Optimizing Power Usage

[Guardian7]

I live is Southern California and just went with a Grid Connected 26 panel and 6KW SolarEdge Inverter System on Net metering 2.0 TOU, now I'm trying to figure out when is the best time to schedule my Intelliflow pool pump which needs to run 6-8 hours a day and we don't heat our pool. Do I run my pump after 10pm or do I run when my system is producing it's most power?

[John_Dumke]

Good Question. I have the same situation with SCE TOU-D-A rate plan and a pool. TOU plan on SCE's website says the cheapest rates are between 8pm and 8am at 13/12 (Winter/Summer) cents per KWh, second cheapest is 8am - 2pm at 27/28 cents and 2-8 pm is 36/48 cents. Since my pool also has water solar panels that kick the pump RPM from 1100 rpm to 1800 rpm when temperature differentials are hot enough, I will keep my pump running throughout the day to allow for my pool solar to work. But if I didn't have pool solar, I would think either night time or before 2pm while I am at least generating enough power to offset that time usage might be best.

But it may depend also upon the size of your solar system relative to your overall usage, I am not sure yet either how NEM 2.0 works as I only have one full months bill on NEM 2.0.

I just looked at my first full months bill and it looks like SCE zero's us out based upon Money rather than on KWh's. Each time period is calculated based upon the cost for that time period and our account is either credited or debited with money based upon the net production or usage then times the cost per KWh during that time period. Then the money balance caries forward from month to month until our anniversary date.

This is how I think they system works based upon my interpretation of my first bill. If this is not correct, somebody please clarify. Thanks.

So this kind of seems weird (or very much in our favor) because our solar systems generate electricity during the more expensive portions of the day, especially during the summer. A system designed around 100% usage should generate about 3 times the energy during the day, when rates are high and then obviously none at night. So if we are net producers of expensive electricity and net users of cheap electricity doesn't the TOU system greatly favor the solar panel owner??? And might we not even need a system designed around 100% of KWh's used to have a zero bill???

If my interpretation of my bill is correct. Then the best time to run your pump will be based upon the size of your solar system relative to your usage and whether it is summer or winter. If you system is smaller then run the pump at night. If your system is larger then run your pump anytime you want except maybe not during peak 2-8pm times in the winter.

This is my best guess with only one month of NEM 2.0 bills under my belt.

Can anybody confirm the above?

[J.P.M.]

First question is how much (or how little) run time is required to maintain a safe and healthy water quality ? Provided you do not have an active solar pool water heating system, figure that out and plan to operate the pump no more than what's required for a healthy water environment.

If you have a solar pool water heating system, and it uses the pool water pump to circulate water through the collectors as most do, operate the pump as needed for health maintenance AND when the sun is shining. Usually or often, differential thermostats control when pool water gets circulated through the solar pool water heating system. Don't defeat that system logic. Doing so will be counterproductive to best and most economical system operation.

If you have a fossil fuel fired pool water heating system, the pump will need to operate whenever the thermostat that controls that heater calls for heat.

Second, is your PV system sized to over generate on an annual basis ? Never a good move. Reason, Depending on how oversized the PV system is relative to your annual usage as it can and usually does kill any PV system cost effectiveness you think you have in short order. But if the PV system is oversized, when and how much the pump runs won't have too much of an effect (but still some) on your bill until you burn through the excess generation the PV oversizing creates. Reason: Excess annual generation is paid to users by the POCO at very low rates. So, using up that excess will not increase an excess generation payment by the POCO very much (~ $0.03 - $0.05 or so per kWh).

After that, if you are not an annual overgenerator, and you are on a T.O.U. rate plan, you'll need to examine that rate's structure, particularly the times of lowest rates. Operating a pump for as short a time as possible while maintaining water quality and doing so will, along with when the pump runs will result in the lowest addition to your electric bills.

If you are on a T.O.U. rate plan that has a tiered rate laid over it (so that the first 130% of any billing period's usage gets a "credit" and so is, in effect, billed at a lower rate than any usage > 130 % of baseline for any period), or if you are still on the old tiered rate plans as many are, at least for now, when you run the pump won't matter much, or at least as much as how much you run the pump. That brings the decision down to how much to run the pump to maintain water quality along with considerations of when the sun is shining if you have a solar pool water heating system.

If you are NEM 2.0 and not on grandfathered rates, staying away from pump operation between the hours of 1600 and 2100 every day during the summer (when rates are highest) will be a good place to start after figuring out how long to operate the pump to maintain water quality.

Spend an hour or so getting frustrated learning about how your current POCO rate plan works and also how other rate plans available to you work with an eye toward seeing how to game the billing system(s) and minimizing pump operation together for the safest and lowest cost pump and pool water filtering/heating system.

A little more involved than you thought ? iWelcome to rate world hell.

[Guardian7]

Wow, you guys offered a lot of information, we have 26 295w Canadian Panels on the south facing roof and a 6kw SolarEdge Inverter, not sure why the inverter wasn't 8kw but we don't heat our pool, we run our pool pump 6-8 hours a day and we haven't seen our first bill yet so I'm curious if NEM 2.0 actually pays according to the TOU Tier system, see TOU Tier attached screenshot. I'm still not sure if we should run our pool pump when we're producing the most power or at night during lowest rate tier?

[John_Dumke]

Second, is your PV system sized to over generate on an annual basis ? Never a good move.

Never a good move? From a compensation from the POCO you are correct. However there are three reasons to disagree.

1) Usage can be flexible OR the "Not having to care and bug your wife to turn off the lights or not use the AC" reason. - Might my usage pick up a little knowing that I am not in Tier 3 of my old rate plan at 40 cents a KWh? Heck yeah! With a large home, five computers running all the time and a pool. I would tend to not run the AC during a couple of hot months. Plus I had to constantly either bug my wife to turn lights out after leaving a room or be very annoyed if I chose not to bug her. Either option is not fun. But now I just bought a couple of small electric space heaters for heating bedrooms in the winter, which may help me get out of tier 3 gas usage.

2) Predicting your actual production can be difficult. - While I have done all of the calculations on PV watts, my annual usage has ranged between 13,000 - 15,000 KWh. Combine that with the PV watts calculator possibly being 10% too conservative what is the "Right" number?

3) Incremental install of solar is much cheaper than after the fact install of solar - My self installed system consists of 24 x 385 watt panels. These panels costs about $230 plus add a $70 optimizer. So overbuilding my system by 2 panels (around 10%) only costs $600. The inverter stays the same and the additional wiring, racking, shipping cost and my labor is negligible. But if done after the fact, I would have the following additional expenses. Re engineering and re-permitting the system $600, additional shipping costs $200 for shipping 2 panels separately. My additional time to install the panels at a later date, which would include, ordering, install and walking permits through the city, probably at least 10 hours. If I billed my additional time at $100 an hour which is reasonable and that is what an electrician would charge then that is an additional $1,000.

So I can spend $600 now and have piece of mind, have added expand-ability and not have to bug my wife and possibly waste a portion of this money, But even if the entire $600 is a waste, the alternative would be to spend $1,800 ($600 + $200 + $1,000) of my time and money at a later date. The risk / reward favors getting the extra capacity at the time of install rather than at a later date.

[John_Dumke]

Wow, you guys offered a lot of information, we have 26 295w Canadian Panels on the south facing roof and a 6kw SolarEdge Inverter, not sure why the inverter wasn't 8kw but we don't heat our pool, we run our pool pump 6-8 hours a day and we haven't seen our first bill yet so I'm curious if NEM 2.0 actually pays according to the TOU Tier system, see TOU Tier attached screenshot. I'm still not sure if we should run our pool pump when we're producing the most power or at night during lowest rate tier?

I would probably set up your pool pump to run after 8pm and before 8am initially. Then look at your bill and decide if you want to run it at a different time. Would there be any reason you wouldn't want to just run it at night? I don't think so?

Then on a separate note, variable speed pool pumps are much more energy efficient. If you don't have one of those, I would encourage you to look into them, unless you have solar over capacity.

[Guardian7]

Thanks John, I will start by reprogramming our Pentair Intelliflo2 Pump for 10pm and run until 6am during the lowest rate tier. I guess this means I'm using power at a lower rate then I'm getting paid for during the day, NEM 2.0, NBC, and various TOU schedules still seem a little confusing for a newbie. I'm also trying to figure why my Solar company undersized the inverter, I expected an 8kw inverter for 26 x 295w panels, my inverter output hits 6kw by 10am, my Solaredge chart looks like a flattop from 10am until 3pm so what is happening to the extra power produced by the panels, is it getting dumped?

[John_Dumke]

Thanks John, I will start by reprogramming our Pentair Intelliflo2 Pump for 10pm and run until 6am during the lowest rate tier. I guess this means I'm using power at a lower rate then I'm getting paid for during the day, NEM 2.0, NBC, and various TOU schedules still seem a little confusing for a newbie. I'm also trying to figure why my Solar company undersized the inverter, I expected an 8kw inverter for 26 x 295w panels, my inverter output hits 6kw by 10am, my Solaredge chart looks like a flattop from 10am until 3pm so what is happening to the extra power produced by the panels, is it getting dumped?

26 x 295 = 7670. Yes it looks like your company undersized your SolarEdge Inverter. SE inverters come in 6,000 ($1,150), 7,600 ($1,300) and 10,000 ($1,660) watt models. From my understanding the newer HD wave models don't have as much over capacity and will clip around their rated number. The different in price between the 6,000 and 7,600 is only $150. Don't know why they didn't put in the 7,600? I would be kind of pissed for such an obvious dumb ass move.

If your panels are already putting out 6kw by 10am in the winter time, it sounds like your setup may produce better than the 7670 rating at high noon in the summer time and you may even want to upgrade to the 10,000 watt unit? Are some of your panels east facing on a higher pitched roof to get such strong morning production???

Yes the energy is just dumped I guess.

[bcroe]

what is happening to the extra power produced by the panels, is it getting dumped?

If your panels are able to put out more power than your inverter rating, the inverter will just shift off the MPPT panel
operating point, typically by drawing less current and allowing panel voltage to rise. The excess current will just be
dissipated by flowing inside the panel and heating a bit more. Remember this is only some percentage points of the
sun energy hitting the panel. Bruce Roe

[Ampster]

Wow, you guys offered a lot of information, we have 26 295w Canadian Panels on the south facing roof and a 6kw SolarEdge Inverter, not sure why the inverter wasn't 8kw but we don't heat our pool, we run our pool pump 6-8 hours a day and we haven't seen our first bill yet so I'm curious if NEM 2.0 actually pays according to the TOU Tier system, see TOU Tier attached screenshot. I'm still not sure if we should run our pool pump when we're producing the most power or at night during lowest rate tier?

Some inverter manufacturers allow over sizing the DC Wattage of the panels versus the AC wattage. The result can be some clipping of energy as bcroe said. I have a Solaredge system that has DC capacity if 5.7kW and a 4kW Solaredge inverter.

I am on NEM 1.0 and TOU with SCE. That plan has no tiers. I have EVs and have had some luck load shifting so based on that I would recommend running your pump during off peak times and allow your generation credit to accumulate at peak rates. BTW, when you see your bill you will see that SCE accumulates dollars and kWrs.
However it is not that simple. Since you are on NEM 2.0 you will be paying Non Bypassable Charges for everything you consume net of generation. I have heard the NBCs amount to about $0.02/kWhr. Also, as the days get longer your solar generation will increase. The only way I can suggest to answer your question is to suggest you keep a spreadsheet and track your accumulated balances by TOU period. If your system is sized such that it cumulatively generates more than you consume then you may want to switch to running the pump when you are generating power so that you wont incur NBCs.

I wish there was a simpler answer. Some installers have programs they can run to let you see how much your historic usage will be offset by generation. Perhaps yours can do that.

[Guardian7]

Ampster, sounds like you understand the dilemma, I've just ordered the Sense Energy Monitor with Solar Electricity Usage Monitor to Track Solar Production and Energy Usage in Real Time. Hopefully this accessory proves to be a helpful tool.

[Ampster]

Never a good move? From a compensation from the POCO you are correct. However there are three reasons to disagree.
...........

So I can spend $600 now and have piece of mind, have added expand-ability and not have to bug my wife and possibly waste a portion of this money, But even if the entire $600 is a waste, the alternative would be to spend $1,800 ($600 + $200 + $1,000) of my time and money at a later date. The risk / reward favors getting the extra capacity at the time of install rather than at a later date.

I agree there are at least three good reasons to oversize a system. You articulated the most important three. As you stated the risk reward for many people would favor over sizing just as a hedge.

[inetdog]

If your panels are able to put out more power than your inverter rating, the inverter will just shift off the MPPT panel
operating point, typically by drawing less current and allowing panel voltage to rise. The excess current will just be
dissipated by flowing inside the panel and heating a bit more. Remember this is only some percentage points of the
sun energy hitting the panel. Bruce Roe

That is a somewhat helpful description of the end effect, but a totally wrong description of the mechanism involved.
When the current drawn is reduced and the voltage rises, some of the charge carriers which are knocked lose near the semiconductor junction area do not cross the gap because of the higher voltage and just recombine on the original side, generating heat. There is no circulating current inside the panel.
It is true that instead of removing some part of the energy from the incoming photon stream by delivering power to the terminals that energy will instead be dissipated as heat within the panel.
I am not sure whether in addition there is some reduction in the absorbed light at the panel, resulting in greater reflection, but I doubt it.
The interesting effect is that a panel which is open circuited and a panel which is short circuited will both get hotter than a panel delivering output at its MPP, and by roughly the same amount.

[bcroe]

That is a somewhat helpful description of the end effect, but a totally wrong description of the mechanism involved.
When the current drawn is reduced and the voltage rises, some of the charge carriers which are knocked lose near the semiconductor junction area do not cross the gap because of the higher voltage and just recombine on the original side, generating heat. There is no circulating current inside the panel.
It is true that instead of removing some part of the energy from the incoming photon stream by delivering power to the terminals that energy will instead be dissipated as heat within the panel.
I am not sure whether in addition there is some reduction in the absorbed light at the panel, resulting in greater reflection, but I doubt it.
The interesting effect is that a panel which is open circuited and a panel which is short circuited will both get hotter than a panel delivering output at its MPP, and by roughly the same amount.

I will not argue the real, complex physics of the situation, but I believe my description fits the equivalent,
simplified electrical model we use. It also fits your description that a panel runs cooler at MPPT operation,
than at either open or short circuit. Bruce Roe

CellModel.png

[Ampster]

I will not argue the real, complex physics of the situation, but I believe my description fits the equivalent,
simplified electrical model we use. It also fits your description that a panel runs cooler at MPPT operation,
than at either open or short circuit. Bruce Roe

CellModel.png

There is another thread which at some length discusses where the energy goes in that situation.. I did a quick search and realize perhaps it was another forum. I'm not concerned about the answer, but I do want to convert as much solar energy as I can into something useful. I have the EV grin and love driving on sunshine.