Grid dependent?

yes, there is, in fact, your system should already be fed to an inverter and that fed to your home side of the meter. If it feeds to the utility side of the meter, then you are being screwed, royally. when you are on the PV full sun time, your meter should be running in reverse. Then when you are at night and in demand, the meter should run normally. 5kw is more than enough to run a normal household with some to spare and since we normally sleep at night and shut down our need for power, your meter should have a net negative value. Now, whether you get credit for this or not depends a lot on your state. Some states and the Federal government require you receive compensation for your contribution to the grid. Best you look into this.

I do believe that the installation has to adhere to certain local regs, be inspected and then you get a special meter......that is the way in most countries. I have not done this personally....

Having done the math on battery backup for a PV system, I long ago determined that one cannot get ahead of the curve on cost/benefit ratio if one uses batteries. Your Grid tied system is the most cost/benefit way to go, using it to store any excess PV power via spinning the meter backwards. Having said that, we still opted for a 17 Kw natural gas powered backup genset and rewired about 2/3rds of our home to use its power, islolated by an automatic switch.

As it happens the PV controler is also on the emergency load side so if the grid power goes down during the day the 230v single phase PV Controler will sync with the natural gas 230v single phase genset. That way we can run our cheaper running but still power thirsty Energy Star Split HVAC System during the day in summer. Bedroom windows (not visible to our neighbors) now sport back up window units for nightime with genset only power and the split system turned off (but having power to keep the compressor crank case heaters hot.). Natural gas is still pretty cheap in Texas, so one does not take much of a hit in cost per Kw if the set is on for a day or so. We test this setup manually bye-weekly; so far no gripes.

One caviet was that within days after taking out the proper city electrical - plumbing permits for the genset - TXU/Oncor pruning crews showed up in our neighborhood after years of neglect and pruned the trees away from the power lines in this area. Power became far more reliable during storms, after that... Coincidence?

Hope that helps.

P.S., Your controller should protect your PV system from overamping if your grid goes down via either a circuit breaker or internal overamp trip switch. I'm assuming that you have an isolating controler somewhere between the grid and your house service panel that opens when the grid goes down so your PV system won't attempt to power your city during power failures. For mre data on the subject of net metering, here is a link to an extensive definition: http://www.green-metroplex.com/factoids/PV/Net_Metering.html

One more thing to consider. I do not know about how your natural gas situation is in San Diego but as TInker65 said, natural gas is still relatively cheap in Texas. I might suggest you check with Siemens SOFC and/or Acumentrics to see if they can make available to you at a reasonable price their Solid Oxide Fuel Cell (SOFC) units. Both are planned to be on the market this year. If so, then the 60% efficiency of the fuel cell vs an engine driven generator at 30% efficiency is worth consideration at any price. At any rate, thank you your use of renewable energy. You are contributing to a better world for our children. I am sending you the link to My Earthbound Space Station, MESS-SEProject, which is linked from http://www.chtank.org/. Please feel free to use any part of this for your personal system. You might, also, like to follow the APIX-SEProject as it develops.

CHTANK I've book marked your links and will have to read it latter when I have the time.

Looks like you've been studying this problem much longer than most and will save me lots of research of my own. I've always wanted to live off the grid but never really got serious about it till recently. Thanks for the help.

Our system is set up as 'Net Metering'. Everything was done to Code with all redundant safety protocol, etc. installed. Everything works great! Our Utility bill has dropped from $500.00 per month to $50.00....yay! The only down side (as you are well aware) is that if the grid goes down......so do we! The only alternative fuel source available to us is Propane which is a tad bit expensive here, ($3.50/gal) which pretty much rules out using a back up generator. My biggest issue is loss of PV energy due to grid collapse. Being a novice, it just seems to me that if the grid ever should go down......my PV panels would still be producing DC energy, 5Kw worth of energy regardless of the condition of the grid. It appears though that this energy can not be accessed. This is what has me confused. Even if the grid is down, my system is still producing 5Kw DC (assuming the sun is shining). It appears that there is no way to capture this energy (which is no longer being fed into the grid due to the interrupt switches) convert it to AC and use it in a dedicated circuit? This seems to fly in the face of the laws of conservation of energy. If the grid is down and my system is still producing 5Kw DC during sun light hours.....where does that energy go?

Chad,

You are driving home to me one of the things we have heard in Texas but not understanding, and that is how unreliable the power grid can be in California. I am in correspondence with some people in South Africa that also have an energy crisis and are, with government support, working to solve the problem. A part of their solution is to use PV enough to power three 100 watt bulbs and a 300 watt computer system.

What I cannot understand is how your PV system goes down with the grid. since your inverter is downstream of your meter, if the grid fails, there should be a failsafe switch to prevent a direct grounding of your system. You might consider simply pulling your main breaker on the meter box if the grid fails. This way, you become isolated from the grid and the full output of your system should go directly to you. You can then reset your main breaker once grid power is reestablished. This will not work, however, if you are a victim of a famous California "brown-out". I think you might want to hire a good electrical engineer to look into your system and see what can be done within the local codes to protect you from brown outs.

I guess a few fellow South Africans are following this thread with interest! We have ample solar energy available, but not a lot of expertise in PV systems. Our utilities are under no obligation to buy back energy. I wonder if the electronic meters we often use will take note of the reverse energy?

gideon,

I am not going to give names, but I know one who already has his system going SA, and another, actually from GB who is organizing seed companies in SA to build these systems. And the people of APIX (see blog on this CR4 forum and in http://www.chtank.org/ for more details) are looking for ways to develop their programs in the whole of Africa was well as in India and SE Asia. Brazil is well ahead in the ethanol production, so you can find examples there, too. Your nation is moving forward on this, you should be proud.

Only if you are "owed" money on the billing date. In truth the utilities are in a technical binde here. They are scrambling in some areas to get tax breaks or political muscle to hold on to their heretofore, pristine profits. To detect reverse meter "incidents" they must retrofit internet through power line capable technology. That represents a significant bite into bottom line profits during a retrofit push. Below I've pasted in a snippet from a webpage that you may be interested in. Current mainstream Watt Meters run either way without a hiccup. As such, the only way the power companies can detect end user power generation is, 1) Their Kw usage for a customer is a negative number. 2) Go out into the field and look for solar panels (and some have gone the extra step of lobbying local municipalities to institute discouraging building code rules that make it difficult to get installation permits.

The new quasi utility on the horizon is one that will install a PV system on an end user's building and then rent the power that user uses back to them at a lock in rate for 25 years. What I don't understand is why the utilities in existance don't see the economics of this and do the installations themselves? Clean energy, no new power plants, no new power lines with their emense transmission line loss problems.

You should review what the solar warriors in California have gone and are going through because they are exceeding their electrical power needs... I've inserted a quote from the Green-Metroplex.com website.

"These wine vineyard folks spun the meter so far backwards that PG&E took them to court. Their public stance is that PG&E is not equipped to upgrade the power lines/transformers of a competing unlicensed utility which could damage existing PG&E transformers if a "customer" exceeds their rated wattage during peak summer hours. Truth to tell - no one had EVER MADE more juice than they used in a month." The link to the full page, which has links to the solar warrior home page as well, is: http://www.green-metroplex.com/factoids/PV/Default.html

chtank......you have kinda hit the nail on the head so to speak. Because of how they design a grid based system (here in Southern California), if the grid goes down...so does your system. This is what doesn't make sense to me. Simple physics tells you that regardless of the state of the grid, your PV panels are still producing DC watts if the sun is shining. And thats my question! If the grid ever does go down.....how do I capture my PV watts so I can use that energy in my home. I have a SunnyBoy inverter on my towers but it is grid dependent as well. I know that the DC watts produced by the panels don't just evaporate into nothingness if the grid should ever go down. (I wish I would have taken those courses in electrical engineering now..lol)

A "proper" installation detects that the grid is/has gone down and stops supply immediately, otherwise you would not only be trying to run your neighbors TVs & Fridges, but you might also kill a Lineman!!!!

That is why there are laws, regulations and you special equipment!!!!

All of those big windmills you see also go off line as soon as the mains fails.....

The only negative point is the pittance they pay you for each unit you put back!!!!!!!

Thanks for all your imput to date guys. I've read all your messages and will continue to do so as they arrive. Perhaps...I do need an electrical engineer to figure out my situation. It seems to me though, there must be someway to continue using the power produced by my PV system even if the grid does go down. Conservation of energy...right?

Chad,

If your controller is not capable of or does not have islolated circuits, by all means install an isolating breaker switch; paralled your solar controller to that and then only hook up house circuits that will not exceed 70% to 80% of your solar array's theoretical max. You probably have 120v AC output and that is the easiest to retrofit under your setup. Takes a bit more expertise with a single phase 230V AC setup (with a "neutral" double single phase 120v capability), so if you've got 120v output, be thankful.

When the grid goes down, the isolation breaker trips and then the solar array feeds not more than 100% of its capacity to the circuits that are on that side of the isolation breaker. On overcast days you will be glad you didn't max out the loaded circuits such that it would be over amped at that moment in time and trip offline, too. If your system is capable of (has capacity for) including a window unit for hot summer nights in bedrooms, or refrigerators which protect food from spoiling, you've got to factor in the 180% instant start loads of those appliances.

Seimens and others make these and related switches. A full spectrum electrical supply should be able to help you size/find what you need and/or direct you to professional Solar Electrical folks.

Thanks Tinker.......I think that this is the information that I have been looking for. I know that my system has an isolator breaker. It is required by code as a safety feature for any linemen working on the grid. I'm not sure if my inverter output is 120 or not. I can check the specs but I think it may be 220. Generally, if the sun is shining......the system is generating 4000 - 5000+ watts. To be safe.....I'll figure 3000 watts as the peak load limit. Back to the drawing board now. Thanks.

Check-out flywheels:

http://www.beaconpower.com/