Introduction: Battery Powered Office. Solar System With Auto Switching East/West Solar Panels and Wind Turbine

The Project:

A 200 square ft. office needs to be battery powered. The office must also contain all of the controllers, batteries and components needed for this system. Solar and wind power will charge the batteries. There is a slight problem of only having west and east ground mounting options for the solar panels with a house aligned north/south directly between the panels. The house orientation causes lots of shade on both the east and west side panels throughout the day.

The system's main battery bank (24v 100AH) overcomes the shade problem and is charged using solar power from sunrise to sunset for a refrigerator, freezer and computer. The smaller secondary battery bank (24V 35AH) is charged by the same solar panels (in shade and peak sun time) plus a wind turbine. The smaller battery bank is for 12 volt security system monitors/cameras, tv, lights and fans.

This Instructable will focus mainly on 4 key points:

1. East & west solar panel configuration - two strings of panels that will have different voltage levels depending on the time of day and one way to overcome this problem.
2. Battery Protection. Using an automatic transfer switch & how to build your own with two simple components to protect against batteries running low.
3. Adding a wind turbine to a solar system in case of long periods of sunless days.
4. Installing the entire controller system and batteries inside the office area. The floor space used is 2.6 square feet.


2 x 100 AH batteries Main battery bank - Hooked in series making 24volt @ 100AH using a busbar for all negative connections

2 x 35AH batteries Secondary battery bank - Hooked in series making 24 volts @ 35AH using a busbar for all negative connections

24 volt inverter 2000 watt inverter to run 120 vac appliances

6 gauge wire running from the main battery bank to the 100 amp fuse and negative busbar

100 Amp Fuse for between the inverter and 24v battery bank

Automatic Transfer Switch to protect the 24v 100AH battery bank from under voltage levels

Solar Controler 40 amp, 1200 watt, 150 volt max pv input

2nd solar controller For the 24 volt 35AH battery bank 100 volt max pv input

Solar Panels 8 of these would be basically the same as in this system

Wire with connectors are expensive but easy to hook up for shorter distances (10 awg)

8 awg extender with connectors are expensive but easy to hook up for longer distances (8 awg)

Panel Connectors to make your own cables

East/West relay for switching between the two solar panel strings

Digital timer to control the East/West relay

Solid State relay for making your own low battery cut off switch (for the 35AH batt)

Low Voltage Protect device to control the solid state relay (protecting the 35AH batt)

24 volt to 12 volt converter to run the 12 volt items from the main 24v battery banks if needed

DPDT knife switch x 2 to direct which battery bank is connected to the 12 volt fuse box and to switch between wind and solar for the 24v 35AH battery bank.

12 volt fuse box to distribute and protect all 12 volt devices

10 gauge hookup wire along with another roll of wire I previously had

Crimping tool along with lugs to create a lot of custom length cables. Should have got a different set of lugs

Wind Turbine for long periods of no sun in a power outage - hooked to the 24v 35AH battery bank with 2nd solar controller

TPDT knife switch for the wind turbine break system using 3 resistors for the break

Step 1: The West Side Panels

The first 4 panels were installed a few months ago on the west side.

These are 12 volt 100 watt Renogy panels. They are currently unavailable, but for reference they were on Amazon.

The time of day in the picture with Charlie the cat, is around 3:40 pm. The solar panels are tie wrapped to two 12' poles. Those two 12' poles are mounted to the deck, first by drilling two holes in the side of the deck, then sliding the poles into the deck holes. The other ends of the 12' poles are bolted to two shorter 5' poles planted in the ground. At the bottom of the 5' poles are horizontal 8" square metal plates. They are impossible for the wind to lift out of the ground. I just lucked in to finding the 5' poles and can't really add a link to them.

It's very easy to clean the panels being mounted so low.

These solar panels are connected to the relay starting with 30ft of 8 awg extension wire, plus another 30 feet of 10 awg cable.

Step 2: The East Side Panels

Here are 4 more 12v 100watt solar panels on the east side at about 3:30pm. They were installed on 10/18/20.

The panels are mounted to the deck with a horizontal satellite dish mounting pole and then by using two 12 foot 1.5" poles, tie wraps and some cinder blocks with brick pieces at the very end (see pictures).

The cables for the west side cost almost as much as a solar panel! I wanted to try something cheaper for the 50 foot east side cables. I remembered this trick from a youtube video about using regular extension cords, cutting off the ends and tying the three wire leads together. So, I used a 100 foot extension cord and it works fine. The wire size ended up being about 10 gauge for both of the 50 foot cables I made. With the higher voltage (80v) coming from the panels, this size wire should be o.k. without too much loss for now. I used this 9 In 12AWG Adaptor Kit to connect the ends of the 50 foot wires to the solar panels with twist on connectors.

Step 3: The Solar Controllers & Relay - Switching the East and West Side Panels

The Solar Controlers:

The Main 40 Amp Epever solar controllerThis controller is for charging the 24v 100AH battery bank. This controller has a 150 volt maximum solar panel input voltage. The maximum panel input wattage is 1,200 (now the limit for this system).

The secondary 40 Amp Epever solar controllerThis controller is for charging the 24v 35AH battery bank. The charger has 100 volt maximum solar panel input (now the limit for this system) and maximum input wattage of 1,500. There is also a wind turbine with its controller helping charge this battery bank.

The Relay:

One half of the DPDT (double pole double throw) relay is used to switch between the 4 east and 4 west solar panels, connecting them to the Main Controller. The other half of the relay switches the solar panels for the secondary controller. Here's what the switching time is set to now, for every day of the week:

7am to 12pm The Digital Timer turns on the 80 AMP RELAY which connects/switches the east side 4 panels to the Main Charge Controller (and 24v 100AH battery bank). Note: The relay is drawing about 6 watts of power from the system for these 6 hours.
The 4 west side panels are also switched to the Secondary Charge Controller at this time (charging the 24v 35AH battery bank). There should be good charging power from 10am to 1pm from the west panels.
12pm to 7am The Digital Timer turns off the RELAY which connects/switches the west side 4 panels to the Main Charge Controller. The relay is now taking zero power from the system.
The 4 east panels are also switched to the Secondary Charge Controller at this time. Should be good charging for another 2 hours (1pm to 3pm).

See the relay picture for wiring information plus the main circuit diagram in step 9.

The negative wires from the east and west solar panel strings are tied together and going to a cut off switch before connecting to the negative inputs of the solar controllers. I had the negative cutoff switch laying around and just added it. This is not reflected in the main drawing. Any high amp type of switch should work fine but it's not needed.

Step 4: The 24Volt 100AH Main Battery Bank and Inverter

Currently, the main battery bank is made up of two x 12volt 100AH batteries in series making a 24volt 100AH battery bank. A 24v 2000 watt inverter is used to power a refrigerator, freezer, computers or microwave oven. There's a 100 amp fuse between the inverter and main battery bank. For these120vac items, there is a power strip coming off of the auto transfer switch.

The system uses sealed batteries and should not leak any hydrogen gas. I had a co2 detector and have read that they will also detect hydrogen gas, so I installed it. A ventilation system will be added soon.

Step 5: Saving the Main 24volt 100AH Battery Bank From Low Voltage

The 50A 5500 Watt Automatic Transfer Switch from Spartan is around $115. It would be fun to build one too.

You can pre-set the low battery voltage level with this to automatically cut all power being used from the 2000 watt inverter. It then switches power for the A/C items to grid power, insuring we save the batteries from running down past the danger level. You can not notice the instant switchover.

This device will then let the batteries charge to a high point set, before returning to battery power again. The device constantly draws 6 watts of power when switched to inverter power mode.

It's easy to hookup. Just connect the inverter to the input labeled "inverter". Connect the appliances that normally would have been connected to your inverter to the "output" section. Connect your house power to the "public power" section. Last, connect your main solar systems battery bank (after the fuse) to the "battery" section. All three A/C grounds connect together on a separate mini busbar. See main circuit diagram.

Step 6: The Secondary 24v 35AH Battery Bank. Adding a Wind Turbine and the Switch for Solar or Wind.

This solar system's secondary solar controller and 24v 35AH battery bank keeps the solar panels in use all the time. Due to the east/west configuration, most of the solar panel's power goes to the 100AH battery bank and less power goes to the 35AH battery bank (which needs less). The 35AH battery bank can be switched to wind power during all off-peak sun time.

The A/C wind turbine was mainly added for a worst-case scenario of long power outages and lots of cloudy days. There should be enough wind power to keep cell phones and laptops charged along with a few 12volt items running (radio, tv & lights).

The $130 Yaegarden 400W Wind Turbine Kit with Controller from Amazon looked like a good deal after a little research. It comes with a 12v / 24v battery charge controller.

I used an angle bracket to help mount the turbine to a pole. You can remove the main antenna center part from this bracket and use that hole for bolting to one of the 4 holes of the turbine mounting circular piece (see pics).

At the very top of the system cabinet, there is a video monitor connected to a camera pointed at the wind turbine. It's great to see what's going on with the turbine speed while looking at the meters. It's also fun to see the break in action.

To switch from solar or wind charge mode, half of a DPDT knife switch is used. The ground wires of the solar charger and wind controller/charger are tied to the main system ground busbar(s).

It's good to have a break system to keep the blades from spinning when the turbine is not charging the batteries.

The TPDT switch is used to change from running mode to break mode. This is done first by connecting the 3 A/C wires coming from the wind turbine to the common section of the switch. The break (three 100 watt 10 ohm resistors) is on the A side of the switch, and the wind controller is on the B side of the switch.

Step 7: The 12 Volt Fuse Box, Battery Bank Switch and 24v to 12v Converter

Half of a DPDT switch directs power from either the main 24v 100AH battery bank or the secondary 24v 35AH battery bank, to the 24volt to12 volt DC converter.

The 12 volt output of the converter is connected to the 12 volt fuse box input.

To distribute the 12 volt power, there are currently three small circuit project boxes with digital volt meters installed along with banana style jacks running from the fuse box. I already blew one fuse. It's always good to have fuses!

Here is a picture of a terminal block bar connected to the 12volt box with banana plugs. The circuit board is a 12volt audio amplifier for the tv system. The digital timer for the relay is also connected to the fuse box.

Step 8: Saving the Secondary Battery Bank From Undervoltage

For the 24v 35AH battery bank, just two items are needed to build your own under-voltage battery protect device.

1. The TeOhk XY-CD60 Lithium Battery Charge Discharge Controller. NOTE* the wiring diagram sticker on this unit is wrong. Open it up and look at the markings on the circuit board.

2. A high amp regular relay or solid state relay.

When the TeOhk XY-CD60 controller detects a pre-set low voltage, it will trigger the relay to disconnect the battery from all loads. See the main circuit diagram.

If you are using lithium batteries, you can let them drain down to about 80% (I think). But if you are using AGM/Sealed or lead acid type of batteries, you should never let the batteries get below 50%. I've read to not let 12volt sealed batteries go below 11.2 volts (22.4v for two batteries in series).

Step 9: Main Circuit Diagram

Special hand drawn circuit diagram.

Step 10: Sunrise to 2pm East-West Panel Switch Test

It's going to be a great day outside. 54 degrees now at 8am. The sunrise today was at 6:58am.

The wind is pretty strong. Currently the 24v 35AH battery bank is at 25.4 volts. We'll keep the wind turbine switched on for that battery bank all day, and see how it is later. [Ended up at 26.0 volts]

11/14/20, Main system (24v 100AH Battery bank)

East / West Manual Switching Test:

8:00am test. With the solar controller switched to the east side, the reading is 27.6v @ 1.5 amps or 41 watts.

If I manually switch the controller over to the west panels, we only get a reading of 27.5v @ .1 amps or 2.75 watts.

The test results throughout the day:

8:00am >>  east = 41 watts   west = 2.75 watts
9:00 am >> east = 78 watts    west = 7 watts
11:00 am  >> east = 120 watts  west = 80 watts
12:18 pm >> east 99 watts  west 105 watts
2:00 pm  >> east 153 watts  west 168 watts

We want the main battery bank using the highest wattage side at all times. So, it looks like sometime around 12pm is fine to shut off the relay and switch to the west panels.

Step 11: Sunset - Voltage Level

With the 4 series wired solar panels, the batteries will charge almost until sunset. We were getting about 26 volts from the west panels when this picture was taken (not much current).

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