that, in fact, the PV tariff , as initially planned, did have a built-in annual price degression mechanism- set at 7% p.a for all categories. And at the time of the launch of the FiT scheme, DECC said it would increase the degression rate by a further 0.5% from 2015, although the start of the degression process was delayed by a year. The final pattern of planned reductions (for all the FiTs) is shown in a helpful table abstracted at

Be that as it may, as it turned out, a more substantial degression may have been needed, DECC had initially estimated that the FiT would put £11p.a. on consumer bills by 2020. The ConDems had upgraded this to £26 and used that to justify the cuts, no doubt also reacting to the spate of media stories about green policies being a major part of the £200 or so some said had been put on bills, and the talk of £2k or £3k bills by 2020.

However, that's all now been put in proper perspective with the governments advisory Committee on Climate Change reaffirming that it was gas prices that had led to most of the energy price rise- 64% of price rises were caused by increasing wholesale energy prices and only 6.5% by support for low-carbon energy. Households that have dual-fuel (gas and electricity) bills had seen their energy costs rise from £605 in 2004 to £1060 in 2010, an increase of 75%. But only £30 - or 6.5% - of this increase related to support for low-carbon energy, compared to £290 for increasing costs of gas and supplier costs. It said that green policies overall would only add around £110 to annual bills per household in 2020, and it could be just £25 if the energy savings programme was successful.

Independent green energy retailer Good Energy, have argued that the direct cuts in tariff levels for PV may not actually be the biggest issue in term of slowing PV growth - the proposal to limit FiTs to buildings reaching a high set level of energy efficiency (above 'C') could have even more impacts. Good Energy said that only about 10% of UK homes would be eligible and that the Green Deal upgrade loans won't actually change that- at best getting to an 'E' rating. So most homes will remain ineligible.

Overall it does look as if, one way or another, the PV programme has been boxed up. We now await the proposals for the FiTs for the other renewables. Further cuts are expected.