Rookie's Questions

[Karl]

All,

Thank you for creating and maintaining this great forum. I find it very instructive with very helpful participants.

I have being doing some reading about solar energy but have questions that reflect my rather weak knowledge base on the subject. My first question is about electricity production. Let's say I have a 10 kW grid tied system and 5 peak hours of sunlight. Will my electricity production be 10 kw * 5 hours, or 50 kwh per day? or should I adjust this number by a system efficiency factor (which I have read someplace else could be around 77%)? That is the electricity to be really available for consumption will be 10*5*0.77 = 38.5 kwh per day.

Second question. Can a grid-tied still function properly in the absence of a bi-directional meter? Our local public grid is not willing to install a bi-directional meter to receive the excess electricity to be produced. What happens to the system and the excess electricity?

Third question. I believe a grid-tied system does not require dedicated loads. Is that correct? I am also under the impression that a grid-tied system with batteries requires dedicated loads. Is that impression correct?

That is all for now! I hope this is covered with my "rookie's bonuses".

Thank you for you help.

Karl

[russ]

Hi Karl, Welcome to Solar Panel Talk!

Best case under best conditions you receive 1000 watts/m2 - for a few minutes per day. In the winter you will receive far less - in my case there is about 1/4th as much solar radiation received in December as in July.

Depending on your location, latitude and altitude along with clouds, fog and or smog interfering you have to adjust your expectations. Putting in a solar PV system in Seattle, WA or Portland, OR is going to do far less for you than somewhere in the sunny southwest.

PV Watts is a program to assist you in determining your locations potential www.pvwatts.org

The power you require in the winter sets the size for the system.

Panel ratings are at STC (standard test conditions) which you do not have in real life. People typically derate the system capacity to 77% for grid tie and around 55% of off grid systems. Seems to be reasonably close.

Your second and third questions I hope Sunking will respond to as he knows this far better than I. It sounds like the utility will accept the power from you free of charge - heck of a deal!

[Sunking]

A1. yes but with losses. So if you have a 10 KW system, on a 5 Sun Hour day with 77% efficiency you get 10 KW x 5 hours x .77 = 38.5 Kwh

A2. It will work, but any excess you generate, you give away for free to the utility to sell to your neighbor. Thank for the free gift.

A3. You have this half right. A true grid tied system does not required dedicated loads. Any excess is sent out on the utility and used elsewhere. The battery portion is where you are misinformed. When grid power is lost, an ATS switch activates and the batteries take over briefly to supply your dynamic loads for a few moments until your generator starts up to take over. When commercial power is restored, the ATC reconnects, generator shuts off, and the batteries are recharged by commercial AC power.

[Karl]

Thank you to both of you. I appreciate your responses.


Karl