Free tool to right-size your system
After looking for a while for a tool that would allow me to model how many solar panels I need, what battery capacity, and what I can get out of shifting hot water preparation but couldn't find anything decent, so I, in a true engineering manner, decided to build vibe code my own: reduck.homes
Disclaimer: It's free and doesn't have any ads, I'm hosting it on my own dime for now and I genuinely want to get your feedback to build a great tool for the community.
It also runs 100% in browser and doesn't save any personal data, everything you configure is stored in the url itself when you click "share".
Concept:
Once you provide your city, it fetches the last 5 full years of weather archives from OpenMeteo and uses Hay–Davies transposition to estimate solar output, then projects it on an average day per season or to an exact day among the fetched data.
Then, using the electricity price, feed-in tariff, and approximate system costs, it estimates payback, ROI, and so on, which can be used to right-size your system.
System costs are especially fuzzy but allow you to visualize the numbers.
Accuracy:
I generated 12 different scenarios all around the globe and compared them to PVGIS and PVWatts models, and in most cases it landed somewhere in between:
| City | vs PVGIS | vs PVWatts |
|---|---|---|
| Reykjavik | +12.1% (bummer) | −0.2% (but PVWatts disagrees) |
| Stockholm | +2.8% | +11.0% |
| London | +2.5% | +9.3% |
| Berlin | −0.3% | +4.8% |
| Madrid | +6.1% | +8.2% |
| Washington DC | +4.8% | −0.9% |
| Tokyo | +7.2% | +1.5% |
| New Delhi | −1.0% | +6.3% |
| Mexico City | +1.9% | −1.9% |
| Singapore | −0.2% | +5.0% |
| Brasília | +5.5% | −1.6% |
| Canberra | +1.8% | −0.3% |
Roadmap: add EV, Wind (oh no, wrong subreddit), solar thermal for hot water, hybrid?
Any feedback and ideas would be appreciated, especially about the model accuracy compared with real-world setups you all have.