Battery not Dispatching without making the cycle degradation penalty negative.

Hello SAM Experts,

I have been trying to simulate FOM Solar+Battery Storage system. For this simulation I am using PV-battery,merchant model and for some reason not able to dispatch the battery.

I want to use automated battery dispatch (look ahead 18 hours). When I run the simulation with cycle degradation penalty as (calculate automatically), I can see in results that the battery computed cycle degradation  penalty is 0.0107031 $/cycle-kWh. Now if I go back to dispatch and try to reduce it to 0.009 or even 0, it does not triggers battery dispatch.

However, if I enter the value as -0.009 it triggers battery dispatch. 

There are 2 questions which I want to ask here:
1. How do I get the battery to dispatch with cycle degradation penalty set to as "calculate automatically".
2. Seems like $/Cycle-kWh is a very sensitive parameter, how does SAM run the codes to calculate this, if you can explain how this works that would be great.

I have attached the .sam file for reference. Please have a look. i]See https://sam.nrel.gov/forum/forum-general/3680 for attached file.[/i

Thanks in advance, looking forward for your reply!

Hi Soheb,

For the front-of-meter automated dispatch option, the cycle degradation penalty represents the cost of future battery replacements. In each time step, SAM calculates revenue that would be earned if the battery charges, discharges, or is idle. It then subtracts the cycle
degradation penalty from that value and attempts to dispatch the battery accordingly.

A cycle degradation of zero represents the no-cost case, where SAM would dispatch the battery without consideration of battery replacement cost. Although SAM allows you to specify a negative value, a negative value doesn't really make sense. If you find that the battery only dispatches with a negative degradation penalty value, that is an indication that the difference between the power price and cost of charging the battery is not high enough to cover the efficiency losses of cycling energy through the battery.

For a detailed description of the dispatch algorithm, see DiOrio, N.; Denholm, P.; Hobbs, W. (2020). A Model for Evaluating the Configuration and Dispatch of PV Plus Battery Power Plants . Applied Energy Vol 262 March 2020, which is also listed on the Battery Publications page: sam.nrel.gov/battery-storage/battery-publications.html

Here are some suggestions for getting the battery to dispatch:

1. Try modeling your project using the PPA Single Owner financial model instead of the Merchant Plant. You can enter hourly or subhourly price data in $/kWh on the Revenue page by choosing the Specify PPA price option and setting PPA price to $1/kWh. Then under Time of Delivery, choose TOD factors by time step, click Edit Array and import or paste the price data in $/kWh. (You can use the same approach with $/MWh price data, just set the PPA price to $0.001/kWh.)

2. In your time series price data, are there time steps where the price changes more than $1/MWh? If not, the small changes in price may not be enough to cause the battery dispatch to respond. This might be easier to explore using the Single Owner model as I describe above in #1.

3. If you stick with the Merchant Plant model, you might try using the Manual Dispatch option. You could try a single dispatch period with both charging and discharging allowed to see how the battery dispatches in response to the power prices, and then make adjustments to the battery size and perhaps the discharge to grid discharge rate.

Best regards,
Paul.

Hi Paul,
Thanks for you reply. 
- As you mentioned, setting the battery cycle degradation cost negative doesn't makes sense and I quote your comment "that is an indication that the difference between the power price and cost of charging the battery is not high enough to cover the efficiency losses of cycling energy through the battery." Sure that makes sense. In the latest SAM version we have the the option to use cambium model  to generate electricity rates from respective states. For test sake, I used cambium to get electricity rates for California to be imported into the revenue tab and again tried it thinking the battery will dispatch as the rates are set via SAM. Unfortunately, the problem still persists and the battery fails to dispatch.

- Setting up battery dispatch as manual dispatch in Merchant model, defeats my purpose optimizing battery dispatch as per electricity market price (revenue). I would like this to be automated so that the battery see's the electricity price and dispatch accordingly. Me dispatching the battery based on the electricity price manually, defeats the purpose of using SAM.

-  I am not looking to change to PPA - Single Owner model. I am interested in making the automated dispatch work via merchant model itself. Could you please guide me what changes can be made within the merchant model itself (.sam file attached).