SolarQuotes Blog

> What's the term of the load in your calculation?

What do you mean by that? The amount you can draw from the power walls?

This page has a chart with specs that cover this: https://www.solarquotes.com.au/blog/tesla-powerwall-2/

I think each powerwall can draw 5 kW continuous and 7 kW peak.

> A PowerWall has a 10 year lifespan, where they guarantee that batteries will have 70% capacity or better during that time. I take this to mean you'll need to size for a 30% capacity drop, and plan for battery replacement in 10 years.

Well, it has a 10 year warranty, not life span. Yes, for sure there will be some degradation with time (although for my car, a Model S, I'm surprised that after close to 5 years and 25K miles I barely "lost" 1% of range). It depends on how you draw and charge.

> Does your loan factor in installation costs, which can be significant?

I believe it does, and also includes the rebates/credits. But you can answer those questions yourself by going to their website and doing a "pretend order" - that'll give you a bunch of knobs to play with and see the various options between buy cash vs loan.

> Since the goal is to reduce the chance of fire, what would the probability of starting a fire be with thousands of powerwalls installed all over the place be in comparison?

Well, the goal isn't just to reduce the chance of fire: it's also to offer availability at reasonable cost.

Some will also like the "independence" aspect of it, like "stick it to the man" - but…

It's mostly just costs.

See Figure 1.2 Global weighted average LCOEs from newly commissioned, utility-scale renewable power generation
technologies, 2010-2021

https://irena.org/-/media/Files/IRENA/Agency/Publication/2022/Jul/IRENA_Renewable_Power_Generation_Costs_2021.pdf

Hydro costs are going up, solar and wind going down. Hydro is still less than fossil fuels, which is great, but that's not the target to beat anymore, and renewables are lower and trending even lower.

And that's before the more extreme geographical constraints for siting, with good locations already used, the project sizes and the longer lead times and investment paybacks compared with renewables.

But Hydro also has flexibility, which is really useful for balancing renewables and nuclear. It's important to switch existing Hydro into this mode to make the most of it. But again, for new build, since the raw power is more expensive than renewables, the flexibility would need to be cheaper than the equivalent flexibility provided by more renewables plus batteries to win back that lost ground. And it isn't.

Same story for pumped storage. Here's a worked example for the Snowy 2 project:

https://www.solarquotes.com.au/blog/snowy-2-vs-battery-storage/

The key thing is, energy production is cheap these days. So storing energy has to compete against just building even more production and a small amount of storage. This applies to batteries as much as it does to hydro. But batteries scale down better.

Yes, it's actually pretty common. See comparisons across generating technologies in "An international comparative assessment of construction cost overruns for electricity infrastructure" [1].

Here's what the researchers found for solar (section 3.4):

Thirty-nine solar PV and CSP power plants, representing 2374 MW of installed capacity and $16.5 billion worth of investment, were analyzed. (These are utility-scale infrastructure projects, thus they do not include the familiar rooftop solar collectors on buildings or residential configurations.) These projects as a class actually came in $4.2 million less than budgeted, or $200,000 less than expected per project. These solar systems had the lowest
average cost escalation per reference class (1.3 percent), the least time overruns (an average of 2 months ahead of schedule), and the lowest standard deviation for amount of overruns and time overruns. They also had the largest total amount of cost underruns, with the entire class of projects costing $163.9 million less than budgeted, though some of this may be explained by dramatic reductions in cost over the past 4 years. As Table 5 indicates, only 3 facilities had overruns greater than $50 million and only 3 facilities had cost overruns greater than 30%, all of which were CSP facilities rather than large-scale solar PV apparatuses.

Here are a few solar projects that outperformed in recent years:

O'Brien solar farm in Wisconsin, completed in 2021, on time and under…

Gas is faster to respond, coal, not so much.

From the Goog:

Starting up a coal-fired power station depends heavily on the plant's current temperature, taking anywhere from 2 to 48 hours to reach full operational capacity. Because of massive metal boilers and turbines, the heating process must be slow to prevent severe thermal fatigue and equipment damage. [1, 2]
The startup time is broken down by the plant's previous state:

• Hot Start (less than 8 hours offline): 2 to 4 hours. The boiler and equipment are still warm, allowing for a relatively quick resumption of steam production.
• Warm Start (8 to 120 hours offline): 4 to 8 hours.
• Cold Start (More than 120 hours offline): 12 to 48 hours. The plant must be heated from room temperature, which involves initially burning expensive natural gas or diesel just to safely warm the furnace and metal pipes before coal can be introduced. [1, 3, 5]

To explore how these heavy thermal operations impact the broader electricity supply, you can review the U.S. Energy Information Administration's grid reliability data or dive deeper into the technical challenges via the Environmental Protection Agency's Coal Startup Report. [6]
If you are interested in the broader power market, let me know:

[1] https://www.quora.com/Why-its-not-that-easy-to-start-operating-power-plants-after-being-subjected-to-a-situation-where-Load-is-remarkably-higher-than-generation

[2]…

This is sort of over stated generally.

In Australia where North is “optimal”, even South facing panels produce only 20-30% less and East/West about 15%. It does vary a bit by latitude but it’s not at all pointless to install them in other orientations in many places. I have not done the math to see how much of the world this extends to, but it applies to a fairly large chunk of Australia.
Source: https://www.solarquotes.com.au/panels/direction/

Tesla’s system also had non solar tiles so you could just skip the panels in whichever parts you wanted.

Roof construction is quite different here to the US though. We never have the plywood layer, it’s either ceramic tile or Colorbond steel directly onto usually wooden sometimes steel beams.

This makes perfect economic sense, without any environmental arguments.

Rooftop solar now produces 11.2% of the electricity in the Australian market [1], as it's the cheapest source of electricity. That percentage is not a peak value, but averaged across the year. On some summer days, rooftop solar is effectively powering the entire grid and is having to be throttled.

That 11.2% only includes the power that enters the market. It does not include power which houses generate and consume on-site, which does not pass through the meter, so the actual percentage is higher.

[1] https://www.solarquotes.com.au/blog/australia-solar-2024-mb3086/