The government’s Warm Homes Plan aims to make homes warmer, cheaper to run and lower-carbon, while also tackling fuel poverty and cutting energy bills. But the US-Iran war has added concerns about energy supply. Quite apart from the climate implications, countries and individuals are seeking ways to become less dependent on imported oil and gas. And there are encouraging signs that some of the challenges of the transition to renewables are being overcome, even on windless winter nights.
Renewable 24/7
Once installed, renewable energy is cheap, because the cost of fuel – sunlight and wind – is zero. But, although it is very rare for us to have no sunlight or wind at the same time, people expect the power to stay on all the time. So ‘firming’ – the process of developing systems which can prevent any potential interruption in supply – is critical. We must be able to transform variable renewable output into a continuous, dependable supply 24/7.
The International Renewable Energy Association, which supports governments in the move to sustainable energy, has recently published a report on firming. They highlight locations where reliable constant electricity supply is already being provided from purely renewable sources, through a combination of solar, wind and battery technology. In the UAE, the Al Dhafra complex is already producing a firm 1GW supply, larger than most conventional power stations in the UK. Such systems are becoming common in the US. In India, Saudi Arabia and China, the firmed costs of such systems are now below the cost of fossil fuels.
The UK is a very windy island, which can partially compensate for relatively low levels of sunshine. But, while sunlight is predictable, there can be long, and unpredictable periods with no wind. There are also periods when we have more electricity that we can use, and windfarms have to be turned off because we can’t store the energy.
To guarantee constant supply, we need a reliable system to provide backup. This could be provided by retaining gas, oil or nuclear generators to provide the backup ‘baseload’. Alternatively we can import electricity from countries with different patterns of generation, and the UK already has eight interconnectors to mainland Europe, with six more under construction. In the short term, these are bound to be part of the mix. However, in the medium to long term, we need to develop effective ways of storing energy on a large scale.
Storing energy
There is a growing variety of systems for storing energy for significant periods. Batteries provide an obvious option, and battery prices have been falling – by 27% in 2025 for large scale systems to back up the grid. And home batteries are becoming more common, enabling people to store electricity from solar panels, or draw it down at cheap rates during off peak periods, to be used later. This reduces peak demand on the grid which is ageing and often operating at capacity.
And energy suppliers are now beginning to introduce systems where that locally stored electricity can be fed back into the grid when demand peaks. So, over time, perhaps our homes will become part of a huge nationwide dispersed battery.
Battery technologies are also evolving. The Li-ion batteries we are familiar with are now being used in large installations, but they have major disadvantages. They are only efficient for storing electricity for a few hours. They degrade over time and use imported rare minerals, some of which are mined in dangerous conditions.
But exploration of alternative battery technologies is progressing rapidly. These use more abundant and cheaper materials, often with lower environmental and human costs. For grid storage, iron-based and zinc-based systems, and flow batteries are all being cited as promising. Australia has just commissioned a sodium-ion battery installation capable of storing 2GW of electricity. And sodium is readily available.
Gravity offers a simpler, mechanical solution. The most established form is pumped hydroelectricity, which uses surplus off peak energy to pump water to a high reservoir, where it can later be released to flow down to drive hydroelectric turbines. Two such plants have been operating in Wales for more than 40 years, and together they can now generate 2.1GW.
But pumped hydro can only be installed in mountainous areas. Alternative gravity projects are exploring the use of heavy weights which are hauled up by electric motors using surplus off peak electricity, and then allowed to fall, turning the electric motor into a generator. These are being trialled in abandoned mineshafts in Australia and South Africa.
Thermal storage is another option in locations with abundant sunshine. Spain has four plants, together generating 100MW by using mirrors to focus sunlight to heat molten salt up to 500°C. This is then stored to be used later to generate steam to drive turbines.
Finally, off peak electricity can be used to create hydrogen by splitting water, and the hydrogen used later to create steam to drive turbines, as we discussed in a previous article.
Sharing farmland
A key objection to solar farms is that they take productive land out of agricultural use. Agrivoltaics solve this by raising the solar panels, sometimes by over 4 metres, so that workers and machines can access the land below. As the climate warms, this has the added advantage of providing shade for workers and livestock, and reducing evaporation from crops. In Europe, France has been pioneering this, supported by a developed legal and regulatory framework.
Over six years, French projects in vineyards have seen grape yields raised, sometimes by as much as 60%, coupled with 40% reductions in water use. The largest established French system, near Narbonne, now covers 11 hectares and there are plans for much larger schemes to generate up to 500MW across a range of crops.
Building
A key focus of government policy is to make new houses more energy efficient. The government’s latest amendment to Building Regulations specifies that any new-build housing approved after March 2027 must have ‘on-site renewable energy generation’. In most cases, this will mean solar panels. Over 40% of new-build houses already meet this – a 13% increase on the previous year – and domestic solar generation reached record levels in March.
Public buildings account for a very large area of open rooftop, and Great British Energy has committed over £500mn to subsidise solar installations on public buildings, including schools and hospitals, and a further £15mn for community projects.
Future?
As a strategy for reducing global warming, net zero in the UK is largely symbolic. We are simply too small to save the world. But we can set an example to encourage others. In the short term, there are real costs in the transition – installing new systems and upgrading the grid. But in the long term these policies do offer a means of making us independent of unpredictable global energy markets.
The impact on the cost-of-living is not trivial. And there are signs that many of the objections to the shift to renewables are being overcome.
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