Solar Self Consumption

It would be great if Sense could keep track of the amount of energy I produced and immediately consumed (self-consumption of my solar energy). As utilities try to roll out less friendly solar policies, it will be a more useful piece of information to track. My utility is attempting to chip away at net-metering, if they get what they want it will be worth 2-3 cents per kWh to use energy as it’s produced rather than export it and use it later that day.

You can already get a rough approximation of this by comparing your billing statement to the actual solar production. (And you could also export your hourly data to excel to analyse). But it seems like it wouldn’t be too hard to add a feature that tracked the amount of solar produced in excess of usage, vs just tracking usage and production completely separately. Adding the feature in the app would open up that information to more than just the energy geeks out there.

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I’ve always wondered about this because Sense is actually measuring net usage and gross production via the CT clamps, right? So in a Sense Solar installation, Sense is synthesizing the gross usage by adding the current value it is getting for each of the pairs of CT clamps, right?

I think this would be a nice to have. I current do an approximate calculation myself based on the net delivered field on my electric bill and gross usage from Sense. I’m doing this calculation in order to track payback of my sister’s solar PV installation.

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Trying to understand where that data would live. Would it be another “bar” in the Trends display ?

ps: It would be pretty easy to do this calculation in a spreadsheet using Sense’s data export.

What’s the granularity of the data export? The issue as I see it is that both usage and solar production can have spiky highs and lows, and these quick spikes and drops mean that the netting needs to occur at least at the half-second granularity of the Sense update interval. Here’s an example showing what I mean:

All of you know that the red is usage and the yellow is solar generation. Brief drops in solar generation come from clouds causing shadows over all or part of the solar array. During this one hour period, generation could match gross usage, but real self-usage is only where there is overlap. The dips in solar generation will require the electric company to deliver power at full retail rates ($0.29 /kWh in Honolulu), while the customer grid supply will only be credited at the contracted $0.15 /kWh customer grid supply rate.

It’s not important for this topic, but just for complete transparency, you only get the customer grid supply rate up to your delivered usage for a given billing period. You get nothing for monthly overgeneration over and above your usage.

Minimum resolution of export is hourly right now. Let me ask you a billing question though ? Is your pricing applied on an instantaneous basis or a cumulative billing period basis as this guide for Hawaii seems to suggest:

I have only heard of a couple places where utilities have attempted to move to instantaneous net metering and billing (FL and UT), and I think in both, there are court battles about the legality of instantaneous net metering.

There’s already a “solar” tab in the app, maybe add something there?

HECOs Net Metering program was close to new applicants in October of 2015:

It was replaced with the Customer Grid Supply program, which only credits customers $0.15 per kWh and charging them market rate (currently about $0.29 per kWh) for power delivered by HECO.

The CGS program also maxed out on applicants in November of 2017 and was replaced with the CGS+ program which only credited you $0.10 per kWh for exported power. There’s also an alternate program called Smart Supply that will credit you $0.15 per kWh, but only for power exported after 4pm or before 9am.



I’m unaware of any court battles against these policies in Hawaii. Note that the rates I quoted above are for the island of Oahu. Other islands have different credit rates.

@dianecarolmark,
Unless I’m reading the explanations wrong, the net accounting for delivered and received electricity is done at the end of each billing period, not on an instantaneous basis. That’s what the example you linked to shows.

But you are right in that Sense will just show you just the differential net usage, not breaking out the total received and total delivered energy each month. Can understand why you would want those numbers as well given your billing. Not that you should need another device, but have you looked at one of the devices that talks to your smart meter ??

ps: This is another flavor of billing that Sense needs to consider as they enhance their costing capabilities. I’m wondering how many other people who have been asking for different delivered and received energy prices, realize that they may also need this feature. The real trick for Sense is that they would need to maintain two buckets, the delivered bucket and the received bucket, instead of netting the two out.

At this point, I’m not sure what we’re disagreeing on, but let me give you and example and our shared understanding of it should be indicative of global shared understanding instead of talking past one another.

I’m going to describe two different one hour generation and usage scenarios, A and B, and illustrate what the important differences are to me and how Sense could help me more.
Scenario A: Usage is a flat 3 kW for one hour. Due to partial cloud cover, solar generation varies from 4 kW to 2 kW.
Sense reports usage: 3 kWh
Sense reports generation: 3 kWh
Electric company meter records they delivered: 0.5 kWh
Electric company meter records they received: 0.5 kWh

Scenario B: Usage is a flat 3 kW for one hour. It is a sunny winter day, solar generation during this hour is a constant 3 kW.
Sense reports usage: 3 kWh
Sense reports generation: 3 kWh
Electric company meter records they delivered: 0 kWh
Electric company meter records they received: 0 kWh

Under the current situation, there’s no way from Sense data to distinguish between these two scenarios and determine that I would be billed the following in scenario A:
(0.5 kWh x $0.29) - (0.5 kWh x $0.15) = $0.07

Note that in scenario B, I’m billed zero.

More to the point, it’s harder to infer things like: What devices are the greatest source of self-consumption, and which are the worst? I’d like to be able to tweak my sister’s water heater timer and easily determine whether self-consumption got better or worse.

The other real-world issue with constant output and production is that it’s hard to determine self-consumption when the dryer uses 5 kW from 10:30 to 11:30 and the solar array is producing a constant 2.5 kW. Both 10-11 and 11-12 will display matching 2.5 kWh usage and consumption, while the electric company will bill for 2.5 kWh retail - 2.5 kWh credit rate.

Note that I agree that the billing is not instantaneous, but is netted at the end of the billing period, but it is clearly helpful to know what was self-consumption vs power company delivered consumption.

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