Problem with timestamps using now() and utcnow(), and adjusting sensors to Daylight Saving Time (DST)

Configuration
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1

Hello,

After hours of reading documentation, forums and tinkering with templates I cannot solve what seems a very basic problem so I need some help.

My energy company has a tariff where the price of electricity changes every 30mins. This information is available in the form of a REST API which looks like this:
Screenshot 2024-05-02 004702

I have the following sensor set up which worked like a charm - until Daylight Saving Time (DST) kicked in a little while ago.

- platform: rest
  name: electricity_cost
  resource_template: >-
    https://api.octopus.energy/v1/products/AGILE-23-12-06/electricity-tariffs/E-1R-AGILE-23-12-06-G/standard-unit-rates/?period_from=
    {% set ts_now = ((as_timestamp(now())/1800)|round(0,'floor')|int * 1800) %}
    {{ ts_now |timestamp_custom ('%Y-%m-%dT%H:%M:%SZ') }}&period_to=
    {{ (ts_now + 1800) |timestamp_custom ('%Y-%m-%dT%H:%M:%SZ') }}
  value_template: "{{ (value_json.results[0].value_inc_vat) | round(2) }}"
  unit_of_measurement: "p/kWh"

The problem is that the REST API provides all values in UTC time. When DST kicked in I simply added -3600 to the calculations and all is well however I was looking for a solution that would work across DST changes without having to modify it manually.

During my research I discovered that templating has several options for current time: now() which displays current time in local timezone as well as utcnow() which displays time in UTC timezones. Now I live in UK which is same as UTC half of the year and then it is at UTC+1 for the other half (right now during DST). For some reason, however, templating both now() and utcnow() gives me the exact same time - i.e. my local time.

Time zone in HA is set correctly to GMT +0 London. I’ve been banging my head against the wall. I’ll admit that working with timezones can get confusing but I’ve checked my work, my settings and documentation Templates, dates and times - Home Assistant several times but cannot find any mistakes.

Questions:

  1. Why is now() and utcnow() returning the same (local) time for me?
  2. If for any reason I won’t be able to use utcnow() for my sensor, what other options are there?

Thanks for any input.

2

The template you used above will give the same result for both now() and utcnow() as input, because you convert it to a timestamp with as_timestamp

a timestamp is always the number of seconds past midnight UTC of 1st of January 1970. So as_timestamp(now()) and as_timestamp(utcnow()) will give the same result.

Your problem is that after that, you use timestamp_custom which by default uses the local time. You should add the parameter false to it so it uses UTC.

This should resolve your issues:

- platform: rest
  name: electricity_cost
  resource_template: >-
    https://api.octopus.energy/v1/products/AGILE-23-12-06/electricity-tariffs/E-1R-AGILE-23-12-06-G/standard-unit-rates/?period_from=
    {% set ts_now = as_timestamp(now()) // 1800 * 1800 %}
    {{ ts_now | timestamp_custom ('%Y-%m-%dT%H:%M:%SZ', false) }}&period_to=
    {{ (ts_now+1800) | timestamp_custom ('%Y-%m-%dT%H:%M:%SZ', false) }}
  value_template: "{{ (value_json.results[0].value_inc_vat) | round(2) }}"
  unit_of_measurement: "p/kWh"

alternative approach without conversion to timestamps

- platform: rest
  name: electricity_cost
  resource_template: >-
    https://api.octopus.energy/v1/products/AGILE-23-12-06/electricity-tariffs/E-1R-AGILE-23-12-06-G/standard-unit-rates/?period_from=
    {{- utcnow().replace(minute=now().minute // 30 * 30).strftime('%Y-%m-%dT%H:%M:%SZ') -}}&period_to=
    {{- (utcnow().replace(minute=now().minute // 30 * 30 + 30)).strftime('%Y-%m-%dT%H:%M:%SZ') -}} 
  value_template: "{{ (value_json.results[0].value_inc_vat) | round(2) }}"
  unit_of_measurement: "p/kWh"
1 Like
3

Thank you!

Took me a little while but now I understand why now() and utcnow() would result in the same timestamp.

Used your suggestions and it works accurately now. Many thanks!