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# Any way to build an excess solar to battery setup?

I have a few bits and pieces in my current setup:

4kw solar
mk2pvrouter for heating our immersion tank, with second box ability
elios4you for monitoring which has 0-10vdc output for controlling an immersion type setup.

what id like to be able to do is charge batteries proportionally based on my excess generation after the hot water is done.

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Have you tried searching? Iâ€™m pretty sure Iâ€™ve seen something like this before - but Iâ€™m not sure how long ago. It might well be in the old â€śArchivedâ€ť forum.

I think the concern then was how the battery charger would react to being turned on and off in burst mode. If you can set the current on your charger (hence to input power it takes) then what you must do as far as mk2pvrouter is concerned is make the battery charger part of the primary load, but turned on (and presumably current-controlled) by the second output.

my thought was to somehow use the 0-10vdc output from the elios to control the current applied to the batteries, so the voltage would be say 60vdc from the charger to the 48vdc battery bank at a constant voltage, and then the current would vary to match the excess going to the grid.

it should work as the mk2 would heat the immersions and the elios has a relay that has a threshold function on time and power, which could inhibit the mk2 once the immersions have finished heating and it sees maybe 5 minutes or so of grid feed. it would then start variable control of the charger via the 0-10vdc out, normally this is used for there own solar immersion router.

my problem is I donâ€™t know how to build a say 1kw constant voltage variable current charger thatâ€™s controllable via 0-10vdc.

A battery charger is a d.c. power supply. You should be able to find details to build one of those.

The problem comes with controlling it. What youâ€™ve written does not make complete sense. If itâ€™s constant voltage, the current will be defined by the battery - specifically the difference between the driving voltage and the internal battery voltage, and the internal resistance of the battery plus the source resistance of the charger. If itâ€™s constant (or controlled) current, the voltage will be defined by the battery. What I think you need is a current-controlled charger that has a voltage limiter to prevent overcharging. So the main control loop is on current. The battery voltage will rise as it reaches full charge, the voltage limit will come into play and the current will naturally drop away.

Youâ€™re talking about 20 A or so in the d.c. side, so you will need fairly substantial active devices (and maybe fan cooling) to handle that.

But personally, I wouldnâ€™t try to build one. Iâ€™d look for a commercial unit - almost certainly switched-mode given the power rating you are calling for - with the appropriate output voltage and current, that can be controlled remotely.

I doubt that will be necessary. If your immersion heater has a thermostat, the Mk2 will be unable to divert any power to the immersion heater anyway.

Good suggestion.
A commercial unit would have the advantage of preventing shortened battery life by using 3-stage charging.

ok I have a mastervolt Soladin 600 spare and ive spotted a cheap circuit that can boost 48v upto enough to get the soladin running. then all I would need is to store maybe 1kwh.

as I have approx. 1kwh of background usage at night this would potentially offset 365kwh, not much but I have the soladin and can russle up some batteries.

the cheap circuit also allows me to adjust the amount of power coming out of the soladin. so I can adjust it down to about 120w.

Do you mean cheap as in cost, but possibly expensive in lost efficiency? I understand your desire to use an inverter you have available, but long-term it might be false economy. Just my 2 pennâ€™orth.

something like this:

I know that the youâ€™re looking for a DIY approach, but a good solution is a charge controller that goes between the PV panels and the inverter, such as the Goodwe BP unit here: http://www.goodwe.com.tr/en/bp-series. I use them at work.

It costs around ÂŁ700 but will look after your batteries properly.

what I have being doing for years. and I never had problem is I have my batteries connected to via a battery charge controller and between the the solar panels and charge controller is a GTI. the GTI is naturally isolated by the charge controller and the batteries. generally a GTI that rated 48 volts generally operates around a 60v 24 volt around 30 and as the voltage drops in the battery the the amps go up naturally to battery. i use it this way in case of power outage . the solar panels charge my batteries and a relay drops and switch my house over to standalone inverter ( house sized ups). but as of last year I added SSR to my GTI that turn down the DC input to the GTI which has worked well for me as it also naturally directs more power to the battery if you using 36 volt panel and GTIs rated for that you can run them in series just have an isolating diode between GTIs â€¦ in my case I am runny 36 volt panels on ~36 volt GTI connected at 36 volt with a series wire running between the GTi bumping up the voltage on either side taking it up to 72 volts to the battery charge controller-- hope you get my drift being doing this for atleast 4 years with out issue-

oops forgot to mention the reason tor mentioning running micro GTI in isolated series to boost DC output to battery this way is that it removes the need for a boost converter mentioned above and secondly gives some priority to battery charging ( battery dependent) as if you let your battery stand too long before charging they deteriorate faster. and I guess I should mention my batteries storage are in my electric utility car so i disconnect and reconnect it offen though all winter it it never is disconnected and acts purely as backup power system for my house

Has anyone had success with a completely AC coupled battery storage architecture like the one in the attached pic? If so, what battery charger and inverter did you use? My customers have microinverters attached directly to the main service panel. No DC off the roof. The battery charger and grid tie inverter would need to have remote power limiting interfaces.

I would like to use a battery charger and GTIL to control the amount of energy exported to the grid. These systems are in the tropics, so diverting to a heater is not a good solution. My net-metered customers have to pay a 15% tax to the utility for energy stored in the grid via ther not-so-net meters. They are also limited to exchanging with the grid no more than 49% of the energy produced by their PV system. They lose credit for anything above the limit, Battery storage makes good sense for some of the properties.

The Simpliphi Power batteries look like a great fit for the application.