Guides
You already run a balcony solar system, the panels are up, the inverter is feeding in, and now the battery is tempting you. Retrofitting balcony solar storage is usually the easy part, technically speaking. Whether it pays for itself is the far more awkward question. So we answer that one first,...
David Reinhardt
Guides
A solar power bank test almost always ends the same way: pretty cell, sobering numbers. The built-in solar cell isn't fake. Real silicon, real charging electronics. The physics just refuse to cooperate, and that's exactly what those product shots in the sun never tell you.
Jonas Keller
Guides
The one hard difference between glass-glass and glass-backsheet that you can actually look up in a datasheet is the product warranty: Trina gives its glass-glass Vertex S+ TSM-NEG9RC.27 25 years product and 30 years power warranty, while the glass-backsheet Vertex S TSM-DE09R.05 gets 12 years...
David Reinhardt
Guides
For anyone renting in Germany, the first question about a balcony solar system is rarely technical. It is whether the landlord can simply say no. Until October 2024 the honest answer was usually yes — permission was needed, and a refusal did not have to be particularly well argued.
Jonas Keller
Guides
A balcony solar system hangs outdoors, weighs about twenty kilos and costs roughly what a decent bicycle costs. That makes it the one household purchase that can be contents, building fixture and a hazard to the neighbours all at once — depending on who you ask and which contract you signed.
Jonas Keller
Guides
Buy a battery for a German balcony solar system in 2026 and the invoice will almost certainly show a zero where the VAT line should be. That is not a retailer discount or a limited promotion. It is the zero rate under § 12 (3) of the German VAT Act (Umsatzsteuergesetz, UStG), in force since 1...
David Reinhardt
Guides
A power station is an expensive thing to buy, so "refurbished" looks like the obvious way out: same hardware, same manufacturer, a few hundred euros less. Both major brands run their own refurbished shop in Germany, and both advertise there with a struck-through price. What the price tag never...
Jonas Keller
Guides
This looks like a choice between two product categories. It is really an arithmetic problem with two unknowns. The first is how much your cooler box actually draws, and two boxes that look nearly identical from the outside can differ by a factor of four. The second is how many watt-hours your...
Sophie Ahrend
Guides
The wattage on the box is the number almost everyone buys on, and it is the number that decides least about whether the panel will work for you. A module can have exactly the right output and still deliver nothing, because its voltage does not fit the window of the device it is plugged into. That...
David Reinhardt
Guides
When the first autumn storm rolls through, the same question comes up in a lot of households: will a power station carry us if the electricity is gone for a few hours — or a few days? The answer turns on a single number, and it is not the one printed on the box. It is energy per day, and you can...
Jonas Keller
Guides
There is one big number on the box: 1,024 Wh, 2,048 Wh, 3,840 Wh. Almost every buying guide online turns it into the same calculation — capacity divided by appliance wattage equals hours. That calculation is convenient, it is memorable, and it falls apart in exactly the cases where it matters:...
David Reinhardt
Guides
Every product page for a balcony solar battery shows the same chart: one bar for yield without a battery, a taller bar with one, and a payback figure underneath. What almost never appears next to it is the set of input values that produced that figure. And the inputs are the entire difference...
Sophie Ahrend
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