Solar By Area

An Eccentric Anomaly: Ed Davies's Blog

My previous entry, PV, ETs and Flatties, compared the outputs of various solar panel types by price. If, like me, you're designing a house to have a large south-facing area for solar collection then this makes sense as price is the key factor. However, if you have an existing house which is not designed with solar collection in mind then area might be the limiting factor. Following a request by Wookey here's a similar graph normalized by area.

It's generated using the same GNUPlot file as the graphs in the previous blog entry with the addition of:

apv(G) = qpv(G) / 1.6236
aet(G, t) = qet(G, t) / 2.403
afp(G, t) = qfp(G, t) / 2.514

to give the outputs of the panels per square metre. (Of course, that could have been done just by setting the areas to one in the original power output equations but I wanted to leave those untouched.) Then:

plot [G=0:1000] [0:700] afp(G, 0), afp(G, 25), afp(G, 45), aet(G, 0), aet(G, 25), aet(G, 45), apv(G)

to plot the outputs in suitable order for the key to match the outputs at high insolation levels.

Note the straight lines. Because we're holding the temperature differentials constant in each case the t² term just causes a fixed offset to the lines making the graph a bit less visually interesting than those in the previous entry.

In other words, if you're willing to only generate in bright sunshine (greater than about 550 W/m²) then flat plates beat evacuated tubes beat photovoltaic. If you want generation in less ideal conditions then, even by area, you have to look at the graphs more carefully which is a bit awkward so here's the bottom-left part expanded:

plot [G=0:600] [0:350] afp(G, 0), afp(G, 25), afp(G, 45), aet(G, 0), aet(G, 25), aet(G, 45), apv(G)