solar shed questions

If the stereo is pulling 10W for 3 hours, that's 30 watt hours a day (10W x 3 hours = 30wh). I don't know where you are, so I'll assume pretty bad solar in the winter or 2 sun hours. 30wh / 2 sun hours / .67 system inefficiencies = 22.3W of solar needed to power for a day. I recommend using at least 30W, 40W would be better to make up for days without sun.

30wh per day x 3 days without sun x 1.57 temp deration (again, assuming you are where winter sticks) x 2 (50% depth of discharge) / 12V = 23.55ah battery minimum, the 46ah is good.

A 40W panel probably has an Isc of 2.5A x 1.25 = 3.1A, so a 4A charge controller would manage charging the battery. I'd get one with a Low Voltage Disconnect (LVD) and connect the radio through that, so it will turn it off if you forget and leave it on and the battery gets low. Maybe a Morningstar SS-6L-12V.

All systems go.

P.S. I just reread your info and see you are in England, the temp deration is probably overkill, as it is good for down to 20F (-7C). As for sun, ugh! Tilt the panel as much as you can, 50 - 55 degree tilt off horizontal. Even then, your December is 1 sun hour. So redoing the math, 30wh / 1 sun hour / .67 = 45W panel. Or stay in your house in December....

Thanks for replying

Hi, I already have a 40w solar pannel, 5a charge controller and 46ah deep cycle battery and was wondering if it was sufficient. I will only really use this system in spring and summer though. So is my system adiquate?

Many thanks, sam

PS. My controller does have lvd/ovp on the load

Sounds good to go! keep an eye on the battery voltage, turn off the radio and whistle instead if it starts to get low.

thanks for help

One last thing, would I have any excess for on a sunny day pull like 5a for 25min or charge my tablet. Also I might run a 5w led for 30min a day, would I need to upgrade my panel and cc?

Thanks for replying, I appreciate it
Many thanks, sam

And the snowball starts to get bigger.

Sam

One of the biggest mistakes that people make when building a solar battery system is to not properly identify their daily watt hour usage or think they can easily add a small load (like another light or electronic device) to their original list.

If you underestimate your watt hour usage you can quickly kill your battery by draining it too much and then not having enough solar panel wattage to re-charge it.

Please make sure you have calculated the correct load in "watts" and the maximum time you need to run for each "load". Add all them up and you will have a better picture of how to size your battery. Also knowing the minimum amount of useful sunlight you get in the Winter will help determine your solar panel wattage.

BY the way, if your solar panel is the 40 watt model from Harbor Fright [sic], it is not particularly good value for the money and if you have plans to expand be sure to look into larger panels which have a lower cost per watt instead of just adding more of the same panels.

OK, new loads list:
10W radio x 3 hours = 30wh
60W mystery x .5 hour (5A x 12V) = 30Wh
30W tablet x 1 hour (?) = 30wh
5W LED x .5 hour = 2.5wh
-----------------------------------------------------
92.5Wh

92.5wh x 2 days (assuming nice weather) x 1.04 temp x 2 (50% DoD) / 12V = 32ah battery
92.5wh / 3.75 sun hours / .67 inefficiencies = 36.8W , with nothing left over to make up for lost days, so don't use anything the next day to give it time to catch up.

So yes, you can barely squeak by if my guesses on the numbers above are right. Again, put a volt meter on the battery to keep an eye on it.

Thanks for replying

I will only use that 5a load on like 1 day every 2 weeks so I think I'm covered.

Many thanks, sam

Thanks everyone

Thank you all, the project is a great success as I finished it this morning and have been playing with it all day. As I said THANKS TO ALL WHO REPLYED!!