PV Gap

Roland Said:

I want to provide solar power and heated water to a 1500sqft home for a family of 4, what do I need?

We Answered:

You'll need to determine how much electricity you will ever need. Will you expect to do some heating? If you're using electric then you'll need to factor that into the size as well. Also, if you're not planning on connecting to the electric grid, then you'll need to determine how much energy you'll need for several cloudy days in a row - and size your system so that you can make that much energy in one sunny day.

Once you have the size of the system you'll need, you can figure on paying between $7 and $10 per watt for the solar system - not including batteries. The components you'll need will be solar electric panels and connectors. You'll need an inverter if you're planning on wiring your house for AC power. If you're going off grid, you'll likely want to look at DC appliances and save on inverter costs.

I've done a quick calc below, just for kicks.


National average household electric use was about 10,500 kWh in 2001. Let's assume that you'll be really energy efficient in your choice of appliances and knock that back to 8000 kWh per year.

Let's also assume, just for kicks, that this electric use will be evenly consumed over the whole year. That means you'll use about 22 kWh per day. This is certainly not true, but it at least gives us a starting point for our costing.

You'll be able to harvest solar power for a maximum of about 5 hours per day, on average (a bit more or less, depending on where you live). So you'll need at least 4400 watts of solar power. At a cost of $7 per watt, that means you'll be paying roughly $30,000, not including batteries, to set up your system.

For comparison, to purchase 10,500 kWh of electricity from the utility, at a price of perhaps 12 cents per kWh, you'd pay $1300 per year in electric costs.

I know that all these costs are wrong, but sometimes it is helpful to get an idea of the relative cost and savings of different options, just so you understand what you're dealing with. Your system will NOT cost less than $30,000, probably quite a bit more. You will almost certainly not pay MORE than $1300 per year in electric costs if you choose not to install the solar system.

If, with all this said, you are still interested in a solar system, then I would find a local vendor and start getting some sizing and costing information from them. Two good resources for finding local vendors of solar systems are below

Hope this helped.

Bernard Said:

Solar Power Eco-Development Engineering Questions...?

We Answered:

Your system is basically doable.

As to pure sine wave inverters, these do not truly exist. All inverters work by taking the DC voltage from the batteries or other source, and chopping it onto the output lines. This is done with solid state devices such as IGBTs. The smoothness of the output power is determined by how fast the DC level is switched. All inverters put out high frequency harmonics. The general method is to run the output of the inverter through an inductive device such as a transformer, the reactance of which tends to smooth out the switching impulses.

Many home appliances could care less about the noise on the power lines. Some home electronics are sensitive and should be run of inductively isolated circuits. Your phone system is most likely not all that susceptible, it probably has it's own power supply that creates the local voltages. These supplies are usually switchers these days, which are just a variation on an inverter. I would talk with the phone system supplier to determine if there is a problem.

Batteries: I would place all the batteries in a central location, for safety and connivance. As to the number of batteries needed, you will need at least 15 in each bank to give you 160 VDC. This will then come down to the 120 VAC that you will want out of the inverters. The total number of batteries you will need is dependent on the peak instantaneous current demands of your systems. The current draw can be determined by I = E/P where I is the current, E is the voltage, and P is the power. You list 1/2 MegaWatt per home per month, but what usage do you expect at any given moment. The 1/2 Mega Watt per month would only come into play if you intended to run the entire system off batteries for one month, and I'm sure that you don't want to do that. You need to determine how much power you will be supplying at a given time and size your battery array to that usage.

Aaron Said:

What is the difference between Power tracker and Inverterter for Solar systems?

We Answered:

It looks like Power Tracker is a brand made by AERL and yes it appears to be the same thing as an inverter.

Tracey Said:

Solar powering an Radio Contoled car for recharge power only?

We Answered:

Any diode will do.

But the voltage out of the solar cells must be higher than the battery voltage by a bit before the battery will charge. For example, a 12 volt lead acid battery won't charge until the voltage gets above 14-15 volts. Add the diode voltage to that.

So you need to find out the voltage needed to charge your batteries, and put enough cells in series to get that voltage. Anything less and they will not charge. I doubt you have enough voltage, even with the cells in series.

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Marvin Said:

Solar Power?

We Answered:

Solar and wind are and need to be implemented a.s.a.p. People have to be ignorant to agree to put more nuke plants in and with the kill rate of a 150 mile radius I'd say we are smarter than the last of the Mohican's! I can't wait till that generation is out of commission!