For Atlantic City Electric, In New jersey I beleive I pay $.089  per KWH, if I'm not mistaken, I get a special rate for having the Geothermal system. Normal Residential Rates are $.1122 per KWH (rate as of 6/1/2008).  We just had a 1% rate increase in May, 2008. A 21% increase in electric rates?! That's outrageous, I highly recommend you switch to heating oil where the price has only increased a modest 116 percent since 2005 or Natural Gas only a 190% increase from 2003 to 2006.  You will save a ton of money, call your local oil heat or natrual gas company today.

 

For proper comparison and calculation of payback period you definitely need complete knowledge of every alternative's raw cost of fuel and its efficiency or Coefficient of performance.

One way to compare apples to apples is to determine each alternative's cost per million Btus delivered into the home.

as TG noted, despite significant rate hikes, electricity is a relative bargain in most places right now.

A geo system nearly always has the lowest cost of operation of any choice generally by a considerable margin. A geo system nearly always has the highest first cost. Such is life. Every projects individual circumstances has to be evaluated to come up with the payback period.

Barring a massive carbon tax, electricity will likely remain a relative bargain since much of it comes from still-fairly-cheap US-sourced coal. A carbon tax will skew the math away from coal and toward natural gas, but raw prices for those commodities will likely readjust in response.

Still with me? Having fun yet?

I'm on a co-op. For the first 700 kW, I pay $.0615 per kWh, the next 800 is $.056, and anything above that is $.037. Geo makes lots of sense here.

Currently live in Wellington (southern Kansas) which I believe has its own power plant that charges $0.06035 /kwh
The electric coop that provides power to our future country home site charges approx $0.11 /kwh. Dave

I am in central jersey. I pay $0.14 / kWh, but we recently installed solar panels that cut our yearly bills in half. If my upgrade to Geothermal is successful, I will expand my solar to the other half and run the system easily from that. You may want to look into PV arrays as a way to hedge electric energy costs.

Payback on PV arrays is now generally measured in decades, not years. Running a geosystem from PV alone (assuming not a grid-tied net-metered PV setup) gives rise to substantial added costs owing to both the size of the array needed and the batteries and inverters needed to punch out the amps needed to start multi-ton refrigeration compressors. Startup surge current is momentarily equal to the locked rotor amps on the unit nameplate, often 6-8 times the running amps. Then there's the not-so-green issue of having to swap out a couple tons of spent batteries every 10-15 years.

If the geo system is divorced from the PV by grid-tie, then by all means go for offsetting all your electricity use by a PV array. payback will still be decades, but fewer decades than with inverters and batteries.

I keep up with PV via my long-standing HomePower magazine subscription, and the gear has come a long long way in the past 10 years or so, but it ain't quite yet ready (economically feasible) for HVAC prime time.

I would agree that unless you’re off grid or REALLY want backup go grid (my case). The payback depends on your rates. A typical grid tied PV will run about 30 cents a kwh when all is said and done. Battery backup run $.70 to $1.00 a kwh, mostly because of added cost of the batteries and battery replacement over time and a bit more for battery losses.

You could use the argument that if you pay $30k now you are "prepaying" for future electricity and once you pass that point it's "free". Or you could hedge electricity rates will pass $.30 / kwh.

In my case I pay $.05 off peak or at night and $.22 on peak during the day (when my panels generate power) so it works out. My payback, based on actual watts produced vs. current electricity cost on peak is 11 years. Again that’s based on real numbers over the last three years of production. Since I do have a battery based system in 11 years I will have to replace my battery bank and that will push it out another 5, then I will be generating free power for 5 more years until my battery bank need to be replace again.

Then again I didn't set up my system to make money or even offset my electric bill, that’s just an added bonus. My system was setup to act as or replace a 6kw automatic transfer standby genset, which was the same price I paid for my system (and what’s a gensets payback?)

I am not knocking anyone, I totally agree that you don't put PV panels on the roof to make or save money at least not any time soon. It is far cheaper to conserve or not use the power in the first place, rather then to generate it via solar PV.

What is the storage percentage of 10 year old batteries? Obviously they don't just stop working all together, there storage ability just degrades as you charging and discharging them. So with that in mind, if you were to replace all you batteries in 10 years, could you keep the old batteries and in 10 years add them to the system to make up the storage shortfall? Does a battery that sits around for years without being charged and discharged last a lot longer? Another question is if your batteries are only for backup when the grid is down, they are not being charged and discharged daily, so they should last longer right? I just wondering if you and get a lot more life out of batteries then the advertised.

One final point, I heard that old batteries for electric/hybrid cars are still useful for grid based electrical storage, so it could be that as 100's of thousands of electric/hybrid cars are added to the roads, the number of used batteries available will skyrocket making you battery replacement all that much cheaper. 
   

In the Detroit MI area, we have several different electric providers. One rate that we see most often is a seperate metered geo discount rate of .075 vs the regular rate of closer to .11. I am evaluating a modest 1500sf home this morning, if I input your .18 and compare to $3.50 gal fuel oil, in this area it's still 1/2 as much for all the heating cooling and hot water production (savings around 3K). That would make their pay back about two more years. Again, this is not a large home so the savings obviously gets more dramatic with more sf or higher fuel oil prices (which are more than likely).
When comparing geo/fossil it's tough for geo to lose as even a 90+ furnace is 75% less efficient than a 3.5 COP heat pump. In our area even natural gas is starting to lose edge against the .075kw rate. With paybacks falling under the 10 year mark we are starting to see more urban/geo interest.
Joe

Batteries come in such a wide range of makes and models, some are made to last a long time, some are made to push out high amperage rates of fast charge rates and some are cheap and won’t last long. The batteries I have are Deka AGM (absorbed glass mat) rated at 245 amp hours at 12vdc at the 20 hour rate, meaning if I can pull 245 amps out of them over 20 hours or 12 amps per hour for 20 hours. If I draw the power out more slowly I actually will have more capacity and if I draw the power out more quickly I will have less capacity.

Batteries are rated for a certain number of charge /discharge cycles to 50% or about 4 times that to 25% or about 10 times that to 10%. So if you discharge to 50% every day they will last one year, then only use 30% of their capacity they will last 4 years and only use 10% they will last 10 years. Their rated capacity is usually to 75%, of course every manufacture has a different point to its rated life.

As batteries age they consume more power to get back to a full charge state. That and capacity is usually the reason they get replaced. For example my last bank lasted 6 years (cheap golf cart batteries from Sam’s)(which is actually a long time for those batteries). I had to put in about 10% more power then I took out of them to get them fully charged, by contrast these new (2.5 years now) AGM’s need 2% more power then I take out of them.

Batteries do age just sitting no matter how deep they are discharged. The worst thing that can happen to any lead acid battery is to let it sit in an uncharged state, which kills more batteries every year then anything else.

If you cycle them very shallow and keep them charged up they will last the longest, again somewhere from 4 to 20 years to 75% depending on make.

I do cycle mine a bit, basically I disconnect from the grid during high rate periods or on peak rates during the day. If it is sunny and my wife isn’t cooking I will make as much power as we consume running refrigerator, freezer, laptop and some other small 24x7 loads. If she cooks or the kids (1.5, 3, 4.5 & 6) leave a bunch of lights on (or for some crazy run the garage door up and down) it will draw from the batteries. Then when we hit the off peak, cheap rates we go back to grid power and if the batteries need to be charged they are topped off with cheap grid power.

Yes you could keep your old bank when you get a new one. You don’t want to mix old and new batteries since the older batteries will pull power out of the new ones just sitting there. Again the catch is you need extra power to maintain the older bank and often off grid that just isn’t there. For example my old bank took about 500 watts a day to stay topped off, where my new bank (twice the size) takes about 100 watts a day. This also gets thrown in to how long it takes to pay back solar systems, you don’t have the battery loss in a straight grid tie system.

Most hybrid car batteries are NiMH which are much more forgiving, lighter for the same capacity and cost more. They could certainly be used in a solar PV system with the right equipment, often systems are set up with old Telcom or old fork lift batteries.

I'd really really like to see time-of-day metering become widespread, and net-metering follow the same exact rate structure.

I also think its odd time of use isn’t as wide spread given at night utilities typically have a surplus of generating capacity and mid day are close to their capacity. Although if your peak aware you would likely save money, maybe that is why they don't push it? Not sure.

I think it is really odd in some parts of the country they charge less as your total consumption of electricity increases and in other parts charge more as your total consumption increases. Now that doesn’t make sense to me, it has to be one way or another, it can't be both...

Much depends on the individual utility's situation...and politics of rate setting. A summer peaking utility welcomes more winter heating load.

Capacity is one variable - other is cost. During peak times utility must pay more, sometimes a lot more for power to attract marginal producers such as combustion turbines whose fuel costs are high. That peak rate is paid to everyone generating at the time.

That $4 gas is cutting Americans' penchant for driving is proof positive that price signals work.

Hmm that's an interesting idea. I know that people with solar panels sell power during peak periods and use it during the off peak times. With that in mind, it's it feasiable to get a bank of batteries, and have them charge during the off-peak periods and either use it or sell it back to the power company during peak times?  

The cost of the batteries and related equipment would likely never pay back, as you cycle the batteries more you reduce their life. I guess if your rates were far enough apart it might pay off? In my system the bank acts as a buffer with the sun producing most of the power for loads. The bank allows us to draw more temporarily and then slowly fill back up. Say we run a microwave at 1000w for 10 minutes; it just used 500w of that from solar and 500w from the bank, once the micro shuts off the bank slowly charges back up. Of course there are other base loads; we typically hover about 300w with nothing “real” on. It is amazing how that adds up with little things, for instance the micro draws about 2w, printer/fax/copier off draws about 5w, garage door openers draw about 3w each and so on. The single largest one is the furnace / geo drawing 22w with apparently nothing on, seems odd, I haven’t tracked that one down.

In grid tied situations you’re basically using the grid as the battery bank, selling you access power when it cost the most and buying power back when it is less expensive. For example a friend of mine technically generates 1/3 of his yearly consumption at high rates, but because the power at that time costs more he ends up paying nothing at the end of the year for power.

The 22 W likely comes from the control power transformer(s). Garage door openers have the same thing (low voltage wiring for control and safeties) so there are transformers there, as well. 22 Watts seems a bit high for standby current for control power transformers, but I'm not speaking from experience backed up with data.

My WaterFurnace units consume 41 - 44 watts when not running. This is for 2 units total, so the 22 watts noted above certainly is in line with what I'm seeing.

One of my pulse output watt-hour transducers is dedicated to my HVAC power line.

Best regards,

Bill

I agree and understand what the losses are from transformers and such. It is pretty common to see 2-3 watts per "off" item, TV, garage door opener, micro. I was just a bit surprised when I saw the 22 watts on the furnace / geo line. I suppose the furnace has a transformer (or two), zone control, geo control (probably a couple in there?) so it makes sense, I just wasn’t expecting it. I am surprised the openers are only 2-3 watts, our last ones were about 5 watts each.

I shouldn’t complain though in my office I see about 35 watts with everything off, fax, monitor, computer, weather radio, cordless phone base and such, it all adds up.