Thursday, May 24, 2012

How low can it go?

Well, my latest PG&E bill hit my inbox this morning.  Since this bill covers the period when we switched from winter rates to summer, I was waiting to see how that impacted my results.  It looks like the results were very favorable.  The weather for the last 31 days has been pretty clear, and not too hot so that helped a lot.

The first 10 days of the latest bill covered the end of April, so it was still under winter rates.  For those 10 days, I used only 15 KWh at part peak, and 153 KWh at off peak.  Solar generation was 283.44 KWh, so my total utilization was just about 45 KWh a day.  The cost for this was a whopping $17.36.  A savings of $48 due to solar.

The final 21 days of the bill were at the summer rates.  The main difference in summer rates is that the day is now broken into 3 rate periods, with the addition of peak.  Peak rates are ridiculously high.  And part peak rates are not much better.  During the winter, the difference between part peak and off peak rates is less than 2 cents a KWh.  For the summer, part peak is nearly 2x off peak rates, and peak is 3x off peak.

This actually turned out to be a good thing for me.  The panels actually generated 18 MORE peak KWh of power then I used.  So, PG&E gave me a credit of just over $5 for this.  I only used 33 KWh of part peak power, and 320 KWh of off peak.  My total cost for the 21 days of summer power was only $31.90, for a total bill of $49.

Without solar, the total would have been just over $250, so savings were just over $200.   The medical allowance was much less a factor this month, as it saved me just a few pennies.  If I didn't have solar, it would have saved me about $60.  Time of use pricing also ended up saving me about $12.  It will be interesting to see what happens when it gets hotter, as I don't think my peak usage will continue to be negative.

Tuesday, May 15, 2012

Calculating savings

Now that I am a couple of months in, I am finding that PG&E does not make it easy to calculate the savings from.  I started trying to calculate savings using a simple spreadsheet, and found that it wasn't simple enough.  I then decided to write a quick program in C to do it for me.  It took only about an hour to have something that was usable and accurate.  Then I tried to share it with a few friends.  Microsoft apparently doesn't make it easy to just share a program, you need to pack up various pieces to make it work.  This got me to thinking there had to be a better way.  So, I started poking around, and found that it was possible to do it as a webpage.  Unfortunately, making a webpage to do the calculations involved learning Javascript, which was a bit frustrating.  After a few days, I managed to get a slightly less featured program to work.  It doesn't allow for easily modifying the rates, but I can add that eventually if I need it.  Otherwise, it has the functionality of the program I wrote in C.  In fact, it has the same basic algorithm.  I just wish I knew of a better way to debug javascript.  Not being a compiled language, I didn't have a compiler to help spot typo's, which was very annoying.  Anyway, I have it done, and if you are interested in trying it out, click here to give it a try.  I would appreciate any feedback or questions.

Tuesday, May 1, 2012

April Data

Since April is now in the books, it is time to look back at how the solar system fared vs what was projected.  Total generation for April was 744 KWh.  The finance company projections show that expected generation was 794 KWh.  So, 50 KWh short of expected.  This is 100 KWh closer to expected then March, but still short.  Projections for May are 930 KWh.  We will see how it goes.