For the last few years we’ve had a 200w mobile solar set up to power our horsebox. This had provided us with enough power to have lights, mobile phone charges, music and laptops throughout most of the year, but in the dark winter months we’re often left short.
We decided to upgrade our power this year to provide for the workshop, barn and house. Our new power set up needed to provide us with a total minimum of 1.53kWh per day, even in the winter and also be able to start up a table saw motor, which peaks at up to 10kw then runs at less than 3kw.
We get an average of 4 hours of sunshine a day here, varying between 6.5hours in summer and 1.5 hours in winter. We calculated that we’d need a minimum of 1.2kw of panels. Reality, however, has little respect for average weather conditions. A few winters back we had 80 days of rain in a row. Our battery bank would need to be able to sustain weeks with very low charge in the winter, with out dropping below 70% of its capacity as this would damage battery life.
We have power lines across our field, giving us the option to connect our solar panels to the national grid. This means we could feed in energy in the day, and take energy out at night, using the grid as a battery. This would eliminate the need for batteries, which have high embodied energy.
After weighing up the pros and cons, and getting a quote for a grid connection, we decided to stay off grid. We liked the idea of being responsible for our own power and understanding how to fix things for ourselves. We decided to use recycled fork lift batteries to negate the embodied energy of the batteries.
This a sketch of our set up plan.
After some research we decided to use:
- 12 x 245w recycled canadian-made solar panels.
- An Outback Flex charge controller.
- A Victron Pheonix 5kw inverter.
- 24 x 2v second hand forklift batteries of 820ah.
The solar panels are arranged in 4 parallel strings of 3 panels in series, giving a voltage of 90v and totalling nearly 3kw.
Our charge controller converts the 90v to 48v and regulates the charging of our battery bank. Our battery bank is made up of 24 2v cells, arranged in series to give a total of 48v. Our inverter draws at 48v from our battery bank and converts it to 240v. Our supply is then sent through a consumer unit to normal house hold sockets.
Our supply is earthed through a copper rod driven into the ground. We calculated appropriate fuse sizes and wire sizes in order to keep things safe. We also ensured adequate ventilation in the shed to avoid hydrogen build up (…and explosion!)
So far everything seems to working well. We’ve managed to afford to spec everything a little bit higher than we initially proposed by using second hand batteries and solar panels. So hopefully we’ll have plenty of power throughout winter. In the mean time, I’m looking forward to getting a washing machine.
I found the following sites useful in researching this..
Evaluate and Tweak!
So after over a year of using this system, I want to share some reflections on how its working, and the changes that we are making.
Generally everything works well, and we’ve had plenty of power coming in, as shown below.
We predicted that we’d have less power in the winter than our calculations led us to be believe. And we were definitely right. Unfortunately we were so right that we actually got to the point of turning everything off for 2 weeks around the winter solstice to allow our batteries to recharge to avoid permanently damaging them!
We noticed that our inverter was using about 40 watts at any given time…. just to be on! This works out at about 1 kilowatt hour a day, without us consuming any electricity at all. On cloudy days this was much more than our panels were absorbing, and left us in a cycle of power deficit.
To solve this problem we’ve decided to buy a second smaller inverter (1.2kw) which will use around 10watts whilst on standby. We’ll use a system of 32amp plugs to allow us to switch over to the higher power inverter when we want to run something juicy.
We’re also aware that our panels are probably not in the optimum positions, but that will all change when we get around to building a house!
And now we know to keep a careful eye on the battery levels during the winter times, and avoid letting them get down to the dreaded 70% before the winter solstice.