Residential Solar Relieving Peak Demand

Started by rickman July 17, 2017
My understanding is the peak usage period each day in the summer is about 3 
to 6 PM.  A few days ago the forecast was for 95F+ for a couple of days. 
The local electrical utility cooperative sent an email asking members to 
reduce power consumption between 3 and 6.  I complied by cutting off my AC 
during that period.  Before I cut it off I lowered the thermostat a couple 
degrees so the house would cool down a bit and become a thermal storage 
tank.  It seemed to work pretty well as the temperature inside the house 
only reached 79 or 80 each day by the time the A/C was turned back on after 
6.  I decided to use the programming feature on the thermostat to do this 
every day.

My utility has an hourly usage view mode and I see the power consumption 
pattern shift dramatically drawing peak usage earlier in the day when the 
A/C lowers the set point until 3 PM when the set point is raised to 82F 
using 2.5 to 3 kW.  Then the usage drops to a fraction of a kW until the 
thermostat is lowered to 77F after 6 PM where it rises to 3 kW for one or 
two hours until the outside temp drops and power usage drops accordingly.

I don't know yet if this is costing me money or saving me money.  There 
currently is no time factor on the metering currently.  The distribution 
charge by the utility is lower after a base amount of 300 kWHr each month, 
so the incremental rate is lower than the average rate.  Once  I have  more 
data I will add up the costs each day and see if I can tell any difference.

But what is notable is the peak demand shift from 3-6 to the periods before 
and after that period.  If the utility is asking us to cut back on demand, 
it must be important to them.  My utility is a coop and so is not motivated 
by profit.  This could be extended by using thermal storage of some sort.  I 
have read about incorporating beads of coconut oil or a particular type of 
paraffin into wallboard as a phase change material.  Coconut oil melts over 
a range of 74 to 80 degrees (approx) and so would be good for this.  There 
are paraffins which melt in this range as well.  During off peak hours the 
cool air can be passed through a tank of these materials for thermal 
storage, then when cooling is needed the A/C is left off and the warm air 
looses heat to the phase change material as it melts.  I've not been able to 
find good info on the latent heat of melting for either of these materials. 
The coconut oil would be the least expensive, but there is little good data 
on it.  So I can't estimate how large a tank would be needed.

-- 

Rick C
On Monday, July 17, 2017 at 7:46:42 PM UTC-4, rickman wrote:
> My understanding is the peak usage period each day in the summer is about 3 > to 6 PM. A few days ago the forecast was for 95F+ for a couple of days. > The local electrical utility cooperative sent an email asking members to > reduce power consumption between 3 and 6. I complied by cutting off my AC > during that period. Before I cut it off I lowered the thermostat a couple > degrees so the house would cool down a bit and become a thermal storage > tank. It seemed to work pretty well as the temperature inside the house > only reached 79 or 80 each day by the time the A/C was turned back on after > 6. I decided to use the programming feature on the thermostat to do this > every day. > > My utility has an hourly usage view mode and I see the power consumption > pattern shift dramatically drawing peak usage earlier in the day when the > A/C lowers the set point until 3 PM when the set point is raised to 82F > using 2.5 to 3 kW. Then the usage drops to a fraction of a kW until the > thermostat is lowered to 77F after 6 PM where it rises to 3 kW for one or > two hours until the outside temp drops and power usage drops accordingly. > > I don't know yet if this is costing me money or saving me money. There > currently is no time factor on the metering currently. The distribution > charge by the utility is lower after a base amount of 300 kWHr each month, > so the incremental rate is lower than the average rate. Once I have more > data I will add up the costs each day and see if I can tell any difference. > > But what is notable is the peak demand shift from 3-6 to the periods before > and after that period. If the utility is asking us to cut back on demand, > it must be important to them. My utility is a coop and so is not motivated > by profit. This could be extended by using thermal storage of some sort. I > have read about incorporating beads of coconut oil or a particular type of > paraffin into wallboard as a phase change material. Coconut oil melts over > a range of 74 to 80 degrees (approx) and so would be good for this. There > are paraffins which melt in this range as well. During off peak hours the > cool air can be passed through a tank of these materials for thermal > storage, then when cooling is needed the A/C is left off and the warm air > looses heat to the phase change material as it melts. I've not been able to > find good info on the latent heat of melting for either of these materials. > The coconut oil would be the least expensive, but there is little good data > on it. So I can't estimate how large a tank would be needed. > > -- > > Rick C
DoE has been experimenting with this concept for some years now. http://www.pbs.org/wgbh/nova/next/tech/melting-to-keep-cool/ National Gypsum has a drywall product that was used in DoE trials, not sure if it's for sale yet: http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/storing-heat-walls-phase-change-materials These are mainly for solar homes to moderate the internal temperature swings. But there's no reason it could not be used in a situation like yours.
bloggs.fredbloggs.fred@gmail.com wrote on 7/17/2017 8:57 PM:
> On Monday, July 17, 2017 at 7:46:42 PM UTC-4, rickman wrote: >> My understanding is the peak usage period each day in the summer is about 3 >> to 6 PM. A few days ago the forecast was for 95F+ for a couple of days. >> The local electrical utility cooperative sent an email asking members to >> reduce power consumption between 3 and 6. I complied by cutting off my AC >> during that period. Before I cut it off I lowered the thermostat a couple >> degrees so the house would cool down a bit and become a thermal storage >> tank. It seemed to work pretty well as the temperature inside the house >> only reached 79 or 80 each day by the time the A/C was turned back on after >> 6. I decided to use the programming feature on the thermostat to do this >> every day. >> >> My utility has an hourly usage view mode and I see the power consumption >> pattern shift dramatically drawing peak usage earlier in the day when the >> A/C lowers the set point until 3 PM when the set point is raised to 82F >> using 2.5 to 3 kW. Then the usage drops to a fraction of a kW until the >> thermostat is lowered to 77F after 6 PM where it rises to 3 kW for one or >> two hours until the outside temp drops and power usage drops accordingly. >> >> I don't know yet if this is costing me money or saving me money. There >> currently is no time factor on the metering currently. The distribution >> charge by the utility is lower after a base amount of 300 kWHr each month, >> so the incremental rate is lower than the average rate. Once I have more >> data I will add up the costs each day and see if I can tell any difference. >> >> But what is notable is the peak demand shift from 3-6 to the periods before >> and after that period. If the utility is asking us to cut back on demand, >> it must be important to them. My utility is a coop and so is not motivated >> by profit. This could be extended by using thermal storage of some sort. I >> have read about incorporating beads of coconut oil or a particular type of >> paraffin into wallboard as a phase change material. Coconut oil melts over >> a range of 74 to 80 degrees (approx) and so would be good for this. There >> are paraffins which melt in this range as well. During off peak hours the >> cool air can be passed through a tank of these materials for thermal >> storage, then when cooling is needed the A/C is left off and the warm air >> looses heat to the phase change material as it melts. I've not been able to >> find good info on the latent heat of melting for either of these materials. >> The coconut oil would be the least expensive, but there is little good data >> on it. So I can't estimate how large a tank would be needed. >> >> -- >> >> Rick C > > DoE has been experimenting with this concept for some years now. > http://www.pbs.org/wgbh/nova/next/tech/melting-to-keep-cool/ > National Gypsum has a drywall product that was used in DoE trials, not sure if
it's for sale yet:
>
http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/storing-heat-walls-phase-change-materials
> These are mainly for solar homes to moderate the internal temperature swings. But
there's no reason it could not be used in a situation like yours. Kinda like streamlining cars. Any car will benefit from using it, but they only seem to apply it optimally to the ones that are otherwise designed for high fuel efficiency or just plain go fast, or in the case of Tesla - BOTH. -- Rick C
On 18/07/17 14:30, Adrian Jansen wrote:
> On 18/07/2017 9:46 AM, rickman wrote: > > > change material as it melts. I've not been able to find good info on > > the latent heat of melting for either of these materials. The coconut > > oil would be the least expensive, but there is little good data on it. > > So I can't estimate how large a tank would be needed. > > Unless you find actual figures to prove otherwise, I would have > thought ordinary water would have a higher specific heat than even the > latent heat of an oil. And its cheap, and easy to handle. > > I often thought about 2 rainwater tanks, one inside the other, with some > good insulator between the 2. Just pump water in from a radiator ( > cooler ) at night, and out to the house in the day. In winter, reverse > the process. > > Havent got around to sizing yet. One of those sometime projects.
If you already have hydronic heating, why not? But it's expensive to fit during a build, and more expensive to retrofit. Clifford Heath
On Tuesday, 18 July 2017 06:05:40 UTC+1, Adrian Jansen  wrote:
> On 18/07/2017 9:46 AM, rickman wrote: > > > change material as it melts. I've not been able to find good info on > > the latent heat of melting for either of these materials. The coconut > > oil would be the least expensive, but there is little good data on it. > > So I can't estimate how large a tank would be needed. > > Unless you find actual figures to prove otherwise, I would have > thought ordinary water would have a higher specific heat than even the > latent heat of an oil. And its cheap, and easy to handle. > > I often thought about 2 rainwater tanks, one inside the other, with some > good insulator between the 2. Just pump water in from a radiator ( > cooler ) at night, and out to the house in the day. In winter, reverse > the process. > > Havent got around to sizing yet. One of those sometime projects.
What does the 2nd tank do? NT
On Tuesday, July 18, 2017 at 1:05:40 AM UTC-4, Adrian Jansen wrote:
> On 18/07/2017 9:46 AM, rickman wrote: > > > change material as it melts. I've not been able to find good info on > > the latent heat of melting for either of these materials. The coconut > > oil would be the least expensive, but there is little good data on it. > > So I can't estimate how large a tank would be needed. > > Unless you find actual figures to prove otherwise, I would have > thought ordinary water would have a higher specific heat than even the > latent heat of an oil. And its cheap, and easy to handle. > > I often thought about 2 rainwater tanks, one inside the other, with some > good insulator between the 2. Just pump water in from a radiator ( > cooler ) at night, and out to the house in the day. In winter, reverse > the process. > > Havent got around to sizing yet. One of those sometime projects.
Water does not have a terrific heat capacity, you will require tons of it. Phase change is the answer for high density storage, the big problem is all of the candidate materials are hazmat.
> > -- > Regards, > > Adrian Jansen
On 18/07/17 00:46, rickman wrote:
> My understanding is the peak usage period each day in the summer is about 3 to 6 > PM.
That very much depends on where you are. For the UK, see http://www.gridwatch.templar.co.uk/ If you want to look at days in the winter, you can download .xls files with the raw data used for those graphs.
On 18/07/2017 00:46, rickman wrote:
> My understanding is the peak usage period each day in the summer is > about 3 to 6 PM. A few days ago the forecast was for 95F+ for a couple > of days. The local electrical utility cooperative sent an email asking > members to reduce power consumption between 3 and 6. I complied by > cutting off my AC during that period. Before I cut it off I lowered the > thermostat a couple degrees so the house would cool down a bit and > become a thermal storage tank. It seemed to work pretty well as the > temperature inside the house only reached 79 or 80 each day by the time > the A/C was turned back on after 6. I decided to use the programming > feature on the thermostat to do this every day.
You can shave quite a bit off your mid afternoon cooling requirement by modifying the house to slow ingress of heat. How you do that is up to you but I found the relatively thin insulator with foil on the inside of sunward surfaces to be very affective at reducing thermal load. My own house in the UK has so much thermal inertia that it stays cool during the day simply by having left upper windows open at night. Aircon load in the UK is virtually non-existent our peak summer load is very flat: http://www.gridwatch.templar.co.uk/ It is a bit spikier in winter when heating is necessary. You would probably use less electricity by tolerating a slightly warmer set point all through the day than by super cooling and switching off for peak. Shading the sunward side of the building with vegetation would make a huge difference (eg ivy or virginia creeper).
> My utility has an hourly usage view mode and I see the power consumption > pattern shift dramatically drawing peak usage earlier in the day when > the A/C lowers the set point until 3 PM when the set point is raised to > 82F using 2.5 to 3 kW. Then the usage drops to a fraction of a kW until > the thermostat is lowered to 77F after 6 PM where it rises to 3 kW for > one or two hours until the outside temp drops and power usage drops > accordingly. > > I don't know yet if this is costing me money or saving me money. There > currently is no time factor on the metering currently. The distribution > charge by the utility is lower after a base amount of 300 kWHr each > month, so the incremental rate is lower than the average rate. Once I > have more data I will add up the costs each day and see if I can tell > any difference.
A smart meter that will show you consumption in realtime and daily usage is quite handy for this sort of thing.
> > But what is notable is the peak demand shift from 3-6 to the periods > before and after that period. If the utility is asking us to cut back > on demand, it must be important to them. My utility is a coop and so is > not motivated by profit. This could be extended by using thermal > storage of some sort. I have read about incorporating beads of coconut > oil or a particular type of paraffin into wallboard as a phase change > material. Coconut oil melts over a range of 74 to 80 degrees (approx) > and so would be good for this. There are paraffins which melt in this > range as well. During off peak hours the cool air can be passed through > a tank of these materials for thermal storage, then when cooling is > needed the A/C is left off and the warm air looses heat to the phase > change material as it melts. I've not been able to find good info on > the latent heat of melting for either of these materials. The coconut > oil would be the least expensive, but there is little good data on it. > So I can't estimate how large a tank would be needed.
Latent heat stores are a bit of a mugs game. Anything that works well enough eventually degrades or corrodes its container in such a way as to either stop working or leak out. Big rocks or scrap iron in a huge insulated pit in the ground is probably as good as it gets. -- Regards, Martin Brown
On Tuesday, July 18, 2017 at 7:46:58 AM UTC-4, Martin Brown wrote:
> On 18/07/2017 00:46, rickman wrote: > > My understanding is the peak usage period each day in the summer is > > about 3 to 6 PM. A few days ago the forecast was for 95F+ for a couple > > of days. The local electrical utility cooperative sent an email asking > > members to reduce power consumption between 3 and 6. I complied by > > cutting off my AC during that period. Before I cut it off I lowered the > > thermostat a couple degrees so the house would cool down a bit and > > become a thermal storage tank. It seemed to work pretty well as the > > temperature inside the house only reached 79 or 80 each day by the time > > the A/C was turned back on after 6. I decided to use the programming > > feature on the thermostat to do this every day. > > You can shave quite a bit off your mid afternoon cooling requirement by > modifying the house to slow ingress of heat. How you do that is up to > you but I found the relatively thin insulator with foil on the inside of > sunward surfaces to be very affective at reducing thermal load.
That has been found to do a number on the exterior cladding/roofing so as to accelerate their deterioration.
> My own > house in the UK has so much thermal inertia that it stays cool during > the day simply by having left upper windows open at night. Aircon load > in the UK is virtually non-existent our peak summer load is very flat: >
Mass of any kind in new construction is prohibitively expensive unless you do something like use dirt. Even most new brick homes in U.S. only use brick on the front wall, use wainscot, or thin brick cladding to give the appearance of brick. Heavier materials require heavier support framing, so they're avoided.
On Monday, July 17, 2017 at 10:48:32 PM UTC-4, rickman wrote:
> bloggs.fredbloggs.fred@gmail.com wrote on 7/17/2017 8:57 PM: > > On Monday, July 17, 2017 at 7:46:42 PM UTC-4, rickman wrote: > >> My understanding is the peak usage period each day in the summer is about 3 > >> to 6 PM. A few days ago the forecast was for 95F+ for a couple of days. > >> The local electrical utility cooperative sent an email asking members to > >> reduce power consumption between 3 and 6. I complied by cutting off my AC > >> during that period. Before I cut it off I lowered the thermostat a couple > >> degrees so the house would cool down a bit and become a thermal storage > >> tank. It seemed to work pretty well as the temperature inside the house > >> only reached 79 or 80 each day by the time the A/C was turned back on after > >> 6. I decided to use the programming feature on the thermostat to do this > >> every day. > >> > >> My utility has an hourly usage view mode and I see the power consumption > >> pattern shift dramatically drawing peak usage earlier in the day when the > >> A/C lowers the set point until 3 PM when the set point is raised to 82F > >> using 2.5 to 3 kW. Then the usage drops to a fraction of a kW until the > >> thermostat is lowered to 77F after 6 PM where it rises to 3 kW for one or > >> two hours until the outside temp drops and power usage drops accordingly. > >> > >> I don't know yet if this is costing me money or saving me money. There > >> currently is no time factor on the metering currently. The distribution > >> charge by the utility is lower after a base amount of 300 kWHr each month, > >> so the incremental rate is lower than the average rate. Once I have more > >> data I will add up the costs each day and see if I can tell any difference. > >> > >> But what is notable is the peak demand shift from 3-6 to the periods before > >> and after that period. If the utility is asking us to cut back on demand, > >> it must be important to them. My utility is a coop and so is not motivated > >> by profit. This could be extended by using thermal storage of some sort. I > >> have read about incorporating beads of coconut oil or a particular type of > >> paraffin into wallboard as a phase change material. Coconut oil melts over > >> a range of 74 to 80 degrees (approx) and so would be good for this. There > >> are paraffins which melt in this range as well. During off peak hours the > >> cool air can be passed through a tank of these materials for thermal > >> storage, then when cooling is needed the A/C is left off and the warm air > >> looses heat to the phase change material as it melts. I've not been able to > >> find good info on the latent heat of melting for either of these materials. > >> The coconut oil would be the least expensive, but there is little good data > >> on it. So I can't estimate how large a tank would be needed. > >> > >> -- > >> > >> Rick C > > > > DoE has been experimenting with this concept for some years now. > > http://www.pbs.org/wgbh/nova/next/tech/melting-to-keep-cool/ > > National Gypsum has a drywall product that was used in DoE trials, not sure if
it's for sale yet:
> >
http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/storing-heat-walls-phase-change-materials
> > These are mainly for solar homes to moderate the internal temperature swings.
But there's no reason it could not be used in a situation like yours.
> > Kinda like streamlining cars. Any car will benefit from using it, but they > only seem to apply it optimally to the ones that are otherwise designed for > high fuel efficiency or just plain go fast, or in the case of Tesla - BOTH. > > -- > > Rick C
A solar chimney is a distinct and economical possibility that works well for solar cooling (oxymoronic I know) when designed properly. You draw outside air in through an underground cooling network and ventilate it out the top. https://en.wikipedia.org/wiki/Solar_chimney