Suburban 5-4-and-a-Door Solar: How Much Power do you Generate?

We now have a year's worth of data to play with, and one of the most asked questions is "how much power are you generating from your panels?" That can be a difficult question to answer because it depends on the month, the weather, the clouds, the pollen (probably) and other factors.

We took the generated power numbers from every day for the year ending on June 30, 2018 and put them into a histogram to see exactly what our power generation looked like over the year. We have a south-facing 6.875kW array with some minor shading in the mornings.

The way the histogram works is that the first column (0kWh generated) represents exactly zero kWh. Subsequent columns represent the range from the previous number to the number shown (just over 0 to exactly 2 kWh, just over 2 to exactly 4 kWh, etc.). The smart meter didn't record for the first 5 days, so there are a total of 360 days represented.

• Our best day was 33.3kWh generated on March 14, 2018. March was an especially good month with a lot of sun and had a few days in the 30kWh range.
• Our worst day was 0kWh on September 12, 2017. September had a couple of very poor generation days due to some major storm activity. Even so, zero was startling to see. Fortunately it only happened once.
• The average power generation in a day is 18.4kWh. Perhaps more relevant, the median power generation in a day is 20kWh.

On a per-month basis, the data shows numbers ranging from 354kWh in December to 688kWh in April, but those can be highly influence by weather so your mileage may vary.

Suburban 5-4-and-a-Door Solar: Which Rate Plan is the Best?

With a years worth of data to analyze, one of the questions we asked is whether or not we are on the right rate plan. Georgia Power offers three plans that are relevant to us. The one we are on now is a flat plan. It costs the same amount to use power at any time of the day. The cost per kWh rises as we use more power during a billing period, but there is no dependence on when we use that power.

The two other options are the Nights and Weekends plan and the PEV (Plug-in Electic Vehicle) plan. Each of those has a rate that changes depending on when you use power. The Nights and Weekends plan has a lower rate outside of the hours of 2pm and 7pm, Monday through Friday. The PEV plan has high rates from 2pm to 7pm Monday through Friday and very low rates from 11pm to 7am every day.

Since our smart meter give us access to our power usage every 15 minutes, we can make a good estimate of what our bills would be under the other rates. (Although one can never be entirely sure - read here for how we estimate some of the fees and charges.)

Based on our calculations and current usage schedule, we wouldn't see a whole lot of savings under the other plans. Our estimate is that we'd save about $41 over the year with the Nights and Weekends rate and about $48 with the PEV rate. It's not nothing, but it's not enough to make us change our plan immediately.

Since Georgia Power only allows changes in residential rate plans once a year, we wanted to wait a year to see exactly what our usage would be before making a change. And since the flat rate was actually lower cost in June, we'll probably wait a month or so to make the change this year.

We suspect that once we change to a different rate, our usage may change as well. We'll be more careful about using power during those low cost times and set the dishwasher and other appliances to run after 11pm. However, since there are two of us working at home right now, there's not a lot we can do to change our patterns. For people who aren't home during the day or who have batteries that can arbitrage power (buy during low cost periods, use battery during high cost periods), your options will likely be more clear.

Suburban 5-4-and-a-Door Solar: Savings in the First Year

We have now had our solar array for a year's worth of bills. Since our array gives us data for every 15 minutes, that's a lot of data to analyze (a 15MB Excel workbook at the moment). But here's some of the more useful graphs from our experience.

Probably the most asked for - what is your bill with solar compared to without solar. Our total bill for the 12 months ending June 30th was $1541. Compare that to last year at $2064 or to our peak year at $2502 and there's a significant savings. If you want to use average bills over the last four years as a comparison, we've saved about $770.

Average bill isn't the best way to compare, because we were making moves to lower our overall energy use during that time period. We're switching burned out light to LEDs, we're using the clothesline more, etc. You can see that dramatically in the graph of yearly grid use.

From a peak of just about 20,000kWh for the year ending in August, 2015, we've dropped to about 12,000kWh for the year ending in June, 2018. That's a drop of almost 40% over three years, and you can see from the graph that the drop started before we had our panels installed in June, 2017. There is a dramatic drop starting when the panels were installed, as would be expected. from what looked to be a leveling off point. We suspect that the graph will start to level off again now and maybe drop again in a year when we start losing kids to college.

Calculating the actual savings versus what we would have paid over the last year without solar panels is more difficult. Determining exactly what the power company charges for power is surprisingly opaque (see this post for how we tried to estimate what power really costs). Using our best information and the power usage information from our smart meter, we estimate that the bills with and without solar would reflect a somewhat more modest savings.

Using those relatively complicated calculations, we see a yearly savings of about $670. So we tell folks that our actual savings is somewhere between the average bill savings and our calculated savings - $670 to $770.

Our original ROI estimates for a 10-11 year return were $740 savings in year one, so we're pretty close depending on our calculations.

Suburban 5-4-and-a-Door Solar: Update to How Much Does Power Really Cost?

In this post last February, we detailed what contributes to actual cost of power from our local utility for our solar-enhanced home. As mentioned, the posted Georgia Power rates are just a small part of the overall charge. There are fixed add-ons like Environmental Fees and there are hidden costs like Fuel that you can only discover by calling and speaking to a supervisor.

We now have a full year of solar-enhanced bills to analyze, and we have a better idea of how to figure out each of the additional fees. These should be more accurate if anyone is calculating for themselves.

For each of the variable fees, we've done a regression analysis of the 12 months of data to determine more accurate formulas. Not that these are the actual formulas used by the utility. If they were, then the points would line up exactly. The formulas used by the utility appear to be secret and relatively randomized. But these formulas have been accurate within a dollar or two.

Nuclear Fee = 0.009965*kWh - $3.12

Environmental Compliance Fee = 0.01314*kWh - $3.87

Franchise Fee = 0.004657*kWh - $1.05

What we also found is that the fuel charge, which we originally assumed was fixed, seems to vary each month. That makes sense, we suppose, as fuel tends to change costs. However, it's hard to find any other industry that changes their prices month to month based on the cost of fuel. In any case, here are the fuel charges that appear to have been used on our bill over the last month. This is in addition to the fixed $10/month fuel charge.

Fuel Charge = $10 + amount below per 100 kWh

July, 2017	$2.84
August, 2017	$2.84
September, 2017	$2.83
October, 2017	$2.56
November, 2017	$2.56
December, 2017	$2.56
January, 2018	$2.99
February, 2018	$2.99
March, 2018	$3.00
April, 2018	$3.00
May, 2018	$2.99
June, 2018	$3.31

So your total bill cost is Nuclear Fee + Environmental Compliance Fee + Franchise Fee + Fuel Charge + Rate*kWh + 7% sales tax. If you have solar, then there is also a $2.82 fee to have a bi-directional meter, but at least you get about 3.5cents per kWh that you overproduce and sell back to the utility.

It's amazing that no one seems to even notice most of these charges. Georgia Power was certainly surprised when I asked. It's important to understand the total cost of power when deciding to put solar on your home. The published rate is just a small part of the total cost of power.

The 21-Word Review: Red Sparrow (Delta In-Flight)

I didn't watch this earlier because of the poor marketing. It is much better than a Jennifer gets naked exploitation flick.

The 21-Word Review: The Kingsfountain Series by Jeff Wheeler

I liked Game of Thrones and asked for advice on a similar series. This was the advice offered. It's bad advice.

The 21-Word Review: The Shape of Water

I really like that directors are being encouraged to develop unique voices and visions, but Best Picture may be overdoing it.

The 21-Word Review: The Pearl Harbor Series by Harry Turtledove

We tend to view historical events as if they were inevitable. Good alternative history writers show us that nothing is inevitable.

The 21-Word Review: Barracoon: The Story of the Last Black Cargo by Zora Neale Hurston

It's hard to understand why this book took so long to be published. A little book with a very big impact.

The 21-Word Review: Dallas Buyers Club

Yes it's a tragic and inspiring story over overcoming hardships, but all I could think of was the amazing cheekbones throughout.

The 21-Word Review: The Ritual (Netflix)

I wasn't all that impressed. Then I read the glowing reviews ... written by horror fans whose psyches have been permanently marred.

The 21-Word Review: 1922 (Netflix)

Pet rats are wonderful, cute, intelligent, and lovable. Having lived with pet rats, it's hard to be terrified by movie rats.

The 21-Word Review: 47 Meters Down (Netflix)

So many good movies are available these days for streaming, yet I still picked the one with the teeny bikini cover.

The 21-Word Review: Suburbicon (Delta In-Flight)

I honestly thought this was a heavy handed, subtle-as-a-sledgehammer student production and was disappointed to see who directed.

The 21-Word Review: Geostorm (Delta In-Flight)

Better than some of the more recent disaster movies in the genre, but that's not exactly a high bar to set.

The 21-Word Review: Coco (Delta In-Flight)

If no reviewer has yet said "I'm cookoo for Coco" yet in their review, then I claim that phrase as mine.

The 21-Word Review: My Adventures with God by Stephen Tobolowsky

Once you start recognizing Mr. Tobolowsky's face, it is unnerving how many times you see it in movies and television shows.

The 21-Word Review: Straight Man by Richard Russo

When the entertainment system went out on my Atlanta to Seoul flight I managed to finish this entire book before landing.

The 21-Word Review: The Revenant (Delta In-Flight Movie)

I read the book so there were no surprises, but that did not diminish the power of the story and performance.

The 21-Word Review: Three Billboards Outside Ebbing, Missouri (Delta In-Flight)

Three dimensional characters with complex motivations, superb manifestations, and gut wrenching stories? If only more modern films were so well done.

The 21-Word Review: The Foreigner (Delta In-Flight)

I have trouble believing a Chinese man could disappear into Northern Ireland so completely that the IRA could not find him.

The 21-Word Review: The Time Traveler's Wife (Delta In-Flight)

A secret to enjoying the movie based on a book that you enjoyed is to wait three years to see it.

The 21-Word Review: Daddy's Home 2 (Delta In-Flight)

Perhaps I am suffering from not having seen the firth movie in the series, but this installment almost rose to dreck.

The 21-Word Review: Ready Player One

Pedantic lovers of the book will find fault in the omissions and plot changes, but the movie captures the atmosphere admirably.

The 21-Word Review: Destiny of the Republic: A Tale of Madness, Medicine and the Murder of a President by Candice Millard

It's a tragic shame that we don't know more about President Garfield. A truly great man cut down by medical hubris.