We have a large solar and battery system on a farm which I’ve been trying to set up on DESS in green mode but had to give up.
It has unpredictable large loads (3 cold stores and a grain dryer). When in DESS, and hourly loads exceed the forecast load for that hour, instead of draining down the batteries which usually are near full - pulls from the grid. Surely instead of this it should be using up my batteries first and then once the battery is used up then pull from grid? I have a small system on my house as well and it does the same on that. Is there a way to set buying from the grid as an absolute last resort during high tariff times?
Another issue with green mode is it doesn’t seem to only charge up the battery with what is needed to cover the first few hours of the day between the solar kicking in and the battery getting to zero? Currently it just charges a battery to 100% every morning just before the expensive tariff kicks in. We expected it to just charge up enough to cover the one or two hours before the solar gets to capacity? And only if there is low solar expected that day then to charge to 100%?
Unforeseen loads can sometimes be a problem. Are the maximum charge and discharge rates configured correctly in the DESS? Based on your description alone, I’d guess that’s the case. Can the system or the batteries even provide enough power for grain drying? And one more question…how long have you been running the forecasts?
Yes it’s all configured correctly - it has 125kw of AC tied PV of which 40kw is on the critical loads side of the quattros (for grid outage). It has 3x 15kva quattros and 60kwh of batteries. Peak loads are 60kw non continuous, continuous is between 25-40kw. (The system is 3 phase).
Cold stores total 40kw.
Dryer totals 25kw.
Essentially it would be nice to see an option to only use grid in certain time periods if the battery is low.
With 60 kWh of storage and loads of 40-60 kW, your battery is beyond its capacity, as is the rest of the system. This can’t really work. Your battery can’t handle that much load. No wonder the DESS wants it to charge as quickly as possible.
I don’t know the exact performance data of the Quatros, but I estimate they have a maximum output of around 12 kW in continuous operation and warm conditions. The system then draws the rest from the grid.
The batteries are rated for 60 kW/h there’s no issue charging them - they charge fine it’s the fact that with DESS it tries to pull from grid instead of batteries with any load over the forecast load.
To be clear total consumption per day is around 300 kW. The solar handles 95% of it the batteries are just there for a cloud goes over.
How the system functions and is designed works perfectly for our scenario. It would just be nice to implement a reliable DESS with it.
Jake
We expect them to pull from grid once loads exceed the rated output and there’s no solar. But essentially it’s pulling from grid even when the batteries are fully charged.
I still believe there’s a connection between your high revenue and the relative battery size. Your AC-integrated PV is taken into account in the DESS, right?
Yes it’s all fronius equipment
The system runs perfectly fine in normal ESS. I’m just having to use manual scheduling for the overnight battery charging.
You have a configuration problem somewhere. Show me your DESS configurations.
Out of interest - how should green mode with dynamic ESS work if consumption goes over the forecast consumption for the hour? Should it take it from battery or grid?
Regards,
Jake
See attach screenshots of a scheduling DESS makes. It’s planning on using grid despite having a full battery and excess solar.
If I compare this to my house system it’s forecasting using solar and batteries.
(attachments)
See attached my configuration.
Jake
I’ll write you something about it this evening
Ok thank you.
If I was confident enough with nodeRED, I would just do it in that. All we want is it to charge up the battery only the necessary amount for the forecast day ahead. On the night tariff.
Jake
So now I have a bit more time. I should add that I’m not a Victron professional, just a user, but I’ve learned a lot. Regarding your system and configuration, I have four thoughts, each of which I’ll try to formulate in a separate post. I’d like to give some of my own thoughts on these topics and test a few things.
The first issue is your cycle costs. €1,000 (I don’t know, was it €?) for a 60 kWh storage system and 10,000 cycles is completely unrealistic in my opinion. I know some people do this or something similar. However, this usually leads to the DESS under-prioritizing PV generation. Despite all the euphoria and cost reductions, we’re still a long way from reaching that range. And by the way, with your charging rates of 0.5 C and above, I doubt you’ll achieve half the cycles. I’ve tested several times (0.01-0.03) and am now doing quite well with cycle costs of €0.02 per kWh per cycle. Think about it and try it yourself.
The next topic is your parameters for maximum charging and discharging power. Are you aware that these are not active control elements? These parameters have no active effect. Whether you enter 1 kWh or 25 kWh, the behavior of the system remains unchanged. These parameters are only used by the DESS to calculate its schedule. This means that the DESS uses these values to calculate when it needs to start charging so that it charges at the most favorable times. It is therefore fundamentally important to enter somewhat realistic values here for what the system can effectively charge into the storage. Any theoretical values based on the theoretical power of the Quatros are not appropriate, because other factors (EVCC or BMS or…) can also limit the effective charging power. Think again here and check the parameters.
Regarding the battery cost I recently (this morning) changed that from £10,000 in an effort to make it try and make it prioritise battery use. It’s warranted for 10 years or 10,000 cycles so that’s what it set at. I find in my home system that doesn’t seem to make much difference, it only really changes the battery cost estimates in the DESS daily costs.
