You could almost hear the pips squeak when Scottish Power and British Gas announced massive energy price rises. With energy costs spiralling, homeowners are looking for greener, cheaper ways to run their homes and renewable energy is big news.  The Government's feed-in tariff (FIT) scheme offers cash payments to homes generating their own electricity from solar photovoltaic (PV) panels, but cowboy companies are marring the industry by employing high-pressure sales techniques and offering poor advice.  In a recent investigation by consumer organisation Which?, three-quarters of the companies selling solar PV panels overestimated how much energy the panels would produce and underestimated the payback time. Furthermore, seven of the 12 salespeople did not take into account that they would be installing panels in a shaded part of the roof and eight didn't ask the homeowners how much energy they used.  "This last one is really important," says Jenny Driscoll, a Which? energy campaigner. "If you live alone and are in the house only at night, solar is probably not going to pay off for you. But if you are at home during the day and you can put on the washing machine and dishwasher, the chances are you are going to benefit from it."  There is a code in place to protect customers - the Renewable Energy assurance Limited (Real) scheme - but there clearly are problems enforcing these rules. The code bans firms from using pressure-sell tactics, but Which? found that one firm, Green Sun, gave the customer only 24 hours to make a decision.  The onus is on you to do the homework. You need to be sure that your roof is mainly south facing with little or preferably no shade, and robust enough to take the weight. If you live in a conservation area or in a listed building, your local authority may refuse permission for solar panels to be fitted.  You've also got to think about your long-term plans; if you are going to move house this could affect the resale value and you may even have to pay for them to be removed.  If you decide to go for it, ensure that the installer is certified by the Microgeneration Certification Scheme (MCS), and ask for a technical survey, rather than just a salesperson's visit.  Get at least three companies to visit and ask them lots of questions to ensure you're dealing with someone who knows what they are talking about, rather than someone who is purely focused on getting the sale. any figures you are given are guidance and the installer should explain how they arrived at those figures, pointing out anything that will affect the performance such as the angle of your roof and your location.  Use the online tool from the Energy Saving Trust (energysavingtrust.org.uk/ cashbackcalculator) which allows you to estimate the payback time and profit you could make.  Familiarise yourself with the Real code of conduct so that you know how installers should and should not act in your house. They should explain that the inverter, which you need to convert the energy produced by the solar panels into usable electricity, must be replaced within the 25-year lifespan and cost at least ?1,000.  On average, the EST says that solar PV costs ?5,800 per kWp installed and most domestic systems are between 1.5kWp and 3kWp, but as is often the case, it won't simply be about finding the cheapest quote.  When you are comparing quotes, consider whether the price accounts for any extra costs covering removal of your old roof, internal wiring work, electrical connection work and any displays meters.  You should also ask about warranties and guarantees. above all, be wary of any firm that offers you an on-the-spot discount.  "If any installer asks you to sign something straight away, I would show them the door. The Real code obliges companies to give cooling-off periods," says Mark Krull from Logic4training, which trains PV installers. "Don't be rushed, don't be bamboozled and do your research."  Many companies such as Sainsbury's Energy, British Gas and Eon do offer rent-a-roof schemes in which you lease your roof for 25 years in exchange for free installation and ma