Just for your enlightenment. Version 1.0 is located here.

My Solar landscape Lights V 1.0

Since my first attempt has gone very well. I thought I would consider another venture. I would like to keep the cost to around $500.

So how many lights am I going to light up? Well, I was at my local home depot and picked up a cheap Malibu light kit for only $8. It was an open box sale and appeared to have everything in it. (Actually, I purchased it for the light bulbs!) They want $5 for four replacement bulbs! The kit had 20 in it.) I also have a few light from another similar kit that I did not use. AND, I have the original light in the front of the house. In other words, I could have 50 lights. I will plan for about 40.

If I run my lights for 3 hours in the evening and I hour in the morning. (4 Hours)
The light bulbs use 0.5W of 12VDC. This would be …. 40 bulbs x 0.5W x 4 hours = 80 Watt Hours
80 Watt hours is a good amount of power for lights.

Solar panel size.

Since most controller have selectable nightlight controls, I will use 3 hours of solar insolation. This means in the winter I need to output less number of hours of light and in the summer I can output more number of hours of light.

Panel size would be…. 80 Watt hours / 3 hours = 27 Watts (Usable Power)

What is usable power? If you look at a 30W 12V solar panel power specs you will note that current short circuit is 1.80A and voltage is zero. The panel produces maximum power at 18V with a current of 1.67 Amps. Power = Amps x Voltage. (30W) If you use a regular solar controller, all it really does is connect the solar panel to the battery. This means you are down around 13V. 13V x 1.8 Amps = 23 Watts. You lose a potential 7 Watts. Introduce the MPPT (Maximum Power Point Tracking) Solar controller. They cost more put will get you back most of the 7 Watts you lost.

With the calculations from above I will need a sightly larger then 30Watt panel if I use a regular solar controller.

Battery Pack Size

A good rule of thumb has always been 5 days storage. Another good rule of thumb is never go below 50% of full charge. If I use 80 Watt hours a day. And I need to add about 20% for battery inefficiencies and wire losses… 80 Whrs / 12V = 7 Amp hours. 7 amp hours /50% X 120% x 5 days = 60amp hours.

Now I know what size of components to buy. All I need to do is figure out what to get. The current debate has been a regular controller vs. a MPPT type. I and thinking I will go with the same one I have in the version 1.0 of the landscape lights. It works very well.

To be continued! (component section and justification)