Using a battery dc source to power the home along with solar

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glyndwr1998
Posts: 112
Joined: Wed Mar 06, 2013 12:34 pm

Using a battery dc source to power the home along with solar

Postby glyndwr1998 » Thu Aug 21, 2014 3:45 pm

Ok,

A question board members who may have some experience with this type of set up.

I have a solar pv array on my roof that is 7.5kw is size, I have 35 panels on my roof that is an east west orientation.
On the east I have got 3.5kw along with a sunny boy sb3800 inverter.
On the west I have got 4kw along with a sunny boy 4000tl inverter.

I would assume I will produce about 6500 units this year.

So, my question,

I would like to capture as much of my produced energy as possible, as well as be connected to the grid.
I am strongly considering the purchase of a nissan leaf in the near future, and was thinking maybe I could utilise the energy in the battery to power my home in the evening, especially from the months of March to September when I produce much more than I consume, and would be able to use the cars battery to power the home in the evenings.

I was thinking maybe connect the cars battery to another pv inverter ( as it's voltage is well in the dc range of most inverters.

I would then need a few current sensors to sense what's coming into the home from the solar pv system, what's available from the leaf when it's plugged in fully charged, and when not enough is available from my own energy sources, the grid supplies the rest.

Can this be achievable without spending an arm and a leg.

I currently have a self modded plug in prius with a 7kwh lifepo4 battery and when am not using the car, I could use those units of energy in the home now, and use the daylight in the day to recharge, obviously when I not actually using the car for small journeys.

I am in the house most of the day, don't use the car a lot am considering the leaf as the pack size is 24kwh large and would be more than adequate for my daily journeys plus power the home in the evenings too.

Not sure if something as simple as a plc or arduino which monitors the current from all sources that could operate a set of contractors on each supply stage, something I could do on a hobby basis.

What's your thoughts on this idea......

Many thanks, anthony.

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Rory166
Posts: 116
Joined: Sat May 17, 2014 7:45 am
Location: Norwich, UK

Re: Using a battery dc source to power the home along with s

Postby Rory166 » Thu Aug 21, 2014 6:49 pm

I have heard it said that they were considering this in Japan. I would not want to waste the life of my expensive li-cells in this way. Lead cells from EVs become nonviable due to their Internal Resistance but still have a useful capacity. Weight and volume is much less of an issue. I would assemble a load of these cells and leave the car alone. I think other members may already be working on this.

Rory
Electric Seicento conversion, Leaf

glyndwr1998
Posts: 112
Joined: Wed Mar 06, 2013 12:34 pm

Re: Using a battery dc source to power the home along with s

Postby glyndwr1998 » Sat Aug 23, 2014 8:19 am

Hi Rory,

I suppose it. All hinges on whether the old used lead acids can be picked up cheap enough.

I personally wouldn't have much issue using the lifepo4 cells from the prius, especially as they are at a 240v dc, when running appliances in the evenings the load from then would be small especially when considering they pull 100 amps sometimes in the car going up hills, so running house appliances after dark would maybe pulling 15a max (obviously have to leave all the big consuming appliances off when running on battery supply)

I'm only thinking about it as with the 7.5kw solar array, it seems a shame to export maybe 25 units every day in the summer and have to buy maybe 6 units after dark every day.

I know the easiest things to do with the excess is to divert the elec generated ino a hot water cylinder and run a small emergen heater for hot water too.

Anthony.

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Rory166
Posts: 116
Joined: Sat May 17, 2014 7:45 am
Location: Norwich, UK

Re: Using a battery dc source to power the home along with s

Postby Rory166 » Sun Aug 24, 2014 7:08 pm

Used lead acid cells should not cost much. Last time I took them to the scrap and got 25p per kilo. As you know the export electricity is usually not metered but you get paid for half what you generate. I am not sure if systems are available to use up the excess from your panels by battery charging. Essentially you would need a variable charger that could be driven at different rates depending on how much excess was being generated. A cruder system would be have several chargers on bring them online separately as required. A current sensor on the meter tail would be used to measure the export and reduce it to near zero.

The hot water idea has merit, I believe the 1Kw immersion heater has appeared as a useful replacement for the normal 3kw type because most houses dont have 3kw excess. The thing is to allow the water temp to fluctuate quite a lot. Then use thermal mixer valves so the used water is not too hot. In the morning the tank may be just hot enough to use then in the evening it is steaming hot.

Rory
Electric Seicento conversion, Leaf

willfromsussex
Posts: 82
Joined: Sun Oct 04, 2015 3:45 pm

Re: Using a battery dc source to power the home along with solar

Postby willfromsussex » Fri May 20, 2016 12:12 am

running a bank is a great idea , just leave the car out of it. i run a 20kwh lead acid battery bank. (48v) i got the batts (6v) from the scrap metal recyclers. they are in such good working order that one really has to wonder about the origin of some of the items brought into these places, but what can you do? let them get melted down or take them home and put them to good use. i run some 48v items (cctv cameras, POE switch etc) and then i run little dc-dc converters to make 12v. i can't recommend this setup highly enough, its awesome. What it means is you get a rock steady constant 12v regardless of whether your bank is at 54 or 47 volts, and when you add loads (more lights etc to the 12v ) the converter just compensates and still gives you full 12v i then run all my lighting at 12v (MR16 and G4 led bulbs are fantastic) . My computer, stereo, modem, router, all that stuff is all running directly off 12v. My solar is completely off grid 2Kwp.

During sunny days I can also fire up my 2kw UPS. (connected up to the battery bank instead of its original internal batteries) This then runs all the mains loads, such as fridge freezer. Only problem with the UPS is that it uses at least 90 watts just running itself. So if I just left that on 24 hours a day it would use at least 2 kwh just running itself. Some days in winter I'd be lucky to pull 1 kwh so it is reserved for summer, and sunny days. Longest continuous run I've done on it is a couple of weeks. Its a great feeling just having your grid electric meter parked, doing nothing for 2 weeks while you carry on as normal!

With your grid tied system it will be a bit different im sure but running a high voltage DC might work really well, (just need to be bloody careful with it)

but your inverter would presumably be trying to export to the grid from your battery if it thinks it is just solar power going in.


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