On-grid or off-grid? Which is greener?

With fossil fuels still providing most of the UK’s electricity mix, should we all be aiming to go off-grid? CAT Information Officer Mim Davies explores the issues.

A common enquiry we get at the CAT Information Service goes something like this: “I want to disconnect my house from the electricity grid. Where do I start?”

There is often a positive narrative around “going off-grid”. We hear that it’s the “greenest” thing to do, and that it should be the end goal of any committed environmentalist. In CAT’s beginnings, our site was off the electricity grid. But after decades of experimentation, research and thought, we don’t think that disconnecting from the electricity grid is the green way forward. We say this for many reasons.

The cost of batteries

Taking a house off the electricity grid and buying batteries to store energy wouldn’t address any environmental issue. In fact, it would actually increase the negative environmental impact of your household, as the production of batteries uses energy and involves hazardous materials.

Battery bank, Isle of Eigg

If excess renewable energy is fed into the grid rather than being kept in batteries, it reduces the need to generate so much electricity from fossil fuel power stations.

There is no financial benefit to disconnecting from the electricity grid. When you calculate the energy a battery can store over its lifetime, the cost per unit of electricity is much more expensive than buying electricity through the grid from large-scale generation. When you’re connected to the grid, you can sell your excess electricity and buy it back when you aren’t producing enough, effectively using the grid as a battery.

We strongly advise against domestic battery storage unless it’s unavoidable. We think it should only usually be considered for remote locations where a connection to the electricity grid would be prohibitively expensive.

Using the grid

The grid itself is not inherently a bad thing. The environmental problem with grid electricity is where it comes from, which at the moment is largely fossil fuel power stations.

CAT’s Zero Carbon Britain project (ZCB) shows that the UK can be powered by 100% renewable energy using technology that already exists today. In the ZCB model, our biggest resources are offshore and onshore wind, as well as tidal and wave power. Wind, tidal and wave power are usually generated away from where most people live and work, so we’ll need the grid to move the renewable electricity to where it will be used.

A way to buffer renewable electricity production would be needed if the UK switched over to 100% renewable energy, but this doesn’t have to take the form of batteries. Pumped storage, synthetic fuel production and heat storage are a few of the approaches ZCB suggests for buffering the grid. Batteries would play a role in a zero carbon future, but we feel they are best suited to electric cars, bikes and portable appliances, rather than for a large number of households to go off-grid.

Moving forward together

For most people, producing their own renewable electricity isn’t possible. While the Feed-in Tariff can pay off the cost of a renewable electricity system over a number of years, you still need to be able to pay for the installation up front. That can mean thousands of pounds. As well as this, most houses aren’t suitable for wind or hydro turbines, and not all houses are suitable for solar panels.

We need to work together as a society rather than split off into lots of individual off-grid households. There is far more justice in decarbonising the grid and giving everyone access to green electricity, than thousands of batteries with big environmental impacts being bought privately.

Rather than going off-grid, consider supporting a community energy scheme, switching to a green electricity supplier, looking at ways to reduce your energy demand and talking to people about what you’re doing. These are things that can help move all of us in the direction of a renewable energy powered future.

If you want to talk about any of these options, get in touch with the CAT Information Service at info@cat.org.uk or on 01654 705989.


Mim Davies is one of CAT’s Information Officers. She is a physics graduate with an MSc in Water and Environmental Management. She first came to CAT to volunteer in the engineering department during the cold winter of 2010.

  • Bill MacGregor

    Let me start my welcoming your blog – however, pumped storage is not currently economic so isn’t, as you suggest, a realistic alternative to battery storage – financial incentives such as FiT, ROCs and CfDs are not available for pumped storage schemes – some big pumped storage projects in Scotland have received planning consent in recent years but none has been built since the economics are poor – battery prices are expected to reduce dramatically in the next year or so but despite that, batteries are already being used by national grid to control system frequency etc – plans exist to link battery installations (including domestic ones and those in electric vehicles with V2G technology) via the web so that they can provide power to the grid at peak and other times, thereby reducing power prices and the need for those power stations that only generate at peak times – reducing the number of power stations required will as a consequence, reduce environmental impact and resource use and as such should be factored into your assessment as should the impact of smart meters, smart time-of-day tariffs, smart appliances and other disruptive ideas and technologies that are currently emerging.

    • Catriona at CAT

      I would recommend looking at the Zero Carbon Britain (ZCB) project reports – http://zerocarbonbritain.org – and in particular ‘Rethinking the Future’ as that looks at all sorts of issues to do with buffering the output of renewable energy sources.

      The report does indeed include smart appliances, smart car-charging, demand management and other measures as part of the energy model.

      However, an important thing to bear in mind is we don’t just need electricity – we also need other types of fuels, such as various liquid and gaseous fuels that we can use for industrial processes and for planes and other large vehicles.

      The Zero Carbon Britain model looks at buffering renewable electricity by using energy surpluses to make these kinds of fuels – such as synthetic methane and liquid fuels, plus hydrogen. These can then be used for all sorts of applications, so offer more flexibility than batteries, which just store electricity.

      Batteries will have their place, but we will need to consider more than just electricity if we want to make a zero carbon model for the whole economy.

  • Madison

    Very interesting, thanks for sharing this valuable advice and insight. It is easy to get caught up in trends and misconceptions when it comes to the best way to be environmentally friendly, it is helpful to know that off the grid isn’t necessarily greener. A very interesting topic to bring to class discussions. http://www.softegg.co.uk/

    • Catriona at CAT

      Thanks Madison – glad you found it useful.

  • Peter Biggins

    The benefit of a number of households using battery storage is that it can even out usage throughout the day, be it a car feeding power back or a home battery system storing solar generated power for use between 5 and 7 when there is peak demand. Effectively it evens out usage reducing the need for fossil fuels to boost the grid at peak times. As electric cars have increasing capacity and will increase in number, their use will mean excess night energy can be used to charge their battery and fed back when needed. There will be so many, in fact, that home storage systems may become unnecessary.