My solar panel plan.

December 18th, 2007, 12:56 pm Josh Houghtelin Home, Projects

Zippy and I are building a pole barn next summer so I’ve been conjuring up a few ideas to help make the building a little more Eco-friendly while helping us save a couple dollars in the long run. I want to utilize solar power in the barn but the initial investment to go completely solar is a out of my reach so I’m going to meet Mr. Solar on the middle grounds.

I want to provide all of the electricity used to light the barn from solar panels. This will push us to buy better, more efficient light bulbs that will last longer, be more green & possibly save a few dollars a hundred years from now. It’s a small goal but I think it will be a fantastic way to get into solar power. I’m building the road map to achieve this and purchasing the gear now so when the barn is being built we can integrate everything & know it will work.

First I need to determine how much light we really use. Right now, being winter, we use more light so It won’t hurt to base my estimations off of our current light use. I want to estimate high. We tend to start using lights at 5:30pm and run them until we go to sleep which is generally around 11:pm. We also use about an hour and a half of light in the morning. We use roughly 3 light bulbs in the main room for 5.5 hours an evening and 1.5 hours in the morning. That’s 7 hours of light on 3 main room bulbs. Just to over-estimate I will say we use three bathroom lights and one spare bedroom light for 3 hours a day. That is 4 light bulbs for 3 hours a day. Based on our normal light consumption, I am over-estimating these figures by a lot.

4 x 3 = 12
7 x 3 = 21
21 + 12 = 33 light bulb hours a day.

Currently we use AC powered CF light bulbs that consume ~15 Watts and produce ~900 lumens. I want to switch to DC powered LED light bulbs so this is a flaw in my plan but I’m going to just go with the CF bulb watt usage to compensate. the LED lights should consume far less (although they produce less Lumen). Anyway, on with the math.

33 x 15 = 495 Watt hours per day to light our house.

I believe grid electricity currently costs around 10 cents per kilowatt hour. That means, at our current rate, it costs me 50 cents a day to use our lights. If we want to produce this electricity with solar pannels we must be prepared to go a few days without power. Lets shoot for four days. The norm seems to be three days but this is Missery so lets shoot high.

495 x 4 = 1980 WattHours

I willl need to have 1,980 WattHours of energy available at any given time for this system to work well. We will need this much energy stored in batteries and unless I want to murder batteries by draining them completely, I will need to actually have a lot more then that. To save these big DC batteries I don’t want to drain them over half way unless I have to.

1980 x 2 = 3960 WattHours

In order to avoid killing my batteries I will need to have 3960 WattHours of storage in them so my 4 day lightless escipade will only drain them down to 50%. Batteries run on AmpHours (which I don’t fully understand yet) and to determine how many AmpHours I need I’ve read that you take your WattHours and divide that by your Battery Voltage. I will be using standard 12 volt batteries.

3960 / 12 = 330 AmpHours

Now I have determined the necessary AmpHours. The standard 12 volt battery used in these systems retains 105 amp hours which brings us to our next equation.

330 / 105 = 3.1428571 Batteries necessary for this operation.

I need 4 standard 12 volt batteries retaining 105 AmpHours each to safely operate. A good solid battery costs roughly $130. Here is a good priced 92 Amp-Hour AGM battery.

130 x 4 = $520 is necessary for capitol to purchase batteries.

Now that I know how many batteries I will need & the cost involved, I will figure how many solar panels I need. I determined earlier that I use about 495 WattHours a day running the lights in our house. I would need a solar panel setup that will produce that plus a little more to charge the batteries if they need it. I get a little lost here seeing as I don’t think you should rely on the max output of a solar panel to calculate how much it will truly produce. I will, for this instance, use the maximum power for the calculations. Where I live we get about 5 hours of good light every day.

495 / 5 = 99 Watts Per Hour…

Lets round that to 100. I must generate 100 watts per sunlight hour to operate this system. I may purchase one 100Watt panel or two 50 Watt panels. Since capitol isn’t jumping out of my pockets I will end up buying three 40 to 60 Watt panels. Either way, if I need to produce 100 watts per sunlight hour we can estimate the cost involved. Currently solar panels sell for roughly $5 a watt.
Here is a $350 80 Watt Solar Panel. $4.375/Watt

100 * 5 = $500 for Solar Panels.

520 + 500 = $1,200 necessary Capitol for Batteries & Solar panels.

That is a good solid estimate to purchase the equipment necessary to get off the ground using solar energy. I didn’t figure in the cost of wires, cabling, light bulbs, or any testing & monitoring equipment but it’s enough to give me a good idea. Please, if you see a serious flaw in all of this, let me know! I foresee buying one solar panel and one battery after we get back from our holiday travels. If we only have to invest a little over $1,200 to disconnect grid electricity to all our light bulbs then I’m 100% positive we will integrate this into our barn this summer. The major problem with getting into solar electricity seems to be the investment capitol. If I can do this intelligently and purchase equipment in affordable chunks then I’m on the bandwagon. As I see it this is affordable and we can do it. Once the infrastructure is in place it’s just a matter of buying more batteries & panels.

I’m excited about it and hope to have it ready and running before we build the barn. Solar in small steps seems to be the way to go. If we can do it with the lights in our house we can progressively build up to more and more items. Also, if there is no other reason to do so, It’s hard to not want to get into solar energy when you realize that solar energy gives life to everything on this planet, not just my ipod.

Here is a $600 DIY kit I ran across. Or you can go ahead and buy a complete on, off, or even tied grid at the alternative energy store.