Solar Shed Bar

[Qscout]

Hi Everyone,

I have read through the other topics, and have concerns about by solar system I am planning for our shed bar. The plan as it stands it to have 300w of solar panel, through a solar controller to trickle charge 12v 200amp battery.

The lights through the bar will be powered directly from the load output on the controller, and there will also a be 4 240v sockets that will be used to occasionally charge mobile phones, run a laptop, or other low powered appliances. The main use of this 240v system is for a fridge that will require a fairly large inverter 1000-1500w, however this will only be for start up. When it is on it will only average 30w, but as it is compressor driven has a large draw for a split second on startup.

I have read the stickies on large inverters, on 12v systems, and wonder since our usage is going to be low in general does the same apply?

What are the alternatives?

Thanks

Martin

[SunEagle]

Hello Qscout and welcome to Solar Panel Talk

Actually that fridge will burn up over 720 watt hours per day (30w x 24h = 720wh) and your 200Ah 12v battery can safely provide about 600wh per day unless you want to discharge it farther than 25%. (12v x 200ah x 25% = 600wh)

So if the fridge starts up every once and a while and you run those lights or charge some phones, you are discharging your 200ah battery too much. Also an inverter can use up to 10% of its wattage rating just being turned on without a load. So a 1000w can also burn 2400wh a day (1000w x 10% x 24hours = 2400wh)

So unfortunately your system is too small for that fridge along with running your other loads. I would not call your system being of low usage.

[Qscout]

Hi SunEagle,

Thank you for your insight. Do you have any suggestions for how better to power, a fridge and a few outlets?

Martin

[SunEagle]

Hi SunEagle,

Thank you for your insight. Do you have any suggestions for how better to power, a fridge and a few outlets?

Martin

A few outlets and lights can be easily powered by your solar/battery.

Unfortunately a load like your fridge will require a much bigger system or a stand alone generator. Usually any heating or cooling load is a lot for a small solar system to power.

As I mentioned your fridge can burn a lot of watt-hours per day along with an inefficient inverter. To size your battery system you need to first know what your daily watt hour usage is and then decide how much you want to discharge it. Remember the lower the discharge the more cycles (or days) you get out of the battery. if the battery is expensive then you may not want to replace it as often as it will need to be.

[Fordtrucksforever]

I assume you are not in the US with the need for 240 volts. If the fridge consumes 30 watts at 240 volts, you need to do the math and then realize why it wont work on a single 12 volt battery for very long. Maybe consider upping the battery voltage with at least two in series and add another solar panel. At bare minimum you might get by with this. Your battery bank still has to be large enough to run everything without the solar panels. During about 6 hours of the day you might get by alright, but before and after that it will rely only on the battery to keep up with the power demands. You need enough battery for the 18 hours there is no power from panels. This is where your setup falls short.

[Mike90250]

My mininum suggestion for a mini-fridge and minimal lights and phone charging

1Kw of PV
4 six volt golf cart batteries wired in series for a 24V 200ah system
a 1kw pure sinewave inverter (1kw is usually a safe minimum for a quality inverter to start a single fridge)

You will find the fridge starting surge is usually over 2Kw, but only for a brief instant, and good inverters on decent batteries can handle the surge. What kills 12v systems is the starting surge also causes an instantaneous voltage sag, often below the inverter shutdown voltage, and the inverter shuts down, usually about 1am in the morning, when the batteries have become a bit low.

Since each install is somewhat experimental, unless you have an AC Peak Hold watt meter ($400) going a little bit overkill is better than under sizing something and in a couple months when the batteries begin to get soft, the system starts having problems. if you are able to get great detail about your loads, you can spec a exact size inverter to handle your always on loads of lights and chargers, and find an inverter that will still have headroom to start the fridge. Or you wake to warm ice in the fridge in the morning.

And flooded golf cart batteries are forgiving and cheap. Great for a starter system and then when you have refined things in 2 years when they die, you can get fancy.