There are some important principles about solar which are best explained with questions which may initially sound a bit stupid, but which are actually quite revealing…
Q1 Do solar panels work better when you put them higher up on the roof because they are nearer the sun?
Answer: Solar Panels sometimes work better higher up on some roofs, not because they are nearer the sun, but because they are no longer shaded, particularly in winter, by nearby trees or roofs.
Q2 Can I store my extra solar electricity in my water tank?
Answer: Yes and no. Yes you can store the energy in a water tank. But not, not as electricity: only as heat. But it is usually better value to sell the electrical energy back to the grid.
Q3 Why will your solar water heating system not run my lights properly?
Answer: Because solar water heating systems deliver hot water in pipes. (Trickle hot water down a lighting cable and your fuse will blow.) The key issue is the distinction between two kinds of solar technology. Solar water heating (=solar thermal) heats things up, usually water. Solar electricity = Photovoltaics = PV) delivers electrons down a wire.
Q4 Why can I not just connect my PV panels directly to the electrical socket in the wall?
Answer: There are several reasons why not. One is because the electrical socket in the wall is alternating current (AC) electricity while your PV panels make direct current (DC) electricity. In AC, the voltage goes up and down 50 or 60 times a second. This is its frequency. In DC the voltage usually just stays up all day. You need a chunky gadget called a PV inverter to electronically turn the PV’s DC into mains-type AC of the right voltage and which also makes sure that the AC is in phase (ie it hums exactly in time) with the AC in the mains. The PV inverter is a really clever gadget. It also provides life-preserving safety functions such has “anti-islanding”. What is anti-islanding? Well, in a power cut this stops the mains from being made live (islanding) by your PV system – an important scenario which could otherwise electrocute an electrician – who thought they were working on a dead electrical system.
Q5 When will you call me back with a solar panel which works really well at night?
Answer: Never. Sorry, but moonlight and starlight are very very dim. Far below 1% as bright as sunlight. Not worth the bother collecting. A thirsty person might as well try to collect collect dew in a bucket while ignoring rainstorms. It’s just a matter of going for the big wins.
Q5 Can I put solar panels on a north facing roof?
Answer: The “Conservation Department” at Chester Council actually told me to do this on our house! Please don’t follow their advice, unless you live in the southern hemisphere (where the sun shines from the north). Solar panels on north facing roofs in Europe, Asia and N America only perform only moderately well in summer and hardly at all in winter. Orient your solar panels where their shadows are large and useful. That’s the deal. Facing south is ideal but often a compromise is needed. Solar panels installed on a 30 degree pitch roof, which is east or west facing still offer at least 80% of peak performance.
Q6 When will you invent a solar panel which works better in winter than in summer?
Answer: Never. But in UK you can reduce the huge 6:1 summer:winter performance difference to about 3:1 by putting your solar heating panel on an unshaded S facing wall. Some water solar heating installations are best done this way with oversized panels. No oversupply in summer and a bit extra in winter, when you catch the low angle winter sun. The solar water heating golden rule is to optimise useful performance, rather than just to maximise what can be sometimes useless excess summer performance. With PV panels, it is different. They are grid-connected for the export of surplus energy so positionally they can usually be maximised (as well as optimised) by being positioned on sunny roofs instead of sunny walls. But take a look at off-grid PV’s such as the ones mounted on poles which operate traffic signs. They face south and are pitched at 70-80 degrees – nearly vertical. This is because for stand-alone PV’s, winter performance is often what needs to be maximised.
Q7 When will you make a nice shiny white solar panel panel? [Or a sparkly mirror solar panel or an invisible window-like transparent solar panel?]
Answer: Never. Solar panels need to be as dark as possible in order to absorb light be as efficient as possible. While reflects light – it bounces off white things – so your pretty solar panel would not perform too well. Sorry.
Q8 Why do most people only use buy solar panels when there are grants?
Answer: because solar panels are only cost-effective for most people if they are either subsidised or stolen.
Q9 I have an amazing idea. Get a solar PV panel, connect a light bulb to it, shine the light on the solar panel and it will work forever. You know when the amplifiers squeal at concerts? A bit like that – only less annoying. Will you design/patent this amazing device for me?
Answer: No. Unlike feedback with amplifiers, where electrical energy is added to boost the microphone/loudspeaker feedback loop, there is no energy top up in the system you propose. Like all perpetual motion machines, it will not work. Back to the drawing board…
I hope these are fun. Regards from Barry.