OK, so my first month of solar power with a rented Tesla system and a Tesla Powerwall is in the books and I have my first preliminary thoughts on the system and the first month in numbers.
Let’s look for that famous three word answer – in my case it would be [reliable] – [no touch] – [efficient]. The install was clean and fast, the system works and unless I have some snow to remove from the panels there is nothing for me to do. Other than snow clearing (I have one of those long snow doohickeys) I do expect to need to wash the panels a few times a year to get rid of dust and pollen that can actually impact solar production significantly, but that is it.
Solar Production and My Initial Usage
Tesla really designs their systems to be set-it-and-forget-it. I do like looking at the phone app and see what the production looks like, just so I can see how the current weather situation and cloud cover translate into solar production. At this time of the year I can expect some production to start around 8 AM and end somewhere around 4:00 – 4:30 PM. The most I produced on a single day so far was 18.4 kWh and the least was 0.9 kWh. My house’s average daily energy usage is somewhere in the 26 – 28 kWh range, depending on how many Christmas ornaments we had running … 😉
Economics – The first Month
As for Connecticut January is pretty much the darkest part of winter, I am looking at this month to be my low end of what I can expect in energy production. I also just received my first electric bill, so now I have actual numbers to put against what my estimates were and I have some conclusions that I can now support with those numbers. In my data below I am only looking at the dates Jan 01-24 as that corresponds with the dates on my electric bill (Eversource here in CT) and the period where I actually had Solar running – here we go:
- Jan 2019 billed to me: 884 kWh
- Jan 2020 billed to me: 638 kWh (= -27%)
This includes the days of the billing period prior to turning Solar on so numbers are a bit skewered.
For the actual Jan 02-24 period the numbers are:
- Home energy usage total: 596 kWh
- Purchased from grid: 401 kWh
- Exported to grid: 14 kWh
- energy saved/created by solar: 209 kWh
So – What does this mean and what are my conclusions?
In Connecticut we do not have time-of-service rates, the generation rate for electricity is the same no matter what time of the day you use it from the grid. Your bill will have a generation portion and then a delivery charge that is made up of several fees that are tied to the amount of kWh you used (i.e. 5009 kWh x $0.0167 … etc.). If I take the 209 kWh that I saved last month that would have amounted to an additional $44.70 on my electric bill. Actually not bad for January.
Next, what about the pure economics of the system? One month in the dead of winter can’t really tell you what a whole year will look like, but it does give me enough to guestimate:
I used 8730 kWh of energy in 2019, costing me about $1870.00 for the year. My Solar rent will cost me approx $1200.00/year (plus taxes, not sure of those yet) so if I am able to produce ~30% of the electricity I use for the year I will come out at even – the savings will be enough to cover the rental fees and judging by January I am confident that will not be a problem. Anything more than 30% will give me money back into my pocket. If I somehow manage to produce enough electricity over the year to zero out my grid usage I will be able to make the maximum of ~$600.00 profit if my energy usage stays the same in 2020 as it was in 2019. Frankly, I have my doubts that is possible with the medium size system that I have on the house, but I do think I can make significant savings and be left with less money out of pocket for my electricity needs.
What is the Case for a Battery?
When it comes to the Tesla Powerwall things are different. Connecticut has net metering without time-of-use rates – what happens here is that a customer is billed for the net amount of kWh used.
So if I use 100 kWh from the grid in a month and sell 20 kWh or overproduction back to the grid I end up paying for 80 kWh of energy. If I export more back to the grid than I use, I create a credit of kWh that rolls over to the next month. Because of this model, there is no economic value in storing excess power production in a battery to use it later – there is no scenario in which I can save money – In effect the grid turns into my battery.
There is a case to be made for a larger solar system to produce more energy overall (especially if I ever get an electric car … I WANT ONE!), but from a pure economic point the Powerwall does not add any saving, it just ends up costing money.
It’s All About the Back-up For Me
This is where I add the “BUT” to the discussion – I did not get the Powerwall for it’s economic value (I already knew I would not be able to save more money), I got the battery to avoid outages and be more energy independent.
I live in the suburbs and do have to deal with power outages now and then. Having a battery back-up that kicks in automatically when grid power fails has value to me. I had 3 outages last year ranging from 1 hour to 6 – two of them were caused by accidents that took out power poles, one was a bad storm where some trees came down and impacted the grid. And .. let’s not think back to Superstorm Sandy a few years back – 6 days of outage.
By law, grid tie systems without a battery backup are required to shut down during a grid outage – no grid power also means no solar power. That is why I went for a Powerwall – I will still have power during a power outage and be also have the immediate back-up that takes over in a few seconds in form of the battery and be able to generate solar power for my daily usage.
Because of this, I also have set my Powerwall to run in “Backup-Only” mode as there is no financial benefit to saving excess power in the battery for later use – I simply reserve all of it’s capacity for a possible outage. My testing shows me that I can expect about 9 – 10 hours of power for my house – longer if I start shutting down things that use electricity. I think I can stretch it to 20 hours if I need to, especially if I turn on my generator to run the critical load circuits as those tend to be big consumers of electricity.
Future plans – there are MANY of those! The main thing I want to look into is possibly switching my hot water generation from oil to electricity. The current hot water system is getting old and will need an upgrade/replacement over the next few years and depending on my electricity production I think I will move it from oil to electricity – probably a hybrid electric one. I will need to wait for another 4 – 6 months so I can see what my real world long term production is so I can make a better determination if that is the right thing to do. Depending on the numbers, it might require an upgrade of my medium sized solar system to a large size system – or if it might not make any sense at all. That is one of the reasons I went with Tesla rental – upping the size of an existing system does not cost any additional money – they come, install the the upgrade and then just bill for the increase in rent. For me that means I’d go from $100/month to $150/month. I will have plenty of opportunity to crunch numbers on that (that is a guilty pleasure of mine …) and I will not know until at least June/July if the savings in fuel oil and the electricity I can expect to use make financial sense overall at all.
I have pother plans in the works along this line, and will share them over time as they come to fruit – some of them will be quite interesting methinks!