1 Posts
Apr 14, 2004 10:09 pm

we are about to build our dream house 0ff the grid need an affordable solar setup to run night time lights can anyone help please
May 9, 2004 03:40 am

What kind of help do you need? Sizing the system? Financial? What?
May 9, 2004 04:50 am
Re: help

>need an
>affordable solar setup to run night
>time lights
Affordable thats kind of a broad term in photovoltaics because of; 1-geographical location, 2-watt hours needed, 3-amount of autonomy, 4-availible funds. 1- location, a photovoltaic module with a high working voltage such as 18 volts will charge a battery bank better in a tropical enviroment better than a 16 volt module. The colder a PV cell is the higher it can drive the battery voltage if the batteries dont get too cold. In northern areas the sun shines fewer hours during the winter days than in the summer. All of these things are figured into sizing a system. 2- watthours, this ones easy if only lights are used. just add up the wattage of each bulb and mutiply by the hours the bukb is expected to be used. But remember if in a northern area short winter days mean less power in and more out which leads us to 3- autonomy, sizing the battery bank so that the power used in one night is 20% or less of the total amp hours availible from a fully charged battery bank, and sizing the array to replace that 20% or more the very next sunny day should give you 2 to 3 days of light even if the sun doesnt shine at all. 4- funds, I'll leave that one to you.
Lets asume that you live in central USA. If the PV array can sit in full, unshaded sunlight from 8:00 am to 4:00 pm in the winter months and is aimed perpendicular to the sun at noon time, this should yeild around 3 hours of equivilent full rated charge. So 2 - 100 watt PV module would yeild 600 watt hours. If your house has 6 - 50 watt incandecent bulbs; 2 of them burn for 1 hour, 3 of them for 3 hours, and 1 for 6 hours this would all add up to 850 watt hours. So you see there is a deficet of 250 watt hours. Either more modules or less lights is needed. But there is the 20% of capacity of the battery to consider as well. Going with the figure of 850 watt hours, 850 is 20% of 4,250, now to turn that into amp hours just divide by a nominal voltage; 12,24,48.
I'll assume 12 volts.
4,250/12=354 amp hours (at the 20 hour rate) total battery bank capacity at 12 volts nominal.
850/12=71 amp hours is needed for lights.
So to replace just this amount in one sunny day divide 71 by 3 which equals 24. In this example you would need a PV array the was rated for at least 24 amps at 12 volts and a battery with at least 354 amp hours (at the 20 hour rate). Whew! This doesnt figure in; charge control, module mounts, disconects and fuses, wire, conduit, battery monitors, battery clamps, battery box, shipping, taxes. It pretty much starts with how much power do you need and from there its in the math utilizing Ohms law, Oh! a thick wallet:)
Thomas Schmidt, North Carolina, USA

May 9, 2004 05:46 am

For the example I gave above this is what I might suggest for part of the system.
6-BP-3160, PV modules - $3,686.40
2-Surette 6-CS21PS batteries - $1,165.90
1-Outback MX60 charge controller - $513.00
1-Bogart TM2020 monitor - $135.00
For a total of $5500.30
This system would use 24 volt modules too charge a 12 battery with an MX60 controller. This is so you can utilize the more readily available 12 volt lights and electric gizmo's. The battery storage I increased by about 50% and the controller isnt max out. This is so in the future more power can be made and utilized. The monitor is important because it can show just how power is made and used which can help you to understand how to use power better for greater satisfation. But there are some many other configurations that could applied to the example above. If you ask 10 different people you might get as many as 10 different systems. A lot of the supporting electrical stuff; wire, fused disconects, and so forth can be purchased locally. I made an array mount out of; old aluminum storm door rails, a couple of heavy duty door hinges, some old steel bed frame angle, and stainless steel bolts all for about $15.00. It holds 6-Solrex MSX77 PV modules and has lasted through the past 5 huricane seasons here in North Carolina. Thomas Schmidt

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