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At least in Germany, small systems up to 0.8 kWp can be connected to any household without any professional installation and these systems are available as "plu

• hnaccount_rng 2y ago
  Ah interesting, I wasn't aware that you can put Balkonkraftwerke _with_ a battery on a normal outlet, too. Thanks for that. I don't think that changes my conclusion though, as the per-kWh-price there is significantly higher (I think mostly due to the transformer that's required) :/ I did the calculation for another discussion yesterday. For larger battery systems you can get 10kWh for about 2.4kEUR and with that 240EUR/kWh the battery would amortise itself quite quickly (6 years, ignoring interest [0]). But the Balkonkraftwerk batteries are more 1.6kWh (+ 1000W panels) + transformer for 1kEUR. The solar generation changes the calculation a bit [1], but if I ignore that then we are at 625 EUR/kWh, which would at least double, maybe triple the payback period (and then ignoring interest becomes much more relevant). However this is largely academic as for my calculation you'd need to use more than 20kWh per day (2 cycles @ 10kWh). The cheapest battery-only normal-outlet system I could find was 900 EUR (but the AC/DC transformer is already included) for 1.6kWh, so 562 EUR/kWh. I don't think I even use the 3 kWh/day for that system... And we are talking <100 EUR/year savings. In the end (residential) electricity is just not that expensive (in terms of household budget) [0] With a dynamic price rate you could do two cycles per day (loading in the night and at midday with lack-of-demand-cheapness and solar-cheapness) on 250 days/year and a spread of 8ct/kWh (there is some variation, but that should be somewhat conservative) you can get 500 cycles/year and about 40EUR per battery-kWh installed. [1] In the calculations above I took a rough look at the pricing data in Germany https://www.energy-charts.info/charts/power/chart.htm?l=en&c=DE&week=11&year=2025&source=total&legendItems=2wgw2w2 https://www.energy-charts.info/charts/power/chart.htm?l=en&c... and picked numbers for reasonably simple calculations. With solar you would essentially do the Midday charging for "free" from the panels, increasing the price spread in the evening. One could also take time-of-use rates for the calculation, which (currently) typically offer a structure of -6ct, -6ct and +4ct at night, midday and evening (vs morning prices)
  • tfourb 2y ago
    Why the battery? Batteries are the least cost-effective part of any solar installation, especially on residential scales. You can buy this Balkonkraftwerk for 1,099 Euros, it comes ready to plug in: https://solarhandel24.de/collections/balkonkraftwerke-mini-solaranlagen-zu-bestpreisen https://solarhandel24.de/collections/balkonkraftwerke-mini-s... If I scale down my (partially shaded) 12kwp installation, this 1.78kwp plant (which apparently is still legal under German legislation, which allows for up to 2kwp, not 0.8 kwp, as I erroneously wrote above), will generate 1.246 Mwh per year. If installed today, you'll get 7,94 Cents per kWh that you feed into the network and buying electricity comes at about 29 Cents/kwh. If you consume half of the Balkonkraftwerk's generation directly you'll save 180 Euros. If you feed in the other half, you'll get paid almost 50 Euros. At 230 Euros per year, you'll have recouped your investment after 4.77 years. A battery does not make any sense on that scale. It would severely decrease return on investment because its main use case (running asynchronous high loads like heating and charging cars) are not available in this type of installation. Pure PV installations (without any battery) are practically always profitable within 10 years in Germany, as long as you can guarantee at least 50%, better 70% direct consumption and your plant is not pointing straight north and/or is shaded completely. Batteries are nice to play with (and ours would have a 12 year break even time at current prices) but if I'd optimize for ROI, I'd never include them and instead scale down the kwp of my solar to hit 65-75% guaranteed direct consumption.