Ok, I’ve been thinking a lot about energy storage recently, and have come to the conclusion that while it’s a great idea, all of the commercial solutions are way too expensive, but it’s something I’d really like to play with.
So, after some thought, I’ve come to the following conclusions and would like some confirmation (or at least wild disagreement) of the results:
- The storage will be sealed deep cycle lead acid (wait for it!), I realise Li-Ion is what a lot of people are using and I understand the benefits, but the cost is expensive either for new cells or stripping down & testing old cells. Joining them requires expensive welding tools and the balancing/maintenance ( & electronics) seems quite complicated. LA is cheap/simple. The space needed is larger, but it’s a fair trade off. As long as the depth of discharge is kept low - I’m thinking 10-15% - they should last a good number of cycles. I’m thinking of starting off with four 110Ah batteries, probably in 2S2P for 24V.
- Charging can be done with cheap e-cycle/scooter chargers at 24V rather than the epic equipment needed to charge big Li-Ion.
- Discharging is though a small Grid Tie inverter.
- Going for the “lowest hanging fruit” target, I think taking the house off grid for 6-8 hours overnight* is the first target, the background use is around 100-110W. So 800W storage would be needed.
- Later on there could also be some support for energy usage during the day, to add to the utility of the system.
- To simplify things, the charging and output will be fixed (much like the Moixa & Power Volt systems), so charging at 125W (or maybe later a two stage charger at 250W) and output at 100W.
- This discharging appears to be an issue, as plugging a battery into an inverter (rather than solar panels) will (as I understand it) just suck as much energy out of the battery as it can until the inverter reaches its maximum output. So even with a small 350W inverter, it will need something to manage the input into the inverter. Any simple/low cost ideas?
- I’m not sure about the electronics package, but think an EmonPi/EmonTx type box (fed with data from the existing Emon system in the house) will be used to start/stop charging/discharging and monitor input/output/voltage of the battery bank (logging the data back to the existing Emon system).
As for costs:
- Four 12V batteries @ £75 = £300
- 350W inverter @ £50
- Intelligent 24V Charger 125W @ £25
- Cables etc @ £25
- Electronics @ £50
Roughly £450 ? Less if you have Pi’s/etc to hand.
So, Ladies & Gents, your thoughts please?
*Obviously it would be better to do this from 5pm - 11pm to support the grid, and this is where it would end up, but to start with monitoring what’s going on will be easier when things are quiet!