Hybrid off grid solar

MFW_ASAP

rogerblack wrote: »

I'm in the middle of a project to do something rather less ambitious.

2*150W 28VPSUs, hooked up to 2 110Ah*12V batteries, for a total of 2kWh or so.

2*250W panels.
750W inverter.

Appropriate 'point-of-load' converters to run various household loads from the 24V bus.

Set fridge and freezer several degrees colder than I want them - and run them from external thermostats, biased so that they run from solar (through the inverter.)

LED lights, and various low power loads such as networking gear run from the DC bus.

I'd be interested in seeing the results of your project. We're not in a position to install grid connected solar, but I was considering putting a few panels on a large shed, connected to a couple of batteries and have it provide lighting for the shed and a range of security lights in the garden.

Martyn1981

rogerblack wrote: »

I've speculated in the past about the use of second hand batteries - they can indeed significantly change the economics.
I have wondered about going down my local scrapyard, and getting a couple of tons of car /leisure batteries for a bit over the price of scrap lead.

When the batteries wear enough that I have half a ton of actually dead ones - swap them out.

Hiya Roger. Whilst I know next to nothing about batts from a practical point of view, I would say that you are spot on, from what I've read on several forums (renewables, on and off-grid).

There does seem to be a view that top quality batts are best, but many are using second-hand ones. However they generally seem to aim (like you) for prices close to scrap lead, but also stress the importance of having matched batts, perhaps from an emergency back-up source (well maintained with little use), or old forklift etc. as mixed batts may be too hard to equalise and end up cooking each other.

One guy has two sets of forklift batts, one of them he bought the forklift too, so easy to move around!

Also different prices (new) in different countries in the EU, so worth looking around. I'm tempted to have a play on a very small scale, but 3 tiny problems:
1. Unlike you, I know nothing.
2. Need to build the utility room extension first (fancy name for a garage without a car door).
3. My PV set up might make it pointless. Tons of gen in the summer and import around 2 to 2.5kWh per day, then low gen in the winter. But I do fancy something similar to what you propose, or perhaps a 500 to 750W inverter back to AC to cover shortfall during PV production (clouds etc) then nighttime baseload.

I suspect that my savings being small summer and negligible winter make this financially pointless, but still maybe, just to go a little more 'less-grid' .... if you know what I mean.

Mart.