We have ignition!
NV Energy replaced my meter and gave me thumbs up on January 6, so I pulled the handle to connect my panels to the grid and my home. That afternoon, the panels generated 4.441 kWh of AC energy. The first full day was 18.292 and we were just getting warmed up as the days after that registered 24 kWh or more per day. Overall trend was increasing production as days grew longer.
I started getting data from NV Energy on 1/16/21 so for the last 16 days of the month I know I received 370 kWh from the grid and delivered 200kWh of solar power to the grid. My total consumption of electricity for those 16 days was 529 kWh, so by my calculation the panels saved about $20. Add in the 10 days without data and I may have cut my expected $65 bill to $35. I’ll let you know exact numbers after I receive my first bill.
These numbers are in line with the estimate from my solar contractor that my panels would generate approximately 628kWh every January. From 1/6-1/31 (25.5 days) they actually generated 593, average 23 per day. 23 x 31 = 713 for a conservative estimate of what total January production might have been. PVWatts was a little optimistic predicting I might generate 902 kWh, but they apparently assume mostly-sunny days, whereas about 1/3 of the days this January were cloudy or partly cloudy. Daily production ranged from 8 kWh to 36 kWh depending on amount of sunshine.
Is it worth it?
Considering that I made the first of 144 loan payments of $182.71,saving $30 on my first monthly bill might not be cause for much celebration. Fortunately, the savings should be much greater in warmer months, and the up-front $5800 tax credit reduces the cash flow pain significantly.
A lot depends on how much I get for delivering excess solar power to the grid during summer peaks. In July I should be able to generate 1500 kWh and deliver much of that back to NV Energy for about 22 cents per. That’s a big chunk of change if I use the AC sparingly during peaks and don’t crank it up too much in the off-peak hours.
Assuming my installation proves reliable and free from major maintenance costs, most other factors seem likely to increase cost-effectiveness of my investment:
- Electricity rates increase
- Public perception of the value of solar panels increases
One factor, however, will reduce cost-effectiveness
- Summer days grow hotter. Solar panels lose approximately 0.3% efficiency for every degree Fahrenheit above 77F. At 100F they will produce approximately 7% less than they would under similar conditions at 77F.
Meanwhile, I can take some satisfaction that I am reducing my carbon footprint (particularly important in US with its inefficient carbon-based generating plants) and have somewhat limited the risk of climate-related impact on energy costs for my home. After one month of production, my monitoring program cheerfully informs me I’ve saved the planet from 1,222 pounds of carbon, the equivalent of planting 9 trees.
At this early stage, it appears I may go a very long time without paying anything for electricity. I will have to pay a small monthly fee to remain tied to the grid.
First Bill (January)
Today I received my first post-solar bill from NV Energy. It covers the day of installation (1/6/21) to 1/28/21, 22 winter days. The combination of TOU Rates and Solar Power are saving a lot of money.
The grid delivered 423 kWh and the panels sent 323 kWh out of about 500 kWh generated from solar panels to the grid, for a net 100kWh billed at full rate, total $6.25. Various fees on the full 423 kWh were $1.36. Electricity costs total $7.61 or $0.35 a day. The base service was $9.53 for the partial month, making the total bill $17.24, an average of $0.78 per day.
Last year my daily average was $2.24, $1.46 more per day. This year we are using a lot more electricity due to the pandemic. Last year we used about 15 kWh per day but this January we used almost double, 27kWh per day.
27 kWh at full rate would have been about $1.69 per day (base service additional.) TOU saves about $1 of that. My original projected solar savings, pre-TOU were $0.12 per day, so it looks like my projections were very conservative.
February, 2021 (Saved $57.00)
For the period 2/1/2021-2/28/2021, my solar panels generated 971kWh. That exceeds the estimates from PVWATTS (924) and my contractor (790). I used 449kWh from the grid and sent back 703kWh for a net of 254kWh to my credit (for use in summer.) My total consumption was 717kWh (971-703+449) which would have cost $47.11 from the grid. Instead my bill was an effective credit of $9.89 for a savings of $57.00.
March, 2021 (Saved $71.44)
Solar panels generated 1274 kWh. This exceeds the estimate from my contractor (1100) but didn’t quite reach PVWATTS (1278). I used 486 kWh from the grid and sent back 993 kWh for a net of 507 kWh to my credit. The credit does not go toward the base (about $15) but it pays for electricity including basic delivery fees for the grid (about $1.50 for the 486 kWh). My accrued credit so far is about $30 which will probably be used up in summertime.
In March my total consumption was 767 kWh (1274-993+486) which would have cost $50.37 pre-solar, but combined with my credit of ($21.06) makes a total savings of about $71.43 for March. This is based on TOU rates which are about half normal rates from NV Energy during non-peak hours.
April, 2021 (Saved $83.76)
Solar panels generated 1475 kWh. This exceeds the estimates from my contractor (1386) and PVWATTS (1404). It was was a sunny, cool month with only 2 or 3 overcast days in Las Vegas.
I lost 1/2 day production due to inverter malfunction. A simple reset fixed it, and it was a good reminder to keep an eye on it every morning.
I used 549kWh from the grid and sent back 1139kWh for a net of 590kWh to my credit. My accrued credit so far is about $55 which may be used up in summertime.
In March my total consumption was 889kWh (1475-1139+549) which would have cost $58.45 pre-solar (TOU rates), but combined with my credit of ($24.35) makes a total savings of about $82.80 for March.
Last year’s bill was at standard rates, before I discovered TOU. At standard rate (0.1134 incl tax) my electricity cost would have been $100.81! So I saved $42.36 by using TOU rates, and $82.80 from solar for a credit of $24.35. Last April’s bill was $128.20 for 1136kWh, this year’s was $13.18 (for the base).
May, 2021 (Saved $98.76)
Solar panels generated 1638kWh. This exceeds the estimates from my contractor (1512) and PVWATTS (1404). It was was a sunny, warm month with only 2 or 3 overcast days in Las Vegas. The average of almost 53kWh per day is probably getting close to maximum production from my 7.92kwP system for any month. Production usually peaks from 6-7 kWh around noon, with occasional spikes above 7. Those spikes may be due to a passing cloud cooling the panels followed by a burst of intense sunlight on the cooled panels.
I used 789kWh from the grid and sent back 1112kWh for a net of 323kWh to my credit. My accrued credit so far is about $68 which will be used up for summertime air conditioning.
In May my total consumption was 1314kWh which would have cost $86.34 pre-solar (TOU rates), but combined with my credit of ($12.41) makes a total savings of about $98.76 for March. (Keep in mind, however, I am paying $188 a month on my solar loan.)
June, 2021 (Saved $188.37)
It seems likely that I will make it through the hot summer in Las Vegas without paying for electricity from the grid. My 7.92kWh system, in combination with Time-of-Use (TOU) rates, produces enough to keep a lid on my bill from NVE, even under less-than-ideal conditions. That bill had been hovering around $250 a month last summer. Our consumption this year was a bit higher due to the unusually hot June.
Production was 1,420kWh, lower than predicted by my contractor (1,511) and PVWATTS (1,498). I lost a full day on June 21 when my system simply blipped out. Maybe it was celebrating Summer Solstice. Service techs mumbled something about a firmware update for my inverter. Production was also affected by hot, hazy days. On days that reach 110F my system struggles to hit 50kWh. Throw in some hazy, downright cloudy days and the average was 49kWh per day for 29 days. High for the month was 57kWh on June 10, low (other than the zero day) was 22kWh(!) on June 23. Still, enough to eliminate electricity charges from my utility, but not much of a credit going forward.
Summer means Time-of-Use rates
Summer TOU electricity rates arrived June 1 and will continue through September 30. During peak times (1-7pm, Mon-Fri) I will be charged $0.347 per kWh delivered from the grid, and credited $0.283 for each kWh the grid receives from my solar panels. Off-peak the rate is $0.053 per kWh delivered and $0.042 received. At those rates, during peak hours I want to “sell” as much solar as I can to the grid, and avoid using electricity for appliances. Dinner preparation now begins at 7pm. I’ve set my Nest thermometer to pre-cool the house to 75F between 11am and 1pm, then set to 81F from 1-7pm during peak. Even on days that reached 108F outside, The air conditioning didn’t kick in until around 5pm and then ran for about an hour between 5 and 7, when the thermostat goes back to its “normal” 79. That’s probably about the best I can do without letting it get uncomfortably hot in afternoon, and the result is that the grid is receiving 8-9 kWh net during peak each day. That seems to have generated enough credit to eliminate the cost of electricity from the grid for the summer months. Fingers crossed! If I really wind up generating that much excess credit, I can perhaps set the thermostat at 79 instead of 81 during peak (still pre-cooling from 11am-1pm) and use up more of that solar power.
Replacing my thermostat
I’ve signed up for a “free” smart thermostat from NVE. The battery on my Nest needs to be replaced (after almost 4 years) but I think I’ll try the freebie instead. It comes with an agreement that allows NVE to fiddle with my thermostat during 2-hour “Demand Response Events”. There were 8 such events in June, all during weekdays at 5pm. I believe the intention is that on those days NVE will bump my thermostat down 2 degrees to pre-cool beginning at 3pm, then bump up 4 degrees from 5 to 7. Right now I’m doing some cooling between 5 and 7, so this would shift that to 3-5. Shouldn’t cost me much, but buying my own thermostat may turn out to be a better investment, and I’m already doing my part to reduce usage during peaks.