Adding battery backup – even if you DON’T have solar!

It’s been a while since I posted any new activities – but only because I’ve been so darned busy! A client in Harrison Indiana wanted a a solar system installed, but he launched his project too late in the year, so rather than fight the weather, we decided to just install the BACKUP portion of the project ahead of time – giving him the benefit of a backup system for the upcoming Winter season. He lives out in the country, and encounters frequent power outages during the winter months, so this was a good compromise, and that’s what this blog entry will be about.

We decided to go with the new OutBack RADIAN 8Kw inverter and the Outback AGM batteries, since they don’t require watering or venting. He had space on the wall where his current Main breaker panel was located, so we just expanded with some extra plywood. We hung the inverter and mounted the battery bank directly below it so that we would minimize the distance the 4/0 Battery cable would need to cover.

Current position of existing main breaker panel

Main panel location at start of project. Room to the right and below.

With that plan in mind, I went in search of some 1 inch plywood, which it seems none of the lumberyards carry. I got the lumberyard to precut a 4 X 8 sheet of 1/2 inch thickness, and managed to squeeze them into our PT cruiser. A couple squirts of glue and some 3/4 drywall screws to hold them together got us the mounting plate we needed for all the things we were going to add: a SUPPORTED LOAD panel – this is the loads that will be backed up when the power drops, another outlet for the freezer next to this panel, and the OutBack MATE3 control center that lets us program the Radian and observe the voltage and operation visually.

The MATE3 also provides the interface to the internet so that this can all be monitored from a PC on the web. We planned on adding solar this year when the weather warmed up, and the Radian PREWIRED INTERFACE took all the hassle out of making this all work. THe interface is directly below the Radian in the next photo. Everything inside this prewired box is clearly labeled and it would be VERY hard to get it hooked up wrong!

OutBack Radian Inverter Mounted

New plywood backer, Radian (top) and prewire box (bottom)

The next step was to move the breakers and wiring for the supported loads from the main panel (at the left) to the supported load panel (in the middle). The lines were too short by a couple of feet, so I went to the electrical supply house and found some neat nylon splice blocks that have compression screws and they come in big strips of 20 or 30, so I could cut them into blocks of 3. This allowed me to splice new romex (same gauge) to the black, white and copper ground wires in a manner that was safe and in compliance with the National Electrical Code.

The wood backing also allowed me to screw the splice blocks in place at the top of the board (out of reach) to keep things safe. Please notice that all connections between the breakerboxes, the inverter and anything else on this board are all in conduit. The only exception is the Romex, which by code is allowed. Just remember that EVERY line of romex going into the supported load panel MUST have a strain relief. You just can’t run wires through the holes in the box – it would NEVER pass an inspection!

Outback AGM Battery bank

Outback AGM battery bank. Great for no-worry storage!

While I was doing all that wiring, the homeowner was busily assembling the battery cabinet and installing the OutBack AGM (sealed lead acid gel type) batteries and all the jumpers to create the battery bank. There are two banks of four batteries, which are then paralleled to achieve a sizeable AmpHour capacity.

These batteries are not cheap, but they don’t require any attention like checking fluid level, or requiring a vent fan, so it simplifies the installation and use of the system. By the way, if you want a closer look, just click on the photos and you will get a full screen size view.

If you look close you’ll find that there is a 175Adc breaker for each ROW of batteries in the cabinet. This will come in handy troubleshooting in the future. It also keeps things safe while connecting the battery cables. The cable used in this setup is high strand count 4/0 with FACTORY TERMINATED ring ends. No, you CAN’T use welding cable, and don’t even THINK about putting ends on by yourself.

Always purchase SOLAR battery cables that are pre-terminated by your supplier. During normal operation DC current out of the battery can reach peaks upwards of 500 to 1000 AMPS. Any weak or loose connection will get hot and create a problem in no time!

Installation almost complete

Almost ready to turn on. No feed from the solar just yet.

Here’s the finished installation – just a few more lines to move from the main breaker panel over to the supported load panel. If you click on the photo, and zoom in, you can just make out those splice blocks I was talking about at the top. There was just enough room below the supported load panel to mount the Mate3, and the finished installation looks pretty nice with all the brushed steel panels and covers re-installed.

Other than the battery cabinet, the backup system didn’t take any additional floor space, so it was not a problem where we placed everything. The homeowner still needs to run an ethernet cable down a chimney chase from upstairs to put the system online – another project for a rainy day. I went back in the early Spring of this year to install the ground mount and a sunny boy inverter at the back of the property.

This is an old farm, and the service is sort of snaked around the property. By intercepting the feed to the barns, we will be able to redirect them THROUGH the RADIAN INVERTER PREWIRE BOX, and effectively create an awesome GRID BACKUP system that will operate AND Charge the batteries when the utility power is down. In Bright sun, we have 8KW from the inverter/battery bank COMBINED with 5 to 6KW of realtime solar power to run some BIG loads like AC or the washer/dryer.

If you look back at the 2nd picture, you can see TWO large boxes with cables coming from them. These are two 4Kw inverters. The RADIAN design is redundant- if one quits, you still have power, just 1/2 power. That’s better than NONE when the power is down. I think this is the best feature of the radiant design!

Proposed changes to tax credits set to expire Dec 2016

Here are some highlights from a recent article in SOLAR INDUSTRY MAGAZINE.

If several recently introduced legislative bills give any indication, Congress has heard the call from solar energy advocates to modify the investment tax credit (ITC).

The ITC, which expires Dec. 31, 2016, currently pays a credit of 30% for qualifying projects. If no changes are made, the credit shrinks to 10% in 2017.

In recent months, both the House and Senate have introduced legislation that not only calls for an ITC extension but also stipulates that solar projects should qualify for the tax incentive based on when they start, as opposed to when they are placed into service.

On Feb. 6, Sens. Dean Heller, R-Nev., and Michael Bennett, D-Colo., co-sponsored the Renewable Energy Parity Act of 2014, which would allow developers to qualify for the ITC if projects are under construction before the credit’s expiration date, rather than having to wait until those projects are completed and in service.
In August, Rep. Paul Clark, R-Calif., introduced H.R. 3017, the Renewable Energy Construction and Investment Parity Act of 2013, which also extends the energy tax credit to solar energy, fuel cell, microturbine, combined heat and power systems, small wind energy, and thermal energy properties – the construction of which begins before Jan. 1, 2017.
While the ITC push appears to be gaining traction – as evidenced by the support of House and Senate Republicans – sources express doubt that any of the bills by themselves could pass, given the grid-locked Congress.


It depends on how much roof space (or yard space) you have, and how many panels you install. A good average system size is 24 panels, which in most cases is a PALLET of panels, which gets you the best pricing. My home has 24 panels on it. 20 of them are 230 watt panels and 4 are 240 watts, added at a later date.

My house faces South West, and I have two large hills on the East and West side that shade my roof for an hour and a half in the morning and an hour before sunset. All that considered, here’s what I just got from the electric company on my most recent bill. It tells the story. I have gas heat, so this is just for my electric usage, but that includes AC in the summer months!

Electric chart for solar equipped home

Electric Usage chart for my solar equipped home.

Serious grid-tied/grid-backup system!

DIY Solar grid backup system

Ground mounts are an attractive alternative if you don’t have much roof space and want a system that allows you to live comfortably WITHOUT the grid!!

Nestled in the middle of a 26 acre plot is this cozy updated farmhouse with almost 6KW of solar power. The home is well insulated, and fitted with all the high efficiency goodies. Propane fired DEMAND water heater, wood stove for heating, LED lighting and more! At first I assumed he wanted a ground mount to keep it away from the house, but when I arrived on site I knew right away the real reason – no room on the roof! But seriously, this setup goes way beyond just a large array. The owner wanted plenty of AUTONOMY – that’s lots of days of off grid operation without worry of running the battery bank down. And plenty of power, so that if he wants to do laundry while off grid, it won’t be a problem. So we got together and discussed the options and the owner decided to DO IT RIGHT the first time. I explained that batteries would be a large part of the project cost, and he would have to understand and CARE for the battery bank if he expected it to last 10 years or more.  He was more than willing to listen, read, study and understand the care and feeding of his battery bank, and as a result is VERY pleased with his installation.


DIY Solar ground mount everything in place and ready to add panels

Trench backfilled, horizontal pipe (3 inch galvenized) added front and back, and vertical rails to carry the solar panels installed. Ready for panels and wiring. Owner and a few helpers accomplished this in 2 days of hard work. Not much daylight in December, but DIY folks are not afraid to work sunup to sundown!!

While all this activity was going on outside,  I was busy in the basement, hanging the TWO Sunny Island inverters on the wall, mounting the small EMERGENCY POWER breaker box and running conduit between the inverters, the main breaker box and the new Emergency power box. I’d come up for air once in a while to check on the ground mount work, just to make sure it was square and plumb, but these guys knew what they were doing and got it all right on the very first pass!  Looking at the pics below, we chose to use TWO Sunny Islands for several reasons. 1st and most important was that the Sunny Island is without question the best BATTERY TENDER around. It can use the grid or the array charge the batteries, and it has sophisticated software to monitor the battery health and adjust things as needed to optimize the battery care. It LEARNS over the 1st 8 weeks how the battery supplies power and how it accepts charge and then adjusts itself for the best possible care. We used TWO Sunny Island inverters so that we could SLAVE them together and create 240VAC “split” phase. The Sunny Island is a 120VAC unit and would otherwise need a lossy transformer to boost the output to 240VAC.   We doubled the available continuous output power to 13,000 WATTS by doing this. That is a LOT of backup power, and will allow completely normal living in an off grid situation. The owner wanted lots of autonomy (days of power off grid) so we went with the largest batteries withing the budget – Rolls FLA 6 volt 820AH.  EIGHT of them to reach the 48VDC the Sunny Islands need.  That’s almost 40KWH of backup power. And remember, when off grid, the sun on the array will recharge them, as well as power the house!  I didn’t have time to hang around while a battery BOX was built, so we put up a poly tent and connected the vent fan. This was only a temporary fix and has since been replaced by an appropriate battery box. The exhaust fan is programmed to come on while the batteries are charging – since this is when they give off Hydrogen gasses which are explosive in small amounts.  The owner has since also installed RECOMBINATION CAPS which reduce the outgassing by 99% and reduce fluid losses considerably – making it only necessary to check acid levels in the battery every two months or so, rather than every 2 weeks. A wise investment – since it minimizes outgassing of Hydrogen if the vent fan were to ever fail! Batteries are a VERY serious bit of hardware and you MUST care for them if you expect to get 10+ years of service!  Always wear safety glasses, a rubber apron and rubber gloves when checking/filling the cells!

DIY Solar grid-tied backup system connected and ready for power!

Some of the AC lines have been moved to the emergency breaker box, all covers are on, and temporary poly cover over battery box has been connected to the power vent fan. When the battery bank charges (at 38 amps DC) the batteries bubble up hydrogen gas and without the fan and cover, the room would reach explosive hydrogen levels in less than 1 minute. NEVER power up a battery system without a vent system!! A 4% concentration level of Hydrogen gas is highly explosive.

Battery bank, inverters and emergency breaker panel on DIY Solar installation

Two Sunny Island battery/inverters on the wall, eight 6 volt 820AH batteries below elevated off floor to make watering easier. DC cables connected and AC interconnections in Plastic conduit for safety. Ready to move some wiring from the main box to the emergency breaker box. Only items in the emergency box will be powered when running off grid. System cuts over instantly when grid drops out. Barely a flicker of the lights, it happens so fast! Same thing happens when power is restored. Back on grid in an instant.















When a lead-acid battery is discharged, the electrolyte (sulfuric acid) and the active material on the plates of the battery (lead) are consumed to produce water and lead sulfate and current flow. The chemical equation for a lead-acid battery during discharge is: PbO2 Pb 2H2SO4 –>PbSO4 2H2O Ideally it’s just hydrogen gas, but when doing Equalization charging, you’re going to get some hydrogen sulfide as well – you’ll know it by it’s Sulfur smell and the stinging sensation to your eyes! Make sure the battery box power exhaust fan works BEFORE you turn on your system. In this setup, I programmed the fan to run whenever the batteries are charging. As long as the fan is running, there is negative pressure in the box (or temporary tent in this case) so even any holes or leaks will take fresh air IN to the box/tent and then OUTside the house through the white PVC vent at the left. Happy to say that the 1st charge cycle was free from problems and there wasn’t even the tiniest hint of any gas in the room. The use of RECOMBINATION caps is HIGHLY recommended. They will eliminate almost all of the outgassing and make the battery liquid levels go down MUCH slower.