It's a good option for low carbon heating, especially people here who have insulated and still need some heat but don't want to burn stuff and can't justify a heatpump.

Sunamp(12kWh) or Warmstone(100kWh) make larger well insulated products, that conceivably could charge overnight and be a gas-boiler replacement during the day. I appreciate there are individual E-7 heaters, but they always seem to leak heat hence be difficult/annoying in practice - are there any enhanced products using eg. VIP panels to improve this?
The form factor of a traditional heater makes it awkward to improve on the thermal time constant though.

Even cheap rate elec usually costs more than gas, but it's certainly greener now.

Looks to me Ed that you're running a very fine magnifying glass very closely over one element. Would it help to maybe stand back and look at the bigger picture? Two very simple points:

1. The new element in the picture is better forecasting and making more people aware of forecasting - if it's not windy tonight but will be tomorrow night, then if you can, it'll be better for all of us if you use electricity generated by wind power when it's windy.

2. The more people think about climate change the better. No ifs or buts on this and if adapting electricity use to coincide with forecast low carbon generation is a way in to making better decisions elsewhere then that is only good for al of us.

On the other hand, I did wonder what the blockage is on here re talking about carbon intensity - thanks for making that clear.

These guys say the current elec carbon intensity is 170g/kWh:
https://electricityinfo.org/real-time-british-electricity-supply/
But I also see we are using 33% CCGT gas, so presumably the "margin rate" is then at the gas rate (much higher)?

I can see in the 5 days the gridwatch graph above covers that CCGT is always delivering something; presumably the marginal CO2/kwh rate is the same all the time as gas is the only dispatchable source in the mix - is there really no CO2 reason to displace electricity to over night then, is it purely a financial exercise due to the energy bidding procedure? I agree that the grid is imperfect - we could easily have turbines curtailed while CCGT is being used due to line overload. This suggests the marginal intensity is impenetrably difficult for an individual to calculate.

I'm trying to wrap my head around the marginal rate as a useful concept, but it also seems to suggest I may as well keep burning gas directly rather than have a heatpump, and I struggle to believe that.

Posted By: RobLI'm trying to wrap my head around the marginal rate as a useful concept, but it also seems to suggest I may as well keep burning gas directly rather than have a heatpump, and I struggle to believe that.

We need to distinguish short- and long-term decisions. In the short term, I don't think it matters much when you run your heat pump, though keeping out of the times when the grid was burning coal (daytimes this week) would be good.

Longer term, putting in a heat pump rather than a gas boiler pushes expansion of electricity generation plant in general which will likely mostly be low carbon (wind and nuclear, mostly, in the UK) so will likely reduce the average grid intensity. In effect, there are short- and long-term grid intensities which may be very different even starting from the same mix.

The marginal intensity applies only to the marginal load: the last infinitesimal bit of load (in the derivative dCarbon/dLoad).

If all the loads everywhere were all assigned the marginal intensity, then the total (integrated) intensity of all the loads, wouldn't match the total grid intensity of all the generators. The arithmetic just doesn't work.

So clearly some of my household's loads are the marginal intensity bit, but most cannot be. It's hard to decide which, but I'd say that if a particular load (such as central heating) is a large proportion of my total consumption and is repeated for many hours per year, then it's not a marginal load. But if I were to occasionally use a fan heater to top up my central heating, that could be marginal.

That's a bit subjective, so it might be better to stick with using average intensity: if we all shift some consumption to a time when the wind blows harder, then on average over the week the UK will burn gas instead of coal, and more wind farms can be built.

(Edit to add: the marginal generator might be (pumped) hydro in Scotland, Wales or Norway. The intensity of pumped hydro is greater than that of the electricity it was pumped with)

I don't like the regional boundaries in that NG analysis, they imply that using an extra kWh in NScotland is less damaging than using it in London, but overall it works out the same. Likewise "green" tariffs and "self consumed PV"

Mmm, presently NG think the intensity in N Scotland is 4g/kWh and in London it is 136g/kWh, so 34x more impact. Don't think that's down to transmission losses, it's based on different mixes of generation assigned to each region. I can't run fan heaters guilt-free!

Posted By: Ed Davies

Posted By: djhIt's clear that the CCGT isn't the main factor.

No, it's not clear. If you use an extra kWh of electricity in Hypothetica it'll cause 1 kWh's worth of extra emissions at the CCGT intensity whatever time of day you do it.

Yes but one can argue that those extra emissions should be shared between all users, not all allocated to the new user. What's the difference between somebody who starts heating his water when the last bit of PV is available and another person who starts one millisecond later? If the emissions become 'too high' then it's not sensible or fair that the last person in should be dumped off. The reality is that the emissions of the electricity I use vary over time, they're not fixed at whatever they were when I turned on my water heater.

We need to distinguish short- and long-term decisions. In the short term, I don't think it matters much when you run your heat pump, though keeping out of the times when the grid was burning coal (daytimes this week) would be good.

You're agreeing with me and disagreeing with your own stated position here. Burning coal doesn't matter to the marginal rate. And you're contradicting what you said about Hypothetica.

Posted By: djhYes but one can argue that those extra emissions should be shared between all users, not all allocated to the new user.

But we're not playing some sort of blame game here.

The question is, does varying the time you use electricity make any difference to the total emissions from the grid, e.g., does is matter if John Walsh heats his hot water cylinder at 03:00 on Saturday morning or 03:00 on Sunday morning? Without JW the grid would run happily enough supplying people from a mix of sources with average intensities of, say, 150 and 250 gCO₂/kWh on each of those days. Perhaps he takes 3 kW for 2 hours on Saturday morning so the grid controllers have to turn up a CCGT power station (intensity 394 gCO₂/kWh) somewhere in the general area where he lives causing an extra 2 × 3 × 394 = 2.364 kg of CO₂ to be emitted. Or maybe he instead takes the same amount on Sunday causing exactly the same amount of extra emissions despite the average grid intensity being quite a bit higher.

Posted By: djhBurning coal doesn't matter to the marginal rate.

Obviously I'm assuming they've started burning coal because the CCGT is maxed out so coal is now the resource being dispatched to follow the load. Presumably that's rather simplistic, particularly on short time scales (seconds to minutes) but over a period of hours I'd guess it's reasonable. The point is that the intensity for coal during the day this week would likely have been what was setting the marginal intensity.

Posted By: Ed DaviesThe question is, does varying the time you use electricity make any difference to thetotalemissions from the grid

Then answer as to whether A whose computer decides to start water heating at time T and whose water heating starts at time t+3dt (because the computer etc is slow) is guilty or is it B whose computer decides at time T+dt but which actually switches on at time t+2dt (because its a faster computer? I'll argue that whatever answer you give is wrong, because such questions aren't sensibly framed.

What happens if I start water heating with CCGT marginal and then somebody else stops and we go to full renewable power? Who gets the credit?

I think it does matter what time you use power in Hypothetica.

Posted By: RobLI think the marginal term is related to saying "the plane is going anyway"... therefore my marginal impact of this particular flight is low. There's a bit of extra fuel required due to my extra mass, but that will be much smaller than dividing up the fuel used by the number of passengers. We here hopefully wouldn't apply this incremental logic to flying, even though strictly speaking you could? I'm sure we all know many people do though, or just don't care enough, but surely that is misguided - it assumes perfect knowledge - but at some point a new plane/wind turbine is operated/built due to these marginal actions.

Nice analogy Rob.

I'm very skeptical of marginal intensity as the primary metric as we live in a transient infrastructure world. If demand follows renewables it gives the confidence to build the right infrastructure for the future rather than for now.

i.e.
An argument based on marginal emissions is:
1. We are always using some CCGTs so why bother sifting anything as the marginal difference is tiny.
2. Demand doesn't follow renewables so we need to build more CCGTs rather than renewables.

Alternative argument based on average emissions is:
1. It's windy and average carbon intensity is low so lets use electricity to displace gas heating.
2. Even when it's windy we still need to run CCGTs so we should build more wind turbines.

Posted By: John WalshAlong with the helpful thoughts from Rob and jms452 I hope that puts to bed the 'marginal' distraction and allows us all to instead think about and focus on doing things better ...

Indeed, and along those lines ...

I use E7 power to heat my water in the winter, controlled by a cronjob, so I'd appreciate seeing the Python script you use to optimise the timing if possible?

Posted By: John Walsh
I'm not sure of the exact technical detail here but assume it isn't the case that all electricity generated by all the different sources is simply dumped into one across-the-nation massive wire which we then all tap into.

I'm assuming (and happy to hear other explanations) this means that the grid is split into regions, it isn't one massive wire around the nation. Each region has it's own generating characteristics and hence it really matters that we're all more aware of carbon intensity where we live and take action accordingly.

Electricity from the large generators is all transmitted around the country via a >200kv "supergrid" which is why its the national grid. Theres a 600kv DC link from scotland landing in northwales a mile from me bringing up to 2.2GW primarily from Scottish windfarms to my doorstep and beyond, so the country is definitely all sharing the national generation mix we have from the principle generators.

Theres lots of smaller generators that are connected into the lower voltage more local distribution networks but I think the bulk of our generation and hence emmisions is from the bigger generators and likely sourced from outside any single DNOs patch

Posted By: djhI'd appreciate seeing the Python script you use to optimise the timing if possible?

The below merely tests fetching data from the Grid's API. Integrating into my time-and-temperature based script then involves setting a new 'time period' for the day - i.e. the code is scattered around so might not easily make sense. Instead, the below is a rough and ready example (e.g. no error checking) which can be run from a command line. Not sure how this will display here and I don't claim to be a python purist, as you'll no doubt see ...

EDIT: obvs it's lost the indenting - does it still make sense?

#!/usr/bin/python

#### best worst/carbon intensity forecasts for a postcode today and next 2 days in the E7 period
#### and for time periods for each device - imh wants 90 min time-slot, mat wants 3 hrs
#### in the E7 period, there are 14 x 30 min ESO forecasts. Find 60, 90, 120 etc. minute blocks of time
#### i.e. 30 min = 14 x 1, 60 min = 13 x 2, 90 min = 12 x 3, 120 min = 11 x4, 150 = 10 x 5, 180 = 9 x 6, 240 = 7 x 8
#### i.e. for 90 mins there are 12 (3 x 30 min) blocks in the E7 period
#### duration_elements = [[14,1,'30 minute'],[13,2,'1 hour'],[12,3,'90 minute'],[11,4,'2 hour'],[9,6,'3 hour'],[7,8,'4 hour']]

duration_elements = [[12,3,'90 minute'],[9,6,'3 hour']]

import requests
import json

headers = {'Accept': 'application/json'}

postcode = 'NG1' ## only first part of postcode

import datetime
today = datetime.date.today()
today2 = today + datetime.timedelta(days=1)
today3 = today + datetime.timedelta(days=2)
forecast_days = [today,today2,today3]

for f_days in forecast_days:
print(f_days.strftime("%A %d"))

time_from = str(f_days)
time_to = str(f_days)
ESO_data_duration_pcode = requests.get("https://api.carbonintensity.org.uk/regional/intensity/" + time_from + "T01:05Z/" + time_to + "T08:00Z/postcode/" + postcode +"", params={}, headers = headers)
ESO_data_duration_pcode_j = json.loads(ESO_data_duration_pcode.text)

n = 0
while n < len(duration_elements):
low_duration_start = 0
low_carbon = 10000
high_duration_start = 0
high_carbon = 0

print duration_elements[n][2],"duration"

for a in range(duration_elements[n][0]):
block_end = a+duration_elements[n][1]
co2_total = 0
block_start = ''
for b in range(a,block_end):
if (a == b):
block_start = ESO_data_duration_pcode_j['data']['data'][b]['from']
co2_total = co2_total + ESO_data_duration_pcode_j['data']['data'][b]['intensity']['forecast']
if (co2_total < low_carbon):
low_carbon = co2_total
low_duration_start = block_start
if (co2_total > high_carbon):
high_carbon = co2_total
high_duration_start = block_start

print "Low carbon av: ",(low_carbon / duration_elements[n][1]),"gCO2/KWh from ",low_duration_start[11:-1]
print "high carbon av:",(high_carbon / duration_elements[n][1]),"gCO2/KWh from ",high_duration_start[11:-1],"\n"
n += 1

exit()

Posted By: John WalshEDIT: obvs it's lost the indenting - does it still make sense?

Thanks very much for posting it. Perhaps it would be better to attach the file (Attachments / Browse... down below)? That way it will keep the formatting and we can be sure we have the loops in the right places.

Perfect, thanks