# What exactly to buy to run TV.

2 Posts
Sep 15, 2007 06:52 pm
What exactly to buy to run TV.

Hi everyone,
I'm really new to the whole alt energy scene, but I'd like to run my 20" 75w TV off solar.  I figured I'd need a solar panel, controller, inverter, and battery, but I'm not sure how "big" everything should be.  The TV is on maybe 3 hours per day.  If I could get 1 hour of solar-powered TV time a day, that would be awesome.  I live in Toledo, Ohio.

Thanks!

184 Posts
Sep 18, 2007 02:14 pm
Re: What exactly to buy to run TV.

Here's what I would suggest.  But these are only rough calculations:

1 - 75 Watt (or bigger) solar panel
1 - 100ah Marine Deep Cycle battery
1 - 125 Watt (continuous power) pure sinewave inverter.
1 - 10a (or bigger) charge controller

You need 75 Watts times 3 hours, or 225 Watt/Hours.

If you get 4 hours of sunlight each day, you'll get 4 times 75 = 300 Watt/Hours.

Since you don't want to discharge your battery more than 50%, you have 50ah of usable stored energy.  The inverter will draw just under 10a (DC) to power the 75 watt load.  Therefore:  50 divided by 10 equals 5 hours of TV viewing, but allowing for system inefficiencies, expect 4 hours at the most.

Hope this helps, John

578 Posts
Sep 18, 2007 04:23 pm
Re: What exactly to buy to run TV.

i agree with john, however we tend to be more conservative.
calculations seem to make sense.

75w x 3hrs per day usage = 225 watt-hours

i would take this number by 1.3 to 1.5 for inefficiencies. = 338 watt hours of load (corrected)

now using stc numbers

338 / 2.8 sun hours per day = 121 watts of rated pv power
(2.8 is worst possible average sun hours for toledo)

10 or 12a charge controller minimum depending on module selection.

1 or 2 group 31 batteries, 1 will give 2hrs watch time, 2 will do 4.

so for fun, john is on the money and the math is easy to trace, if this MUST work to meet your demands, the sizing would be more conservative as you see in the numbers above.

you can find info like this including sun-hour charts and walkthroughs of system design like this in this book.  we use it to train our staff as well.

http://store.altenergystore.com/Books-Workshops-Videos/Solar/Photovoltaics-Design-Install-Manual/p481/

james Alt-E staff

AltE
"Making Renewable Do-able"
http://www.altEstore.com/

Tel: 877.878.4060 x107  or +1.978.562.5858 x107
Fax: 877.242.6718  or +1.978.562.5854

2 Posts
Sep 18, 2007 06:40 pm
Re: What exactly to buy to run TV.

Awesome, thank you!  I might end up buying a 40w to start out with and to just get into the hobby, but I'll see what I can do.  Thanks again!

578 Posts
Sep 18, 2007 06:52 pm
Re: What exactly to buy to run TV.

great, be careful, you can get hooked like the rest of us.

for starter systems, charge controllers with display can give very useful info.  also a basic battery monitor can provide good load management info.

here are two of my favs for beginning small systems

http://store.altenergystore.com/Charge-Controllers/Solar-Charge-Controllers/Pwm-Type-Solar-Charge-Contollers/Morningstar-Charge-Controllers-Pwm/Morningstar-Prostar-Ps-15M-15A-1224V-Charge-Cntrlr/p788/

and
http://store.altenergystore.com/Meters-Communications-Site-Analysis/Meters-Battery-Monitors/Ammeters-Voltmeters-Battery-Monitors/BZ-Lpm10-U-122448V-Batt-Voltage-Monitor/p290/

good luck and be careful, call us if you need help

james Alt-E staff

AltE
"Making Renewable Do-able"
http://www.altEstore.com/

Tel: 877.878.4060 x107  or +1.978.562.5858 x107
Fax: 877.242.6718  or +1.978.562.5854

184 Posts
Sep 18, 2007 09:30 pm
Re: What exactly to buy to run TV.

I like the idea of adding a meter to the charge controller, or getting a battery monitor.  I use a high-quality digital voltmeter to keep close track of my battery condition.

The point is; it's important to have some way of monitoring your batteries, since they can easily be damaged if you don't.

John

8 Posts
Nov 2, 2007 05:25 am
Re: What exactly to buy to run TV.

Hi John,

Good day. I have further queries on the below calculation I hope you and other members can help enlighten please (despite being a old post).

First: How did you work out that the inverter will draw just under 10A to power the 75W load?

Is it from the inverter specification (if so, from a manufacturer leaflet, what wud this figure be termed as)

OR is this based on the 10A controller? If so, does it mean a 20A will draw 20A to power....

To concrete my understanding. Pls help verify below:

I have one 80W panel- assuming 5hr daily avg. sunshine = 400wh.
I have a 100Ah deep cycle battery, with 300W inverter and 10A controller. On the load side, I have 2x10W energy saving bulb to run for 5hr each and a 1x50W table fan for 3hr (total= 250Wh)

Q1) Since supply > load demand, is the system ok?
Q2) assuming 50% discharge cycle, how do I work out many day it will continue to work on cloudy day?

A million thanks

Here's what I would suggest.  But these are only rough calculations:

1 - 75 Watt (or bigger) solar panel
1 - 100ah Marine Deep Cycle battery
1 - 125 Watt (continuous power) pure sinewave inverter.
1 - 10a (or bigger) charge controller

You need 75 Watts times 3 hours, or 225 Watt/Hours.

If you get 4 hours of sunlight each day, you'll get 4 times 75 = 300 Watt/Hours.

Since you don't want to discharge your battery more than 50%, you have 50ah of usable stored energy.  The inverter will draw just under 10a (DC) to power the 75 watt load.  Therefore:  50 divided by 10 equals 5 hours of TV viewing, but allowing for system inefficiencies, expect 4 hours at the most.

184 Posts
Nov 2, 2007 09:39 am
Re: What exactly to buy to run TV.

Vincent,

It looks like your math is correct, except that you didn’t take into consideration system inefficiencies.  To simplify my answer to your questions, consider an off-grid system with batteries to be only about 65% efficient overall.

Concerning the inverter input current that flows to provide 75-watts out, use the formula:  Power = Volts times Amps, and then consider inverter inefficiency, or:
10 (amps) times 12 (volts) times 0.65 = 78-watts.

To compensate for cloudy days, you’ll need more panels and batteries (obviously), and you can use that 65% efficiency factor to do your math.

I hope this helps.

John

8 Posts
Nov 3, 2007 12:47 pm
Re: What exactly to buy to run TV.

John,

Thanks for yr reply. I sorta understand but still not postively sure. Are the 10A x 12V specifications of the inverter?

If you have some time to spare, can you help answer the example which I quoted earlier to help me understand.

If this is taking too much space and airtime on Alt-E site, you can perhaps send reply to my email: kmv_chow @ yahoo.co.uk
Cheers!

Vincent
4x4 and Solar

184 Posts
Nov 3, 2007 09:30 pm
Re: What exactly to buy to run TV.

No problem Vincent;

You choose an inverter that can handle all of the loads you intend to connect at the same time.  If the most you'll run is a 15-watt light, and a 75-watt tv, and a 25-watt fan, you'll need an inverter that can supply 115-watts (as an example).  Keep in mind that some motors and other devices have high starting current, so your inverter needs to be able to handle that as well.  But a 250-watt inverter would be a good choice for the example I've stated here, since it exceeds your 115-watt needs.

If you'll play around with the power formula I provided in a previous message, you'll notice something interesting:

Power (in watts) = Volts X Amps

120 Watts = 12 volts X 10 amps
120 Watts = 120 volts X 1 amp

It follows then that to power a 120-watt, 120 volt, light bulb you'll have about 1 amp (at 120-volts) at the output of the inverter, but 10-amps (at 12-volts) going into the inverter.

This is just an example, and doesn't take into consideration inverter inefficiency.

I hope this helps to clear things up.

John

8 Posts
Nov 4, 2007 01:15 am
Re: What exactly to buy to run TV.

Hmm, John....thanks again.

Can you help answer my Q2 on how many days my model will continue working on cloudy days?

Thanks a zillions

vincent
4x4 and Solar

184 Posts
Nov 4, 2007 02:11 pm
Re: What exactly to buy to run TV.

You have 80-watts of PV and expect 5 hours of sunlight each day.  80 X 5 = 400wh X 0.65 (for system losses) = 260wh.  At the load you've specified, you barely have enough power for one day.  If you doubled PV and batteries, you'll have the capacity to compensate for one full day of clouds.

Having said that, I would also add that I wouldn't want to cut it that close on batteries.  Chronic undercharging, or leaving batteries discharged for more than a day or two, will shorten their life.

If you want to become an off-grid "expert", study batteries.  The rest is easy.

John

578 Posts
Nov 5, 2007 11:22 am
Re: What exactly to buy to run TV.

vincent,

dont be bashful.  i answer these questions 10 times a day.  for every person that writes in like yourself, there are dozens learning from your question.  there is no need to take questions like these offline.  you certainly can, but we want these exchanges out in the open, so you as well as others can benefit.  a community of active participants and enthusiasts benefits us all; and the questions that are submitted give our staff ideas on what new stuff to add to the learn section when we are not going crazy answering hundreds of calls and emails.

good luck with your project, and feel free to continue to use us as a resource.

james  Alt-E staff

AltE
"Making Renewable Do-able"
http://www.altEstore.com/

Tel: 877.878.4060 x107  or +1.978.562.5858 x107
Fax: 877.242.6718  or +1.978.562.5854

Disclaimer and Disclosure

The Alternative Energy Store, Inc reserves the right, within its sole discretion, to refuse or delete any posting or portion thereof, or terminate or block the access to this forum.

The opinions and statements posted on this forum are the opinions and statements of the person posting same, and do not constitute the opinion or act of the Alternative Energy Store, Inc (AltE). The Alternative Energy Store, Inc does not endorse or subscribe to any particular posting. No posting shall be construed as the act or opinion of the Alternative Energy Store, Inc.

## Share

Click on an icon to share! If you don't see the method you want, hover over the orange "+".