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Solar Systems: A Practical Approach

Posted by Don Adams

Unless you are looking to get totally "off of the grid" right now, you can instead consider a "phased in" approach to growing your solar power electrical system as you can afford it.

You can do this by building in chucks or sections at a time, BUT making sure that your system will be fully compatible for future growth. It is with this design goal that we advocate use of grid tie inverters. Using grid tie inverters, it does not have to be an ALL OR NOTHING approach to implementing solar power. Just the opposite in fact! The ability to "stack" grid tie inverters allows to add inverters as needed, and add panels as you can afford them.

You can start with a basic system consisting of just a few solar panels and one gird tie inverter sized to grow with you into the next steps. We have selected a 1200watt inverter for our first step.

You can then add panels as you money and time allows to max out the power of this inverter.

By staying "compatiable" we need to be concerned with the operating voltage of the panel and the operating voltage of the inverter, then adding the wattage capabilities of each added section with the final maximum wattage of the inverter.

The typical voltage ranges of the systems would be something like: 12 v, 24 v, 48 v. (With the first two voltages as being the most common systems out there)

Next is the common wattage (power ) ranges.

The panels are typically in the 200 watt range for each panel.

The grid tie inverters typically have power limits (wattage rating) in the following ranges: 300w, 600w, 1200 w, 4800 watt, etc.

So, typically, we will need multiples of solar panels to get to the power level that an inverter can handle. Keep in mind that an inverter can be used at a lower power level, but that it maybe less efficient at low power ranges. BUT this will still allow you to build out a system as you can afford it.

Here's how we implemented our own system and our decisions along the way:

We decided to use a 24 volt system with the solar panels. There were some reasons for this... First, it is still one of the "standard" systems. Second, it is a more efficient mode of operation than running at 12 volts. We can use smaller wires for the lead in's with less (IR) voltage drop. Our panels were originally constructed as 12 volt panels, but by putting two 12 volt panels in series, we got a 24 volt level to run to the grid tie inverter.

The next is using grid tie inverters of the 1200 watt size. Why, you ask? Because it represents a good " building block " size that could allow for easy up sizing to a household system of 6000 to 7000 watts. Using 6 of these inverters stacked would provide for the energy needs of a typical home. Using multiple inverters also spreads out the concern of "single point failure" path of a system. The final consideration is that the cost of these 1200 watt inverters has come down in price to such a level as to be extremely cost effective. It also boils down to the ease of use. The 1200 watt level keeps the unit as a "plug and play" model that can be directly plugged into a wall outlet with out additional concern. These newest 1200 watt inverters also have built in monitoring and seem to be very reliable. A winning combination.

So, here's the "phased in approach" and costs in each step.

(Prices are from readily available sources that are currently available online)

PHASE 1 (starter level)

2 Each 200 watt panels and one 1200 watt inverter: $532 total

PHASE 2 ( add more panels to max out power of inverter)

4 more 200 watt panels: adding $640 to the package [total power now at 1.2KW]

PHASE 3 (add another inverter and 6 more panels as a building block chunk)

6 each 200 watt panels and one 1200 watt inverter: adds another $1,172 per 1200 watt step)
 

PHASE 4 (completed system at either 6KW or 7.2KW) Final costs of $5,860 for the 6KW system or $7,032 for the 7.2KW system (if we go that far...)

Our expected return on investment will be in about 3 years, but the nice thing is that we didn't have to do this all at once and layout the money in one huge chunk.

this was originally posted on earthineer.com, back in 2012 (so, the numbers will likely have changed dramatically)

 

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