diy solar

diy solar

Mitigation of demand from utility with solar

When it's over 100 degrees outside after dusk and A/C set for 77 degrees, indoor temperature grows very fast if A/C is not running. However my DIY "Smart Demand" system described earlier on this forum is mitigating demand spikes with A/C pretty well keeping demand level under 5kW. Please see a screenshot above

However I cannot convince anybody in my family to save ANY electricity during peak time. Showing them $33.48 charge for running a dryer just for 20 minutes together with oven during peak time doesn't make any effect. They simply don't care. Hence the solution should be purely technical without touching human habits

This is how that $33.48 is calculated per E-27 plan from SRP for 7.1kW demand peak on 4/29/21 shown on a screenshot above:

First three kilowatts of 7.1kW:
3kW x $3.49 = $10.47

Next 4.1 kilowatts (7.1kW-3kW):
4.1kW x $5.58 = $22.87

Total: $33.48
 
In California demand charges only apply to commercial accounts. Unfortunately for me that includes apartment buildings and makes it tough to give my tenants EV charging. It is really a shame because I can put them on a timer so that they are off peak when demand on the grid is at its lowest.
 
Odd, when it’s -15f out and we lose power (thus heat) it takes quite some time before our house goes from 68 to say 55, talking 12 hours.

Have you done an efficency audit? See where you could improve the envelope of the house? Even ours built in 2002 is considered out of date for modern efficiency standards.
 
Cooling off, it is only heat conduction and air leakage.
Heating up, there are those two plus sun shining through windows and onto exterior surfaces.

For either case, wind will remove air from near external walls (which had transferred some heat one way or the other) and bring in more air of ambient temperature. In the case of sunshine having heated exterior higher than ambient, wind would help carry the heat away.

I think heat load from the sun is a significant factor.
 
But with the demand charges specifically timed till after peak solar, turning off AC in that window solar gain shouldn’t be much.
With a properly sealed house envelope 3-5 hours without AC running shouldn’t dramatically impact heat gain.

The other thing that would help mitigate it would be if the solar array were south west facing, capturing that afternoon KW more than peak solar irradiance. This would help in a new design but still something that helps concerns with peak demand charges.
 
But with the demand charges specifically timed till after peak solar, turning off AC in that window solar gain shouldn’t be much.
With a properly sealed house envelope 3-5 hours without AC running shouldn’t dramatically impact heat gain.

The other thing that would help mitigate it would be if the solar array were south west facing, capturing that afternoon KW more than peak solar irradiance. This would help in a new design but still something that helps concerns with peak demand charges.

Solution described above might work if all house residents cared about saving money on electricity. Unfortunately they don't. So all those efforts break because of the human factor

The solution I'm looking for must be purely technical and meet following requirements:
  • Mitigate energy consumption between 6-8pm. That's the only concern (see screenshots). Typically it's around 10kWhr total
  • Indoor temperature should NOT exceed 78 degrees and cannot go lower than 75 with precooling. Any out of range temperatures will cause a LOT of complaining
  • The worst case demand might be A/C 6kW+Oven 4kW + Dryer 4kW = 14kW
  • Allowing 5kW as reasonable demand limit is comes to ~9kW deficiency that should be covered by battery-based system
1620930099999.png
1620930167827.png
 
Solution described above might work if all house residents cared about saving money on electricity. Unfortunately they don't. So all those efforts break because of the human factor

Coin-op (or these days, needs to be a bill reader that only takes $20's)

Current transformer + timer rigged to shut off the TV (or internet) if excessive power drawn from grid.

"Negative Reinforcement" (bark collar providing appropriate feedback.)
 
I think the idea of disabling the dryer from 6PM to 8PM as a good move to make.

Charging the batteries during the day and then using the power during 6PM to 8PM is a great idea if you can figure out all the moving pieces. There are deals that pop up for LifePo4 that are around $200/kwh. 5kW of battery for ~$1000. Limit your DoD to 80% or 4kW to make the batteries last a little longer. Would pay for itself after 1 year which is awesome.

We have APS and have a similar peak/off peak plan but APS' peak runs from 3PM to 8PM. After reading your post, if I ever move, I'll try to avoid a house with SRP.
 
I think the idea of disabling the dryer from 6PM to 8PM as a good move to make.
That's what I'm thinking as well. However completely disabling (same as trying to do it with A/C) would raise a lot of yelling in my house

My already running DIY "Smart Demand" system is pretty effective with managing demand under 5kW just by manipulating with A/C compressor at peak time. Please see a chart:
1622221501201.png
The only concern when dryer and oven were turned on simultaneously. Even with A/C compressor off, that created a demand peak of 7.1kW on April 29th at 7pm.

So I'm thinking about controlling a dryer's heater with "Smart Demand" as well similar to A/C compressor. The motor in dryer will run as normal during peak time. Not a big deal as it's just 300W. However the heater (4.5kW) will be turned on only if calculated demand within 30 minutes combined from all electrical systems in the house (A/C, Dryer, Oven, Stove, Microwave and other misc. loads) will NOT exceed 5kW

The oven will have priority as the process of its usage cannot be interrupted. Then dryer heater (on an off to keep demand under 5kW) and then A/C compressor with lowest priority. If somebody complains, "It's hot," the answer is, "Don't use oven in Summer time."

The only technical challenge with this, I have to open a dryer casing to install a relay in heater circuit and connect it with a USB controller coming from my server running software. Then updating a PowerShell code in "Smart Demand" software

I don't want to run a wire from the Laundry room to a controller PCB next to server in a different room.

Can somebody suggest a wireless solution for transmitting 12V/300mA DC control signal to relay that I have? Or wireless relay with a USB -connected transmitter capable of controlling 240V/40A AC circuit? It must have and SDK for controlling it via PowerShell (e.g. by using .NET)

Ideally the transmitter to be hooked up into USB port in server and receiver installed inside of the dryer will provide that signal to activate a relay when I need to turn off the heater there
 
Last edited:
The only technical challenge with this, I have to open a dryer casing to install a relay in heater circuit and connect it with a USB controller coming from my server running software. Then updating a PowerShell code in "Smart Demand" software

Can somebody suggest a wireless solution for transmitting 12V/300mA DC control signal to relay that I have? Or wireless relay with a USB -connected transmitter capable of controlling 240V/40A AC circuit? It must have and SDK for controlling it via PowerShell (e.g. by using .NET)

Dryer typically has motor and controls between L1 and N, heating element between L1 and L2. (or motor/controls are on L2 instead of L1).

If you install a relay to disconnect the hot which is only used by heater, dryer will be on "air fluff".
If relay switches that leg of dryer circuit from hot to neutral, it'll operated on 120V at 1/4 power.
You can do that somewhere in the house wiring instead of dryer if desired.

I'll probably do it in an outlet box with cord to plug into permanent outlet, so it can simply be disconnected. I'm considering using RJ45, with voltage (48VDC) control between a pair of pins that aren't a signal pair for Ethernet, so no Ethernet magnetics get burned up if somebody plugs networking gear into my control wiring.
 
Back
Top