[RE-wrenches] Offset charge rates vs system sizing to meet 100% production

[Dana Orzel]

Agreed -time of day vs. usage, home all day vs working folks.
IPC monthly kwhr excess rolls over month to month with a reset in January that at which time you need to request that the roll over continues (for a $10 fee) or they clear the excess to 0 & you start over building your credit bank up.

Dana Orzel - dana at solarwork.com - 208.721.7003

On Feb 22, 2025, at 9:23 AM, Mac Lewis via RE-wrenches <re-wrenches at lists.re-wrenches.org> wrote:


Hi Dana,

If I understand your situation correctly, this can get complicated and depends on how the usage pattern is.  A user that consumes during the day will need a smaller system than one that consumes when the sun isn't shining.  Usually it's not one or the other but a blend of course..

I think it means that anytime you are spinning the meter backwards, you get about 4/9 credit that can be applied to your bill.  Your usage will be lowered 1:1 when the sun is shining, but at the time of export, it will only get a 4/9 return (the utility can't tell what is non-usage and what is production).

You can set up the bounds of the system size by saying,

What would the system size be if all usage occurs when the system is producing (the old net metering approach)? 1 usage:1 production
What would the system size be if all usage is at night?  In this case, you would need a system that produced 9/4 of the kWh to fully offset or a multiplier of 2.25.

To make it more complex, you would need to find out if credits carry forward month to month or if its trued up each month.

Utilities can make it hard to get data to size the system correctly, but I'd probably shoot for 130-150% for an average house where people work.
Its not very easy to sell solar now and give assurances at all.

On Sat, Feb 22, 2025 at 8:42 AM Jay via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:
Hi Dana.

Do you mean offsetting the $ amount or the kWh amount?
Jay

On Feb 22, 2025, at 8:33 AM, Dana Orzel via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:


I am wondering if anyone else has this offset on Kwhr net meter discrepancy & how to design accurately design for this discrepancy.
Idaho Powers’ version of net metering goes like this: 1 KW received from IPC charge is $ 0.09/Kwhr & solar input into the grid you are credited $0.04/Kwhr.
The difference is 44.44% in the exchange for purchased vs solar export rate.

So, will oversizing the solar system by 44% to achieve a goal of 100% production of a client’s current 100% usage achieve this goal?



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--



Mac Lewis


"Yo solo sé que no sé nada." -Sócrates

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