We want­ed to install solar pan­els for years — in my case decades, since I was involved in the “Alter­na­tive Tech­nol­o­gy” mag­a­zine Under­cur­rents in the 1970s. In the past, the idea of a solar PV sys­tem has just been too expen­sive (friends down the street paid £15,000 for their sys­tem just a few years ago), but we’d been watch­ing prices fall until, by the mid­dle of 2014, it looked as if prices had fall­en to an afford­able level.

We inter­viewed four com­pa­nies and it quick­ly became evi­dent that the height of the roof would­n’t allow the con­ven­tion­al 16 pan­els in two rows “por­trait” style that is com­mon for a 4kWp sys­tem – they would have to be mount­ed too close to the top and bot­tom of the roof (you need 500mm clear­ance all round — oth­er­wise you can risk less sta­bil­i­ty in high winds). We could, how­ev­er, man­age two rows of six, “land­scape” style. The com­pa­nies we talked to var­ied in the amount of work they did spec­i­fy­ing the instal­la­tion, and I regard actu­al­ly get­ting up into the loft and tak­ing real mea­sure­ments as an indi­ca­tor that the installer is worth considering.

The lim­i­ta­tion of 12 pan­els imme­di­ate­ly made the choice a rel­a­tive­ly sim­ple one. We need­ed high effi­cien­cy pan­els, and the Sun­Pow­er design, it was easy to see from the data sheets, was not only supe­ri­or in engi­neer­ing terms (they are not only more effi­cient, but they have a stur­dy back­plane sys­tem with no bus­es run­ning down the front of the pan­els, mak­ing them less prone to dam­age; and if a cell does get dam­aged, it does­n’t take the whole row out or worse), it also enabled us to install a sys­tem that would deliv­er a lit­tle under 4kWp from just 12 pan­els. Per­fect! Two com­pa­nies out of the four had offered us Sun­Pow­er pan­els. One was an enor­mous sup­pli­er in the Mid­lands that in fact I would rec­om­mend for any­one look­ing for a com­mer­cial instal­la­tion, but they were rather expen­sive — sig­nif­i­cant­ly more than any of the others.

We select­ed our sup­pli­er, Solar­works of Laven­ham in Suf­folk, who have been installing renew­able sys­tems since 1983. Just a cou­ple of weeks lat­er the scaf­fold­ing arrived and while it was set up, Solar­works fit­ted the invert­er – an ABB “Uno” sin­gle-phase mod­el – and asso­ci­at­ed switchgear in the clos­et under the stairs (see pic­ture left — note the black rotary switch bot­tom right, which is a prop­er DC iso­la­tor on the input path from the pan­els — which were still to be hooked up when this pic­ture was tak­en). Above the AC iso­la­tor on the left is the Gen­er­a­tion Meter. The next day, they installed the mount­ing rails on the roof. Because our pan­els were to be mount­ed hor­i­zon­tal­ly, the rails were ver­ti­cal and each of the 12 was attached to a dif­fer­ent rafter, giv­ing excep­tion­al strength.

The fol­low­ing day, the pan­els went up, and as soon as they were con­nect­ed, by mid-late after­noon – in two strings of six each – the invert­er was indi­cat­ing that we were gen­er­at­ing 3.6kW of elec­tric­i­ty. And the sto­ry has con­tin­ued, with the sys­tem reg­u­lar­ly gen­er­at­ing more kWh than we use in an aver­age day. This year, we saw the out­put exceed 3.7kW as ear­ly as March! (Which sur­prised me in fact, as you would have thought there would be loss­es between the 3.9kWp nom­i­nal pan­els and the invert­er.) The instal­la­tion, just after com­ple­tion, is shown above.

We’re very pleased with the results and would rec­om­mend both Sun­Pow­er pan­els and Solar­works as an installer.

We sub­se­quent­ly had our old Fer­ran­ti rotat­ing-disc import meter replaced so that it would­n’t go back­wards. The lat­ter sounds like a cool thing but actu­al­ly isn’t, because you are already being paid for the elec­tric­i­ty you are export­ing and the elec­tric­i­ty sup­pli­er can claim it back ret­ro­spec­tive­ly; plus I want­ed a mod­ern meter with an LED indi­ca­tor on to which I could strap a counter for metering.

The meter­ing sys­tem I installed came from Geo (Green Ener­gy Options) in Cam­bridge. It mea­sures the pow­er out­put from the pan­els (via the flash­ing light on the Gen­er­a­tion Meter), the amount import­ed from the Grid (via the flash­ing light on the new Import Meter), and the raw cur­rent flow in or out of the build­ing (from a clip around the main pow­er input cable), and cal­cu­lates a range of data from those raw inputs. Very nice. On the dis­play shown here, the blue curve rep­re­sents the out­put from the pan­els (quite good for an over­cast day, I think) and the orange is the amount of ener­gy we’re using – these val­ues are shown numer­i­cal­ly in the cen­tre left of the dis­play. The lit­tle blue arrows at the bot­tom show we are export­ing elec­tric­i­ty, and the lit­tle green wave­form above the wattage dis­plays indi­cates that we have enough “free” pow­er to run a major appli­ance such as a wash­ing machine or dish­wash­er, with­out effec­tive­ly pay­ing for it; and on the right is our elec­tric­i­ty usage so far today and how much our income from gen­er­a­tion and our spend have been. The sys­tem is con­nect­ed to the Inter­net so you can remote­ly mon­i­tor sys­tem per­for­mance via the Web.

Our elec­tric­i­ty sup­pli­er is Ecotric­i­ty, and set­ting up for their Microtric­i­ty scheme to receive the Feed-in Tar­iff (FiT) was sim­ple to do. Now they are often bank­ing with me, and have had to revise my elec­tric­i­ty pay­ments down sig­nif­i­cant­ly as a result.

Hav­ing had the pan­els installed for almost a year, it looks as if we are run­ning some­what ahead of sched­ule as far as these pan­els pay­ing for them­selves is concerned.