New user struggling  


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Hi
Im an 18 year veteran of off grid power systems incorporating PV small wind with diesel and batteries, both DC and AC coupled, so have a fairly keen 'seat of the pants " knowledge about what works and the expected battery life etc
I signed onto Homer to model a tender, a fairly basic system, a 100kW approx. PV array, a 6000 ah battery bank AC coupled 360 kWh per day, auto start 50 kw genset
I carried out a rule of thumb simulation with pen and paper and calculator to arrive at the battery and PV size, uploaded the load model Ok, managed to get my PV array in, however the issues are
The battery database wont let me ( or I don't understand how to simply do it ?) input the Ah/Kwh capacity of the battery ?
Wont let the genset auto start at battery DOD and load set points
Gives me a whole stack of simulations of different arrays from the library that I have not selected, I have been through and checked that I am only modelling what components I wish to use
This is a supposedly really simple modelling exercise , with an AC couple array, a genset, a battery bank, which of the tutorials will get me on the right track with this please
Thanks ina dvance

 
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Hey Jim,

You can modify the battery capacity by using the "search space" option in the "quantity optimization" field, this will multiply the number of batteries simulated so the net kWh storage capacity will be that number times the capacity of the battery you are simulating.

Modifying the generator operation is a bit more difficult, you can force the generator on at certain points using the "schedule" tab under your generator options, but under standard controller methods the generator will not charge the batteries, solar and wind are preferred. There are a few roundabout ways you can push the system to work in a way that you want but if you really want to dig into custom operation, you will have to model your own controller which is a bit more advanced.

- Andrew

Thanks Andrew,

So there is no ability to just simply insert the usable battery capacity ?
Or to model stand alone power systems how they work in real life ?
What then is the purpose of this program , if it does not reflect reality ?
Jim

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You can input the battery capacity, it is simply a factor of the capacity of the battery you are simulating and the number of batteries. You multiply the two to get the battery capacity.

The software is really designed to help compare different combinations and scales of energy generation and storage as a preliminary design tool. Obviously the closer you can get to modeling real world operation is better.

I'm not sure specifically what you are trying to accomplish with your generator but if you could describe it to me perhaps I could assist you. There are a number of options under battery settings that could help you out, perhaps setting the minimum state of charge would accomplish what you are looking for.

 
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Thanks Andrew

Minimum SOC of Sonnenschien A602 /2V cells is 60%,  using a Selectronics SPPro inverter Charger as the brains of the system I can start the genset (or charge via an AC couple PV array or DC coupled ,when either the SOC falls to that level, or the load rises to higher than the inverter can handle(genset start), typically I have the genny turn off at around 90% SOC
I know from the battery spec sheet the AAH capacity at different C rates, pretty easy on the back of an envelope to work out kWh capacity of the 40 usable %, not so easy to get that into Homer setup ?

 
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HOMER doesn't to C-rates, because HOMER doesn't do power flow. HOMER's primary function is economics. HOMER's battery will uphold the 60% min state of charge, meaning that when the battery is drained to 60%, the generators will cover the rest. The generators cover what the battery can't. Try one of the other controller options to see if the dispatch is different. If you're looking at a solution with Cycle Charging, then the generators - once turned on - will fill up the batteries completely. This seems to be what you're describing. If you look for a Load Following dispatch strategy, then the generators should only serve the load, and the batteries should await being filled by the PV power.

Thanks Andrew

It appears that Homer is unable then to accurately model economically the SPS systems as they operate in the real world ?
Glad I only paid for a months subscription

  
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