PV Gap

Micheal Said:

Are there any good active solar websites and if so where are they?

We Answered:

You need to size your wiring according to the Universal electrical code. They recently adopted low voltage home energy systems into the code for a more standardized means of inspections for safety considerations. What that means for wire sizing is the amount of current allowed for each wire gauge should be considered when determining the connection between the solar array and the batteries. The current rating for a wire gauge is based on thermal rise of the wire. The current rating is independent of the potential. In other words a wire suitable for a maximum current rating in a 120 Volt application has the same maximum current capacity at 12 volts, even though it is 1/10 the wattage.

If you are using 150 Watt panels, I would run the drops as 10 gauge wire. Mainly due to less of a voltage drop between point A and point B. I would also locate the charge controllers near the battery array. I would use dedicated controllers for each panel in the event of a failure of a component. (commercialy produced controllers are not worth what they charge for them.)

The thing to remember about low voltage systems is that a power rating (in Watts) has meaning. 120 Watts on 120 Volts AC is 1 amp. At 12 volts, it is 10 amps. As that applies to inverters- you want the inverter as close to the battery bank as possible due to the current draw by the inverter, and the distance run to the appliance has less effective voltage drop at 120VAC than at 12 VDC

As Wattage applies to the wiring, it is only the amperage portion of the Wattage rating that counts.

So if you sized circuits for 16 gauge wire, on low voltage based on the 120 VAC guidelines, that limits you to about 15 Amps for a current rating for that circuit, but increasing the wire size keeping that same load as your calculation is not a bad idea as the resistance of the wire itself decreases as diameter increases. This also applies to 120VAC installations as well.

If you install the correct transfer equipment to isolate from the grid, you can use your conventional 120 Volt appliances as always, it is only that the current you are drawing through the house originated with the batteries instead of the grid. The only time synchronization would be needed is if you plan on selling surplus energy back to the power company. Otherwise, once you isolate from the grid, no synchronization is needed.

If you plan to install some parallel low voltage power runs, using LED lighting simplifies a lot because you no longer need to use a voltage dropping power supply- you can run the inherent low voltage devices near the range they were designed for. You can also get low voltage appliances, like toasters, coffee pots, microwave ovens etc. most are intended for truckers or RV use, but will work fine in the home as well. I have a small "all in one" stereo system that was rated at 45 Watts dissipation at 120 VAC, after the conversion to 12 volt operation (with everything fully functional from remote to turntable.), it had a calculated watted derived from measured current draw and assumed 12 volts at the battery at about 15 Watts dissipation. yes, the power supply is that inefficient.

As for specific sites that you seek, there are few. Some of the wire sizing and load factors will be part of some aspects I will be addressing in my blog as it develops.
http://altenciruits.wordpress.com

Ther are some sites out there most are poorly written because they don't even come close to a code compliant installation- which is crucial for selling a home or getting insurance. And all code means is you pull the permit, and do the rough in, get it inspected to make sure your installation meets the minimum requirements and then proceed in steps. What is contained in the code is the minimum accepted. If you use 10 gauge where 16 was adequate- there is no problem. There are no good magazines on the subject. What few there are fail to fundamentally understand a few principles, so they end up reading like a sales brochure that you paid good money for (Homepower) and Mother Earth News), or they do things akin to building a car starting with the radio knob. The one website that has some information, but you have to pick through a lot is http://www.builditsolar.com

Constance Said:

Please help me with the math question?

We Answered:

Okay, first find out the amount of surface area that it takes to power the helios prototype at 18%. They give you everything there. You have the surface area of a single cell, 1.25 x 2.75 and you know there are 65000 of them.

So... 1.25 * 2.75* 65000 = 223 437.5 square inches.

Now. That is the surface area if each cell is only 18% effective at collecting solar energy. Now, if the cells were 12% effective you need more to make up for the loss of power due to ineffiecency.

So let's suppose that each cell absorbs 1 unit of energy at 100%. And lets find out how much that is. But the cells are only .18 (18%) effective. So we get 65000 * .18 and we find out the total units of energy.

65000 * 0.18 = 11700

So, this is how much we need to power the Helios Prototype. Okay, now we replace the cells with 12% effecient cells. So, we need 11700 units and we need to divide that by 0.12 to find out how many cells are needed.

11700 / 0.12 = 97500 cells.

Okay, we now know the amount of cells, we can then calculate the amount of surface area.

1.25 * 2.75 * 97500 = 335 156.25 square inches.

That is the answer, it only takes a lot of words to explain.