How-to difference two feeds.

[Roland]

There seems to be enough ways to add or sum Feeds but no way I could
find to take a difference.

I have two feeds, one is power generated by solar , the other is power
consumed in the house. I would like to synthesize the net energy from
the grid as power_consumed - power_generated. Any suggestion on how to
do this? E.g. can I change the sign of one flow and add?

Later I would like to integrate over time ie Net_power * time_interval
Where time intervals are not necessarily constant and may need to be
calculated from timestamps. Am I expecting too much from a beta
product?

[Franck]

Hello Roland,

To make the difference between two (or more) values I would suggest
using the 'Calculator' application (http://open.sen.se/apps/44/).

For your second need (calculating time differences) there is no
application/feature I can think of which could fill it. However, I
note your suggestion, do not hesitate to give us a little more
background information for your use case at to...@sen.se.

Franck

[Roland]

Thanks Franck, 

I used the calculator app to do it but got some funny results.

My input data is 

Time     Solar      Consumption
t1           s1           c1

t2           s2           c2

t3           s3           c3 etc

Using the Caclulation Data=Solar-Consumption This was the output from the app

time     Data

t1         s1-c0  

t1         s1-c1  

t2         s2-c1

t2         s2-c2

t3         s2-c3

t3         s3-c3

The first datapoint at a given time is wrong, The second is correct

Is there a way to avoid passing the wrong values on?

I'll send details of the time issue to your email address.

Thanks

Roland