Question For Electricians or Engineers-

[dsnyder]

OK... my 1978 Spider is running great so on to my next project.

The knowledge base here is so broad, I thought I'd see what people's thoughts. I am searching for electrical conservation/efficiency solutions for my house.

Here are the details:

My house is connected to the power grid.

I have a grid tied solar system that generates up to 5500 watts of power.

The house has a load controller and is on a load control utility rate.

From 9pm to 9am (night) I am on a cheap utility rate .03 a KWH.

From 9am to 9pm (day) my rate is more expensive- .11 a KWH plus a load multiplier.

So basically, after 9 at night, I can run whatever and not worry about cost.

The solar system helps (Keeping the load down) during the day but as soon as the sun goes down or it is cloudy everything that is running begins sucking from the grid and my load goes up.

Now to my question, I would like to add a diesel generator that will supplement what the solar is generating so that I can automatically have the generator run to make up what the solar system can't provide. That way during the expensive times, I don't suck from the utility grid.

Now, some more factors... My solar inverter converts to solar DC to AC and is synked with the grid. Could the generator hook in before the inverter and be set to only generate up to the capacity of the inverter?

Or, could the generator be tied in after the inverter and still synk with the power grid.

I know... it is complicated but there are a lot of creative people out there...

[baltobernie]

Could the generator hook in before the inverter and be set to only generate up to the capacity of the inverter?
Or, could the generator be tied in after the inverter and still synk with the power grid.

I think you'll find that you can't generate power as cheaply as you can buy it, even at "peak" rates. By the time you amortize the cost of the generator and its installation, plus fuel, maintenance and eventual replacement, your cost per KWH will be far greater than $0.15 The lure of a generator, IMO, is limited to backup power during outages.

[courtenay]

Then there's the noise and smell of the generator. Have you thought of adding a battery bank that can be charged by the solar panels during the day and used to supply power through the inverter at night? Again, though, as Bernie points out whatever you do, make sure you do the economic math to determing the payback vs the cost of Hydro power.

[maytag]

Many utilities are beginning to supply two-way meters to folks who generate their own power, like you are. They actually buy-back the power you generate in excess of what you are using, so that when you need to pull from the grid, you're working against a "credit" of sorts. The idea would be to get you to zero. Check with your local utility.

Then I'd suggest looking at wind-turbines before a generator. Depending on what part of the country you are in, wind power can be much more cost-efficient than fuel-generators, or even Solar for that matter. Wind-turnbines have come a long way and they no longer suffer from the catastrophic failures that turned people away from them in the past.
ALSO be sure to check with ALL of your utility companies. There are MANY MANY rebates right now that differ throughout the country, paid from stimulus money and also from green-grants that will help offset the cost of implementing whatever you choose. I'm sure you used some of this for your solar installation?

And LAST-BUT-SHOULD-BE-FIRST:
The first thing I tell people when they start looking down this road is to look inside first: every $10 spent on lowering your power NEEDS will reduce the cost of your power-generating-system by $1000. Energy-efficient appliances are of course a must, but I'm assuming you've done that already? And LED technology has reached a point where the price-points start to make sense. At the very least, look to CFL's, but in my opinion, there is very little reason not to start the conversion to LED's now. And you'll be amazed how much you reduce your power consumption.

Good topic!

[TX82FIAT]

You may want to look at a capacitor. They do not save as much as some of the sales organizations say they do 15% to 25%. However, they can help store and evenly distribute load during high heating or AC times of home use a 5% savings would add up over time and pay for itself in lifecycle costing. I do not know what your electric consumption is but it is reasonable to assume a 3 - 5 year break even on the cost to purchase.

Ray

[manoa matt]

You need a 2nd shift job. Sleep from 7am to 3pm, go to work from 5pm to midnight, come home and use all the power you want during off peak hours.

[FulviaHF]

I'm confused here. If, as you say, your .03/KWH nighttime rate is cheap enough that you can "run whatever and not worry about cost", then why are you worrying about cost? Why spend money on the installation and operation of a diesel generator to try to save money (which you won't, as others have pointed out) if you're not worrying about cost? I don't get the logic.

As maytag correctly points out, it may be possible to sell the excess daytime solar power to your local utility with a two-way meter that you can drive backwards with your excess generation. This is by far the most efficient and cost effective. And if you can set that up, and still want to invest money in more equipment, just install more PV panels to run the meter backwards faster.

But failing all that, if you're really determined to build in serious complication just to prove you can do so, you can use the excess daytime solar generation to drive a flywheel or lift a counterweight that can mechanically drive a generator off-hours. That won't be cost effective either, of course, but it won't rely on buying a steady stream of fossil fuels for a diesel generator.

[maytag]

I like Matt's suggestion BEst!

[dsnyder]

To clarify a bit, the real issue is the load factor. My bill goes up $30 a month for every 1000 Kilowatts used at a time. So... with my solar cells and not running the heating or air conditioning, I can keep the load down to 3000 KW... actually lower if nothing is run when the cells are not producing from 5pm to 9pm. That gives me a monthly bill of about $150. Once I turn on the Air Conditioning or the Heater, the load goes up to 5000KW or even 6000KW and in addition to the 12 cents a KWH peak cost, the utility adds $30 for each 1000KW of load. The bill can jump to $280 in a heartbeat.

I can make it without running the heater during the peak hours in the winter but in the summer, you can't make it in Phoenix without the AC. To make it worse, if you turn it off during the day when at work, you get home around 5 or 6, the solar is not producing so the entire AC load comes off the grid.

What I am really looking to do is have a diesel generator that will chug along as a supplement when the load starts going up and thus keep that utility load factor down low. In that way, by taking advantage of the solar and the diesel, I am sort of mimicking the hybrid car concept. I live on a acre with two outbuilding so noise is not a huge problem and I have access to biodiesel.

[puddin]

i work in an industrial plant that has 17000 volts comming in and breaks down to 4000 then to 480 for most machines--- we have Power Factor Cabinets that are banks of capacitors that take the load demand fluctuation and stabilizes it .. u mostly pay for peak wattage ( like when air cond starts up they peak then gradually run lower consumtion) this would help with the peak load but these cabinets are really expensive and not really for household use..

i suggest the cfl bulbs or led - they reduced my utility bill... also i was thing if any of you folks know air conditioning well == how about this

shading the area around the heat pump's outside unit would decrease power consumption == this unit just transfers heat so if on a sunny day when it's 90 degrees it should transfer the heat out side better if it wasn't so hot from the sun= whatta think???? i was also thinking about a spray mist of water to cool the coils electrically activated when the fan comes on== whatta think ???

same in winter if you put black roofing paper around the base of the heat pump the sun should warm it more thus giving more heat for the house..

or do i just have nothing better to worry about.

[baltobernie]

Ah, now the picture is clearer. Just for giggles, figure $10k for the generator. Permits, etc. plus a tricky installation. I don't know how you can share the load of your A/C between PV and genset. One way would be to have the generator dedicated to the A/C or heat (heat pump would make this easy). You'd need some starting mechanism to fire up the generator when the thermostat calls for action.

Forget the fuel cost; only a gallon or two per hour. Use of biodiesel would mean higher maintenance, but may be worth it if the fuel is truly free.

So you figure the cost of $10k over time vs. the price of their electricity. Tough call in this example. I'm liking Fulvia's suggestion to add more PV; lots of incentives out there right now in MD; check out what AZ is offering. For example, a neighbor is installing a 5kW rooftop for $30k, but incentives bring that down to $12k immediately, plus a monthly renewable rebate of several hundred dollars per month. That's enough juice to run your A/C, and probably a better ROI than the generator.
The utility must buy back your excess at retail, correct?

[maytag]

You're in PHX?

Okay. Call these guys:

http://www.cedgreentech.com/
or 888.8 CED SOLAR (I know it's too many characters.... but it dials.... )

They are really the best knowledge-base I've found in that area. This sort of thing is their bread-n-butter. They'll know about (and can help you with) ALL of the rebaes and incentives right now down there, as well as help you come up with the most cost effective way to handle what you're trying to do. Don't let the phone # steer you wrong; they're not just solar.