Home Worker – Solar Energy Bench Test

In the last edition, I highlighted the challenges faced by home workers who live in locations where the power supply is either intermittent or is not available at all. Since the article was published, I have carried out rigorous testing of two systems. Both performed well. One system was “Out of the box” and the other system was built from separate components I was able to source from suppliers in the UK.

The quickest solution is to buy a solution which has been pre-built. But with the world in lockdown and many flights cancelled it may not be possible to import solutions, so the “Build your own” option may be the only way to provide power. In addition to the home solar designs below, I was recently asked to look at design for 20 staff.

Voltaic Arc 20W Solar Charger Kit: This system is supplied by Planson International. Over the course of four days, I was able to use a Lenovo X390 laptop without needing to connect to the mains power to top up.

The Lenovo X90 uses around 65 Watts when charging which is a little more than the capacity provided from the solar panel, however it only takes just over an hour to charge. Testing was conducted in the UK during sunny weather (early April). During the testing enough energy was created to produce two full laptop charges a day.

It is also possible to get more from a charge by doing the following:

  • Use battery save functions
  • Do not play music – it consumes power
  • Reduce the screen light power (try to work in a shaded place
  • During conference calling, avoid video if possible.

The Voltaic kit also comes with a LED light which is more than sufficient for a desk and a mains charger which can be used to charge the battery in the places where intermittent power is needed.

 100W Home kit (Built from separate components: This system can be built from components purchased locally. In the UK, the following components were purchased from RS components (rswww.com).

  • 100W Solar Panel             $160                                                 
  • 100 A/H Lead acid battery                     $280
  • 100W Inverter                                        $70                                          
  • Controller (10A)                                          $80
  • Cables and plugs                                        $80

For a total of approximately $680, this system is sufficient to power a few LED lights, a laptop, mobile phone and a printer. The purpose of the controller is to manage the power from the solar panel so that the batteries is now overcharged. The controller also has a display which indicates how much charge is being generated, and how much energy is stored in the battery.

This system can also be scaled up. With the same controller, two further 100W panels can be added (Bringing the capacity to 300W or 9A). Additional batteries can also be added to the system to increase storage capacity. Important Note: Energy loads must always be connected to the output terminals on the controller and not to the battery directly. This will prevent the battery from being completely drained (which can cause damage to the battery).

The inverter in this design provides a maximum power of 100W. Larger inverters can be used, but till consume power more quickly. Given that it often takes just over an hour to charge many laptops, I think a single invertor will be sufficient for charging laptops.

For lighting, I would recommend 12V LED lights rather than using 220V lights connected to an inverter. This is more energy efficient as there are often energy losses within most inverters.

Small office Design for 20 users

When designing a system for a small office, it’s important to work out what the overall load is. This will help to identify what components will need to be purchased to build the system. Once the system has been set up, it must only be used for the power load it was designed for. If more items are loaded (e.g. more computers) the system may not have the capacity to support the increased load without upgrading the solar system first.

Many years ago, I developed a tool to estimate the size of a solar energy system. This first screenshot lists the items we need to power.

The load list does not contain items like fridges and security lights as I would recommend buying dedicated stand-alone solutions which have their own panels built-in. Please note that in addition to power load information, it’s important to include information about how long each item is used each day.

The next table calculates the amount of panels and batteries needed to provide the power for the load listed in the first table. The battery bank has been specified to store enough energy for three days. The solar panel has been designed to produce enough energy to service the load and provide a little extra power which can be used to store up energy for three days.

So for this load, if we use 100W solar panels, and 100A/H batteries, we will need 29 Panels and a bank of 50 Batteries. In addition to this, we will need a fairly large controller which can handle 150 Amps. Larger controllers also require bigger cables to transfer the power. In some places higher capacity cables and controllers can be difficult to source, but it’s possible to achieve the same result by building three smaller 50A systems.

As a very rough guide, here is an estimate for building the system above.

  • 150 Amp controller:        $2300
  • 50 Batteries:                      $1250
  • 29 Panels                             $4640
  • Inverter 2KW                     $1000
  • Cables etc                            $1500
    Total                                    $10,690

This is a rough estimate which does not include shipping and taxes. Whilst the initial set up cost is high, over time, the overall return on investment is good as no fuel is used. The only component which needs to be changed from time to time is the batteries.

Conclusion: Solar energy can be a great solution for remote locations where power is not available. It is also a cleaner method of providing energy. With some good planning, selection of low powered office systems, smaller power systems can be purchased. Good discipline is also important as it’s easy for a system to fail to deliver if extra load is added which was not planned for.