PV Gap

Howard Said:

Question about electric current being drawn for a DC motor?

We Answered:

1. Go buy a digital multimeter from Radioshack for about $25 dollars.

2. Plug the test leads into the middle and right sockets by corresponding color (black and red). Turn the dial to the Amp setting. You may have to set the range to measure "mA" (thousandths of an Amp)

3. Connect the batteries to the motor in series so that it is powered up and spinning.

4. Take a reading across the positive and negative terminals of the motor (while it's running). You could also do this anywhere else in the series.

Your measurement should read something like ".123 mA", for example. Just make sure the motor is under the same physical load as when you power it by the solar panel(s).

Jean Said:

What are the items needed for 15 kW on Solar Power?

We Answered:

You need to do a lot of work.

There are contractors that will do it all for you.

Questions you need to answer:

Battery power or sell power to the power company?

How long must you operate when the sun is not out? Probably 20 hours at a minimum, 4 days at a maximum. Be aware that this quickly can bring the number of batteries up to a huge number -- that is the advantage of selling power to the power company, you can buy it back on cloudy days.

If you are not connecting to the utility company, what voltage and voltage purity do you need from the inverter? How are you distributing this power thruout the house? You cannot connect it to the house wiring, you will need a separate set of wires.

Do you have a place to locate the panels facing the sun? Be aware that even the shadow of a branch falling on part of a panel will reduce the output of a panel to almost zero.

If you are connecting to the power company, first see if they allow it, and see if the local and state laws allow it. See if they sell you the equipment, or do they allow you to purchase it, and if the latter, a list of suppliers.

the list goes on...



Batteries (no utility connection):

Batteries can be a major problem, which is why connecting to the utility company is a good deal.

If you want to store enough power for one overnight and one cloudy day, that's 36 hours. At 15kW plus losses that is 648 kW-hrs. A large sealed lead acid battery ($200-300) can store 100 amp-hrs, equivalent to about 1 kW-hr.
That totals 650 batteries, enough to run a submarine! Plus the room to store 650 batteries, plus the heat they generate, plus the electronics to control them. That is for one cloudy day, what about three!

This number of batteries is impractical, so you will need a backup diesel driven generator for those cloudy days.


How about storing power for overnight when the sun is out? still 16 hours in the winter, or 300 batteries. Perhaps you will use less power at night and can scale it down.



Now we get to the number of solar panels. I assume you got the number of 15kW from your power needs. but the panels have to deliver power for your immediate needs AND to charge up the batteries for night time use. With number of hours of sun as low as 6 per day, you will need 3 or 4 times that amount of power so you can store up power for the hours the sun is out.



you see the hugh number of trade-offs and decisions you have to make before you even start.

Delores Said:

will a 15v 52watt solar panel charge four 12c dv 55ah batteries?

We Answered:

>will a 15v 52watt solar panel charge four 12c dv 55ah batteries?

Eventually. But the panel seems way undersized. Some rough calculations assuming you live in a nice sunny desert:

Under ideal conditions the mppt charger should supply about 4 amps into the 12 volt batteries. Lets say 70 hours to do a complete charge. Optimistically lets say you get half of that for 6 hours per day and don't use any power from the batteries.

(140 hours to charge)/(6 hours per day)= 23 days Actually it will be longer because the batteries have a self discharge rate and the charging isn't 100% effecent.

Another way to look at it is from a power standpoint.

(26 watts) X (6 hours per day) = 156 watt-hours per day. So maybe you can run a 26 watt (100 watt equivalent) CFL for 2-3 hours per day plus charge the batteries enough to make up for the self discharge rate of the batteries.

Of course, if you don't live in a nice sunny desert, the situation is worse. And even in nice sunny desert, things will be worse in the winter.

Info from your second question:
--------------------------------------…

Now has three 52 watt panels
Needs 12 volts at 93 amps to run all his equipment 12 hours per day.
671 amp-hr of 12 volt batteries
three 60 watt charge controlers
Located in PA, USA

OK, your equipment needs 1120 watts to operate (12 volts X 93 amps= 1116 watts)

That's 13.4 kWH per day or 402 kWH/month

Under ideal conditions your three 52 watt panels produce 156 watts. Figure 1/2 that under ideal conditions in PA.

1120 watts/ 78 watts = 14.4

In other words, you would need about 15 times as many panels to just directly operate your equipment on at noon on a sunny day in PA! That should give you an idea of how far off your calculations are.

There is a calculator at http://sunelec.com/index.php?main_page=p… for estimating how big a system you need. I punched your numbers in, it came back with a 4444 watt minimum system. Their 4500 watt system includes twenty two 205 watt solar panels. http://sunelec.com/index.php?main_page=4…

>OK here is my idea that i am in to far to back out

For this kind of project, you need professional guidance.

Amanda Said:

what are the specification of a solar panel generating 400w?

We Answered:

Solar panels aren't usually designed at the nameplate size of 400 Watts. The largest nameplate size I've ever seen in the industry is 330 Watts. Build any larger, and it ends up not meeting OSHA regulations for portability.

Wade Said:

What specification of solar panel do I need?

We Answered:

You will need, A battery to store the electricity from the solar panel. The amount of electricity from the panel varies up and down as things such as clouds, position of the sun, etc. reduce the amount of solar rays hitting the panel. The battery stores it all, the ups and downs, and sends it back out at a steady voltage so you can operate your p.c. / appliance.

A minimum of 45 watts solar panel. 60 watts would be preferable. 45 watts will charge a battery in one day under ideal conditions. You turn the panel as the sun moves across the sky, no clouds. 60 watts will charge a battery in one day with out moving and regardless of clouds.

A controler to prevent the electricity from flowing backwards from the battery to the solar panel when the sun goes behind a cloud or sets at night and the charge drops below the voltage of the battery. A good controller will tell you the charge condition of your battery so you know when it is too low to operate your p.c. safely.

And finally an inverter with "True Sine Wave" capability to change the electricity from the battery into usuable power for your PC and other electronics.

Not all inverters produce true sine wave electricity. The electricity has static in it and will make your pc screen jump around and not function as it should. New digital T.V.'s also require true sine wave electricity to operate. Go the extra cost and get the inverter with true sine wave and be happy with the way your p.c. functions.

Figure out how many Watts your p.c. or appliance will draw. and match the Inverter to the need. Do not go too big, as they cost more and consume more of your stored electricity to operate. Save as much electricity as you can. You will be able to operate your p.c. appliance longer.

When not using your p.c., you can operate your T.V. or other low watt appliance.

Willie Said:

70w Solar Panel wattage calculation?

We Answered:

I'm not exactly sure of the answer, but I would ask this question at a solar forum