ECN Forum Forums General Topics of the Trade General Discussion Area "wiring solar panels for residential"

I once gave a tree-hugger some advice (which they were upset about) to take what they were willing to pay for the system and maintenance and buy stock in the electric company.

Then you can pay the electric bill with the dividends, the power ends up costing you almost nothing, and there's nothing to maintain...

The real secret of these people's success is switching to low power everything and consciencously saving power. If they just did that they make the greatest gain with almost zero out of pocket expense.

The manual from Sandia National Labs is an excellent reference.

If the solar array is going on the roof of the dwelling, it will need GfCI protection. Also the roof must be able to support the weight plus if it ever snows it has to support that weight too.

Aiming, tilt, and shadowing on the arrays from surrounding obstructions are just a few things you need to know need to know and understand prior doing the work. What type of inverter, charge controller are you planning to wire? Although it may not be a big as a problem in NC as it is here in Alaska is the open voltage (Voc) of the array is an issue. There are charge controllers out there where you can wire the array at a higher voltage which has many benefits like voltage drop. In colder climates the open voltage can be a problem.

I presume (never assume) that there are batteries involved. It is essential to understand the different types and charging characteristics. Grounding a system can cause heartburn. It is a matter to understand what you are installing before more specifics can be explained.

The problem with changing over to "green" power is the average home is not wired in a manner where alternative energy is economically viable. The bigger the system you need, exponentially the cost goes up and it is the home owner's responsibility to maintain it. Reducing your electrical needs is good start. Up here there are hundreds of folks living remotely that rely on these systems for all of their lights and power. They are tickled pink with their systems. Sizing the system takes a sharp pencil and whole lot of knowledge. It is much easier to design a building power to meet the power supply instead of sizing the system to meet the building needs.

It is a growing industry and it behooves sparkies not to jump on the band wagon but it you get in it and it get deep really quick, you will be in deep doo-doo. I recommend professional training and certification. I know of only one certification. All I know about is that it is the only one I have come across and sound like a good program. I have no idea what weight it carries being certified by them. If anyone has any insight on this, please share.

http://www.nabcep.org/

The long-running saga in this thread shows how solar sometimes comes into its own simply due to circumstances making grid-power impractical (or unaffordable).

It's certainly a juggling game for the owner of that property to make solar work reasonably given his limited resources. From memory, at the moment he has about 300W of PV panels plus a wind turbine which is nominally 20A peak output, feeding into a battery bank of about 600 to 700Ah and an inverter to convert to 240V 50Hz A.C. for feeding the mobile home. Consumption in the latter is mostly compact low-energy lamps, plus radio, TV, computer/phone chargers, etc. Heating and cooking is LP gas.

To supplement the solar/wind power, he has a generator (see here) which can be cranked up as needed to give a boost via a 60A fast charger and make best use of the fuel to run a washer/dryer at the same time (if he ever gets around to upgrading the feeder cable, that is).

There's also a changeover switch to put the whole mobile home onto the generator instead of the inverter while it's running.

I'm surprised that you're seeing this. As a first-order approximation, the cost should go up linearly with the load, not exponentially. There is no exponential term at all that is involved with the load-cost relationship.

Let me clearify my comment. As a system gets bigger, more bells and whistles you will need to make it all work together. Also more space and better structual support will be needed.

I just ran some numbers with info from a reputable company's info on packaged systems. Their smaller systems run about $6200 per KW for a 1.8kW system. At the larger end, they are over $10,300 per Kw for a 5.1 kW system. I am currently working on a project that puts the price at about $10,000 per kW. Keep in mind this numbers covers wages of professional trades men and does not nessasary reflect the cost of DYI'ers but the increase in material cost still holds true.

For example, the bigger any electrical system gets, the bigger the capacity and components must be. For example if you need to double the capacity of you wire due to amps, you actually have to more the double the wire size to achieve the capacity. A #6 wire at rated 60 degrees is 26240 kcmils in size and rated at 55 amps. If you double the wire size, that would be a #3 which is 52620 kcmils but is rated at only 85 amps. If you needed the to double the amperage, you would need to use #2 wire which is 66360 kcmils or 2.5 times bigger then #6. Cost wise, a #6 to #2 is around 223% of an increase.

The inital costs can be prohibitive. With savings in operation cost from instead of burning fossil fuels are big savings plus there is less impact on the enviornment which is an added benefit. If connect to the grid, utitilites buy surplus power and there are many tax insentives out there for even more savings plus a good system adds value to the property. All these combined can can offset the high constuction costs.