Lowest night time rates to charge a battery, if you do not have an EV ?

smj

What is the best electricity tariff for the lowest night time rates to charge a battery if you do not have an EV ?

Trying to estimate the best sized battery to give a sensible ROI.  Octopus Go or Intelligent would be great at 7.5p night rate but do not have an EV.  So trying to see what is next best.

Planning 4kW PV with annual use around 8000kWh (22kWh per day).  So annually can generate about roughly half of our electricity from PV, rest we have to import from grid. 

So if most of the imported energy was at night into a battery, can try to work out the cost saving, versus a day time rate.

TIA

EricMears

smj said:

What is the best electricity tariff for the lowest night time rates to charge a battery if you do not have an EV ?

Trying to estimate the best sized battery to give a sensible ROI.  Octopus Agile or Intelligent would be great at 7.5p night rate but do not have an EV.  So trying to see what is next best.

I don't think you need an EV to join Octopus Agile.  Not so sure about Intelligent but worth asking Octopus.

JSHarris

The problem I've run into with choosing an off-peak tariff relates to the time needed to charge both the car and the house battery.  The house battery charges at about 3kW and when run right down takes just over 6 hours to charge. 

The car is worse, I got back from a long trip recently and couldn't charge it back up beyond about 70% in the 7 hour off-peak window from our Economy 7 tariff.  If I had a shorter off-peak slot then that could well lead to a serious problem (I have an aged relative that lives a long way away so need the car to be ready to go at a moments notice).

Another concern is the amount of power we pull from the grid overnight in winter.  With the car charging, the house battery charging, the hot water charging and the heating on overnight we are already at the absolute maximum our electricity supply can provide.

We're off the gas grid, so are 100% electric.  We're also in a mobile "not spot" so can't have a smart meter.  My only option was to have an E7 meter and luckily that works well with the house battery and the solar system.  Last year we used 54kWh at the peak (day) rate and 4,103kWh at the off-peak (night) rate, mainly due to the battery running the house during the peak rate period, as well as the battery enabling us to use no grid power at all during the summer months.

I would very much like to see a cheaper off-peak rate, currently we are paying about 15.5p/kWh.  I don't really care what the peak rate is, as that has very little impact.  If our off-peak period was less than 7 hours then our bill would be a lot higher, I've no doubt.  It annoys me that by not being able to have a smart meter we get penalised by having to accept higher tariffs, though.

QrizB

JSHarris said:

The problem I've run into with choosing an off-peak tariff relates to the time needed to charge both the car and the house battery.  The house battery charges at about 3kW and when run right down takes just over 6 hours to charge. 

The car is worse, I got back from a long trip recently and couldn't charge it back up beyond about 70% in the 7 hour off-peak window from our Economy 7 tariff.

Another concern is the amount of power we pull from the grid overnight in winter.  With the car charging, the house battery charging, the hot water charging and the heating on overnight we are already at the absolute maximum our electricity supply can provide.

We're off the gas grid, so are 100% electric.

It sounds as though you would benefit from a three-phase connection. You'd be able to charge your car at 20+kW as well as everything else.

Have you enquired about this?

JSHarris

QrizB said:

JSHarris said:

The problem I've run into with choosing an off-peak tariff relates to the time needed to charge both the car and the house battery.  The house battery charges at about 3kW and when run right down takes just over 6 hours to charge. 

The car is worse, I got back from a long trip recently and couldn't charge it back up beyond about 70% in the 7 hour off-peak window from our Economy 7 tariff.

Another concern is the amount of power we pull from the grid overnight in winter.  With the car charging, the house battery charging, the hot water charging and the heating on overnight we are already at the absolute maximum our electricity supply can provide.

We're off the gas grid, so are 100% electric.

It sounds as though you would benefit from a three-phase connection. You'd be able to charge your car at 20+kW as well as everything else.

Have you enquired about this?

Sadly 3 phase isn't an option as we're on the end of a long single phase cable.  I thought it was available when we built the house but the DNO have told me that although the long cable is 95mm² ABC only one phase and the neutral is available.  Apparently the 100kW PMT that feeds this cable (about 1/2 mile away) is maxed out already. 

Cost to go 3 phase would include removal of the existing  PMT plus the costs associated with purchasing land to put a ground mounted substation where the PMT is, as well as the infrastructure costs associated with that, re-routing the 11kV overheads, etc.  I think we could easily be looking at a bill of well over £100k in total, so not really an option.

michaels

I wonder if the rest of us should be thinking about this now when perhaps there is more capacity available.  We went from 60A to 100A when we got the car charger and solar panels but if we switch from gas to a heat pump and want to use overnight rate electricity then perhaps we would also need more.  No idea of the cost and availability of 3 phase on a standard suburban street but if all the house tried to go for it then no doubt there would not be enough capacity so best to get in first?

Has anyone made the upgrade and have ideas on the cost?

1961Nick

JSHarris said:

The problem I've run into with choosing an off-peak tariff relates to the time needed to charge both the car and the house battery.  The house battery charges at about 3kW and when run right down takes just over 6 hours to charge. 

The car is worse, I got back from a long trip recently and couldn't charge it back up beyond about 70% in the 7 hour off-peak window from our Economy 7 tariff.  If I had a shorter off-peak slot then that could well lead to a serious problem (I have an aged relative that lives a long way away so need the car to be ready to go at a moments notice).

Another concern is the amount of power we pull from the grid overnight in winter.  With the car charging, the house battery charging, the hot water charging and the heating on overnight we are already at the absolute maximum our electricity supply can provide.

We're off the gas grid, so are 100% electric.  We're also in a mobile "not spot" so can't have a smart meter.  My only option was to have an E7 meter and luckily that works well with the house battery and the solar system.  Last year we used 54kWh at the peak (day) rate and 4,103kWh at the off-peak (night) rate, mainly due to the battery running the house during the peak rate period, as well as the battery enabling us to use no grid power at all during the summer months.

I would very much like to see a cheaper off-peak rate, currently we are paying about 15.5p/kWh.  I don't really care what the peak rate is, as that has very little impact.  If our off-peak period was less than 7 hours then our bill would be a lot higher, I've no doubt.  It annoys me that by not being able to have a smart meter we get penalised by having to accept higher tariffs, though.

On the rare occasion that my car needs more charge than the 6 hour Intelligent Octopus can deliver, the off peak period starts earlier to ensure the target charge is met. So far I've never paid peak rate to charge even if I've needed 70kWh.

69bertie

3 phase comes with additional costs. Standing charge etc. Very rare to find houses having 3 phase, even if it is available in the street outside. btw, 100amp = nigh on 24Kw of power! Most supply cables in the street in towns and cities tend to be 3 phase coming out the sub anyway.

But regarding best tariff without EV, I've stayed with Scottish Power at the moment, simply because their E7 rate is cheaper, in my area, than Octopus. I've thought about going over to Octopus tariffs - I looked at Agile, Flux - but hit a slight problem when I look at our usage. Flux can cost lots if I was to use energy at peak time. Unfortunately our peak period usage isn't something we can avoid. While I have batteries that usually do the biz come evening time, I've noticed that we can exceed their max output, such that we start importing off the grid. Not much admittedly but it does happen.

But even worse, back in May, I decided to reduce the time for recharging the batteries from 2 hours, then to 1 hour, then to half an hour just to see how they performed. We had a run of 3 days of pretty dismal weather, where our PV output (E/W elevation) was, tbh, pretty poor. We ran out of battery, down to the 10% cutoff by 7pm. During the day there wasn't enough PV output to a: export, b: barely enough to supply the house and c: none for the battery. Big wakeup call. I think I will need to add at least one more battery, as a minimum, for the winter months.

Come winter, I will be setting up the battery to be charged overnight for 2 hours minimum @3.5kw. It seemed to work fairly well in March when the system was installed. From April to September, yes, if it is sunny, like now, I could manage with half an hour charge (or no charge at all) and the PV will not only recharge the batteries to 100% but also export. But if I was to get a run of cloudy days, one hour charge is a minimum. Which is what I've currently settled on for now.

I think to find the best tariff one needs to really do the maths and look at your usage. It's not as simple as looking at who is cheaper and what hours you get for your money. And do look at the day rate too!

JSHarris

1961Nick said:

JSHarris said:

The problem I've run into with choosing an off-peak tariff relates to the time needed to charge both the car and the house battery.  The house battery charges at about 3kW and when run right down takes just over 6 hours to charge. 

The car is worse, I got back from a long trip recently and couldn't charge it back up beyond about 70% in the 7 hour off-peak window from our Economy 7 tariff.  If I had a shorter off-peak slot then that could well lead to a serious problem (I have an aged relative that lives a long way away so need the car to be ready to go at a moments notice).

Another concern is the amount of power we pull from the grid overnight in winter.  With the car charging, the house battery charging, the hot water charging and the heating on overnight we are already at the absolute maximum our electricity supply can provide.

We're off the gas grid, so are 100% electric.  We're also in a mobile "not spot" so can't have a smart meter.  My only option was to have an E7 meter and luckily that works well with the house battery and the solar system.  Last year we used 54kWh at the peak (day) rate and 4,103kWh at the off-peak (night) rate, mainly due to the battery running the house during the peak rate period, as well as the battery enabling us to use no grid power at all during the summer months.

I would very much like to see a cheaper off-peak rate, currently we are paying about 15.5p/kWh.  I don't really care what the peak rate is, as that has very little impact.  If our off-peak period was less than 7 hours then our bill would be a lot higher, I've no doubt.  It annoys me that by not being able to have a smart meter we get penalised by having to accept higher tariffs, though.

On the rare occasion that my car needs more charge than the 6 hour Intelligent Octopus can deliver, the off peak period starts earlier to ensure the target charge is met. So far I've never paid peak rate to charge even if I've needed 70kWh.

If, as happened recently, I arrive home with only 15% charge remaining (yes, I know, I was cutting it a bit close!) then a 6 hour charge is only going to get my car up to 65%. That's not enough to make an urgent trip to see said aged relative without stopping to charge.

I try to make sure that the car always has enough charge to get down there without stopping, which means being charged to at least 85% (preferably a bit more).  This is really just because the last thing I want to have to do is add any extra delay to what will almost certainly be a very short notice trip.

I accept it's an edge case, and perhaps unique to my circumstances.  However, one of the things I really like about having an EV is always being able to have a "nearly full tank" when it's sat at home.  Our nearest filling station is about 10 miles away, and I often used to have to make a 20 mile round trip just to top my old car up.  It's a relief not having to do that any more.

QrizB

JSHarris said:

1961Nick said:

On the rare occasion that my car needs more charge than the 6 hour Intelligent Octopus can deliver, the off peak period starts earlier to ensure the target charge is met. So far I've never paid peak rate to charge even if I've needed 70kWh.

If, as happened recently, I arrive home with only 15% charge remaining (yes, I know, I was cutting it a bit close!) then a 6 hour charge is only going to get my car up to 65%.

But 1961Nick specifically states that, under those conditions, Intelligent Octopus will give him more than 6 hours at the cheaper rate.

JSHarris

69bertie said:

 btw, 100amp = nigh on 24Kw of power! Most supply cables in the street in towns and cities tend to be 3 phase coming out the sub anyway.

Sadly having a 100A main fuse in the cutout doesn't mean you can draw anything like 100A from a single phase supply.  The fuse is only there to protect the incoming cable if there was a short (the incomer will usually be 35mm² concentric, rated at around 130A). SSEN (as they were then) gave me the option of either a 13.5kVA supply (80A cutout fuse) or a 15kVA one (100A cutout fuse) when I built this house.  15kVA is the maximum they offer to any domestic premises for this region.

This all makes sense looking at our local LV network.  We have a 100kVA PMT, fed from 11kV overheads, that supplies around 15 homes.  This is quite generous, in urban areas it's not unusual to find 20 or more homes run from a single 100kVA transformer.  In our case the mean load per home (to stay within the transformer nominal power rating) is about 6.7kVA. 

The fact that the LV network doesn't go up in smoke is because the DNO rely on not every home drawing a lot of power at the same time.  Works fine during the day, not so good when everyone switches to an off-peak tariff.  They can also over-run the LV network at night. 

Transformers are thermally limited, as are cables, so in cooler weather it's OK to let them carry more current.  Increasing thermal limits is a standard way to allow higher power to be handled.  NG do this all the time.  They recently upped the thermal limit on some of their HV cables from 70°C to 90° for example.  Gave them something like a 20% capacity boost without doing any work.