Any recommendations for a vendor? I'm planning to solar power my shed. At first I'll be running a light or (two, probably LED), a small radio and a box fan. I won't use them often, and only need them for an hour or two at a time.
If it goes well, I'd may consider running some landscape lighting off it.
What happens when I run out of juice? Obviously things will stop running, but will it damage any of the hardware?
I haven't bought any components yet, only researched off an on for a few years, so take my advice with a grain of salt.
If you have a local supplier of solar system components you might want to check with them. Solar panels are bulky and batteries are heavy, so shipping could be troublesome. For example, about 100 miles away from me is Northern Arizona Wind and Sun (
http://www.solar-electric.com/), and if I were constructing a large solar system I'd probably buy parts from them.
For a small system, you can buy all the parts off of Amazon. Everything here has free shipping with Amazon Prime; you'll have to check shipping cost if you don't.
Main components:
100 watt solar panel, $122 (out of stock for now, maybe check back later)
http://amzn.com/B00HTSVDAM 100 watt solar panel, $140 (this one is actually in stock)
http://amzn.com/B00DCCOSV0 2X 35Ah deep cycle AGM batteries, $120
http://amzn.com/B007Q2CS46 A basic charge controller, $32
http://amzn.com/B00MB0N8K6 Inverter, $80 including cables and fuse, larger than you need
http://amzn.com/B00T564EIY Other things you'll need:
wire to connect solar panels to charge controller, $10
http://amzn.com/B00IFWKBIG fuse and fuse holder for batteries, around $15, search for "ANL fuse" for one kind
if using more than 1 battery, wires to connect batteries together, $7
http://amzn.com/B003RCJB62 or
http://amzn.com/B00JGJGIKW wire to connect batteries to inverter (may be included with inverter depending on what you buy)
The AGM batteries are not ideal, but they should work for a small system. Large systems more often use big flooded batteries which you have to top off with distilled water occasionally.
The LED bulbs and a small radio will take very little power, they will be no problem. The box fan will use a lot more electricity and require a much larger inverter. You'll want to measure the power draw of the fan to see what size inverter you need. You can use a watt meter like this one ($18
http://amzn.com/B00009MDBU ); some libraries also loan these out. If you get a 12 V fan like this one
http://amzn.com/B0000AY2Z6 then it doesn't have any impact on the inverter, only on what size battery you need.
The landscape lighting I'm not sure about. Is this LED or CFL bulbs? How many hours does it have to run for?
This might be a good opportunity to go with an all 12 V system and skip the inverter entirely. You'd need a 12 V box fan, 12 V LED lights, and possibly an adapter for your radio depending on what voltage it's expecting.
The inverter will automatically shut off when the battery is drained, so it will not cause any damage. Many charge controllers have a "load" connection for running 12V things which will also shut off when the battery gets low. However, lead acid batteries do not like to be deeply discharged. You can run them to dead a few times, but this will drastically shorten their life. It's better to size the system large enough that you never have to go below 50% on the batteries.
I have to make some assumptions here, so you'll want to re-work this with your own numbers, but this is how you calculate the requirements for solar panels, batteries, and an inverter. For each thing you're running, you need to know the continuous power required, peak power required, and total usage per day:
2 LED lights, 8W actual power use, running for 4 hours each day:
2 * 8 W = 16 watts continuous usage
2 * 8 W = 16 watts peak usage
2 * 16 W * 4 hours = 64 Wh/day usage
1 box fan, 100 watts on high, maybe 1000 watts startup current, run for 2 hours each day:
100 watts continuous usage
1000 watts peak usage (motors require a high current for a couple seconds when they start up.)
100 W * 2 hours = 200 Wh/day usage
1 small radio, used 4 hours per day, 2 watts:
2 watts continuous usage
2 watts peak usage
2W * 4 hours = 8 Wh/day
6 LED landscape lights, 1W each, running for 8 hours each day:
6 * 1W = 6 watts continuous usage
6 * 1W = 6 watts peak usage
6W * 8 hours = 48 Wh/day
Adding everything together, your total power requirements are:
124 watts continuous
1024 watts peak
320 Wh/day
You can see that the fan is the biggest power hog here!
Sizing solar panels: You first need to know how much sunlight you get per day. Check a solar insolation map (
http://www.nrel.gov/gis/solar.html) or table (
http://www.eventhorizonsolar.com/insolation-window.html) DFW gets lots of sun, the equivalent of 5.4 hours direct sunlight on average each day, 6.0 in the summer, 4.8 in the winter. Let's go with the 5.4 average and we'll over-size the solar panels a little.
According to what we calculated above, your lights, fan, and radio will need 320 Wh/day. You have 5.4 hours of full sun on average in your location, so 320 Wh / 5.4 hours = 59 watts of solar panels required. This is practically nothing! Let's say you just need a single 100 watt solar panel, and you'll have a little extra capacity on average.
Sizing battery: this is also based on the 320 Wh/day number. Let's assume that all your power usage is at night. Watts = Volts * Amps, so 320 Wh/day with a 12 V battery is 27 Ah/day. Lead acid batteries don't like to be discharged below 50%, so 27 Ah * 2 = 54 Ah of batteries. This is assuming that you can recharge the batteries each day; if you want to store power over multiple days to account to cloudy weather you may want larger batteries. Amazon has 35 Ah batteries for a good price, so let's plan on 2 of those for 70 Ah in total.
Sizing inverter: this depends on the continuous and peak power requirements. You need 124 watts continuous, maybe as much as 1024 peak, mostly because of that box fan. You probably want a 500 or 600 watt inverter to handle the startup requirements of the fan. I'm going to be lazy and link a 1100 watt one because it includes cables and a fuse, but it's larger than you need.
Another thing to consider is that some AC motors do not like running on the cheaper modified sine wave inverters. They prefer the expensive true sine wave inverters. You may want to consider a 12V fan if it will work for you.
So for your shed power, this should be all you need (see Amazon links earlier in post):
$140 1x 100W solar panel
$120 2x 35Ah AGM batteries
$32 charge controller
$80 1100 watt inverter, includes cables and fuse
$10 MC4 extension cable, cut in half to wire solar panel to charge controller
$7 wire to connect two batteries together
total: $389
If you go for an all 12V system with a lower power fan and maybe run the lights for less time than I estimated, one battery with a 50W panel would probably be OK (all components still sourced from Amazon):
$90 50W solar panel
$63 35Ah AGM battery
$16 cheaper charge controller
$10 MC4 extension cable, cut in half to wire solar panel to charge controller
$15 fuse holder and fuse
$??? wiring and fuses to connect each 12V DC device
total: $194, not including wiring for 12V devices, not including DC box fan
As an alternative, Harbor Freight has a kit which includes 45W of panels, a bracket to hold them, a charge controller, and 2 LED lights. I bought one of these a few years ago, but haven't looked at them recently because they're a very poor value in terms of price per watt. However, they do include a few other things you would need like the charge controller, 12V LED lights and the mounting bracket.
$152 Harbor Freight 45W kit including panel, charge controller, bracket, and 2 LED lights ($190, use ubiquitous 20% coupon to get down to $152.)
$63 35Ah AGM battery from Amazon
total: $215, not including DC box fan
This post is a little disorganized since I'm writing it in little pieces during breaks at work. I'll stop back later and answer any questions.
