PV Gap

Clifton Said:

If Homeowners and Small Biz used Renewable Energy and owned their Power would overall Energy needs be reduced?

We Answered:

yes, but the ROI does not justify it

Mathew Said:

Where can I find steam engines and /or generators for home use? I?

We Answered:

Reinventing the wheel is never a good idea. A lot of research has gone into solar energy systems. Look what´s on the market right now, and ask yourself why nobody has improved on it.

Steam engines and generators are not efficient, about 30%, nor easy to run or install. You will need a superheated steam boiler, a turbine and a very complicated installation. They require a lot of operation and maintenance.

If you want to store heat for overnight use, the best thing is solar with a very large storage tank.
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Marshall Said:

solar panels and electrocution?

We Answered:

solar panels are usually 12 or 24 volts for the smaller ones, and those voltages are pretty safe.

larger arrays can be connected in series or parallel, depending on the battery configuration. It's likely for a large installation to produce 48 volts or even higher, and those voltages can be dangerous.

Higher voltages are used on large installations to cut down on the cost of the wiring.


But, any solar array has an inverter somewhere, running off a battery, and that will output 120 or 240 VAC, and that is definitely dangerous.

So this raises an interesting point. Should all solar panel installations include a cutoff switch accessible to fire fighters? It looks like they should. The switch has to cutoff the voltage from the array, and also turn off the inverter.

edit: but switching off the voltage from the array is not enough, as the array is still putting out power (assuming the sun is shining). One possibility is to use a multiple pole relay located very near the array to open both + and – leads from the array. Thus there is no path for the current to get to ground. If water got everything wet, the array would short across itself but still be isolated from ground. But what if the relay fails?


Max, you seem to have the idea that it takes a lot of current to be dangerous. No, 20mA can shock you, 50mA can kill you, and there are a lot of arrays that can put out 48 volts at many amps.



edit2:
"edit: you could place a normal off switch on the solar array and hook it up to the fire alarm for industrial systems, the switch should open even when power fails. And you are correct in saying that it is the current that kills, but you still have to have enough volts to get a decent current trough a human (no mater what the max current output is). The real question is then do solar panels have a fixed current output (then its dangerous) or a fixed voltage (then with max 50 volts is even wet not a problem)"

sorry, 50 volts IS a problem, lots of people have been killed from 50 volts. I admit it is not as likely as with 100 or 200 volts, but it is still possible, specially with a lot of water around. I don't remember the UL spec offhand, but I think it is somewhere around 20 volts.

solar panels have a variable voltage, dependent on the amount of light on them. You have to plan on the highest possible voltage. The current output is usually in the tens of amps or higher, more than enough to kill, so it is the voltage that will determine the current through your body.


edit3: dividing up the world into constant voltage sources and constant current sources is meaningless, as neither exists in real life. All voltage sources are a imperfect voltage source or an imperfect current source or something in between.
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Ivan Said:

What are best wind and solar powered generators?

We Answered:

You're asking a difficult question only because the technology is improving each month. What is the best today probably won't be the best next year. For wind power you will need a wind availibility survey describing the average wind conditions throughout the year for your locality. Every homesite is a bit different. To establish a cost/benefit analysis your first have to know how much wind energy is available.

Bertha Said:

Need help comming up with a name for our store?

We Answered:

Smart Power or Smart Energy