How are you calculating that? Solar installations are around $2.50-$3.50 per watt, so $20k would get you 6-8kW. Assuming actual output is 10% of capacity, that's 14-19kWh/day or 5,000-7,000kWh per year. Current residential electricity prices in SF are 38.9 cents per kWh[1], so that's $2,000-2,700 per year in savings, or $40-54k over 20 years. The actual amount saved depends on how much electricity you're consuming during peak times, but I doubt that number is off by a factor of 10.
Ahh, ok the tool sucks it doesn’t seem to calculate based on your current cost per kWh or the local cost per kWh.
It’s ignoring inflation on those calculations, acting like your electric bill will be the same in 20 years. It’s also ignoring residual value in the system after 20 years they typically last 25-30, and you don’t pay taxes on savings.
There install estimates where also really high for my area, but I don’t know if that’s a general issue.
Your electric bill 20 years from now is just as likely to go down as it is to go up.
In two decades, we could see advancements like mobile generators offering free power, ultra-affordable battery packs delivered to homes to meet energy needs, or even the widespread adoption of low-cost fusion energy.
The key takeaway is that predicting the future cost of electricity is as challenging as it was to predict today’s solar energy costs—now far lower than anyone expected.
None of what you just said is even vaguely realistic. Prices can’t drop below zero but they can easily more than double, so even if you assume equal odds in either direction it doesn’t cancel out. Worse, any physical device is going to have a cost to produce it which requires charging people to use it thus they can’t even drop to 0.
Beyond that none of their prices or timelines are accurate, even ignoring the issues with inflation.
With solar technology, powering a home with a mobile generator is possible. Yes, the generator and batteries will have associated costs, but the long-term benefits make it worthwhile. This assumes uninterrupted access to sunlight over the next 20 years without new restrictions.
Key Considerations:
Energy Need: The average home uses 30 kWh/day, requiring 6 kW/hour over 5 peak sunlight hours.
Multijunction Panels: Lab efficiencies are already at 47% (2023), and with 20 years of progress, 60% efficiency is probable.
Efficiency Impact: At 60% efficiency, panels generate 600 W/m², requiring 10 m² (e.g., 2 m × 5 m) to meet energy needs.
This size fits on most home roofs or could be mounted on a pole or hung through an apartment window.
System Components:
High-efficiency solar panels.
30 kWh battery storage for nighttime or cloudy days.
An inverter to convert solar DC power to home AC power.
Outcome:
A mobile solar generator with advanced panels and efficient storage provides a sustainable and portable solution for powering homes.
So you’re assuming the big competition for home solar is… home solar but ignoring what makes home solar expensive (permits, electricians, tariffs etc panels are already shockingly cheap). Installing solar in 15 years also means you’ve lost 15 years of cheap solar power and are buying panels after inflation, waiting just hasn’t seen instillation costs drop for a while.
But you’re also wildly mistaken about the rest, it’s not actually 47% or now 47.1% efficient when placed outside. Panels get more efficient as extreme levels of light so people going after records create wildly irrelevant numbers as a dick measuring contest.
Further the day someone invents 60% efficient panels isn’t the day we put those suckers into mass production we hit 40% in 2006, but they are nowhere near commercially viable for home installations. We might see widespread use of 60% efficient panels long after we’re dead, but that’s not exactly relevant for these calculations.
It seems like we're talking past each other. My main point, as stated in the parent response, is that there is a plausible future where energy prices, adjusted for inflation, could decline rather than continually increase.
Many here are relying on inductive reasoning, arguing that since this hasn't happened historically, it can't happen in the future. I'm presenting a counterpoint: with current technology and 20 years of advancement, this outcome is entirely possible.
To clarify, I'm not suggesting that mobile generators and solar panels would be free. Rather, the energy they generate could become effectively free. The current challenge is that centralized grids are often necessary because we can't store enough solar energy in batteries. However, with advancements in battery technology over the next 20 years, it could become possible to go completely grid-less. If that happens, we could see significantly lower energy prices—something we should remain as open to as the possibility of higher prices, all on an inflation-adjusted basis.
Specifically in terms of batteries, you can also add batteries to an existing solar installation.
Rather than competition what you’re describing is a way to increase the value of installing solar today.
> adjusted for inflation
I brought up inflation because buying a hedge that keeps up with inflation and selling it in the future results in paying taxes on that nominal increase in value but saving money doesn’t have that penalty. You also lose out on the lost productivity from a solar while waiting for prices to drop so it takes a lot more than just moderate inflation adjusted savings to make waiting advantageous.
Now you're sounding all pie in the sky. The cold hard reality is that hedge funds and billionaires control most power utilities and lobby governments to keep the cash flowing.
We know for certain that pricing is going to get really bad in CA due to a 2022 law that permits PG&E and other utilities to charge large connection fees based on your income (will probably hit in 2026).
I would gladly be the counterparty to any wager that 20 years from now electricity is going to be cheaper.
I find this argument short sighted time and again based on personal life experiences as a former electrician given the life impacting results I have witnessed from power losses.
My electrical experiences are regional to my area in the NorthEast US where long duration events have caused many thousands of US dollars in lost food, tens of thousands of dollars in losses from flooded basements, and when temperatures in Winter often drop below freezing and the power goes out pipes begin to freeze causing even more damage structure wide. In time we will see insurance companies reducing rates for those with local energy storage as the corporate insurance machine catches up to understand the benefits of having such power storage locally. I laugh when people make this exact financial reasoning argument because so few people look at the big picture and fail to comprehend the impacts to their life when that switch on the wall leaves one in the dark. Then again I have designed and architected many successful software systems for high availability and my foundational starting point with any system is always energy. Most of those in society assume that switch will always turn on that light and when it does not then those impacted begin to realize what a "centralized grid" truly means.
Decentralizing the grid is already happening as CA very recently announced any new residences built as of 2026 and beyond must be constructed with PV and storage. Individuals can act in ignorance on the energy problems for now however in time everyone will be forced to participate as the issues continue to compound.
Proactive versus reactive, because by the time it matters it will already be too late.
i've heard of some business models that install these and have you pay what would be the difference to your electric bill to the company until they pay themselves off, not sure if the panels last long enough to make that work though
Yes. In Germany they are selling a lot of models, but none, I mean, really, none asked about the rentability. So I went to a neighbour who just installed his 25kW and was very proud and happy, and asked him, in how many years is the return of investment. Siderated, he could not answer and then a few days later, with a very stern face: 25 years or more because if more people install these, the price that the city is paying for the pumped energy goes down.
So no. 20kw is not the answer. I showed my setup: 3.5kw + big battery. Pays the bill approx 60 70% of the daily usage. Investment payback : 5years.
What if he added previous generation crypto miner (so it's cheap) and use the excess electricity instead of selling it to the grid? This could also save some money on heating in winter unless he has a heat pump priced in already.
prev gen crypto mining is phenomenally inefficient in terms of energy that ends up being converted to heat, but it is absolutely not what you would use to take electricity and create heat given any other choices.
What are other choices? Heat pump is obviously the best but any other thing is just electric heater with 100% efficiently of heat generation. Pushing some bits around doesn't change that. I guess for some applications you might prefer higher temperatures but for residential heating crypto mining is as good as anything else, right?
25kW? That is crazy huge! How many panels? What does this guys house (mansion!?) look like? Google tells me that average installation size is about 7-8kW.
This exactly the case when a battery would make an immense difference.
(9 USD / kWh sounds terrifying. Not only an electric kettle begins to cost you; probably playing computer games at high quality / resolution comes with a noticeable price tag in electricity that the GPU would eat.)
$20k upfront cost.
$4k in savings over 20 years.
That's an implied rate of return of 0.9% annually.
No thanks.