Comment by choeger | Hacker News Reader

Comment by choeger | Hacker News Reader

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Cool project. I think we really need some free software sensor/controller libraries/frameworks for solar setups.

The reason is that here in Germany, and presumably elsewhere in Europe, these "balcony powerplants" are taking off. You are allowed to plug up to 600W (soon up to 800W) into your socket without further trouble.

But unfortunately, most people will waste a lot of energy this way. Very few people will have permanent usage of 100W or more. Instead, consumers like refrigerators will turn on and off multiple times per hour.

So the ideal setup would consist of one or more load-measuring sensors, a smallish long-lasting battery (LiFe?), some oversized panels (say up to 2kW) and a converter that hooks everything up.

The controller should ensure that you feed power into your grid only when you need it and otherwise charge your battery. I think that such a setup could easily get you 4kWh/day of consumption in spring and summer. And potentially still 1kWh during most winter days.

Not sure if you saw but there's a great little German startup called "We Do Solar" who produce solar panels specifically for use on Balconies. My house has a flat roof and we'll be putting solar up there in the near future but I also plan to get panels for the balcony on our second floor as it runs the full width of the house and should add quite a chunk of generation capacity (downside is it's west facing so will only really provide power from the afternoon until the sun goes down).

It's not wasted energy. The country (perhaps even the continent) still benefits from it by having to burn less gas and coal

With regards to the wasted energy that is potentially made by the panel but unused, that doesn't offset any other power production since the power wasn't going to be used anyway

Of course the power is used. It's in the grid, and every power source has to be compensated by a power sink, otherwise you have instable grid = blackout if the deviation is too big

Are you assuming the panels are grid-tied? I may have missed that in the article, the setup sounded very off-grid to me at which point the power potential is lost if not used immediately.

Balcony powerplants (see comment I responded to) are connected to the grid and offset self consumption by their production

Are there actually inert (non-flammable) batteries that have a decent energy density for this? I would be worried about having any kind of sizeable lithium battery in an apartment, considering even laptop-sized batteries have enough firepower in them (but at least that one can more or less be picked up and thrown out the window in an emergency).

LiFePo4 batteries are very safe and do not have the thermal runaway problem that LiPo batteries do when they are damaged due to improper charging, abuse, or manufacturing defect.

As long as you stay away from the prismatic ones. If you do use those make sure you only use a properly designed enclosure to contain the forces exerted by the batteries as their charge, there is a reason manufacturers quote battery capacity at 300 or 500 kg clamping force. These are not at all easy to work with.

What would be the consequences of non-containment? Do those batteries swell and completely fall apart or do they just move a bit (if so, flexible cables and leaving decent room for expansion should be enough)? Do they merely need the compression to achieve the rated energy densities, or do they fail dangerously because of insufficient compression?

They can fail dangerously because the deformation can cause the busbars to become dislodged. Definitely not just a capacity thing.

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