Brighton Webs Ltd.
Statistics for Energy and the Environment
One of the few useful bits of advice given to me by a senior manager when I was a software person was "first make it work, then make it work faster". Complexity is sometimes necessary, but it is seldom a good starting point. Maybe others will recognise this thought process, the objective is clear, a rather nasty solution is kludged together, for software this can be a large ball of sphaghetti, if its electronics, it can be a box of wires. The next step is to remove the muddled thinking, add comments and occasionaly produce some documentation. The last stage is the hardest, that is to produce something that runs quickly, can be maintained by a stranger and which the bean counters might include on the balance sheet.
These days I work with renewable energy projects which involve software, power electronics (about which I know very little) and instrumentation (aaaaaaagh......). Old habits die hard, so the starting point is the simplest solution.
This weeks task has been to produce a distribution hub to make use of between 50 and 200 watts. It's all low voltage stuff, so the current is high. The hub is required to provide some protection for the things connected to it. The first line of defence is thermal fuses. In addition to this, the design includes "fool's diodes" to provent high current devices like batteries being connected with the wrong polarity and a high voltage disconnect to prevent delicate electronics being connected to an almost open circuit solar panel.
The design was drawn up and the constructed. Unusually, everything worked OK. As always, there was a "but", in this case, we had 12.0 volts going in and 11.3 volts coming out. If this was a grid-tied device, this might not be a problem, but its a solar powered one. Minimizing losses means increasing resiliance to overcast skies. The solution is relatively simple, put all the protection functions into a MOSFET based disconnect. MOSFETS offer little resistance to current, but they do require some control electronics to make them do what is required of them. This will require a few days work involving design, prototyping, testing, swearing and some thought as to what a production unit might look like.
Saving mA is important in an off-grid system. If PV panels teach you anything, it is respect for the weather and the value of conservation. What would be the effect of applying the same disciplnes to grid-tied solar systems or even domestic and commercial electrical systems in general. Consider the energy flow in a typical grid-tied system. The panels generate electricity at somewhere between 12 and 48 volts DC, this then gets converted to 240 volts AC by an inrerter with an efficiencty of aroun 90 - 95%. During the day, say 10 - 50% of this is converted back to low voltage DC for use in boxes with electronic bits in them like computers and entertainment devices. This efficiency of this conversion process can be estimated by how warm the device gets, it can be as low as 40%. At night, electricity from the grid flows back into the house with further (small) losses.
PS - The fool's diodes referred to above were omitted from the design, the risk of incorrect connection being reduced by the use of appropriate connectors. The only diode to survive was 16A Schlotky device to protect the solar panel when the battery emf is higher than that produced by the solar panel (23-Feb-2012).