Sunday, July 17, 2016

200 watts of Solar Panels Provides How Many Amps a Day?

Solar Panel Amps Delivered Every Hour for 12 Hours

There are many questions people new to Solar Systems ask. The most common is how many watts do I need to run a fan, compressor type refrigerator, laptop, some lighting and also how many batteries will I need?

First you need to find out the watt consumption of each device. A simple call to the manufacturers’ customer service will provide that information. Or buy a Kill-a-Watt meter and measure it yourself.

My System:
It’s a simple 200 watt system, two 100 watt panels, similar to what is being used by many van-dwellers and RVers’. The panels are aligned pretty close to perfect to the sun.

The Results:
For test comparison accuracy I used a 750 watt electric heater for a few minutes at a time to maintain a 12.2 volt battery state of discharge between the hours of logging the results.

The chart below shows the measured amps going to the battery on clear sunny Florida day. The chart shows the hour of day and the delivered amps at that hour.

Time of Day:       AMPS Delivered
7:00am                  0.0                 
8:00am                  1.1
9:00am                  1.9
10:00am                4.2
11:00am                8.8
12:00pm                9.7
1:00pm                  12.0
2:00pm                  10.2
3:00pm                  8.1
4:00pm                  6.0
5:00pm                  4.1
6:00pm                  2.0
7:00pm                  0.0

                   68 amps total delivered for the day


  1. Considering they are fixed and in partial shade 68 is not bad. If my math is right that's around 1000 watts. That's a big increase. With your 1 battery down to 70% your recharged 100% way before noon. You need a 2nd battery.

    1. Gary,
      I did have two batteries until a lightening strike next door fried my controller and my pure sign wave inverter. I thought I cold save the controller but found out the charge set point failed and over charged the batteries then boiled out all the water. Since that happened they would never hold a charge. So I went to a single battery to save some money. I looks like I now could use a second battery.

      I regret throwing out the old #10 wire without checking the ohms resistance. I now suspect that the China made wire was made with inferior copper and could never carry the amps it was supposed to. Another lesson learned about critical components and China.

  2. Mike,

    Great information to know. I'm sure my husband will be testing out solar on the trailer when things slow down here.

    1. If you want to read some excellent information about RV Solar read
      He lives in an RV and uses solar only without a generator. Smart man (Electrical Engineer) with a lot of detailed information and not much nice to say about RV dealer installed solar. He corrects a lot of them.

  3. Mike, you could probably make a living up here installing and maintaining those systems. I see them everywhere, including huge commercial banks of solar cells on the road to Chattanooga and also in a small town in the next county. When I installed my system in 1999, solar cells were largely unheard of up here. The people who built my system came from Spartanburg, South Carolina and I had to pay for their travel time and to put them up in a motel for three days. And then the damn thing didn't work because I had no area on my property that got enough sunlight to keep the batteries charged, it's too steep and too thickly wooded. We put the solar panel next to a parking pad, but in winter it only got about four hours of direct sunlight a day. The generator was activated by the inverter when the batteries got low, and it was on almost all the time if I tried to use the system instead of the grid.

    1. As soon as the wife agrees I want to move the extreme Northeast corner of Georgia. I have friends living there an always liked that area when visiting.

      I really don’t want a job anymore, too old, but have no issues with helping people fix a bad install. In the early days of solar like yourself, setting up a new system was mostly by luck an the lack of skill or even caring was common and forget about an hourly printout of the performance and a solid seasonal projection of amps to be expected. Today it’s better because of experience and competition.

      It’s interesting to me that here in Jacksonville we have a utility owned 100 acre solar farm. The green weenies pushed hard for it now we hear nothing about its operation and money savings to we grid people. I do smell a rat there.

  4. Mike I meant to send this to you a while back. Its a cheap pointer for solar panels. the site is one I scan weekly for ne tips.