preparing contract change from fixed/year to hourly buy/sell prices.
steps taken so far
for a couple of weeks, I ran DESS in “Green Mode” with “sell back to grid” disabled. Sun was abundant the entire trial period, so no “grid” consumption required for entire trial period. DESS behavior was that my batteries would be charged as soon as “pv inverter” generated more than “critical loads” consumed
for a couple of weeks, I ran DESS in “Green Mode” with “sell back to grid” enabled. Energy provider sets Buy price equal to Sell price always. Sun was abundant the entire trial period, so no “grid” consumption required for entire trial period. DESS behavior was that my batteries would be charged as soon as “pv inverter” generated more than “critical loads” consumed
two days ago I changed DESS to “Trade Mode” with “sell back to grid” enabled. Energy provider sets Buy price equal to Sell price always. Sun was abundant for the entire period DESS was in trade mode. DESS behavior is that battery is slowly drained (between 20 and 80W) constantly, with no peaks in discharge or charge. All “pv inverter” load is directly moved to “grid”
Even though the buy- and sell-price are equal for the given energy provider, the price does fluctuate during the day, with relatively high prices for peak hours (between 6-10 and 16-22) and relatively low prices for off-peak hours. Difference between peak and off-peak is between 20 and 30 eurocents/kW
With this price curve, I would have expected DESS trade mode to “charge” batteries with solar between 10-16 and “discharge to grid” either in evening or morning peak hours
Is my expectation correct? And if so, what can I change in settings to achieve the expected behavior?
PS. for those that assumed that we (the Netherlands) are experiencing abundant sunshine for several weeks on end, you are correct, the weather has been UnDutch for several weeks
From what you describe, your expectation seems about right.
Sometimes it is tricky to understand, why dess favors a certain strategy, and the devil is hidden in the details.
What have you configures for battery cycle costs in DESS?
Feeding in solar instead of charging during a low price phase seems like dess is calculating that this behaviour is more benefitial than adding a battery roundtrip with 20% efficiency losses and sell later.
That indicates highly exagerated battery cycle costs.
Eventually you wanted to set these to 3 cents, but entered 3 EUR instead?
NOOB here
I went through all settings once again and found that I had set “charge/discharge restrictions” to “yes, enable discharge battery to grid restrictions”………which I guess did exactly what it intends to do
After having changed that setting at the top of yesterdays sell price curve, my battery started discharging like there was no tomorrow. And today’s forecast/plan is to charge to 100% during 10-16 and then discharge to 25% (which is my set minimum SoC)
So I guess DESS is working as expected
Onto the next question I have…..expect to find out sunday-evening/monday-morning…..if today’s evening peak price is lower than tomorrow’s morning peak price (with the normal night time low prices in between) can I expect DESS to hold it’s horses until tomorrow, or will it discharge at the earliest peak/high price?
It depends. If DESS sees an opportunity to charge again (maybe cheap from grid) it will discharge at evening, charge at night, discharge at morning, …
If there is no opportunity it will act “most cost efficent”, that means during the night, it will most likely use some battery for your consumption to avoid (expensive) purchases from grid or idle the battery if grid is cheap enough to cover loads but not yet cheap enough to buy (efficiency losses) etc.
Also unforseen consumption or change in solar may affect the plan. It is updated quiet frequently always based on the current values the system reports.
Planning now is that it will not discharge until tomorrow’s morning peak hour, so again, that is as per expectation
I want to minimize grid consumption, so I set “restrict battery usage” to “restrict battery charge from grid”.
But that still showed grid usage when buy price is lower than next discharge timing’s sell price. I guess this makes sense as long as battery costs are greater than delta buy/sell.
So I decided to change “buy price calculation” by adding 20 cents on top of provider given price.
Would this tweak minimize overall grid usage or is there a better way of configuring DESS to achieve this goal.
By the way, I really enjoy playing around with DESS, thumbs up for Victron’s UI and UX team!
Hmm, switched to green mode earlier today and battery is currently discharging at max threshold…planned to discharge until 25% which is minimum SoC. That is not expected behaviour, right?
I am looking for a middle ground between trade and green mode. Trade mode focusses on grid input/output, whereas green mode focusses on solar as input without optimizing sell moment.
What I would like to achieve is that solar is used to load and discharging is maxed at peak sell prize hours until next solar peak is expected to load to 100%.
DESS will also discharge to grid in Greenmode, based on various parameters.
For example, your buy-prices at night could be that cheap, that DESS calculates its preferable to feedin energy early and run of the grid during the night.
If you could give me the numeric id from your vrm url, I could look that up.
However, you could also influence this, by setting a time-based Feedin restriction and only allow energy to be sold to grid in the early morning hours for example, when it can be immediately recharged through solar.
