Gas station without pumps

2018 August 13

PG&E trying to screw people with home solar systems

Filed under: Uncategorized — gasstationwithoutpumps @ 11:22
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PG&E informed me that they were requesting an increase in minimum bill amounts for electricity “to reduce bill volatility”, but did not say how much an increase they were requesting. I looked at the complete language of the proposal at http://docs.cpuc.ca.gov/PublishedDocs/Efile/G000/M218/K401/218401655.PDF, but all it says is “Approval of this Proposal would increase electric rates for distribution customers by less than one percent; therefore, a statement setting forth PG&E’s proposed increases or changes to electric rates is not needed.”  So I have no idea how big a change they are proposing to the minimum bill.

I am currently paying the minimum bill amount monthly, so increasing that minimum amount will not “reduce bill volatility” for me, as bill volatility is already zero.  The change will definitely increase my bill, and probably by much more than 1%—but  it seems to be top-secret what my new bill will be.

So far as I can tell, PG&E’s primary aim is to extract more money from customers with net energy metering (NEM), making home solar energy systems less cost-effective, which works against California’s carbon-reduction goals.

If the increase in the minimum bill is less than 1%, then I have no major objection to the change, but if (as I suspect) it is much larger than the rate of inflation, then I strongly oppose the attempt to transfer costs primarily to NEM customers without even saying how much the increase is.

If anyone reading this blog is also a PG&E customer, you can send comments to
public.advisor@cpuc.ca.gov, making sure to include “R.12-06-013” somewhere in the subject line.

2016 October 25

Solar power annual cycle

Filed under: Uncategorized — gasstationwithoutpumps @ 16:25
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I’ve been running my solar panels for almost 15 months now, and I decided to plot the daily energy production:

The sinusoidal fits are to all the data (the lower curve), and to the data after cleaning up the bad-weather drops in energy.

The sinusoidal fits are to all the data (the lower curve), and to the data after cleaning up the bad-weather drops in energy.

When I first looked at the data, I realized that a sinusoidal fit to the data would be heavily affected by the cloudy days, which drop power production substantially, so I wrote a script to delete any day whose power was less than the day on either side. Doing three passes of that resulted in most of the really low values being gone, so I fitted a sinusoid to that subset of the data—what I would have gotten if there were no bad-weather days.

When using all the data, I averaged about 7.1 kWh a day, with a ±3.4 kWh annual fluctuation. With just the good-weather data, I averaged about 8.1 kWh a day, with a ±3.5kWh annual fluctuation. That means that I’m losing about 1/8 of the potential solar capacity to cloudy weather. The max and min are within one day of the solstices, so the fitting is doing a pretty good job of finding the phase.

The fluctuation is not perfectly fit by a sine wave, though, as the summer peak is a bit broader than the winter valley. If I were ambitious, I would try seeing how well the data fits with the equation of time or the sunrise equation, instead of a simple sinusoid. I don’t think that would actually help the fit much, as I think that the biggest part of the error is due to shadowing by trees or buildings in the early morning and late afternoon, and this shadowing is more pronounced with the low sun angles of winter.

2016 September 6

PG&E time-of-use Schedule E-6 gone

Filed under: Uncategorized — gasstationwithoutpumps @ 17:19
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The time-of-use rate schedule for electricity that I’ve been using (the E-6 schedule) is no longer available. It ended 2016 May 31, but those of us who already had it will be grandfathered in for a few years, but transitioned out of it by 2022.

E-6 was a good rate schedule for customers with solar panels. Under E-6, summer peak electricity is 34.159¢/kWh, but summer off-peak is only 14.854¢/kWh.  Winter part-peak is 17.071¢/kWh, and off-peak is 15.388¢/kWh. Note that the summer time fluctuation in rate is a factor of 2.3, so generating during peak times (which solar power does) and using electricity at night (which we do) results in substantial financial benefit, even when net usage is near 0.

The available time-of-use schedules now are much less favorable to the customer, especially to net-energy-metering customers.  ETOU-A has only 5–25% price differentials, and ETOU-B has only 10–30% price differentials, so the incentive to time-shift usage is tiny compared to E-6. The peak prices are about the same as under E-6, but the off-peak prices don’t drop nearly as much.

ETOU-A has higher rates 3pm–8pm weekdays, while ETOU-B has higher rates 4pm–9pm weekdays.  The summer/winter difference is only a change in the rates for the two time periods, not in when the higher charges apply (unlike the more complicated E-6 schedule, which has 4 time periods on weekdays, 2 on weekends in summer, and 2 on weekdays, 2 on weekends in winter. Winter is October–May for the ETOU schedules, but November–April for E-6. Because May is a month with high solar output, it is better for me to have it at summer prices.

The ETOU-A schedule has low rates up to a baseline amount, then somewhat higher rates.  Because of net-energy metering, I would nearly always be at the lower rate, which would be good for buying electricity, but is terrible for getting credit for energy I’m selling them.  The lowest rate on the ETOU-A plan

I’m certain that the E-6 schedule is much better for me than the new ETOU-A and ETOU-B schedules, but I don’t know by how much. PG&E has a rate-comparison tool that compares what bills one would pay with one’s current rate or any of the available alternatives. Of course, it does not work with E-6 plus net-energy metering—not only does it not work, with that rate schedule, but it then refuses to show what the bills would be with any other rate schedule—customers are left trying to calculate this themselves, which is unfair, because PG&E has all the data about how much electricity the customer used at different times, but the customer does not, and PG&E does not make access to the information easy.

When the time-of-use rate schedule changes in a few years, I suspect that my break-even time for the investment in solar panels will stretch out even further.

2016 September 5

Dehumidifier

Filed under: Data acquisition — gasstationwithoutpumps @ 00:05
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In Average annual power use, I mentioned

I will be buying a dehumidifier for our house, to reduce the condensation on the walls. Current Energy Start rated dehumidifiers remove about 1.85 liters of water per kWh used, and I don’t think we need to remove 2775 liters of water a year (7.6 l/day) from our house, so the dehumidifier will add nothing to our electricity bill.  Based on reviews (in Consumer Reports and on Amazon), we’re looking at the 30-pint Whynter RPD-321EW Energy Star Portable Dehumidifier, as it has good performance in cool rooms (our house gets quite cool in winter, especially when we’re both at work) and is relatively easy to empty (we don’t have a convenient way to rig up a drain hose).

We bought the dehumidifier and it seems to work ok. The timer is a bit crude, as it does not have a time-of-day clock, but you can set up a delay of up to 24 hours for turning on and turning off.  This means that we’ll have to reset the timer daily. That’s not as much of an imposition as one might think, because we have to empty the water daily any way.  People running a dehumidifier with a drain hookup might find the need to reset the timer more of a nuisance.

Our biggest disappointment with the dehumidifier is that it is loud. They claim that it is only 53dB, but it seems louder than that to me—unfortunately, I don’t have a sound pressure meter to measure it with. The compressor is fairly quiet, but the fan is loud, which suggests a poorly designed air flow. We can run the dehumidifier in the living room, but not in the bedroom, because of the noise it makes.

I can’t measure the loudness of the dehumidifier in calibrated units, but I could record chunks of sound from it using an electret mic, an amplifier, and the BitScope USB oscilloscope. I then wrote a program using SciPy to take the FFT of each recorded trace, and averaged the absolute values of FFTs for a hundred or so traces:

The noise is "pink" noise, with more low-frequency components than high frequency ones. The 5kHz cutoff is not an artifact of my amplifier, which has fairly flat gain out to about 100kHz, nor of the microphone, which is fairly flat to at least 20 kHz.

The noise is “pink” noise, with more low-frequency components than high frequency ones. The 5kHz cutoff is not an artifact of my amplifier, which has fairly flat gain out to about 100kHz, nor of the microphone, which is fairly flat to at least 20 kHz.

We can use a lower sampling rate to zoom in on the lower frequency end of the spectrum:

The 60Hz peak is sharper here, and 120Hz is clearly missing, but the next several harmonics of 60Hz are present. I don’t have an explanation for the dip between 400Hz and 480Hz.

I don’t know whether the spike around 1067Hz (in both plots) is an artifact of my test setup or is present in the sound. I suspect it is present in the sound.

The dehumidifier takes 340 watts to run (about 40W for the fan and 300W for the compressor), and it extracts about 5 pints in 5 hours (somewhat slower than its claimed 30 pints/24 hours, but that is probably based on warmer, wetter air, which is easier to extract water from). We only run for 5 hours a night, because we don’t want to be woken up by the loud beeping that occurs when the 7-pint bucket fills up.  (There is no way mentioned in the manual to disable the alarm—my son and I might disassemble the dehumidifier to disconnect the irritating beep.)

We plan to run the dehumidifier only during off-peak hours (at night or weekend days), for about 45 hours a week, which will consume about 800kWh a year. At PG&E off-peak rates, that is around $120 a year, but we had $98 of unused Net-Electric Metering (NEM) credits, and our minimum bill is around $111, so the extra electricity use will make no change in our bill. We will probably want to pay for carbon offsets, though, since we are increasing our carbon footprint by about 0.23MT (so about $2 in carbon offsets).

2016 July 30

Average annual power use

Filed under: Uncategorized — gasstationwithoutpumps @ 00:47
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I just got my “True Up” bill from PG&E—it has been about a year since the solar panels were installed. During that time, the panels generated about 2.63MWh of electricity (7.2kWh/day): 77kWh more than we used during the year. PG&E reimbursed me $2.11 for the extra electricity, but wiped out the $106 of Net Energy Metering credits that we had accrued from generating electricity during peak time and using electricity during off-peak times.

Next year, we’ll be facing a minimum delivery charge of about $120 for the year. If we follow the same peak/off-peak usage, that means that we could use about another $226 worth of electricity without increasing our bill (other than losing the $2.11 credit). That would be about 1.5MWh off-peak, or only 660kWh peak consumption. What that translates to for us is that I will be buying a dehumidifier for our house, to reduce the condensation on the walls. Current Energy Start rated dehumidifiers remove about 1.85 liters of water per kWh used, and I don’t think we need to remove 2775 liters of water a year (7.6 l/day) from our house, so the dehumidfier will add nothing to our electricity bill.  Based on reviews (in Consumer Reports and on Amazon), we’re looking at the 30-pint Whynter RPD-321EW Energy Star Portable Dehumidifier, is it has good performance in cool rooms (our house gets quite cool in winter, especially when we’re both at work) and is relatively easy to empty (we don’t have a convenient way to rig up a drain hose).

We are fairly light users of electricity by US standards. We used about 2.63MWh a year, but the US average is 10.932 MWh/year, and the California average is 6.744MWh/year [https://www.eia.gov/tools/faqs/faq.cfm?id=97&t=3].  PG&E also reports what people in our area use: similar houses use 6.042MWh/year, and efficient similar houses use 3.262MWh/year [https://pge.opower.com/ei/app/myEnergyUse].

Part of the reason we use so little electricity is that we rely on natural gas for heating, hot water, cooking, and clothes drying, using about 433 therms a year.  Here we are not particularly efficient: PG&E reports that similar houses use 548 therms/year, but efficient similar houses use only 293 therms/year [https://pge.opower.com/ei/app/myEnergyUse]. Shorter showers and setting up a clothes line would probably reduce our usage, but heating is the biggest chunk, and our house is already as cool as we are willing to live in.  We’ve invested in insulation over the years, but there is only so much you can do with a poured-concrete house for sane amounts of money.

A therm is about 29.3001 kWh, so our natural gas use is about equivalent to 12.7MWh—much more energy usage than our electricity!

We’ve been planning to buy carbon offset credits for our energy usage this year (see previous estimates in Solar lies).  Nothing for electricity of course, since we had a slight surplus there.  According to PG&E, natural gas produces about 6.1 kg CO2 per therm (and their electricity generation is about 238 g/kWh, only slightly more than the 208g for the same amount of energy from natural gas) [http://www.pge.com/includes/docs/pdfs/about/environment/calculator/assumptions.pdf].

I calculate approximately the following CO2 production from our various uses this year:

My wife and I have considered taking another trip this year, to Boston, which would add another 4.9MT. Note that flying is by far the most energy intensive thing we do—reducing travel is probably the only way we could significantly reduce our carbon footprint.  As carbon offsets, we’re considering projects like https://www.cooleffect.org/content/project/efficient-cookstove-project/, which cost $6–$10 per MT.  Do any of my readers know of good carbon offsets that aren’t scams or just enabling polluters?

 

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