{"id":273,"date":"2008-05-28T10:14:46","date_gmt":"2008-05-28T10:14:46","guid":{"rendered":"http:\/\/dalelane.co.uk\/blog\/?p=273"},"modified":"2009-05-17T16:16:08","modified_gmt":"2009-05-17T16:16:08","slug":"a-daily-currentcost-bill","status":"publish","type":"post","link":"https:\/\/dalelane.co.uk\/blog\/?p=273","title":{"rendered":"A daily CurrentCost “bill”"},"content":{"rendered":"

As I’ve finally got my home server<\/a> capturing the electric meter readings<\/a> from the CurrentCost<\/a>, I thought it’d be good to try doing something with it. <\/p>\n

I want to start with something a bit different to graphs, because there’s already been a lot of cool<\/a> work<\/a> done in different graphing approaches. <\/p>\n

As I wrote yesterday<\/a>, I’ve got a MySQL database that is storing the watt reading from the electric meter captured once every six seconds. <\/p>\n

I wondered<\/a> whether it makes sense to try and turn these figures into a financial cost. It might be interesting (and useful as a behaviour-altering thing) if we could get a “bill” from the CurrentCost meter each day that told us how much we spent on electricity the last day. <\/p>\n

+=============================================+\r\n  Your CurrentCost bill for 2008-5-27\r\n\r\n     Electricity usage   4.9802 units\r\n      Cost ==           \u00c2\u00a30.4874\r\n\r\n     Standing charge    \u00c2\u00a30.1582\r\n   ---------------------------------------\r\n     TOTAL COST FOR 2008-5-27 : \u00c2\u00a3  0.65\r\n+=============================================+<\/pre>\n
I’m not entirely sure of my maths here, but I thought it could be interesting to give it a try.<\/p>\n
<\/p>\n
Turning a watt reading into a cost<\/h3>\n
Consider a single reading (set articificially high, to make the numbers easier to read!):
\n$watts = *75000* watts<\/code><\/p>\n
Turn it into kW:
\n$kWatts = $watts \/ 1000 = 75<\/code><\/p>\n
Take the unit cost from my bill:
\n$unitcost = 0.0932<\/code><\/p>\n
Add VAT:
\n$unitcostIncVAT = $unitcost * 1.05 = 0.09786<\/code><\/p>\n
How many hours in a year:
\n$hoursInYear = 365 * 24 = 8760<\/code><\/p>\n
kW hours over a year:
\n$kWHInYear = $kWatts * $hoursInYear = 657000<\/code><\/p>\n
Calculate the cost of staying at this rate all year:
\n$costPerYear = $kWHInYear * $unitcostIncVAT = 64294.02<\/code><\/p>\n
Compare this with the values reported by the CurrentCost meter:
\n$costPerMonth = $costPerYear \/ 12 = 5357.835<\/code>
\n$costPerDay = $costPerYear \/ 365 = 176.148<\/code><\/p>\n
If I put in watt values I see on the CurrentCost meter, the ‘Cost per day’ and ‘Cost per month’ figures agree with what I get from these sums. <\/p>\n
So, if I assume that a reading is valid for 6 seconds, I can work out a cost for the period of time covered by the reading:
\n$costPerHour = $costPerDay \/ 24 = 7.3395<\/code>
\n$costPerMinute = $costPerHour \/ 60 = 0.122325<\/code>
\n$costPerSecond = $costPerMinute \/ 60 = 0.00203875<\/code><\/p>\n
$costPerUpdate = $costPerSecond * 6 = 0.0122325<\/code><\/p>\n
This can be simplified down a bit to:
\n$costPerUpdate =(($watts\/1000) * $unitcostIncVAT) \/ 600<\/code><\/p>\n
Getting the readings for a single day<\/h3>\n
This is simple – I can get the total for all readings in a single day from MySQL with a query like:<\/p>\n
mysql> select DATE(time) as \"Bill Date\",\r\n    ->        COUNT(power) as \"Number of updates\",\r\n    ->        SUM(power)\r\n    -> from currentcostdl\r\n    -> where (DATEDIFF(time, '2008-05-27') = 0)\r\n    -> GROUP BY DATE(time);\r\n+------------+-------------------+------------+\r\n| Bill Date  | Number of updates | SUM(power) |\r\n+------------+-------------------+------------+\r\n| 2008-05-27 |              5404 |    2988128 |\r\n+------------+-------------------+------------+\r\n1 row in set (0.93 sec)<\/pre>\n
I’m wondering if it might be better to use the number of updates rather than assuming how many updates I will get in a day. But for now, I’ll stick with the six seconds assumption<\/strike>.<\/p>\n
Update:<\/strong> After Alexis’ comment (below), I have switched my script to use the number of updates. It still assumes that each update is valid for approximately the same period of time, but that’s probably accurate enough for my purposes:
\n$costPerUpdate = $costPerDay \/ $NumberOfUpdates;<\/code><\/p>\n
The number of updates for yesterday is very low because I only started up the Perl script to capture updates yesterday<\/a>. By tomorrow, I should hopefully get a number of updates closer to 14,400.<\/em><\/p>\n
Generating a “bill”<\/h3>\n
From here, I’ve put together a cron job on the server that will once a day at 8am. It runs a perl script that gets the values from MySQL<\/a> for the previous day, does the sums, turns it into a pretty “bill”, then sends me an email<\/a>. <\/p>\n","protected":false},"excerpt":{"rendered":"
As I’ve finally got my home server capturing the electric meter readings from the CurrentCost, I thought it’d be good to try doing something with it. I want to start with something a bit different to graphs, because there’s already been a lot of cool work done in different graphing approaches. As I wrote yesterday, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[194,214,105,211],"class_list":["post-273","post","type-post","status-publish","format-standard","hentry","category-code","tag-currentcost","tag-electricity","tag-mysql","tag-perl"],"_links":{"self":[{"href":"https:\/\/dalelane.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/posts\/273","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/dalelane.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/dalelane.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/dalelane.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/dalelane.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=273"}],"version-history":[{"count":0,"href":"https:\/\/dalelane.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/posts\/273\/revisions"}],"wp:attachment":[{"href":"https:\/\/dalelane.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=273"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/dalelane.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=273"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/dalelane.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=273"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}