What a year of solar and batteries saved us in 2025

Tldr; their full costs of the system are returned in 11 years.

Whether that's good depends on your perspective and assumptions, you can take a look at opportunity costs.

Imagine you have 100k for say 30 years, and you have three choices: 1. put it in a UK government bond at 4.4% -> 100 * 1.044^30 = 363k 2. put it in the S&P500 (dividend reinvested) at nominal 10% rate -> 1.7 million 3. buy a system that can't be made liquid after 30 years, but returns 11k flat per year = 330k.

1 is very safe and virtually guaranteed. 2 is considered less safe, but over 30 years broad based stock indexes are far less risky than short-term stock investing.

3 is perhaps the most difficult to make assumptions, as its house-tied and operational. Switch houses for any personal reasons, and you'll not be able to fully make your investment liquid and recuperate it. Blow an inverter, see panels degrade and replacement costs must be factored in. This pushes down the final cash position of 330k.

We could be generous and say that the 11k flat savings will increase, as electricity prices rise. Prices grew by 5% yearly in the UK, under that rate so the 11k savings today would grow to 47k annual savings in year 30, and total savings over 30 years would be 870k, pushing up the final cash position, but still not getting close to a long-term stock index investment.

But even that's somewhat generous for two reasons: one is that the 5% inflation was unnaturally high due to the EU's energy crisis from the Russian invasion, and not necessarily indicative of the next 30 years. Various countries in the EU are also curtailing renewable production because there's too much of it (precisely during the moments solar systems were making their biggest profits On the other hand, AI seems likely to push electricity prices higher for a long time... but it's the newest and biggest question mark compared to the other assumptions we've made above.

In my house I only run LED lighting and an occasional oven, some phones and laptops, a cycling fridge and two weekly wash cycles, in other words, virtually no electricity. I'm at like 2 kWh per day.

The ~45 kWh a day for this family is gigantic compared to mine, like >20 of my homes in one.

But I don't have an electric car, nor electric heating or cooling, nor an electric stove.

If you have say a standard electric car like a Peugeot 208 which uses 15 kWh per 100km, and you both drive one hour (say 60km) to work and back, five days a week, that's already 25 kWh per day.

My heating bill (gas, europe) is an order of magnitude of my electric bill. Even if I'd electrify it (cheaper), it'd likely be an additional 10 kWh per day.

If you have slightly more fancy lifestyle (they run home-servers and a hottub for example), you can easily get to 45 kWh.

I think the fair comparison is to look at a household total energy expenditure (energy & $). My household has a low electrical share, theirs has an almost exclusive electrical share.

Still, I think the grid is very vulnerable with that amount of weather-based energy. If there can be enough batteries to sink all that power generated and have it during evening til morning then that's great.

Perhaps that _can_ work in California, I really don't know what an acceptable level of storage would be. That is, how many days worth of battery power you'd want in case of bad weather conditions.

The reality is that many battery factories might be operating at 40-50% capacity only. Exact figures are hard to come by but there are lots of warnings about over production, surpluses, etc.. That spells a lot of trouble for some of the newer battery producers promising more efficient batteries. Because unless they price match, they price themselves out of the market almost immediately.