4 steps to solar panels – a quick test to see if PVs could work on your roof

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Over the last few weeks, I have talked to quite a few people about whether panels for electricity from solar ( photovoltaic panels (PV) ) are plausible for their roof. A lot of this is due to the government consulting on cutting support for PVs from January 1st (by up to 87%), meaning the financial payback on installing panels would typically increase from ~10 to 27 years. I’ve blogged before about when we when through the steps of getting our install together (to PV or not to PV), but I thought I would throw together a more general simple step-by-step…

If you live in a flat, the roof is one you do not solely own, or the install is on the larger side, some further steps are needed ( e.g. structural survey, certificate of easement…) however the general steps below are effectively the same.

      1. Work out a few details about your roof area and angle.

You will need to know roof area, roof angle, what angle it faces, how much shading it has, and whether the building has an energy performance above the minimal criteria (an EPC of D or above).

You can calculate the approximate area from eye or just use satellite photos. I tend to use Google maps through an app on a website like comparemysolar. Using this app you just place pins on the outline of the roof to get an approximate area. Google maps also gives you an compass orientation. As for angle, I would say it should be possible to get a estimate just from looking at the roof and comparing against a few examples. Then check for shading (e.g. chimney pots, neighbours roofs, trees…) and estimate what % of day you think the roof is shaded (another approach would just to check the roof at several times of day, but bearing mind this will change a lot by season). To check an the energy performance of the house according to its EPC certificate, and you don’t know it off hand, you can quickly check it on this website. If you do decide to get quotes, then all these estimates will be refined then anyway.

(e.g.  20 square meters, 30 degrees, south facing, no shading, EPC=D,  and in York)

      2. Estimate the rating of the PV install

There are lots of different panels of differing shapes, sizes, capacity and performance around. Choosing panels for the install may be easiest once you have quotes. I would recommend two sets of calculations, one for a lower capacity (e.g. ~100 W/sq m & cheaper) set of panels and one for higher capacity set of panels (~200 W/ sq m) . To get the peak output ( rating ) of the install just multiply the panel capacity by the area.

(e.g.  20 square metres * 200 W/square metres =  4000 W)

      3. Use some apps to estimate the output and payback of the PV install

We can now just plug the numbers from steps 1 & 2 to one of many online apps that use past solar data to predict how the panels would perform.  There are lots of apps to check whether PV is worthwhile and they give give a variety of different information from just the basic payback, to yearly/monthly break downs of energy production, and ones with lots of technical gory detail. I would personally recommend getting a broad overview from the Energy Saving Trust (EST solar calculator) and the Centre for Alternative Technology (CAT solar calculator, Caution: the monetary values were out of date when I last checked so just use for solar). If you are interested in more detail then the Joint Research Centre (JRC solar calculator) provides a lot more technical background.

The payback is made up of payments for generated clean renewable every (feed-in-tariffs or FITs), electricity savings (from use of electricity on site), and export tariffs (price paid per unit exported to the gird for someone else to use). The is more detail on this here and this will be broken down by the apps also. I understand that Installs for a typical residential install are generally between £4-6.5k at present.

(e.g. estimated to generate ~3300 kWh/year and have a payback of 9 years)

     4. Get a few quotes

There is a great list of recommended installers (need to be MCS certified) and a list of good questions to ask on the YouGen site. I also used the quote service from EcoExperts who quickly got us 3 quotes for comparison. The industry has taken a big shock from the recent government proposals to cut the fit in tariff and a lot of people may being trying to get installs before the expected changes to the tariff so it could be quite busy at the moment.

Once you have your quotes you can choose obviously between suppliers/installers, but also the capacity/spec of your install…. and whether you want to go ahead with it. The installs typically take a day for a 4kW domestic install and then the install will need to be registered via the installer through the government’s micro generation scheme (MCS), which installers tend to help with or just do for you.

Our installation was done whilst we were away on holiday; it was done quickly and without disruption.

(e.g.  Ecoexpert say from £3950 for a 4kW install. – Ours cost a little over £6k, but was rather technical and high spec for two years ago)

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