Fixed maximum capacity

[silfab20]

Hi REopt team,

In the Netherlands, residential grid connections have a fixed maximum capacity. For example 3x25A, which translates to roughly 17 kW. This is a hard physical limit: the client simply cannot draw more than this from the grid at any point in time.

We want REopt to optimize PV and battery storage sizing under this constraint, so that the battery covers any demand peaks that exceed the connection limit.

We explored ElectricUtility.interconnection_limit_kw, but it seems this doesnt limits the actual grid import power at each timestep. We also looked at coincident_peak_load_charge_per_kw in ElectricTariff, but this applies a cost to the absolute peak rather than enforcing a hard cap.

Our question: is there a way in REopt to enforce a hard maximum on grid import power per timestep (e.g. 17 kW), so that the optimizer is forced to size storage to cover any demand above that threshold?

If this is not currently supported, is it something on the roadmap, or would you recommend a workaround?

Thanks in advance!

[kurt-verdant]

Maybe a custom rate? If going from 17 kW to 18 kW incurs a demand charge of $1,000,000 then presumably REopt will size the battery to avoid that

[silfab20]

Good point. If i'm right (i'm using the API, not the web app) demand charges are calculated per month, not per 15-minute interval or per hour.

[kurt-verdant]

Yes, demand charges are calculated per month. When developing approaches such as this I've found it helpful to use the Custom Rates tool on the web site, then run a toy REopt analysis in the web app, then export the input for that toy to json. In this way a template for the new rate structure can be created easily, then modified programmatically later before sending 'real' input files to the API.

I think you could peek at this result:
https://reopt.nlr.gov/tool/results/a027cbb5-9c7e-4504-ac0f-4e41590649da

If the only demand charge is $1,000,000/kW for anything over 17 kW, REopt sizes PV+Battery such that import from grid never exceeds 17 kW. This is for a building that started out with a flat 18 kW load during every hour of the year.

[silfab20]

Thanks @kurt-verdant! Very clear instructions. Now i'm gonna try to find out how i can do this setup with the API.

[silfab20]

Not much succes so far. The parameters in the custom price json file are different then the ones in de API. Or do i have to work with:

urdb_response::Dict=Dict(), # Response JSON for URDB rates. Note: if creating your own urdb_response, ensure periods are zero-indexed.