woodwork with off grid power

As a business that is devoted to working with reclaimed and recycled wood, we would like to offer an insight into what literally powers us.

Our farm, house and business are totally powered from sustainable energy produced from the solar panel array above. No grid connection at all and utilising battery storage when our panels are not producing power, we have been existing on renewable energy for over five years now.

When we purchased our property, the cost of a grid connection was excessive, and utilising my background in renewable energy, battery backup systems and electrical work, a solar  array with battery backup was the natural choice.

Early in the design phase we looked at our power consumption history, adjusted our dependence on energy required when the panels are not producing and finally looked at the maximum load our wood working machines required when operating. The end result was a plan that we could follow and with some simple adjustments to our lifestyle enabled a cost effective and productive system to be built.

We built an energy efficient home, with wood heating and cooking facilities for the winter, reduced our dependence on electrical appliances, used LED lighting in all areas. To manage the size (and cost) of our battery storage system, a critical component of the plan was our static load at night when we were drawing energy from the battery bank.

Our load at night is primarily for the refrigerator, lighting,  television, computer, (we use a satellite connection for the Internet) and cooling fans over summer, plus water pumps. We are conscious not to leave equipment on if it is not being used and not to use appliances such as the washing machine at night.

The most important aspect we have learned about energy requirements has led us to make some subtle changes in our lifestyle, we now only run heavy loads during daylight hours, always give our batteries priority to charge when sunlight is reduced, (especially in late winter when day hours are shortest) and observe the weather conditions a day or two in advance.

Our workshop is the heaviest user of energy by far, this has probably been the most significant influence on our system design, and how we operate our machines. Once again we follow the principles outlined previously, and we have developed a more flexible approach to our work. Our largest motors are rated at 2.5 horsepower, so running multiple machinery at once is definitely out of the question.

We schedule our heaviest work primarily after allowing time for our batteries to bulk charge, on sunny days, which thankfully in North East Victoria, are not in short supply. On marginal days, we paint, assemble, and complete other productive work so as not to compromise the charging of our batteries.

Some days especially the late winter months of July and August, we curtail our woodworking activities, this time of the year we spend a significant amount of our time and labour on working on our property, fencing, weed control, garden installation work and just generally catching up. This suits us as during the summer months daytime temperatures often exceed 35 degrees Celsius and it is not unusual to see periods of 40 – 45 degree days. Our winters are milder and hard physical work is less tiring on the cooler days.

Our system has performed flawlessly now for over 5 years, we have adapted to a slightly different lifestyle as well, but the changes are not great and have imposed no significant challenges for us.

On a technical note, the design of the system and its components, ratings, etc. were devised over a period of time. Prior to moving to this location we measured all the electrical usage of our equipment, especially items that operate 24 hours a day, this gave us the base daytime peak usage, the minimum power usage we could live with and the nighttime power requirements.

Having captured this data, we could arrive at the sizing for our solar panels, battery storage and charging equipment and the power inverter rating to run all of our loads.

The first component was the selection of the solar panels, their sizing and installation details. When installing solar panels for off grid systems, (as opposed to grid connected) we need to maximise our power production capacity for the shortest daylight hours in winter. This angle is determined by the latitude of where the solar panels are installed, the sun is at its lowest in mid winter.

As a result of this the tilt angle of our panels is significant, being about 60 degrees, so roof mounting was difficult for us, we have selected a ground mounted system at the correct tilt angle. A bonus of this is the panels were easy to install, and cleaning is a simple matter of a quick hose down occasionally in summer to remove any dust buildup and the solar array shades the north wall of our workshop.

We used 28 panels of 185 watts each, which nicely cover the frame and the space allowed for them. The panels are split into two separate arrays of 14 panels each with a separate charge controller on each array to charge the batteries. An added bonus of this dual system is redundancy if we have a panel or charge controller fail, we still have capacity from the remaining bank, all but at a reduced rate.

Our battery bank is composed of sealed lead acid batteries, connected in a 48 volt DC arrangement with a capacity of 500 amp hours. We only draw down our batteries by about 10 – 15 percent of their capacity at night, this contributes to the longer lifespan we expect from the battery bank. We never significantly discharge our battery bank.

The charging of the batteries is handled by two charge controllers, (one for each solar panel array), these automatically control the current supplied to the batteries, providing three distinct charge periods. The first period is the bulk charge, which occurs until the battery bank is charged to about 85 percent of its capacity. Then follows an absorption charge of  1.5 hours at a reduced current and finally when the batteries are fully charged they switch to the float charge, to maintain the batteries at 100 percent capacity.

The controllers are quite intelligent and will remember the previous days charging history and adjust the charging times each ‘new’ day. They also provide the monitoring information that gives us a snapshot of the system. A quick visual confirms to us that both arrays are functioning and the part of the cycle the controllers are in. A separate monitor is used that records charge into and out of the batteries, minimums and maximums of the system voltage and the estimated battery condition in percent.

The most important component is the power inverter, our system is rated at 230 volts and 5 kilowatt capacity. This size is a requirement, even though the average load is significantly less. When a normal induction motor starts it draws up to seven times the full load current (momentarily) of when it is running, an inverter of lesser capacity would not be able to give us this required starting current.

Another point for the inverter we selected was a low standby power consumption, because at night the base load is quite small, peaking if a water pump runs or the refrigerator runs, so once again a low standby power rating reduces the amount of energy drawn from the batteries.

We should add that we do have a backup generator available if we need to use it. We have found that in general, we would only run it for 1 or 2 days a year! Even then we observe the weather conditions and if we need to run it,  it is used to provide the bulk charging current to the batteries, we then disconnect it and allow the batteries to complete their charge on whatever sunlight is available.

The secret to this is to run the generator in the morning when it runs efficiently supplying a high current to the batteries, then turning it off to allow the lower charging current produced by the solar panels to bring the batteries to their fully charged condition. In short we run the generator for about 2 -3 hours, at almost full load (bulk charging – about 85% capacity) and when we observe the battery charging current reducing (absorption period) turn it off for the absorption charge and float charge to occur generated from the solar panels.

Generators do not like running at low loads, and can cause problems with the slip rings of the generator, (technical term is glazing), plus our inverter will disconnect and reconnect the generator at this low current requirement.

And that is our  story of how we have survived and continued to operate our home and business using solar power, with only a slight readjustment being required for off grid living. We have a reliable and conservatively rated system, that is a key component of our off grid experience!

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