Is a smart electricity tariff worth it?

@edent — Mon, 15 Apr 2019 11:30:26 +0000

(Long and data-filled post ahead!)

I've switched to energy provider Bulb (£50 off if you join using that link). They offer a "peak time" electricity charge which looks like this:

23:00 to 07:00 = £0.0815/kWh
07:00 to 16:00 = £0.1235/kWh
16:00 to 19:00 = £0.3263/kWh
19:00 to 23:00 = £0.1235/kWh

By contrast, the standard tariff is £0.1359 per kWh. That means my electricity is 2.4x more expensive for 4 hours per day, during peak time. But cheaper the rest of the time.

Let's look at a typical(ish) day's usage. This is what our home monitoring says we consumed on February 28th. If we ignore the solar power and battery storage, this is the result:

Normal tariff = £0.95/day
Smart tariff = £1.06/day

Ooof! Considerably more expensive. We come home in the evening and start cooking and watching TV right on the peak schedule.

Solar

We have solar panels. When the sun is shining, it reduces consumption from the grid. If the amount of power generated by the panels is greater than or equal to our home's energy usage, the meter stands still and we don't get charged.

This is what happens when we sum in the solar power:

Normal tariff = £0.68/day
Smart tariff = £0.91/day

Yikes! Dramatically more! During the daytime, we import virtually no electricity. Even when I'm working from home, the sun provides most of our needs - so we wouldn't benefit from the cheaper day rate.

Batteries

We also have a 2kWh solar battery. When the solar panels generate more power than the house can use, the battery is charged. When we're importing electricity, the battery slowly discharges. Let's sum in that as well.

Normal tariff = £0.60/day
Smart tariff = £0.76/day

Quite an impressive drop. The battery tends to discharge in the early evening, after the sun has set. So usually peak time for the Bulb tariff. With a bigger battery, we'd save even more in the evening.

Based on this average(ish) day in February, you might think that the smart tariff isn't right for our set up. But that's not the whole story. Let's take a look at a few more interesting days.

Car Charging

We have an electric car. I'm using a regular 13 amp charger (3kW) - rather than the fast (7kW) charger. Here you see the car being charged to full over the weekend - right at peak time:

Solar power was also pretty pathetic those two days, and there wasn't much in the home battery.

Normal tariff = £3.15 for two days
Smart tariff = £2.97 for two days

Aha! Even without shifting my car charging time to be after 19:00, the smart tariff could save us money.

Very roughly, if we'd deliberately not plugged the car in until after 19:00, the cost for two days would have been £2.26!

A whopping saving of 45p per day compared to the regular tariff.

Changing behaviours

And that's kind of the point, isn't it? If we shift our energy usage a bit, we get a significant saving. Can our lifestyle cope with waiting until 19:00 to start cooking? That sounds doable.

Can we set our battery to prioritise those peak times? Moixa - the manufacturer - have said they can set the battery to be aware of tariff rates.

Do we need the car to be fully charged? Nope - telling it only to charge in the cheap hours works for us.

If we're willing to change, our power bills drop.

Big Exhaustive Data Crunching

Over 2017-2018 I recorded all of our energy usage. I used it for graphs like this:

Here's what happens if we compare the Bulb standard tariff with a year of data.

There are a couple of caveats. Previously we charged our car with a 7kW charger. We've purchased new electronics and appliances which are more efficient. We also have a part-time lodger. So the energy profile isn't identical - but hopefully illustrative.

Normal tariff = £386.93
Smart tariff = £321.83

Assuming my calculations are correct - and I've got my daylight savings time the right way round - we could save a fairly hefty sixty quid per year!

With some lifestyle tweaks the savings could be even greater.

If you'd like to take advantage of this smart tariff, switch to Bulb (we each get £50 if you join using that link).