We were asked, by a good friend from Wild Stoves, to produce a portable solar PV off-grid power supply system.
Wild stoves supply equipment for efficient outdoor cooking on wood. They run workshops on efficient burning of wood and sell equipment at a number of festivals over the summer. We had been asked to add solar to their 50's caravan a few years ago.
They wanted to be able to provide higher levels of energy to the festivals they attend, but wanted all the equipment to be portable, all parts to be moveable by one person and to fit within a specific space (within a Land Rover and then under a caravan).
Together we designed a 3 box unit with 200Ah of Lithium Iron Phospate batteries at 24V DC, an 800W solar PV array with MPPT and an 1200W inverter unit. This also has battery montioring, various controls for the outputs and 12V outputs for each box.
This post covers the design, build and testing of this system.
This equipment comprises of three power boxes (two battery boxes and one inverter box) and two arrays of 4 semi-flexible solar PV modules.
These have 2 x 100Ah 12V LiFePO4 batteries in them. They also contain fusing and battery volt-meter for checking their voltage. A 24V to 12V DC-DC converter also provides up to 10A of 12V DC power via a car-type 12V socket.
This contains the MPPT charge controller (a BlueSolar MPPT 100/50 from Victron Energy) which connects to the two 400W solar PV arrays via PowerCon conenctors.
The PV arrays are 100W 12V nominal/ 20V max modules put in series to make a 100W 48V nominal/ 80V max. The maximum input voltage of the MPPT charge controller is 100V, hence the 4 panels ins series limit. There are 150V 20A DC fuses on both arrays in case of any problem.
There is a 800W Victron Phoenix 24V Sine-wave inverter which provides two 240V AC outputs at up to 5A each. Both of these are protected via and RCD and there is a connection point for an earth spike to be attached. Two AC sockets have been provided, one for local supply and one as the main output to supply at the festival. This means the supply is split and so one or the other can be switched off, if needed.
A BMV-700 battery monitor is also used to measure the energy into and out of the battery bank. This shows battery voltage, current and state of charge. It is very accurate when left plugged in. This has had some issues, as the information resets to 100% when the batteries are removed, even though they may not be fully charged.
The boxes are connected together via 150A Anderson conenctors and thick 10mm2 cables. The two battery boxes link to the inverter box.
This system will be used by Wild Stoves at a number of smaller festivals they visit. They will be powering lighting, sound systems and recharging systems. Here are some photos from their first outing to Fannys Meadow Festival 2016.
The complete 1kW system, including batteries and inverter, fit into the back of a Land Rover (along with two children..).