Sunday, January 1, 2012

Sunny days make me so happy.

Sunny days make me ever so happy. Why?  Because every day it is sunny, I get an email at the end of the day from the SunnyBoy inverter that tells me how much energy our PV system generated.  Every overcast, cloudy day, I get a lousy, depressing number. So, go SUN go!

So, here are the monthly utility bills- not as brilliant as $3.26 from September.  Especially now as we kick in some electric baseboard heaters.

September 20, 2011 to October 19, 2011

Consumption: 505.19 kWh
Production: 389.0 kWh
Net use: + 116.19 kWh
Cost: $52.92

October 19, 2011 to November 18, 2011

Consumption: 713.00 kWh
Production: 300.0 kWh
Net use: 413 kWh
Cost: $95.23

Notes: November had a few -20 C days.  We started turning on baseboard heaters this month too.  And we fired up our wood stove.

If you want to track our production on the SunnyBoy website, click this link!


  1. Are you monitoring the electrical use within the home outside of what you find on your electrical bill? I am always interested to see the ratio of the solar energy produced and used in house versus what is exported to the grid.

    This of course changes the 'value' of the energy produced as you receive retail rate for energy exported and [retail + transmission, dist, LAF, etc] for energy produced and used in house. From my latest research for Edmonton, the trans, dist, etc charges (per kWh; energy use based) add up to more than 4 cents/kWh! This includes the per kWh charges hidden within the transmission and distribution charges, the riders, and local access fee.

    Considering that you will pay 15.11 cents/kWh retail in January, electricity produced by your system and used 'in house' will be worth close to 20 cents/kWh! Fire up those electric heaters when the sun is shining!

    Looks like your solar contractor did a great job. Thanks for sharing all of these details in your blog.

  2. You're right, David. It's economically better to use produced energy directly than export it and later import it at a higher price. This would change if we ever get a feed-in tariff such that the higher price for exported energy mitigates the transmission and distribution charges for imported energy. You don't want to get too carried away and overheat the house too much, because apart from the comfort factor, the warmer the house is the faster it loses that heat (rate of heat loss is proportional to delta T). Your comment also applies to year-round electrical loads such as baking and (heaven forbid) drying clothes - do these when the sun is shining. This is a very good economic argument in favour of a ground source heat pump. A heat pump gives you roughly 3 kWh of heat for every 1 kWh of electrical energy you use, so you're importing less energy in the heating season.

  3. Bob actually wrote me a much more elaborate email- which I will copy below:

    I just read your blog entry from today (January 01) and thought I should
    take a moment to clarify the terms that you used. In your blog, for the
    period from October 19 to November 18, you showed consumption of 713 kWh and
    production of 300 kWh for a net use of 413 kWh.

    Rather than consumption and production, the readings on your Epcor bill are
    for import and export. This can best be understood by thinking about energy
    flows into and out of your main panel. In a house without on-site energy
    production (i.e. 99.9 % of houses in Edmonton), energy flows into the panel
    from Epcor (import) and flows out of the panel into the branch circuits of
    the house (consumption). This situation is described by the very simple
    equation (import) = (consumption). So the number on your bill which is how
    much energy you imported is also the amount that you consumed.

    When you add on-site production, the situation is a little more
    complicated. In this case, there are two sources of energy flowing into the
    panel - energy inported from Epcor (import) and energy from your on-site
    generation (production). Energy can flow out of the panel to branch circuits
    (consumption) or to the grid (export). Since the total energy flowing into
    the panel must equal the amount flowing out of the panel, this situation is
    governed by the equation (import + production) = (export + consumption).
    Epcor has given you two of those numbers (import and export) so the equation
    becomes (713 + production) = (300 + consumption). By subtracting 300 from
    each side of the equation, we get (413 + production) = (consumption). To
    calculate your consumption for the period, you'd need to know how much you
    produced. For the period from 19-Oct to 18-Nov my system produced 708 kWh.
    Looking at the numbers on the SMA site, your system produces about 75% of
    mine, so you probably produced 530 kWh in that period. Therefore you
    consumption for that period is 413 + 530 = 943 kWh.

    In other words, total energy flow into the panel was the 713 kWh you
    inported plus the 530 kWh that your inverter produced = 1243 kWh. Total
    energy flow out of the panel must also be 1243 kWh. You exported 300 kWh so
    the balance of 1243 - 300 = 943 kWh is what flowed into your branch circuits
    (i.e. consumption).

    On 31-Dec I imported 18 kWh, exported 23 kWh and produced 27 kWh. My
    consumption was the 18 kWh that I imported plus the 4 kWh that I produced but
    didn't export so my consumption was 22 kWh.

    Hi Shafraaz,

    I did a closer comparison between your PV production (from Sunny Portal)
    and my production and it looks like the ratio is more like 2/3. On 01-Jan
    your production was about 17.9 kWh and mine was 26.5 kWh (ratio 0.675). So my
    production of 708 kWh from 19-Oct to 18-Nov would translate to about 472 kWh
    for your production for the same period. This would put your consumption at
    885 kWh rather than the 943 kWh that I had calculated.

    import (713) + production (472) = export (300) + consumption (885)


  4. Thanks Bob and Shafraaz,

    It will be interesting to track this over the course of a year. Dave Kelly's 2kW system in Calgary is producing about half of his annual electricity. In his case, roughly 50% of the energy produced by his PV system is used in house, the other 50% is exported to the grid. His home has high efficiency gas heating, so the electrical load profile is likely to be quite a bit different from a home with electric heating.

    Smart metering and time of use billing should further improve the economics of these systems as the peak summer demand that Alberta sees (11-5) matches quite nicely with PV system production.