Tonight, starting Sunday 24 November 2024, 00h00, a 16 hour window opens with near zero electricity prices (before tax and cost).
Although I’m planning to enable the battery balancing feature (with a long 28 day interval) manually at midnight to make optimal use of this, I wonder what would be the best way to automate DESS to do this for me when such an opportunity presents itself again in the future.
For context, I run a MP II 5000 GX in DESS trade with a 42kWh battery and no solar (yet) with the intent to lower the monthly electricity cost for a small, ‘gas free’ 48m^2 apartment.
Good question.
When I checked the planned behaviour (which is broken at the moment…) the system will charge nothing. Probably because there is no opportunity to sell the energy for a good price on the 23-11-2024. It is expected that the price will be higher on the weekdays, but then the opportunity to charge for € 0,- is missed.
Just activating battery balancing could be counterproductive. After charging, the DESS uses the stored energy again. Tomorrow in particular, this makes little sense as the whole day is cheap and therefore does not even make up for the loss of effectiveness. I have been using a different strategy for a few weeks. On Sunday, at the right moment, I increase the Min SOC to 75-80%, thereby loading energy into the battery and storing it. Over the course of the week, every day when new prices come in and there are times when prices are high, I release some of the energy again. I then gradually reduce the Min SOC again 65-45-35-15. This has proven very useful in the last few weeks.
The problem is that this behavior is purely speculative and assumes that prices will rise. But DESS only calculates for the period in which it has fixed prices.
That pretty much sums up precisely what I have been doing the past few months. I didn’t mind because it was a good way to get to know the system and platform this way but by now I need to start considering the value of my time, which means I either need to increase system size by an order of 100 or so, or automate it.
Well, the DESS does the automated distribution of the available energy very, very well. As far as the time required is concerned, it is limited. I get the current prices every day between 1 and 1:30 p.m. and then decide via my cell phone and VRM portal how much energy I want to release. Simply change the slider accordingly. At the weekend, simply move the slider back up at the right time. Ultimately, this is pure speculation that is difficult to automate.
I understand but once I start tinkering with settings dayly, my ocd brain kicks in, a time costly affair only manageable by finding an acceptable ‘set and forget’ automation strategy that allows to reduce the need to intervene to once weekly at most. Not to mention dealing with customer sites.
I don’t expect Victron to add a weekly heuristic forecast any time soon, hence my question how to best automate some of the most obvious opportunities like today’s low prices. Preferably without having to move DESS to node-red.
From reading the other threads as well, I think a good starting point could be a manually adjustable minimum soc agenda. Which will most likely mean adding node-red skills to my learning curve. Alternatives anybody?
The problem is not the forecasting of any empirical data. The problem is the forecasting of traded prices and their forecasting. I think that exceeds the requirements of the DESS. With such systems you could make much more money elsewhere
As far as predictability goes, some heuristics are easier then others, such as weekend prices being lower in general. But I think it’s easy to get sidetracked, perfection being the enemy of good enough. What I seek is to automate the most obvious low hanging fruit, in today’s example a fully deterministic case of free electricity (excluding cost and taxes that I plan to earn back in full next year by solar production).
I see three time-frames in play here:
- the dayly where DESS seems to outperform any manual attempts to trade.
- the weekly where DESS is missing obvious opportunities
- the yearly where, in NL at least, cost and taxes paid in winter can be reclaimed with solar production in summer, up to the point where total yearly consumption turns in production.
I also noticed the availability of scheduled charge levels in ESS that are advised not to use with DESS.
All in all I got a bit lost what tools are available and can be combined as-is to cover opportunities in the weekly timeframe, without resorting to node-red automation, or even an external (paid for) DESS scheduler.
As I said, I use the Min Soc for weekly speculation and am very happy with it. As far as the country-specific regulations on the energy market are concerned, it is a difficult task for Victron, which they have faced up to bravely so far. Here in Germany, there are currently opportunities to save a lot of money through variable network charges. The difference is sometimes over 12 cents per kWh. I really hope that Victron finds an integration. But that is difficult for all countries.
I appreciate the feedback but would like to stay on topic, please.
On another note, I had a great charge run today 
.
tonight after midnight negatives prices again
can dess be setup so you can enter a minimum price where it skips inverting?
so for example if power is 5c/kwh or less don’t use batteries just keep charging and or pulling from grid
I have not found any price based controls. For now I’m just tweaking the ‘no discharge’ scheduler to limit discharging to expected high price hours and then adjust the minimum soc setting to steer the charging when prices are low. Far from ideal as it requires continues monitoring which I find distracting to a point where it’s not worth my time. Grid imbalance trading can be worth the capital investment when averaged over a year or longer but not so much my time. Maybe a solution can be found in a community effort to create a public scheduler of sorts, someday.
I think you’re making it too complicated. Simply increase the Min Soc at the best time and leave it at that. Then the DESS essentially locks the energy in the battery. Then reduce the Min Soc every day until it is enough to cover the most expensive times. You don’t need to change anything else on an hourly basis.
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not a bad idea, can this be done with the VRM API? i dont see that it can from the docs
I do it manually. Every day when the new prices come in, I estimate how much additional energy I want to release. I look at the price and solar production, sometimes I look at the weather for the next few days. 3-5 minutes in the afternoon on my mobile phone
if you can set minimum soc through vrm control panel then it’s ez to program the same request to their servers
i assume they haven’t added this to their api documentation, but the possibility exists