Solar Panel setup. Reg & Inverter advice

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Solar Panel setup. Reg & Inverter advice

Postby jason411 » Thu Jan 27, 2011 11:52 pm

Hi,
I have a "BP Solar 255", I would like to set it up to charge 1 or more 12V batteries and then hook them up to an Inverter. I know very little and would like some advice.
- Is this panel best for multiple batteries? or just one?
- Where's the best place (for price/quality) to acquire the recommended batteries? (I'm in Brisbane)
- I'd like the ability to operate small to medium power tools for short durations. Is this too optimistic?
- What size inverter would you recommend?
- Can I get good enough quality components from eBay?
Thanks for your help.
~Jason
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Re: Solar Panel setup. Reg & Inverter advice

Postby zzsstt » Sat Jan 29, 2011 11:16 am

jason411 wrote:- Is this panel best for multiple batteries? or just one?


We need to know some more specs for the panel before making any judgements. From what I can find, the BP255 seems to be a 55W panel, producing 17V at full output. If that is the case it will directly charge a 12V battery. However common sense suggests that a charge controller of some sort is used between the battery and the panel, both to optimise the battery charging and avoid ovecharging and damaging the battery.

The number of batteries is irrelevant. If several 12V batteries are wired in parallel they will still "look" like one big 12V battery and the panel will still charge them. If a charge controller is used that supports 24V battery banks, then the batteries can be wired in series (as pairs) to give a 24V system. In all these cases however it is best not to mix different batteries if possible.

jason411 wrote:- I'd like the ability to operate small to medium power tools for short durations. Is this too optimistic?


If the panel outputs 55W at full tilt, and the power tool uses 550W, then if the system is 100% efficient the panel must charge the batteries for 10 minutes to allow 1 minute of use. Of course, the system is unlikely to be anywhere near 100% efficient, so it will probably be more like 20 minutes of charging for 1 minute of use. Remember also that the panel is unlikely to run at full output very much, so the numbers will decline further. Your 55W might produce about 0.2kWh of power per day (average, so more in summer less in winter). If we assume 70% efficiency, thats about 0.14kWh of usable power, which might run a 500W tool for about 15 minutes per day. Personally I'd say that's "optimistic". However remember that the tool is running from the batteries, so a big enough (deep cycle) battery bank will run the tool for longer, but may take many days to recharge (which is not really good for the batteries, but hey!). So if you bought a good charge controller, a few good "deep cycle" batteries and a good inverter then it may provide you with enough power to do a bit of work at the weekend, if you then left it all week to recharge. But at what cost?

jason411 wrote:- What size inverter would you recommend?


Electric motors can take 5x their rated power at start-up, but power tools under no load will take less. A cheap inverter will be a high frequency modified sine wave unit, which will have minimal reserves for start-up loads and will not be very efficient (the inverter mat be efficient on paper, but electric motors tend not to like square waves so will use more battery power to do the same amount of work). A sine wave inverter is more efficient, will start motors slightly better and use less power from your batteries. A low frequency inverter will have far more grunt for starting motors, but will cost you an arm (at least). If your "power tool" is a Dremel (140W), then it will have minimal starting load and a 500W inverter may well run it. If you power tool is a 9" angle grinder, then you need a huge amount of power (a 9" grinder won't run well on a 2.2KVA generator) and we're talking very large low frequency inverters costing 4 figure amounts.

jason411 wrote:- Can I get good enough quality components from eBay?


Yes, and you can also get absolute rubbish and everything in between!

My honest advice, forget the whole idea. A 55W panel is nowhere near what you need to run power tools in any useful way, and the cost of inverters and batteries would be way too large to justify it. If you have mains power, use that. Otherwise buy a small petrol generator, it will cost you much less than the charge controller + deep cycle batteries + inverter, is far more portable and versatile. It will also give you power when and where you need it, regardless of sunshine. All you need to do is fill it with fuel and pull the handle!

Notes:
The exception to this is if you are mounting the panel on a motor home, at which point it is only providing a trickle charge and the motor home engine will charge the existing deep cycle batteries (and also feed an inverter if required). In this case we are only talking about adding an inverter, which may well also be useful for other 240V appliances in the motorhome. In this case it may be worth spending a bit on a decent inverter.
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Re: Solar Panel setup. Reg & Inverter advice

Postby Gordon-Loomberah » Sun Jan 30, 2011 3:10 pm

As zzsstt says, its probably best to forget the idea. Trying to set up a cheap system will most likely end in disappointment and wasted money, when you have to spend it all again on better quality/larger sized gear.

Stacking multiple 12V batteries in parallel and only having a 55W panel to charge them will likely result in sulphated batteries, that panel doesn't have enough grunt to properly charge a large capacity battery.
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