Charging battery during night time (lower price) and DESS selling with losses

Q&A and troubleshooting
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1

Hi

My system:

  • 3x MP2-8kVa
  • 96 kWh battery, 6x EEL boxes with JK V19 BMS
  • Solis 3P15K with 13kW PV array

I currently have fixed energy costs, with somewhat cheaper price during night time (22-06).

I would like to save money by charging the battery during night time, and use the charged energy during the day. The DESS doesn’t understand this, and it wants to sell the energy from the battery during the day even if the sell price is lower than what I bought it with. I would like to see the DESS working so, that it remembers the price of the charged energy and the costs of the energy in the battery, and sell only when it truly profits. With DESS cofigured with fixed prices I find it odd that it sells the energy with losses.

Kind regards, ej

2

Graph from yesterday:

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Today:

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Also, it would be more than nice to have the lower graph follow 15min time steps.

Kind regards, ej

3

Today DESS decides to sell with a low-ish price and later on I have to buy more expensive energy.

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4

That’s not how DESS works. imagine if at one point the charged energy has a high price, the system would use grid only from then on.

You can do that without DESS, scheduled charging is part of ESS.

5

Using scheduled charging instead of DESS will forego any potentially financially beneficial selling opportunities, though.

With a fixed (time based) price contract like OP has, it does not take a rocket scientist to decide whether to sell or not.

1 Like
6

For humans, yes. DESS does not differentiate between fixed and dynamic.

7

Maybe it should? Seems like an easy “low hanging fruit” to increase profits and avoid losses and thus improve DESS

1 Like
8

“That’s not how DESS works. imagine if at one point the charged energy has a high price, the system would use grid only from then on.”

Well, it should use the bought energy, not sell it with losses.

9

This evening I noticed that the DESS started to charge up the battery at 21:30 even though my prices get cheaper at 22:00. The settings for this should be correct.

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There’s a 30min offset in both evening and morning:

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@dognose , could you check this?

Thank you!

Kind regards, ej

10

Actually, I had the same thing! A series of incorrect DESS behaviours - #12 by jkoljo

Maybe there is something wacky going on with time slots in DESS that causes such a systematic issue. I remember someone at the forum had time offset issues as well.

11

Right now the DESS has decided to get energy from grid, and the backstory goes…

Previous hour there wasn’t any planned recharging to be sold later on. I thought to manually set the min. SoC to force recharging. I missed the 13:00 time by one minute, and now DESS buys energy from grid:

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..and had decied not to sell at all when the price is the highest.

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I set the min SoC to 0% ofcource. I also tried to set the grid setpoint to -17250W as it’s my maximum output to grid.

Ping @dognose , is it not possible to manually force recharging to optimize profits? How should this be done?

Kind regards, ej