Tuesday, 8 October 2013

Economy 7 Tariff & Solar Panels. Take 2...

Once again I return to the "Economy 7" tariff and how it might help those of us with solar panels. 
I'd previously discussed the potential for savings in a piece written in June 2012. I raise it again based on a comment posted anonymously about the dilemma facing all of us in trying to reduce energy bills.


"I've just had a chap in to talk about the new Quantum storage heaters by Dimplex. We've been going around the houses with ideas to replace an old oil fired central heating system. We've looked at air heat source, bio mass but have hit a hurdle as we took out our oil system 2 yrs ago ( we've just been relying on electric immersion for hot water and a wood burner in the lounge with some occasional small electric heaters, hot water bottles and blankets for keeping us warm in bed! for 2 winters) but have just been told by the guy doing our energy certificate that this means we won't be eligible for the full Renewable Heat Incentive (RHI) rates which is what would have made the bio mass option affordable! So hence me looking into these Quantum heaters.

We are definitely going ahead with solar voltaic panels and possibly solar thermal too to cover the hot water. I've been trying to work out whether we should change to economy 7 to use the Quantum heaters which look like a cost effective option in terms of capital cost but need to work out running costs. 

Ideally they look like they'd be a good option with solar panels heating up in daylight using up the electricity we generate but I don't think they do this! I think if we do go onto economy 7 they'll heat these energy efficient storage heaters on the cheap rate at night and the electricity we generate in the daytime will cover the cost of the electricity we can use in the daytime like household appliances and computers etc that we use running our office from home. 
We're not on economy 7 at the moment but we are  with npower. Just done a price comparison on what we pay at the moment and we should change on price grounds!"

For some people Economy 7 is the perfect answer to their energy usage. Not all of us have access to a mains gas supply, or have a blank canvas to build into our homes the most cost/ energy efficient heating systems.

Obviously, I don't know all of the factors affecting the person who left the comment, but here are some of the  "pros and cons" involved.


1: Cheaper night time tariff. All electricity used between the hours of 23:00 - 07:00 (the hours vary depending where you live, are currently offered by Npower at 5.775p kWh.

My new energy contract offers 24 hr electricity at 15.52p kWh.

2: You're being a good citizen. By using under utilised night time electricity you're saving the planet.


1: More expensive day time tariff. The daytime economy 7 tariff is 18.501p kWh. You need to be certain that the majority of your energy usage will be during the night. Npower state on their website: "Currently an Economy 7 npower customer on our standard product with average consumption of 5,000 units per year would have to use a minimum of 35% of their electricity at off peak times to make it more cost effective than being a standard single rate customer. This figure will necessarily vary according to the customer’s actual consumption, payment method and the area in which they live, and may be lower."

The anonymous poster mentions computer usage from their "home office" which suggests that the potential for energy usage during the day may be significant.

2: Any existing oil based boiler, radiators and pipework will become redundant.

3: We currently have 9 various sized radiators in our gas based central heating system. Based on prices quoted on a website offering Dimplex Quantum products we would need;

3-large radiators @ £805 each.       £2,415
4-medium radiators @ £681 each.   £2,724
2-small radiators @ £610 each.       £1,220
That's an initial outlay of £6,359 on radiators, that's before factoring in electrical wiring consumer units, decorating etc.

4: Using economy 7 it's vitally important that you optimise your energy usage during the night. This calls for organisational skills and probably timing devices fitted to electrical equipment. 

Would you want to be ironing clothes in the middle of the night?

SupplierPercentage of off peak electricity usage required to make the Economy 7 tariff more cost effective than a standard tariff
British Gas45%
Cooperative Energy35%
Ecotricity20 – 35% (depending on the region)
EDF Energy20% – 30% – (varies depending on region and consumption profile)
First UtilityDo not currently offer an Economy 7 tariff
Good Energy15% – 40% (varies depending on region, consumption profile and price rises)
Green Energy20% – Economy 7
LoCo219% – Planet tariff13% – Pocket + tariff20% – Pocket tariff
OVO30% (some variations depending on region and consumption profile)
Scottish Power15%
Spark EnergyDo not currently offer an Economy 7 tariff
Utility Warehouse40% (35% for low users)

5: Will the heat from storage radiators last until you go to bed?

Particularly in cold weather, you'll need a supplementary back-up system "just in case."
We're retired and are at home during the day. In winter we rely on a low wattage halogen heater to heat our lounge during the day until the gas heating kicks in. We can afford to leave this on for hours on end because its being fed from the PV panels on our roof, but daytime energy usage without solar would be very expensive using economy 7.

6: Would you have to pay your energy supplier for a new meter? Not all suppliers are prepared to fit an economy 7 meter at no cost.

I'm a HUGE fan of alternative energy usage. If I was looking for a sustainable and cost effective method of heating my house I'd certainly look very hard at the economics of laying underfloor heating cable in conjunction with a ground source, or more likely a air source heat pump. Whilst the initial costs are higher, the long term running costs are negligible and the heating runs 24 hours a day.

Alternatively, replacing an boiler with a more efficient oil fired condensing unit which uses the generated heat more efficiently could be the answer. If the pipework and radiators are still in place I'd put thermal heating panels and PV panels on the roof and upgrade my boiler to reduce fuel bills. 

What I wouldn't do is rely on the panels on my roof to provide any meaningful contribution to heating my water or warming all the rooms in the house. During the cold months of January and February 2013, I used 500 kWh of electricity and 3,500 kW of gas. My 2.66 kWp system during the same period generated 155kWh.

Admittedly my system isn't the largest, but I exchange monthly generated output figures with a number of others and the largest system in Jan/Feb generated approximately 200 kWh.

Solar may be very good, but in the dark and cold miserable months when we need the most heat it doesn't work in the UK.

For a small percentage of householders economy 7 IS the answer to heating and lighting their homes. Unfortunately, for the majority of us the jury is out. 

With so many of us trying desperately to reduce our energy bills I suspect that the take-up for a night time reduced rate tariff would be far higher than it is, IF it really was cost effective.

So, Anonymous. (you know who you are). I wish you luck in heating your home. I'd be very interested in further details about the solution you adopt, the chosen system cost and monthly energy usage.

Twitter: (@solaricarus)


  1. "What I wouldn't do is rely on the panels on my roof to provide any meaningful contribution to heating my water or warming all the rooms in the house. During the cold months of January and February 2013, I used 500 kWh of electricity and 3,500 kW of gas. My 2.66 kWp system during the same period generated 155kWh."

    We are a couple (like you) and one of us (me) is semi-retired so the comparisons are valid. I generated 162 kWh in Jan and Feb 2012; and 173 in Jan & Feb 2013 (3.92kW PV system, Manchester). The maths agrees with you that PV solar will only help in winter and early spring months to mitigate the electricity used for the fridge, the washer and the kettle. The heating cost does not come into it. Unless you are a large family and do a lot of ironing (or toasting) the iron and toaster will not use much.

    1. Hi Chris.
      Looking at old James Bond film "Die Another Day" which features an Icarus satellite beaming concentrated sunlight down onto earth. In that particular film it was fanatical "bad men", but I'd like to use something similar during the winter months to improve output on my roof.
      Shaken NOT stirred!

  2. We got 81.75kwh in January 2013 and 169.55kwh in Feb. We have a 3.99 system in West London! Great website by the way!

    1. Thank you for the compliment on the website, I try to make it interesting.
      You seem to confirm that you "soft southerners" have the best weather! Your 3.99 system is very similar to Chrisso's in Manchester in size, but you have a much better output for the first two months of the year. I'm assuming that Chrisso's figures are totals for both months?
      Chris, correct me if I'm wrong.

  3. Wondering about moving from SSE to Ecotricity. Do you or anyone else have experience of them?

    They say "When you join us you'll pay a few pounds less than the standard Big Six tariff in your region. Frack free: Now and always. No fracked gas in our mix and no investment in fracking from us. Green Electricity didn't exist in the world back in 1996. When we offered it for the first time, we became not just Britain’s but the world’s first Green Electricity company – and we kick-started the now global Green Electricity movement. Our mission was and remains to change the way electricity is made and used in Britain. We use our customers’ energy bills to fund the building of new sources of Green Energy. We like to refer to this as turning ‘Bills into Mills’ – energy bills into windmills. We’re a not-for-dividend company – all of our profits go into our mission. With no shareholders to answer to we’re free to dedicate ourselves to the task of building new sources of Green Energy. And that’s what we do, on average spending more each year per customer on new sources of Green Energy than any other energy company in Britain - bar none."

    They are a non-shareholder company that puts its profits back into developing green renewable energy sources. Sounds to be far better than any of the Big Six.

  4. Having totally remodelled my late fathers' farm cottage and converted an adjacent barn two years ago I can tell you that with solar PV and ground source heating installed the tenants in both properties have been using about 65% of their power during the economy 7 hours so it is definitely well worth it. I am about to fit a small upgrade to both systems in the form of Optimmersion electronic controllers which use as much solar as possible for the immersion heater.
    My ground source heating doesn't provide hot water on purpose as it is the most inefficient way of using heat exchangers due to the high temperatures required to protect against legionella. I do have solar hot water systems fitted vto both properties as well but most hot water comes from the immersion heaters which are presently on timers to work in the middle of the day and during economy 7 times.
    By the way, all the ground source heat exchangers I researched use wet under floor heating systems as they cannot produce electricity for a "cable" system.

    1. I'm delighted that you're making "Economy 7 tariff" work. The important point to bear in mid relates to your 65% electricity usage during the nightime cheap rate. The ability to model the property to utilise the cheaper tariff isn't available to all of us, but I realise that it can work for some.
      Did you include the necessary building work costs into your payback period for the 65% usage? I'd be very interested as a cash rich/long term poor consumer.

  5. The building work had to be done as the cottage was literally falling apart with plaster off the walls and ceilings and a tree growing from the chimney stack.
    I am interested in eco building so I put everything I could think of into both the cottage and the barn conversion including rain collection. I also managed to convert my own house to some of the systems, I installed solar PV and went from oil to Ground source heating but was only able to use under floor heating on the ground floor so the bedrooms are still on standard sized radiators which isn't ideal but it seems to work as long as you don't want temperatures in excess of 20C in your bedroom.
    The savings to be made by buying 3 set ups at a time are huge, I negotiated 3 heat pumps for a little over the cost of 2 and I got a very favourable quote for installing all 3 solar PV systems at the same time whilst the FIT payments were at their maximum. I even got a good rate on the borehole drilling, I didn't want to put in trenches despite it being cheaper as not only is it about 1% less efficient but it could cause future problems having pipes buried everywhere.
    I, like you was cash rich having come out of farming and was looking to get a long term rental income whilst improving my surroundings and making something that I will be proud to leave to my three sons.