Notes on off-grid living on the cheap

Over the past more than 20 years we have slowly built a solar system for our home. We started with about 1 thousand watts of panels when the average cost per watt was $6. Now the cost has fallen to around $1.20. We have increased our panels to around 1400 watts and installed a 3kw sine wave inverter. Throughout our past we have maintained a monitor of our power use and reduced our consumption to around 3 killowatt hours per day from 13 before we started paying attention. There are two of us (adults) living in the house and we have undertaken a number of initiatives to achieve our present modest consumption.

Our storage:

We have 6 of 200amp hour 12volt batteries and 80 of 7amp hour 12volt batteries making for a total storage of( (80 x 7) =560 )+ ((6 x 200) = 1200) = 1760 amp hours of storage at 12 volts which calculates to a nominal 21.12 thousand watt hours . All batteries are sealed lead acid. Because our system runs at 24 volts and batteries are wired in series we have (half of 1760) 880 amp hours at 24volts. Notice that both 12volt and 24volt calculate to the same number of watt hours storage which makes watt hours (whr or kwhr) the most useful method of comparing storage.

Theoretically this means we can use 21 kwhr of energy without charging but this is not the reality and its more likely that we can use around 10kwhr before needing to recharge the batteries. Because we use around 3kwhrs of energy each day we can stand around three days without charge. This length of time is slightly extended by dark days giving some charge from light without sun.

Our load:

Energy use is best considered in two ways. Firstly as a peak then as an amount per day or week.

Peak appliances are oven at 1.8kw, vaccuum cleaner at 1.8kw, lawn mower at 1.5kw, coffee machine at 1.5kw, induction cooker at 1.5 kw per ring, hair dryer at 1.4 kw, microwave at 1.4kw, small convection oven at 0.8kw and toaster at 0.7kw. Lesser loads are typically; fridge 0.170kw, 48” led television 0.04kw (run in energy saving mode), micro computers 0.05kw. Various other bits and pieces along with led lighting add up so in our situation we use between 200 and 300 watts when awake and around 50 watts when asleep. With a 3kw inverter limiting our peak load we have learnt to only use one appliance at a time. In practice this means judiciously shuffling the use of appliances when cooking. Breakfast and dinner are the times of heaviest use and only in mid summer is storage helped by the sun at breakfast and dinner times. It is practical to use two appliances together if they are both limited in their energy use. So two induction rings may be run together if one or both are set to simmer. Usually though its one appliance coupled with the background use. Our fridge is very efficient and converted to use an electronic thermostat using around 700whrs per day leaving 2.3kwhrs to complete our daily use.

Making breakfast involves first placing a porridge pot on to boil and later turning on the coffee machine while the porridge is simmering. You can usually hear when an appliance is struggling.

Our inverter:

We have a 24volt 3kw pure sine wave chineese inverter purchased second hand for around NZ$400. The most recent inverters are generally much better than those of a few years back that often broke down. We keep a 1.5kw inverter as a backup.

Our solar chargers:

We use two in parallel because we purchased one before the other but both are the same model. They are Tracer MPPT (maximum peak power tracking) both 40 amp giving us the potential to feed 80amps total to the batteries at 24 volts. This allows us up to about 2kw of solar so we can add more another 500watts or so if we feel the need and have the money along with roof space. Note that the batteries when charging at their maximum can be around 29 volts so the 80 amps limit allows 2.3 kw of charging.

Some of the things we have done:

• We moved from a normal electic range to a modern electic oven using around 1.8kw when the thermostat is active. This results in a real use averaging around 1kw per hour and on sunny days we can usually afford 2 hours of use.
• We use a small convection oven using 800 watts as our most common cooker.
• We moved from a radiant hob to a induction hob and most recently to a mixed gas and induction hob with two induction and two lpg gas. This greatly increases our options as our batteries drain and makes survival off grid likely during the worst of winter so long as we apply strict limits to our load as dark days accumulate.
• We sold our previous LED television (using around 250 watts) as the new ones have become much more energy efficient. We used a portable watt meter to measure the power use before we made our purchase. We usually run the display for a maximum of 3 hour per day.
• When buying appliances it is best to measure their power before purchase. We did have a full induction hob but found it was using nearly 500 watts even when off so have made the change to another brand which uses almost no energy when off.
• We both have computers but use a touch pad as often as possible in prefence. The touch pad can run an efficient HDMI LED display and use an external keyboard and mouse(bluetooth).
• We use an android TV stick to play movies or recorded TV shows on our LED television. Also use the stick for playing music. We have a full digital 5.1 amplifier that is very energy efficient.
• All lighting is LED. We started out using three 150watt light bulbs in our living area more than 20 years ago then moved to compact flourescents and lately to LED. Our energy use for the same area is now about 38 watts. We are inclinded to use a number of smaller lights in place of one big one in our kitchen, bedroom and living areas where feasible.
• Careful power monitoring has become a feature of our living but is no real hassle as the rewards are so great.
• We have been off grid for more than 3 months now but retain the mains power as a backup. Our power bills are around NZ$15 per month for the supply charges. With the addition of the LPG gas rings we should be able to terminate the mains supply completely and are considering this at present.

Why:

Firstly to reduce our energy foot print. Secondly to be self sufficient. We use wood for our heating and this also supplies our hot water through a wet back. We have fires around 8 months a year and are able to run the hot water heater from solar on sunny days for an hour or so. This is enough for our showers and washing.