So we are four days into operation of the solar equipment. Right now, we are operating on a limited basis, more on that in a moment. I am not home because we are on the road, but both air conditioners, all vampire loads, and the water heater are running.
Output
We chose a system that is 10 kilowatts DC. That translates to about 8600 watts AC. The system begins generating electricity at about 9am, and reaches a peak of 8kw at around 10:30. By 1pm, the Powerwalls are fully recharged from the night before. At that point, there is no place else for the generated power to go, so system output drops to match whatever the house is using. More on that later.
We haven’t used any electricity from the grid since the sun came up on Friday morning. That indicates that I have enough panels for my house.
Storage
There are two places that I can store the power I generate. One of them is in the Powerwall, which has a total capacity of 27 KWh. Right now, I am maintaining a minimum of 30% as emergency backup, and using the rest to compensate for lower output at night or overcast conditions, or to make up for transient high loads, like when both air conditioners and the water heater are running at the same time. The advantages of using the battery are that the power stays within my home, and losing the grid means that I can still access it. The disadvantage is that the upfront cost of batteries is high.
The second place that I can store generated power is in the grid. The electric company buys my excess power in the form of credits that I can redeem when my system can’t keep up with the loads that I am placing on it- nighttime, stormy weather, or when loads simply exceed what I am producing. The advantage of this is that the upfront cost is low, but the disadvantage is that it relies on the electrical grid for redemption.
I can’t use the grid as storage because I don’t yet have permission to operate (PTO) from the power company. I should get it within two weeks after our final electrical inspection, which is supposed to be this week. So we should be fully operational by August 9.
Results So Far
Each day, we are generating between 35 and 45 kWh before panel output is reduced when the batteries are full. The solar energy being generated is directly running the house during the day, with the rest charging the Powerwalls, which run the house at night.
The water heater is using 4 kw when running, the upstairs AC is using 1.5kw, the downstairs AC uses 2.7kw, and the rest of the house uses 0.3kw. Since the ACs and water heater don’t run all of the time, the panels are more than capable at this point of keeping up by charging the batteries during the periods when the large appliances aren’t running.
Once we get our PTO, I will know more.
15 Comments
J J · July 24, 2024 at 7:16 am
Could you add an additional Powerwall to your system without having to increase the capacity of the panels?
Divemedic · July 24, 2024 at 7:49 am
Yes, and I may have to eventually, but we aren’t done gathering data.
JaimeInTexas · July 24, 2024 at 8:01 am
If you were building from scratch, with a solar system, would you go all-house DC instead of AC?
Divemedic · July 24, 2024 at 8:06 am
No. It adds unnecessary complexity and is more expensive in the long run.
Stefan v. · July 24, 2024 at 9:27 am
You’ve mixed DC and AC modes in your tally of loads….the batteries take DC to charge, your household loads are standard AC to keep things “normal”.
What kind of return could one get on that unutilised potential, if the grid is no longer an option? Could one run a 200 Amp welder, or a sizeable compressor, or a lathe or a drill or a mill? Water pumps to manage cisterns, once the aquifer is depleted/contaminated? Can this system be combined with other local panel arrays as a local shared power system?
What are the single-point failure nodes, and how are they avoided or repaired? How far can the system be degraded before it is totally ineffective; e.g. a hailstorm or a naughty neighbour kid that shoots the panels up with a .22? What spares and tools and skills are necessary for repair/maintenance, and which of these are only available from outside sources and dependent on supply chains and technicians that may become impossible to obtain? What is your hierarchy of demands, from luxury hvac to barebones small batteries for radios, lamps, and data storage and access?
Just throwing ideas on the wall, see what sticks, what slides, and what dribbles….
Divemedic · July 24, 2024 at 10:32 am
I haven’t mixed them. The 10kw of panels are DC. Because the output is AC, the Powerwall is also rated in AC.
Stefan v. · July 24, 2024 at 1:12 pm
Are you measuring the input DC to charge the power wall, the nominal stored potential, or the actual output W? Apples and oranges and bananas. Many variables….but at least you have something. How much can you tweak and repair and replace by yourself? I ask from the standpoint of an old sailor and bushman…my questions may be annoying, but I hope your answers are solid and true. I hope you are spared the hard tests.
Switch off the grid for two weeks and ninety percent of the people are dead, and many of the last ten will try to make it so for the rest. Going back two centuries in a few days will be tumultuous….and no accident.
Bad Dancer · July 24, 2024 at 9:53 am
What about things like the washer/dryer and how do you think this would jive with an induction cooktop?
I’m pretty dang impressed at the sustainment value and may have changed my mind on the powerwall as a management and storage system wow.
Divemedic · July 24, 2024 at 10:30 am
The testing continues
dc · July 24, 2024 at 10:21 am
Question about separability; If the grid goes down (local power outage), can you switch OFF the out feed and keep your home running?
Divemedic · July 24, 2024 at 10:29 am
Not only CAN you, it’s mandatory.
D · July 24, 2024 at 4:18 pm
Sheesh. I’m jealous. I consumed 112 kilowatts yesterday.
J · July 24, 2024 at 6:25 pm
As meticulous as you are, do you have a final total cost?
I’m very envious of your setup.
Slow Learner · July 25, 2024 at 4:04 pm
Just bought some rural property in Texas and will be putting up a metal building (with good insulation) shortly. Any up front considerations before getting the electrician out for installing the breaker panel?
I was going to go with a propane generator for backup power, but from your writings, it seems like solar/powerwall might be more feasible considering how remote we will be.
Stuck in Pugetopia · July 29, 2024 at 4:10 am
There is a third storage method that could be useful for when it gets colder, and you switch from cooling the house to having to heat it.
Not particularly easy to implement, but it does work. Use the ‘surplus’ power after the power wall is fully charged to heat the largest insulated volume of water you can manage. At night, the water could be used to heat your home, (perhaps using something like a hydronic floor system,) and even do things like preheat the cold water feed to the hot water heater.
Once you start thinking in terms of ‘thermal mass’ as another form of energy storage, I’m sure that you’ll come up with a few other ideas as well.
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