Ive had solar for a year and now the utility company charges a demand fee... not cool.
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Ampster
Renewable Energy Hobbyist
It is actually a lot of single measurements and the one fifteen minute period which has the highest demand determines the fixed fee.
OzSolar
Whatever you did, that's what you planned.
To that point: It's worth mentioning there's difference between energy management systems and demand management systems.
Common to both is that they tend to be full of pitfalls and eventually get bypassed/overridden after they've repeatedly proven that they both don't work AND dramatically effect occupant comfort/lifestyle. (I've been in the energy efficiency business for over 30 years)
The biggest difference is that a demand management system only has to screw up one time during the month at which point you've set your peak.
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Hedges
I See Electromagnetic Fields!
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At significant expense, a whole-house grid interactive battery inverter can shave peak current to target level.
A Power Wall (AC coupled battery) can try to do the same. Typically has max power output in the 5kW to 10kW range. You could tell it to start inverting whenever draw exceeds say 5kW, recharge when draw drops below 5kW. Or whatever peak demand you want to remain under.
As for managing loads, that does/should make sense. One Miele washer/dryer combo had water heating, and dryer plugged into washer. I think it was able to limit current draw from a single outlet by cutting out dryer element when heating water.
For water heater, low wattage and more energy storage seems like the way to go. Larger tank and/or higher temperature + tempering valve. 80 gallon? 120 gallon? More than one? Tanks are cheaper than batteries, and cheaper than one-off programming/implementation of control systems. I went for 120V and a timer.
A Power Wall (AC coupled battery) can try to do the same. Typically has max power output in the 5kW to 10kW range. You could tell it to start inverting whenever draw exceeds say 5kW, recharge when draw drops below 5kW. Or whatever peak demand you want to remain under.
As for managing loads, that does/should make sense. One Miele washer/dryer combo had water heating, and dryer plugged into washer. I think it was able to limit current draw from a single outlet by cutting out dryer element when heating water.
For water heater, low wattage and more energy storage seems like the way to go. Larger tank and/or higher temperature + tempering valve. 80 gallon? 120 gallon? More than one? Tanks are cheaper than batteries, and cheaper than one-off programming/implementation of control systems. I went for 120V and a timer.
Within the next few weeks I'll be adding 20 KWH of batteries to my Sol-Ark 15K. I would set up peak shaving if my utility added Demand charges to residential service. We have a dedicated service for a detached garage that powers the well pump. This they call general service and includes Demand charges above 5 KW. The Sol-Ark 15K with 5 KW peak shaving would serve my needs.
Ampster
Renewable Energy Hobbyist
Does your well pump cycle for more than fifteen minutes or draw more than 5kW?
For load control, you might consider the QO-PL (Powerlink) breakers with remote control. They have a motor that clicks the breaker on or off. Datasheet attached. My brother used this for controlling his lights in his hangar to avoid running a lot of AC wires everywhere.
Runs on 24 VDC. Unlike a relay, it doesn't consume power in either state (maintains state with power off). Unlike a relay, it doesn't require a separate enclosure/box. Just switch out the breaker in the panel and wire up a controller to drive the control inputs.
Not particularly cheap, but relatively simple to use and a lot cheaper than a rewire or load management box. Examples:
1 pole 20 A:
2 pole 30 A:
You basically need some discrete signal to control whether the load is allowed or not.
Mike C.
Runs on 24 VDC. Unlike a relay, it doesn't consume power in either state (maintains state with power off). Unlike a relay, it doesn't require a separate enclosure/box. Just switch out the breaker in the panel and wire up a controller to drive the control inputs.
Not particularly cheap, but relatively simple to use and a lot cheaper than a rewire or load management box. Examples:
1 pole 20 A:
2 pole 30 A:
You basically need some discrete signal to control whether the load is allowed or not.
Mike C.
wattmatters
Solar Wizard
Has it really jumped, or have the units just been changed from Xc/kW/day to $Y/kW/month?
With c/kW/day charge, that is multiplied by the peak demand and also the number of days in the month.
With a $/kW/month charge, that is multiplied by the peak demand only.
e.g. if the demand charge was previously quoted as 10c/kW/day, then that's equivalent to $3/kW/month (for a 30 day month).
As I understand from earlier in this thread and viewing the invoice, the units are kW without a time basis. Use 10kW for 15 minutes (measurement interval) one time in a billing cycle and you're nailed for a 10.000 x $3.00 amount.
Now if you repeat that every day for the entire billing cycle the only difference in the bill is the usage total for 2.5kWh that accrues for each instance.
I've never seen a demand charge on that meter. I suppose it's possible for the well pump to run continuously. Run current on 240 VAC is 10 amp. Other measurable loads are an 18,000 BTU heat pump and fish pond pumps that together with UV lamps consuming about 800 watts. It isn't likely to exceed 5 KW for 15 minutes.
wattmatters
Solar Wizard
Normally demand pricing has a quid pro quo with general consumption tariffs being lower than for TOU-only billing. Some however may have no choice in the matter.
IOW there's some swings and roundabouts. If you are able to not have high demand in the peak demand window, then the lower consumption tariffs can result in a lower bill.
I track our peak demand so I can assess the impact should I move to such a tariff type (we have a choice of TOU or demand).
Turns out the demand tariff for us is A$100/year more. It's $100 I rather have than the power company but it's not exactly a massive difference either.
My issue is I can't peak shave our ducted aircon, particularly in Summer as it is not powered via our off-grid system.
I would need much more capacity to do that. More PV (which I have, so no cost for that other than some instal help), more battery, about another $3k worth, and more inverter capacity to power the ducted AC with. Need at least 6 kW, so that's ~$2k by the time I include all the bits for connecting it. Add $500-$1k for sparky time (a legal requirement here) and I'm looking at ~A$5.5-6k. I need to do the numbers on actual consumption but given our total annual bill is ~$1200-$1500, the payback is likely to be pretty crap. Maybe $500-600/year tops.
IOW there's some swings and roundabouts. If you are able to not have high demand in the peak demand window, then the lower consumption tariffs can result in a lower bill.
I track our peak demand so I can assess the impact should I move to such a tariff type (we have a choice of TOU or demand).
Turns out the demand tariff for us is A$100/year more. It's $100 I rather have than the power company but it's not exactly a massive difference either.
My issue is I can't peak shave our ducted aircon, particularly in Summer as it is not powered via our off-grid system.
I would need much more capacity to do that. More PV (which I have, so no cost for that other than some instal help), more battery, about another $3k worth, and more inverter capacity to power the ducted AC with. Need at least 6 kW, so that's ~$2k by the time I include all the bits for connecting it. Add $500-$1k for sparky time (a legal requirement here) and I'm looking at ~A$5.5-6k. I need to do the numbers on actual consumption but given our total annual bill is ~$1200-$1500, the payback is likely to be pretty crap. Maybe $500-600/year tops.
wattmatters
Solar Wizard
I assume this is the change you are referring to from this post by the OP:
The demand charge of $3.75 (which would be a monthly amount x the peak demand value for the month), e.g. have a peak demand during the month of 5 kW and there will be a monthly demand charge of $18.75.
Some power companies express demand charge in units of kW/day, others use kW/month. In the former the monthly peak demand is multiplied by the per kW rate and the number of days in the month. In the latter the number of days in the month is already built into the tariff.
But see the quid pro quo? A demand charge is added but the consumption tariff is reduced.
The consumption tariff dropped by ~9% from 9.7c/kWh to 8.9c/kWh (0.8c/kWh). That drop applies to all consumption, not just what happens in that 15 minute interval.
Granted that's not much of a quid pro quo as the monthly consumption would need to be pretty high to make up for the demand charge.
Where I am the drop in consumption tariff if I choose demand tariff is 7.3c/kWh. So if my peak demand is say 6 kW, then the demand charge would be $5.13/kW/month x 6 kW = $30.78.
At 7.3c/kWh, that's equivalent to 422 kWh of consumption. So if I consume (from the grid) more than that per month, the demand tariff plan is cheaper. We only consume, on average, 276 kWh/month, so the demand tariff option costs more.
Hedges
I See Electromagnetic Fields!
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So long as different neighbors "Tower their Power" at different times, just the same for utility as all of them leveling out the load at the same time.
In other words, added complexity and concern for the consumer, with no benefit to the grid and no benefit to the operator except if he gets to stick it to the consumer.
10% cut in rate offsets $4 increase in monthly fee at $40/month usage.
Demand charge could be much more. Is that charged on every kWh, or only on kWh above a threshold like 5kW?
In other words, added complexity and concern for the consumer, with no benefit to the grid and no benefit to the operator except if he gets to stick it to the consumer.
10% cut in rate offsets $4 increase in monthly fee at $40/month usage.
Demand charge could be much more. Is that charged on every kWh, or only on kWh above a threshold like 5kW?
The demand charge comes about because of how power plants actually work. They can't throttle the plant precisely to meet demand, it just doesn't respond that way. So instead, the generate an excess amount of power and then throttle a load dump, usually a cooling tower or pond. They can quickly regulate that load since it is just a big resistor.
The more variability in the load, the more excess energy they have to generate and waste, and thus the more cost. Also, the more spikes in load, the heavier the transmission lines need to be to avoid excessive voltage drop.
For industrial users, demand charges are a fact of life from the start due to their high needs. For the highest users, like aluminum smelting, they have their own power plant just for that.
For homeowners, the theory is always that there are so many users the load levels out. But that's changing in modern times.
Case in point, there is a plant in Wales England called Dinorwig, also called Electric Mountain.
en.wikipedia.org
It is a pumped hydro station with 1.8 GW of turbines. It exists because of football (soccer) and because of electric kettles. The football provides the synchronizing event, the game is over, and that's time to put the kettle on. The little kettles in the UK are up to 2.8 KW (!!). They boil the water FAST! The average house in the UK doesn't use that much electricity, so the kettle is like a major spike in usage over the average.
At Dinorwig, they watch the game, say Manchester against Aresenal which might draw lots of viewers. When the game is near the end, they will pressurize the turbines with air and spin them up using the generators as a motor. This is the quick start mode. When the load spikes, they open the penstock and the plant can go from 0 to 1.8 GW in 16 seconds to meet the demand spike.
During the day, they pump the water back up to the reservoir during times of low use. So the plant doesn't generate new power, it just stores it like a huge battery.
If you had a community with lots of grid attached solar, it kind of acts like the kettles. With clouds, the plant is pumping out a lot of power since everybody's panels are weak. The cloud passes by and suddenly everybody has excess power they are pumping into the grid. The plant can't reduce production that fast, so it all goes to waste in a cooling tower. So the dream of generating clean energy hasn't saved any dirty power plant energy at all in this scenario. This is why grid tied residential solar doesn't scale without storage.
Of course, it isn't black and white like that. The cloud doesn't block and uncover the entire service area all at once, but residential grid tied solar worsens the peak to average ratio the power plant has to work with. The plant can use forecasts and models to adjust to some degree, but it is getting worse and not better.
EV rapid chargers are also making it worse. My car can charge at well over 250 KW and that load comes and goes when you hit a roadside fast charger for 15 minutes.
This is why you see utility scale battery systems being installed. Huge plants of trailer sized batteries. What these do is allow the utility to reduce the power plant output to close to average and let the battery produce or absorb the difference, much like your EV either drives or regens. This is exactly like residential battery system but on a much larger scale. With those systems, you can start to save power by wasting less of it in a load dump.
Another area I expect to see is demand control for EV home charging. EV charging can be used to eat the excess power *if* the power plant can control the demand precisely and quickly. This would allow the plant to load dump far less saving energy. Home EV charging is usually an overnight thing, so the plants can let it happen during the low use times.
Electricity is complicated and political as evidenced by the differing rules all over the country. At a certain point, going off grid is the ultimate treatment for being enslaved to the utility, but does require you manage you energy and loads carefully. The tech to do this is improving every single day and I expect the number of off grid homes will increase significantly over time.
Mike C.
The more variability in the load, the more excess energy they have to generate and waste, and thus the more cost. Also, the more spikes in load, the heavier the transmission lines need to be to avoid excessive voltage drop.
For industrial users, demand charges are a fact of life from the start due to their high needs. For the highest users, like aluminum smelting, they have their own power plant just for that.
For homeowners, the theory is always that there are so many users the load levels out. But that's changing in modern times.
Case in point, there is a plant in Wales England called Dinorwig, also called Electric Mountain.
Dinorwig Power Station - Wikipedia
It is a pumped hydro station with 1.8 GW of turbines. It exists because of football (soccer) and because of electric kettles. The football provides the synchronizing event, the game is over, and that's time to put the kettle on. The little kettles in the UK are up to 2.8 KW (!!). They boil the water FAST! The average house in the UK doesn't use that much electricity, so the kettle is like a major spike in usage over the average.
At Dinorwig, they watch the game, say Manchester against Aresenal which might draw lots of viewers. When the game is near the end, they will pressurize the turbines with air and spin them up using the generators as a motor. This is the quick start mode. When the load spikes, they open the penstock and the plant can go from 0 to 1.8 GW in 16 seconds to meet the demand spike.
During the day, they pump the water back up to the reservoir during times of low use. So the plant doesn't generate new power, it just stores it like a huge battery.
If you had a community with lots of grid attached solar, it kind of acts like the kettles. With clouds, the plant is pumping out a lot of power since everybody's panels are weak. The cloud passes by and suddenly everybody has excess power they are pumping into the grid. The plant can't reduce production that fast, so it all goes to waste in a cooling tower. So the dream of generating clean energy hasn't saved any dirty power plant energy at all in this scenario. This is why grid tied residential solar doesn't scale without storage.
Of course, it isn't black and white like that. The cloud doesn't block and uncover the entire service area all at once, but residential grid tied solar worsens the peak to average ratio the power plant has to work with. The plant can use forecasts and models to adjust to some degree, but it is getting worse and not better.
EV rapid chargers are also making it worse. My car can charge at well over 250 KW and that load comes and goes when you hit a roadside fast charger for 15 minutes.
This is why you see utility scale battery systems being installed. Huge plants of trailer sized batteries. What these do is allow the utility to reduce the power plant output to close to average and let the battery produce or absorb the difference, much like your EV either drives or regens. This is exactly like residential battery system but on a much larger scale. With those systems, you can start to save power by wasting less of it in a load dump.
Another area I expect to see is demand control for EV home charging. EV charging can be used to eat the excess power *if* the power plant can control the demand precisely and quickly. This would allow the plant to load dump far less saving energy. Home EV charging is usually an overnight thing, so the plants can let it happen during the low use times.
Electricity is complicated and political as evidenced by the differing rules all over the country. At a certain point, going off grid is the ultimate treatment for being enslaved to the utility, but does require you manage you energy and loads carefully. The tech to do this is improving every single day and I expect the number of off grid homes will increase significantly over time.
Mike C.
Ampster
Renewable Energy Hobbyist
That is how my demand charge with Southern California Edison works. In other words, the highest fifteen minute usage, determines the fixed charge for the entire month. I can't speak for others.
vwaudiguy
New Member
The lower consumption tariff does look good on paper... but when they hit you with power cost adjustments each month that are typically over 2 cents per... you start to realize that the lower tariff is mainly to look good to customers of other power companies comparing one company to the next.I assume this is the change you are referring to from this post by the OP:
The demand charge of $3.75 (which would be a monthly amount x the peak demand value for the month), e.g. have a peak demand during the month of 5 kW and there will be a monthly demand charge of $18.75.
Some power companies express demand charge in units of kW/day, others use kW/month. In the former the monthly peak demand is multiplied by the per kW rate and the number of days in the month. In the latter the number of days in the month is already built into the tariff.
But see the quid pro quo? A demand charge is added but the consumption tariff is reduced.
The consumption tariff dropped by ~9% from 9.7c/kWh to 8.9c/kWh (0.8c/kWh). That drop applies to all consumption, not just what happens in that 15 minute interval.
Granted that's not much of a quid pro quo as the monthly consumption would need to be pretty high to make up for the demand charge.
Where I am the drop in consumption tariff if I choose demand tariff is 7.3c/kWh. So if my peak demand is say 6 kW, then the demand charge would be $5.13/kW/month x 6 kW = $30.78.
At 7.3c/kWh, that's equivalent to 422 kWh of consumption. So if I consume (from the grid) more than that per month, the demand tariff plan is cheaper. We only consume, on average, 276 kWh/month, so the demand tariff option costs more.
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Hedges
I See Electromagnetic Fields!
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What prices do people see for home AC batteries, which can shave these peaks?
I just picked up some Sunny Boy Storage & LG RESU-10H. Battery is 10kWh and supports 5kW 0.5C charge and discharge. Inverter supports 5kW and up to 3 batteries.
Retail for battery & inverter is about $10k. I got them at liquidation prices (of course). Retail, the battery costs around $0.50/kWh of cycle life so not cost effective for shifting time of use, maybe for reducing peaks and demand charge.
As for the kettle, lower wattage (get a transformer to step down to 110V or lower power kettle) and start sooner. But they don't know when the game will end, correct? Need an insulated pot, table top storage water heater.
Question is how to motivate the soccer fans. Demand charge doesn't help get them to boil water at a different time; each person would still be charged the same.
I just picked up some Sunny Boy Storage & LG RESU-10H. Battery is 10kWh and supports 5kW 0.5C charge and discharge. Inverter supports 5kW and up to 3 batteries.
Retail for battery & inverter is about $10k. I got them at liquidation prices (of course). Retail, the battery costs around $0.50/kWh of cycle life so not cost effective for shifting time of use, maybe for reducing peaks and demand charge.
As for the kettle, lower wattage (get a transformer to step down to 110V or lower power kettle) and start sooner. But they don't know when the game will end, correct? Need an insulated pot, table top storage water heater.
Question is how to motivate the soccer fans. Demand charge doesn't help get them to boil water at a different time; each person would still be charged the same.
Ampster
Renewable Energy Hobbyist
It may vary by region as well. In California when a lot of plants which were ocean cooled, had to stop using the ocean, those plants were rebuilt using combined cycle technology, and those plants are more responsive to changes in demand. California has been dealing with a steep neck of the duck curve for some time and grid scale battery packs allow the grid to respond quickly and the batteries cover the deficit caused by the slower ramp up of tradtional generation.
Ampster
Renewable Energy Hobbyist
I am in the process of replacing a DIY pack that cost about $100/kWh with UL listed rack batteries which came in just under $400/kWh including the external enclosure which was required because the AHJ wanted to see them mounted on the exterior. That cost does not include the hybrid inverter and that can add thousands of mor to the equations but it is hard to use a cost per kWh metric for a device which puts out kWs. As a ballpark, Tesla Powerwalls which include an inverter cost over $1,000/kWh. The unit price for two Powerwalls goes down because they can share a common controller which also serves as the automatic transfer switch.
Hedges
I See Electromagnetic Fields!
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My SMA + LG equipment is about $250/kWh. Liquidated storage and e-waste disposal (both new in the box).
Rated for a little over half the cycle life of yours (assuming those are LiFePO4), but instead of 0.5C I may discharge up to 0.25C and charge maybe half that, wonder if that will extend life.
I don't have demand charges, rather time of use (off-peak 2/3 or 1/2 of on peak), so playing arbitrage would get me more credits for off peak use. Or let me use on-peak hopefully without blowing through my surplus again.
Santan offers Tesla Powerwall 2 but doesn't name the price.
Anybody know how much, and why at Santan?
www.santansolar.com
Rated for a little over half the cycle life of yours (assuming those are LiFePO4), but instead of 0.5C I may discharge up to 0.25C and charge maybe half that, wonder if that will extend life.
I don't have demand charges, rather time of use (off-peak 2/3 or 1/2 of on peak), so playing arbitrage would get me more credits for off peak use. Or let me use on-peak hopefully without blowing through my surplus again.
Santan offers Tesla Powerwall 2 but doesn't name the price.
Anybody know how much, and why at Santan?
Tesla Powerwall2 Battery | SanTan Solar
www.santansolar.com
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