Special Purpose Timer Needed

SolarJohn · December 2007

I've just enrolled in a plan where I'll be charged for electricity at a rate that depends on demand. Generally speaking, rates go way down after 10pm, and are higher during the day. I would like to purchase a timer that allows me to connect the load to either my PV systems inverter, or to grid-supplied power, based on the time of day. Does anyone know of an off-the-shelf product that will do this? If not, I'll consider building one around a low-cost mechanical. Instead of connecting the load directly to the timer, I'll wire the output of the timer to a heavy-duty relay. The relay will connect either the inverter output to the load, or grid-supplied ac to the load (but not both, or my inverter will probably fry).

John

mike95490 · December 2007

Re: Special Purpose Timer Needed

You need a Transfer Switch to do this safely

This sounds like California's plan to "solarize" the state, if you have PV, you get stuck on a rate plan that runs high rates till 10AM-8pm, way after solar output shuts down.

BB. · December 2007

Re: Special Purpose Timer Needed

I have been using a digital 120 VAC lamp/appliance timer from the local hardware store... You can have custom days (by day, by work week/weekend, etc.). I use one to control my freezer on the E7 plan (two tier, weekday higher rates, weekend lower rate)... Off from noon to 6pm weekdays, on all other times (plus I have set the thermostat to maximum cool for the 6 hour carry thru of no power).

In California (at least Northern California--PG&E territory), they are trying to close off the E7 plan (or already have again), and getting people to use the E6 plan. Three tiers during the week, two on weekends, different times between weekdays and weekends, etc...

For awhile (beginning of 2007?), if you wanted any grid tie solar connection--the state forced the new E6 rates. Even if you only had a few hundred watts of solar panels. People would install grid tied solar and see their bill shoot up! :cool:

Problems like this just about killed solar in 2007 for California (plus complex rebate procedures, etc.).

I looked at the E6 Rate, and even with gird tied solar, and if I was forced to make a choice, I would choose either E7 (if still available for new installs), or E1 (flat rate residential).

One of the big problems with the E6 (and to a lesser degree the E7, and other PG&E rate plans) is that you have to look at the tiered usage--both energy you consume and generate with your solar panels... The power used and generated in all of the different tiers can easily push even the low night-time rates quickly higher.

If you use just 30% more than baseline power usage (~300 kWhr/month), your low nighttime rate goes from $0.09 to $0.20 per kWhr.

If you are over baseline, these low off peak rates get to within 10% of the standard E1 (residential flat rates). And the peak rates are hugely more expensive.

Plus, if you have periods were you are pushing power back to the utility, with E1 that also "unwinds" your tiered power usage.

With E6 (and E7), I have been told that (this was last year), PG&E will take the (example) 300kW hours you consumed off peak, and add that with the 300 kWhrs you generated to the grid on peak. So, instead of ZERO net usage of power (and lowest rate tier), you have "moved" 600 kWhrs across the grid (direction does not matter)... Placing you in the 200%+ rate structure...

I have not seen this explained by PG&E anywhere in writing. And this may have changed this year--but it was a real problem for folks with a second meter for cheap power to charge their electric cars... They were taking out the second, supposed to be, very cheap midnight to 7am power, because it was pushing the whole address power bill into higher rates...

I would be very interested in how the E6 and tiered rate plan was explained to you (and if you are using some form of Grid Tied inverter).

-Bill

icarus · December 2007

Re: Special Purpose Timer Needed

Wow! My head spins faster than a meter with the dryer running!

At least you have time of day metering. In places where solar makes little sense, the Coastal Pacific NW for example, and conservation is the (current) best source of new energy, utilities still haven't gone to time of day metering.

As a result John and Joan Q Public still use heavy demand appliances, (water heaters, dryers etc) at the time of peak demand, rather than when demand is low. It doesn't make sense in the broad picture, but since the cost is the same, most people don't have a clue.

As to the op. A transfer relay (available from NAWS) should do the trick, coupled to the timer that Bill mentions.

Icarus

SolarJohn · December 2007

Re: Special Purpose Timer Needed

Thanks for the info. I'll order a transfer switch from NAWS. I wonder how much energy it takes to power the transfer switch??? It seems like most people would use a transfer switch to connect an alternate source of power when the grid fails, while my application is just the opposite.

I'm locked into the plan for one year, so I hope it works out. Of all the things I'm planning to do, cutting back on my central AC will no doubt help the most. My programmable thermostat will allow me to automate that task. I can easily do with out it during the day, but like to be comfortable when I sleep. This fits into the day/night rate structure very nicely. If I didn't have a couple of kids in the house, I'd use a window ac instead of central.

As for my loads; I'll use as much solar and battery power as I can up to 10pm. Then I'll switch to grid power until early morning. My PV panels will not only have to power daytime loads, they'll have to charge batteries at the same time. That seems like a lot to expect from my small PV array.....

John

mike95490 · December 2007

Re: Special Purpose Timer Needed

A transfer switch is for moving your entire household from grid to local power. I sort of think this is what you are thinking of wanting to do ?

You'll need an electrician to connect it up, and maybe some sort of inspection.

You will also get dropout of power every time you switch. Clocks, TV's cable boxes, all may reset themselves, and need "resetting" 2x a day ??

You will need a massive PV array to:
recharge battery bank &
run your house
for the 9am - 10pm shift.

You may want to also consider using the cheap midnight - 6am power, to recharge your batteries, saving your solar to actually power the house. The problem I see is the daily load 6pm - 10pm, when it's likely folks are home, and using power strictly off the batteries.

You can put timers on your fridge, so it cycles ON while you still have sun, and OFF in the expensive evening hours, and back on @ 10pm

SolarJohn · December 2007

Re: Special Purpose Timer Needed

Mike,

My PV system is way too small to power my entire home. I'm thinking of using it to power a chest freezer, my refrigerator, and maybe a couple of cfl's. I'm looking at the 30A transfer switch from NAWS. My system is not wired in to my existing house wiring, and I don't plan to do that anytime soon. I'll want to add panels and batteries before I do that.

Your suggestion to use cheap grid power to charge batteries is an interesting one. I hadn't thought of that. I might benefit more by enlarging (replacing) my battery bank than I would by adding solar panels. I know there would be tremendous inefficiencies, but I'll be buying grid power sometimes for less than 0.02 per kwh. Using that cheap electricity to charge batteries, which will contribute power to the daytime load, seems like a good idea. I'll have to give that some thought.

John

mike95490 · December 2007

Re: Special Purpose Timer Needed

Can you say what your PV system is ? volts - amps KW ? Is it installed, or in planning stages?

SolarJohn · December 2007

Re: Special Purpose Timer Needed

Mike,

I currently have:

340 watts of pv on the roof
420ah Marine deep-cycle batteries (My beginner's set, 2yrs old)
TriStar 60 with meter
1100 watt true sine wave inverter (exeltech)

I'll be installing another 85-watt panel in January, and one or two more before the end of 2008.

John

SolarJohn · December 2007

Re: Special Purpose Timer Needed

It looks like it might benefit me to charge my battery bank at night using grid-supplied power when rates are lowest (.02 to .04). I'm considering an Iota 30a charger from NAWs. I can connect it to a timer, set to start charging when rates go down (about 10pm). Once the batteries are fully charged, the charger goes into "float" mode, and therefore draws little current.

I can then use that stored power during the day, instead of grid-supplied power, when utility rates will be 0.10 to 0.15 per kwh.

I understand that there will be losses, but it looks as if I might come out ahead. Of course I'll have to enlarge my battery bank to make this work.

John

BB. · December 2007

Re: Special Purpose Timer Needed

John,

Are you on a flat rate plan or a tiered rate plan in your place... As I have said before, in California, the "low cost" tiered rate plans go up in price very quickly once you are above baseline (I live cheap--so I am usually about 2/3'rds of baseline--which is around 300 kWhrs per month in our area).

Also, you have to allow for charger, battery, and inverter inefficiencies... As an example:

%eff=90% charger * 80% wet cell battery * 85% inverter = 62% overall efficiency.

Or, your 0.04 rate becomes 0.04*1/0.62=$0.065 per kWhr--Still cheap compared to my area ($0.09 is my cheapest TOU rate, there is another cheaper one for electric cars at ~$0.05 for deep night rates).

But you also, at a minimum have to include the cost of batteries and replacements (you can also include the inverter/charger/installation charges divided by lifetime of the electronics of say--10 year replacement schedule).

-Bill

SolarJohn · December 2007

Re: Special Purpose Timer Needed

Bill,

My rate depends upon demand at any given hour of the day. For example; last night at 1am the rate was 0.0258 per kwh. The rate jumped to 0.07699 at 7am and peaked at 0.11699 at 6pm. Summer rates are different, but are lowest in the very early morning hours. I don't think that I'll be charged extra for exceeding any baseline.

John

BB. · December 2007

Re: Special Purpose Timer Needed

John,

Sounds like an exciting way to live~! I too have wondered if using batteries to load shift would make sense on a home by home basis...

In general, every time I looked at the "spread", the tiered pricing (which pretty quickly flattens out the difference in rates once you are 2-3x baseline), and the costs of batteries/inverters/etc..., I have decided it was just cheaper to conserve (insulation, double pane windows, new appliances, etc.).

And with solar (and positive generation during sunny times), it got really complicated to even figure out the costs of power, tiered rates, and that tiered pricing "penalized" as "use" positive generation kWh at the end of the month).

-Bill

SolarJohn · December 2007

Re: Special Purpose Timer Needed

Thanks Bill,

It seems like my electric rate plan is pretty good then, since I'm not being penalized for excessive use. I've already added insulation, replaced windows, switched to cfl lights, replaced appliances, etc., so it's time to move to the next stages.

I'm also thinking ahead. I hope to buy a plug in electric car in the future, possibly a Chevy Volt, and I'll be charging that at night. I'm hoping the car can be charged with 120vac so that I don't have a big expense for inverters. With a charger, battery bank, inverter, and help from solar panels, it might work out well.

John

niel · December 2007

Re: Special Purpose Timer Needed

i looked up the chevy volt out of curiousity and it says it will need a 15amp 110vac connection to charge a large 16kwh lithium ion battery.
http://www.chevrolet.com/pop/electriccar/2007/process_en.jsp
the general site for the car is at
http://www.chevrolet.com/electriccar/
this car is a multi-source fuel configuration built up around an electric car and is meant for 40 miles roundtrip per charge with extensions possible with other sources.

SolarJohn · December 2007

Re: Special Purpose Timer Needed

Niel,

Thanks for the links, they were helpful. I've learned that the Volt will have a 16kwh battery, and a complete charge will take 6 to 6.5 hours. So..... If I recharge at night, when my electric rates will be less than $0.04 per kwh, I've calculated that I can recharge the battery for less than fifty cents. Knowing that the car can go 40 miles on a charge, it seems that I'll be replacing $3 to $6 worth of gasoline with 50 cents worth of electricity. Outstanding! Am I wrong?

John

BB. · December 2007

Re: Special Purpose Timer Needed

An electric car is one reason I "over-sized" my grid tie array when I first installed it 2 years ago... I have enough power (money in my utility net metering account) to probably get "free" car travel for all of my around town/dance/swimming trips for the kids... If I had an electric car, my tiered rates would double or triple my actual electric rates (off peak rates a low of $0.09 to a high of $0.32 per kWhr)

However, I am waiting to see if California (and the Feds) figures out that they are missing fuel taxes (and oil company income taxes) of something like $1.00+ per gallon.

Let alone in Europe where they are probably getting USD$6.00+ per gallon in taxes on close to USD$8.00 per gallon fuel...

There have already been major enforcement actions by some states to get the "missing taxes" from bio-diesel. It was kind of easy to tag one guy at a racing event (where they were looking for un-dyed/un-taxed fuel in RV tanks)--he was the one driving the diesel car with "powered by 100% vegetable oil" (from Costco?) bumper sticker.

At some point I worry that, GPS/Toll Roads/etc., taxes are going to catch up and, probably sink, large scale road/highway electric vehicles. Several States (Oregon, California included) years ago started working on GPS/Gas-pump interfaces to see if they could "properly" tax the road usage of Prius/VW TDI type cars that are not "paying their fair share" of road taxes...

-Bill

icarus · December 2007

Re: Special Purpose Timer Needed

For those that are interested: www.priuschat.com has some very insightful threads on both electric cars and plug in Hybrids. The site is not very well moderated, but with some searching you can find a lot of useful information. There are vast discussions on the Chevy Volt, and whether it will ever get built.

As Bill says, as we move toward different fuels, the infrastructure will still need to be build and maintained. A drop in gasoline/fuel tax revenues will require a requisite increase in some other tax/fee to make up the difference. The simplest fee is to do nothing, and the costs are born by future generations, as well as the cost of traffic snarls, air pollution etc.

Unfortunatly, we have neglected our basic infrastructure for so long that the cost to repair and replace is almost insurmountable. We have evolved into a society that doesn't want to pay for anything up front, but will put up with hidden costs without complaint.

Icarus

SolarJohn · December 2007

Re: Special Purpose Timer Needed

I'm moving on with my project. I've just ordered the 30a transfer switch, a 30a Iota battery charger, and another 85 watts of PV. Next I'll need to upgrade my battery bank. Then I hope to use cheap grid-supplied power (nighttime rates) to charge batteries, and I'll apply that stored energy to daytime loads to minimize my use of grid-supplied power when rates are highest.

Question: Can I attach the Iota 30a charger to the PV system battery bank without any damage to the TriStar 60 charge controller, or the Exeltech 1100w inverter? I've ordered the charger with built-in IQ4, and I'll turn it on and off with a timer. I need to do that so it doesn't try to charge batteries during the day, when grid power is expensive.

Thanks NAWS for the 5% end of year discount.

John

crewzer · December 2007

Re: Special Purpose Timer Needed

Question: Can I attach the Iota 30a charger to the PV system battery bank without any damage to the TriStar 60 charge controller, or the Exeltech 1100w inverter?

SJ,

Shouldn't be a problem, with or without the timer. For example, see: http://www.morningstarcorp.com/products/FAQ/#bank .

HTH,
Jim / crewzer

crewzer · December 2007

Re: Special Purpose Timer Needed

Your suggestion to use cheap grid power to charge batteries is an interesting one. I hadn't thought of that. I might benefit more by enlarging (replacing) my battery bank than I would by adding solar panels. I know there would be tremendous inefficiencies, but I'll be buying grid power sometimes for less than 0.02 per kwh. Using that cheap electricity to charge batteries, which will contribute power to the daytime load, seems like a good idea. I'll have to give that some thought.

It looks like it might benefit me to charge my battery bank at night using grid-supplied power when rates are lowest (.02 to .04). I'm considering an Iota 30a charger from NAWs. I can connect it to a timer, set to start charging when rates go down (about 10pm). Once the batteries are fully charged, the charger goes into "float" mode, and therefore draws little current.

I can then use that stored power during the day, instead of grid-supplied power, when utility rates will be 0.10 to 0.15 per kwh.

I understand that there will be losses, but it looks as if I might come out ahead.

I'm moving on with my project. I've just ordered the 30a transfer switch, a 30a Iota battery charger, and another 85 watts of PV. Next I'll need to upgrade my battery bank. Then I hope to use cheap grid-supplied power (nighttime rates) to charge batteries, and I'll apply that stored energy to daytime loads to minimize my use of grid-supplied power when rates are highest.

Also, you have to allow for charger, battery, and inverter inefficiencies... As an example:
%eff=90% charger * 80% wet cell battery * 85% inverter = 62% overall efficiency.
Or, your 0.04 rate becomes 0.04*1/0.62=$0.065 per kWhr

SJ,

I'm struggling with this operational model. On one hand, there are many cost, infrastructure, and environmental benefits to lowering energy demand (fewer Wh/hr = fewer Watts) and/or shifting demand from day to night.

On the other hand, as Bill discussed, there are other associated costs with this approach. One way to look at it is as higher cost per net kWh. Another way to look at it as reduced efficiency. Specifically, it will take more energy to operate your loads from the grid, charger, batteries, and inverter than from operating them from the grid alone.

For example, a load that might require 1 kWh to operate from the grid will require 1 kWh / (90% x 80% x 85%) = 1.63 kWh to operate from the grid, charger, batteries, and inverter. At some point, using 63% more energy from the grid translates into more fuel consumption and more pollution.

This dilemma has vexed me for a long time, and I don’t have a perfect answer. For example, my FX2534 inverter/charger features a “Grid Use” mode that allows me to switch loads from the batteries to the grid at specified times of the day so that I can top off my batteries. This function is essentially the same as the operational mode you’re considering.

Another approach worth considering is something akin to OutBack’s “HBX” mode. This feature switches loads from the batteries to the grid when the battery voltage drops to a minimum value. The batteries are then recharged by the inverter’s internal charger and/or PV array until the batteries reach a certain voltage for a specified period, and then the loads are transferred from the grid back to the batteries.

A variation of this latter approach is to set the charge current to “Zero”. The result is that the charger is not used to recharge the batteries, loads are powered from the batteries when there’s sufficient stored energy, and loads are powered from the grid – with no energy efficiency penalty – when the batteries are low. Battery recharging is entire at the mercy of available solar insolation.

In the end, the configuration you’re considering may reduce your energy bill, but it may also increase your “carbon footprint”. Accordingly, an option for you to consider is to exchange the charger for another PV module, and then buy/build a “low battery transfer” gadget.

Interesting dilemma, and, to me, anyway, an example of how complicated this energy conservation equation can be.

Regards,
Jim / crewzer

BB. · December 2007

Re: Special Purpose Timer Needed

To even make the point that using more off-peak power than peak power is less than environmentally friendly...

Generally, off peak "excess power" available for cheap rates are coal and nuclear power plants. And peak power plants (at least in my areal) are natural gas...

So, you are now increasing the very high carbon fuel coal fired or the nuclear genie consumption and cutting the use of natural gas (which is less carbon "rich" fuel)...

And you are also cycling the batteries more (night/day/deeper discharge) with the offsetting of heavy loads and spending money/resources for early replacement vs spending the money on conservation (insulation, energy star, ground sourced heat pumps, etc.).

And, in the end, I believe that saving money is about the best one can relate to using less resources overall (day/night battery load shifting)--I di wonder how long the differentials will remain (in California, electric rates are highly political--and, from my point of few, this muddies the whole environmental "damage" picture one can glean from rate costs).

In the end, load shifting only shifts loads (and increases over all energy/resource use "forever"), whereas conservation is a one-time expense with savings in costs and resources "forever more."

-Bill

niel · December 2007

Re: Special Purpose Timer Needed

it sounds like this could be revamped to a gridtied pv system thus reducing the overall carbon footprint by selling excess during the day and using some power at night from the utility being used as a battery, so to speak. more efficiency with less carbon as pv power is not giving a carbon footprint. to use the utility power during the evening to charge the batteries will ultimately use more overall power due to efficiency losses to do the same work the daytime utility power would've done and done cheaper than your proposition imho.

SolarJohn · December 2007

Re: Special Purpose Timer Needed

You’ve all given me a lot to think about, and I appreciate your comments. I do hope to reduce my carbon footprint, and to save money on my electric bill, and to be more self-sufficient, etc., but I’ll have to do these things one step at a time as my budget will allow. My plan also includes conservation, and energy efficiency improvements, and I’ve done quite a bit in that area already. Right now, all I want to do is take advantage of an opportunity to buy electricity at an unbelievably low nighttime rate, store that energy, and use it when rates are higher. I’ll start small, and expand if it looks like it will be worthwhile to do so. When $1 per watt solar panels become available to the public, I’ll really reduce my carbon footprint……..

Special Purpose Timer Needed

Comments

Categories