Solar energy storage with an adaptor

[Joseph Fredrick]

We're thinking of building a 10kWh battery with an adaptor. This will be specifically made to store solar energy. We are also thinking of connecting this device to the grid. It will have an inverter/converter. We are also thinking of an automatic or manual switch between grid use and using from the battery, but we don't know which approach we should go with. Do you all think that this product is viable, and if people with existing solar panels want it?

[Brian McGowan]

I think Outback Power already does this kind of thing.

[Rob Beckers]

Brian, yes, you are correct. In particular their Radian series of inverters can be set up to use the grid as a glorified generator, or sell back excess energy to the grid, use grid power at the cheap times to charge the battery etc. Easy to stack those things too, in case you need a 80 kW inverter. Works quite nicely actually!

Joseph, besides Outback other manufacturers are working on similar product as well: Fronius wants to combine a special version of their grid-tie inverters with a Tesla Powerwall to enable 'load shaving', where you use cheap power to charge the battery, and use it up during the expensive hours. Fronius also allows for PV to be hooked up and charge the battery, and can be set to either sell-back (net-metering) or never export power to the grid (a god-sent here in Ontario where many areas have no 'capacity' on the grid for more solar).

There may be room for more and new products, maybe better products, but you won't be the only one in that market. Big players are there already.

-RoB-

[Joseph Fredrick]

Thats actually very interesting concept of load shaving. Since there are alot of products in the market, but what would be one feature people would look for in a product like this? We are based off Vancouver, BC. Thank you all for the feedback!

[Ying The Thing]

Thats actually very interesting concept of load shaving. Since there are alot of products in the market, but what would be one feature people would look for in a product like this? We are based off Vancouver, BC. Thank you all for the feedback!

Integrating the power conversion system (PCS) with the battery into a single product would be good. I think load shaving is sometimes called peak shaving, and is an exciting market space where there are demand charges. Having a PCS that would allow the battery to charge from the grid is also important (for consecutive days of little sun).

[Joe Blake]

My system has two separate sets of panels (each 1,600 watts with its own inverter) running into a Selectronic SP PRO interactive inverter charger. This is almost infinitely programmable. The link below will take you to the manual.

http://download.selectronic.com.au/manuals/OI0005_02%20SP%20LINK%20Manual.pdf

As of about 2 weeks ago, when we started getting some unseasonably wet weather, I began experimenting with charging my Sealed Lead Acid batteries "off peak" (ie 21:00-07:00 hrs) because of the low price of grid power. Initially I wanted to see if I could limit the depth of discharge to no greater than 65%, to extend the life of the batteries. With the weather now returning to a more "normal" state, with days reaching 40+ deg C and lots of sunshine, I'm seeing that not only am I keeping the batteries charged well up, I'm still able to make a small amount of money by selling my excess power to the grid.

An example was yesterday when the batteries began grid charging at 21:00 hours, with the cut-in at 85% DoD. The program can be set to simply maintain DoD at a point such as 85%, bringing in power to match outgoing, or go up to 100% charge, and hold the batteries at float until 07:00, by which time (at this time of year) there is sufficient sunlight to bring in about 100 watts from the panels. What I've found pleasing is that although I might be importing 3 kWh of power overnight, the following day, because the DoD was very high and not using much solar to maintain 100% charge, I was exporting 12-13 kWh. So even though off peak power is 13 cents/kWh to import, and excess power is purchased by the grid at 7 cents/kWh, it cost me 21 cents to import but I made 91 cents, giving me a "profit" yesterday of 70 cents. So from my point of view I make 70 cents to keep my batteries fully charged.

With the summery weather, temperatures of 40+ degree maxima for 3-5 days in succession are not unknown, and despite good insulation, the house begins to heat up, so I run my small aircon during daylight hours, keeping the internal house temp at about 26 degrees. Since I've charged the batteries off peak the night before, it might cost me about 20-30 cents to import sufficient power to keep the house cool.

I'll be interested to see what happens in winter when it's shorter hours and darker days.

[Ralph Day]

Sounds like you've got your finger on the pulse of your system Joe. (as always)

I do much the same, but just manually. Hit the "use" button on the Mate3 if I want to a)carry loads with the utility or b)carry loads and charge as well.

In the winter months here I have the loads picked up at 7pm, dropped at 7am (cheapest utility power, like yours). If it's windy overnight I'll manually "drop". If it's going to be sunny the next day I might drop the previous night. If it's still and dull, I'll 'use" all day. My utility bill varies between $55 and $70 per month in the winter, less in the summer. The utilitie's minimum is $45 for just having the service. Overall I spend less in utility in a year than I did in diesel for the generator while off-grid. That's in consumption cost per kwhr, not including the $45 per month line fees.

Rlph